2024-07-29
ISO/DIS 9806:2024(en)
ISO/TC 180/WG 4
Secretariat: SA
Solar energy — Solar thermal collectors — Test methods
© ISO 2024
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Contents
5.1 Test overview — Sequence of the tests 5
5.3 Testing of collectors with specific attributes 6
5.3.2 Collectors using external power sources for regular operation 6
5.3.3 Collectors with active self-protection 7
5.3.4 Collectors co-generating thermal and electrical power 7
5.3.6 Air and liquid heating collectors 8
6 Internal pressure tests for fluid channels (liquid heating collectors only) 8
6.2 Fluid channels made of non-polymeric materials 8
6.2.1 Apparatus and procedure 8
6.3 Fluid channels made of polymeric materials 9
6.3.1 Apparatus and procedure 9
7 Air leakage rate test (air heating collectors only) 9
7.2 Apparatus and procedure 10
8 Standard stagnation temperature 10
8.2 Testing under stagnation conditions 11
8.3 Measurement and extrapolation of the standard stagnation temperature 11
8.4 Determining standard stagnation temperature using efficiency parameters 12
9 Exposure and half-exposure test 12
9.2 Initial outdoor exposure 13
9.3 Method 1 (Outdoor exposure) 13
9.4 Method 2 (Heat transfer loop) 13
9.5 Method 3 (Indoor exposure) 13
9.6 Exposure test for collectors using active mechanism to protect against overheating 14
10 External thermal shock test 14
10.2 Apparatus and procedure 15
11 Internal thermal shock test (Liquid heating collectors only) 15
11.2 Apparatus and procedure 15
12.2 Apparatus and procedure 16
13.2 Freeze resistant collectors 18
13.2.3 Results and reporting 19
13.3.3 Results and reporting 20
14 Mechanical load test with positive or negative pressure 20
14.2 Apparatus and procedure 20
14.2.2 Methods for the application of the loads 20
14.2.3 Particular specifications for tracking collectors or other specific collector types 21
15.4 Method 1: Impact resistance test using ice balls 22
15.4.3 Specific aspects of the test procedure using ice balls 22
15.5 Method 2: Impact resistance test using steel balls 23
16 Active self-protection mechanisms 23
16.2 Apparatus and procedure 23
16.3.2 Loss of communication test 24
16.3.3 Overheating protection test 24
16.3.4 Adverse climatic conditions protection test 24
18 Thermal performance testing 26
19 Collector mounting and location 26
19.2 Shading from direct solar irradiance 27
19.3 Diffuse and reflected solar irradiance 27
20.1 Solar radiation measurement 27
20.2 Thermal radiation measurement 28
20.3 Temperature measurements 28
20.3.1 Heat transfer fluid temperatures (Liquid heating collectors) 28
20.3.2 Volume flow weighted mean temperature ϑm,th (air heating collectors) 28
20.3.3 Measurement of ambient air temperature 29
20.4.1 Measurement of mass flow rate (liquid) 29
20.4.2 Measurement of collector fluid flow rate (Air heating collectors) 30
20.5 Measurement of air speed over the collector 30
20.5.3 Mounting of sensors for the measurement of air velocity over the collector 30
20.6 Elapsed time measurement 31
20.7 Humidity ratio (air collectors) 31
21.1 Liquid heating collectors 31
21.1.3 Pipe work and fittings 32
21.2 Air heating collectors 32
21.2.2 Closed loop test circuit 33
21.2.3 Open to ambient test circuit 33
21.2.5 Pump and flow control devices 34
21.2.7 Fan and flow control devices 34
21.2.8 Air preconditioning apparatus 34
22 Thermal performance test procedures 35
22.2 Preconditioning of the collector 35
22.3.3 Air speed parallel to the collector plane 36
22.4.3 Quasi-dynamic testing 37
22.5.2 Data acquisition requirements 38
22.6.1 Steady-state testing 38
22.6.2 Quasi-dynamic testing 39
22.7 Performance test using a solar irradiance simulator 42
22.7.2 Solar irradiance simulator for thermal performance testing 42
22.7.3 Additional measurements during tests in solar irradiance simulators 43
22.7.4 Solar irradiance simulator for the measurement of incidence angle modifiers 44
23 Computation of the collector parameters 44
23.1 Liquid heating collectors 44
23.1.2 Steady-state test method for liquid heating collectors 44
23.1.3 Quasi-dynamic test method for liquid heating collectors 45
23.2 Air heating collectors 45
23.2.2 Steady-state test method for closed loop air heating collectors 45
23.2.3 Steady-state test method for open to ambient air heating collectors 46
23.3 Standard reporting conditions (SRC) 46
23.4 Standard uncertainties 47
23.5 Reference area conversion 47
24 Determination of the effective thermal capacity and the time constant 47
24.2 Measurement of the effective thermal capacity with irradiance 47
24.3 Measurement of the effective thermal capacity using the quasi-dynamic method 48
24.4 Calculation method for the determination of the effective thermal capacity 48
24.5 Determination of collector time constant 48
25 Determination of the incidence angle modifier (IAM) 50
25.2.2 Quasi-dynamic method 52
25.3.1 Steady-state liquid heating collectors 52
25.4 Calculation of the collector incidence angle modifier 53
26 Determination of the pressure drop 53
26.2 Liquid heating collectors 54
26.2.1 Apparatus and procedure 54
26.2.2 Pressure drop caused by fittings 54
26.3 Air heating collectors 54
26.3.1 Apparatus and procedure 54
26.4 Calculation and presentation of results 55
Annex A (informative) Test reports 56
A.2.2 General Information for sample identification 56
A.2.3 Protection mechanisms 56
A.2.4 Design operational range 57
A.2.6 Frame, enclosure, casing 57
A.2.10 Glazing/transparent cover 58
A.2.14 Additional Information 59
A.3 Test sequence and summary of main results 59
A.4 Internal pressure test for fluid channels 60
A.5 Air leakage rate test for closed loop air heating collectors 60
A.6 Determination of standard stagnation temperature 61
A.7.1 Test conditions of the initial outdoor exposure 62
A.7.2 Test conditions for Method 1 62
A.7.3 Test conditions for Method 2 62
A.7.4 Test conditions for Method 3 62
A.7.5 Climatic conditions during the exposure test 62
A.8 External thermal shock test 63
A.9 Internal thermal shock test 63
A.11 Freeze resistance test 64
A.11.1 Freeze resistant collectors 64
A.12.1 Positive pressure test of the collector and the fixings 65
A.12.2 Negative pressure test of the collector and the fixings 65
A.13 Impact resistance test 65
A.15 Performance test results 66
A.15.2 Collectors using external power sources 67
A.15.3 Thermal output measurement 67
A.15.3.3 Radiation distribution (indoor testing only) 67
A.15.4 Thermal output reporting 67
A.15.4.1 Coefficients for the calculation of the thermal output 67
A.15.4.2 Power output per collector unit 68
A.15.5 Thermal performance reporting for open to ambient air heating collectors 69
A.15.6 Incidence angle modifier 70
A.15.6.2 Radiation distribution (indoor testing only) 70
A.15.7 Effective thermal capacity 71
A.15.9 Pressure drop measurements 72
Annex B (normative) Solar collector performance rating 73
B.1 Gross Yield calculation 73
B.1.3 Gross Thermal Yield GTY 74
B.1.4 Gross Electric Yield GEY 74
B.1.5 Gross Solar Yield GSY 74
Annex C (normative) Steady-state and quasi-dynamic model 75
Annex D (normative) Density and heat capacity of water 77
Annex E (informative) Assessment of the standard uncertainty in solar collector testing 78
E.2 Measurement uncertainties in solar collector thermal efficiency testing 78
E.3 Fitting and uncertainties in efficiency testing results 80
Annex F (informative) Measurement of the velocity weighted mean temperature 82
Annex G (normative) Material efficiency aspects 84
Annex H (informative) Area conversion of thermal performance parameters 85
Annex I (informative) Validation of collector parameters 86
I.2 Collector mounting, instrumentation and test installation 86
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This document was prepared by Technical Committee ISO/TC 180, Solar energy.
This third edition cancels and replaces the second edition (ISO 9806:2017), which has been technically revised.
This edition includes the following significant changes compared with the previous edition:
— Clause 5.2: The language used, concerning maximum operating conditions is harmonised by introducing the concept of the design operating range.
— The previous rupture or collapse test for air heating collectors is integrated into Clause 7 air leakage test.
— The description of the testing of tracking collectors such as parabolic trough collectors and Linear Fresnel collectors is updated in several places to improve coherence with the standards of the IEC/TC 117 Solar thermal electric plants.
— Clause 16: A new clause is introduced to clarify the procedures for testing collectors with active self-protection mechanisms.
— The mathematical model for the thermal performance is simplified. The thermal performance parameter a7 is removed without direct replacement.
— The reduced wind speed 
is replaced by 
. The default wind speed parallel to the surface of the collector is reduced to ≥ 1.3 m/s instead of the previously used target wind speed of 3 m/s. At the same time, all collectors are considered as wind and infrared-sensitive collectors. If the thermal performance is considered as not specifically sensitive to wind or long‑wave radiation exchange or upon request of the ordering party, a simplified testing procedure (see Clause 22.1) can be applied and the parameters 
are set to 0.
— Annex I: A new validation procedure (Valicol) is introduced to allow verification of the measured thermal performance parameters.
In addition, the following changes were introduced, following the ISO Guide 84:2020 to support the ISO London Declaration Action Plan:
— Introduction: A comprehensive statement on the environmental impact of thermal solar collectors and their potential contribution to achieving the United Nations Sustainable Development Goals (SDGs) is added.
— Annex B: The gross yield concept is introduced to allow for a standardized rating of the possible energy yield of solar thermal collectors. Based on these figures it is possible to rate solar thermal technologies' Green House Gas (GHG) reduction and avoidance potential under different climate conditions.
— Annex G: The material use assessment is now a mandatory part of the final inspection. This material use assessment supports all kind of life cycle assessments and includes a rating of the material identifiability, material recyclability and product repairability.
Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.
0.1 Solar thermal collectors
According to the International Energy Agency (IEA, www.iea.org), heat is the largest end-use of energy, accounting for nearly 50% of global final energy consumption. This is significantly more than the shares of electricity and transport, which are approximately 20% and 30%, respectively. More than 50% of the total heat consumption is used in industrial processes, with the rest consumed in buildings for space and water heating, and other applications. Furthermore, heat generation is responsible for over 40% of global energy-related carbon dioxide emissions. This significant contribution to CO2 emissions is primarily due to the continued reliance on fossil fuels for heat production, with renewable sources meeting less than a quarter of global heat demand.
Solar thermal technologies directly use the sun's energy to produce heat for various applications. Solar thermal technologies are, therefore, key technologies for reducing global carbon dioxide emissions. The core element of any solar thermal system is the solar thermal collector. There are several different types of solar thermal technologies and solar thermal collectors, with typical characteristics and applications such as:
— Solar thermal water heaters use solar collectors to heat a fluid to heat water stored in a tank for domestic or commercial use. These systems can be active, using pumps to circulate the fluid, or passive, using natural convection to move the fluid.
— Solar thermal space heating systems use solar collectors to generate heat, which is then transferred to indoor spaces for heating purposes. These systems can use liquids or air as heat transfer fluid.
— Solar thermal process heat systems provide heat for industrial processes such as drying, food processing, pasteurisation, washing, cleaning and all other manufacturing processes at medium temperatures.
— Solar thermal district heating (SDH) uses solar thermal collectors to provide heat to centralised heating systems serving entire neighbourhoods or communities. This approach enables greater efficiency and cost-effectiveness by exploiting economies of scale and maximising the use of solar energy.
— Solar thermal pool heaters use solar collectors to heat water in swimming pools, extending the swimming season and reducing the need for conventional pool heating methods.
Solar thermal applications are also used to power many other technologies, such as solar thermal desalination, solar thermal electricity generation, ground source regeneration or as a source for heat pumps, to name only a few. Solar thermal technologies can be used wherever heat is used, either as a replacement or as a supporting technology to reduce the use of other energy sources.
Various solar thermal collector technologies can be used for the applications listed above. The most common products are
— Flat plate collectors consist of a flat absorber plate with tubes or channels through which a heat transfer fluid flows. These collectors are manufactured with transparent glazing for higher-temperature applications or without for lower-temperature applications.
— Evacuated tube collectors consist of rows of parallel glass tubes, each containing an absorber. The space between the absorber and the outer glass tube is evacuated to reduce heat loss.
— Concentrating collectors, such as parabolic trough collectors or linear Fresnel collectors, use reflectors to concentrate sunlight onto a receiver to achieve higher temperatures.
Some solar thermal collectors combine the generation of heat with the direct generation of electricity, usually by using photovoltaic elements as absorbers.
The heat transfer fluid in solar thermal collectors is usually plain water, water-based antifreeze or air. For some specific applications other media such as high-temperature oils or evaporating liquids are used.
0.2 Application range of this international standard
Collectors tested according to this document represent a wide range of applications, e.g. glazed flat plate collectors and evacuated tube collectors for domestic hot water and space heating, collectors for heating swimming pools or other low-temperature systems or tracking concentrating collectors for thermal power generation and process heat applications. This document applies to liquids, air, and heat transfer fluid collectors. Similarly, collectors using external power sources for regular operation and/or safety purposes (overheating protection, environmental hazards, etc.) and co-generating devices generating thermal and electrical power are also considered.
This document defines procedures for testing fluid heating solar collectors for thermal performance, reliability, durability and safety under well-defined and repeatable conditions. It contains outdoor test methods using solar irradiance and natural or simulated wind. as well as indoor procedures using simulated irradiance and simulated wind. Outdoor tests can be performed either as steady-state or as quasi-dynamic measurements.
The standard intentionally does not specify any product requirements, as these depend on the intended use and place of installation. Requirements shall be defined by specific local standards, building codes, certification schemes, tax rebates and incentive schemes as appropriate. This standard is intended to provide a solid basis for these schemes with harmonised and reliable product testing.
Climate change is expected to accelerate the degradation of all exposed products, such as also solar thermal collectors, potentially undermining their performance, reliability and safety. Requirements should be re-evaluated and adapted from time to time to future operating conditions to lower degradation rates and the chances of failure using the methods set out in the ISO 14090. This process also ascertains solar thermal collectors' durability, functionality, and safety amidst changing climate patterns and reinforces the commitment to advancing sustainable and adaptable technologies to environmental and climatic shifts.
WARNING – This International Standard does not purport to address all the safety or environmental problems associated with its use. The user of this International Standard is responsible for establishing appropriate safety, health, and environmental practices, including climate change mitigation efforts. Such efforts could include but are not limited to, reducing greenhouse gas emissions, minimising waste, using renewable resources where possible, and conducting regular environmental impact assessments. Users should also determine the applicability of regulatory limitations prior to use.
0.3 Environmental impact of Solar thermal collectors
By providing the tools to assess the materials used in the production of solar thermal collectors and their potential for energy savings and greenhouse gas reductions, this international standard is aligned with the principles of the ISO 14000 series on environmental management, with the ISO 50000 series on energy management systems and with the ISO 59000 series on circular economy.
The annual yield and the efficiency of converting incoming solar radiation into useful heat can reach more than 80%, depending on the temperature required and the technology chosen. In fact, the annual energy yield per area is higher with solar thermal collectors than with any other technology. The yield per area is around three times higher than photovoltaic power generation and 50-100 times higher than photosynthesis for biomass production. Given the range of products and applications, it is impossible to quantify this technology's greenhouse gas reduction or climate change mitigation potential in general terms. The greenhouse gas reduction potential of a solar thermal collector depends on the environmental conditions and the application in which it is used. It is recommended to make this quantification using the global warming potential (GWP) for each GHG as per Table 7.15 of the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) by aggregating the reduction potential in CO2 equivalent emissions[1]. Quantification should be made for the whole heating system’s lifecycle in analysis, from raw material extraction to end-of-life disposal. It should account for direct (scope 1) and indirect (scope 2 – from electricity, heat, or steam use; scope 3 – all other indirect GHG emissions in the value chain) GHG emissions. Special care should be taken regarding GHG emissions if supplementary external power sources are used, which might lead to indirect GHG emissions that should be considered. Special care should also be taken regarding other GHGs, such as freon-charged solar heating systems, as these systems are associated with the potential release, intentional or unintentional, of fluorinated gases (F-gases). Quantification must first define the baseline GHG emissions associated with a specific system's most commonly used technology (e.g., conventional water heater – natural gas or electric). Comparing the projected GHG emissions of the system when using solar thermal collectors using the methods defined in Annex B with the baseline GHG emissions will give the potential GHG reduction.
Solar thermal collectors are typically made of separable and clean materials such as glass, copper and aluminium, which have a high potential for recycling and reuse. Considering the potential energy yield and the greenhouse gas emissions associated with producing solar thermal collectors, typical carbon and energy payback times are 0.5 to 2 years. To further reduce the environmental impact of solar thermal collectors, no material, form of construction, fixture, appurtenance, or items of equipment shall be employed that will introduce toxic substances, impurities, bacteria, or toxic chemicals into potable water and air circulation systems in quantities sufficient to cause disease or harmful physiological effects. Following circular economy and green procurement principles, all goods and services used in solar thermal collectors, instrumentation, test installation, and facilities should seek to incorporate as much as possible reused and recycled content, make efficient use of energy and materials, promote waste reduction, and the use of renewable energy to minimise overall environmental impact. Adopting a comprehensive eco-design strategy that encapsulates the entire product lifecycle, from material sourcing to end-of-life management, is recommended for the design and production of solar thermal collectors. This approach should include the application of Life Cycle Assessment (LCA) methodologies to systematically evaluate and aim to minimise the environmental impacts associated with all lifecycle stages of solar thermal collectors. Such impacts include but are not limited to greenhouse gas emissions, resource depletion, and energy consumption. Materials and components selected for the construction and testing of solar thermal collectors should be scrutinised for their environmental certifications and performance characteristics. This scrutiny ensures that these materials contribute positively to the collectors' sustainability profile, thus aligning with the broader objectives of climate change mitigation. It is advisable to prioritise materials that offer a balanced compromise between minimising environmental impacts and maintaining or enhancing solar thermal collectors’ performance efficiency, durability, and reparability. This selection process should particularly consider materials with lower embodied carbon, higher recyclability potential, and those that adhere to recognised environmental standards and certifications.
0.4 Supporting the UN Sustainable Development Goals (SDGs)
Achieving the Sustainable Development Goals (SDGs) established by the United Nations in 2015 has become a high priority for society. This International Standard is aligned with the following United Nations Sustainable Development Goals by promoting and supporting:
— Solar thermal collectors and solar thermal technologies to reduce dependence on energy prices to increase the resilience of humanity to climate-related extreme events and other economic, social and environmental shocks and disasters (SDG 1.5).
— Solar thermal collectors and solar thermal technologies for water treatment and disinfection to reduce water-borne diseases (SDG 3.3).
— Solar thermal collectors and solar thermal technologies as a clean and safe energy source to replace other energy sources to significantly reduce the number of deaths and illnesses from hazardous chemicals and polluted air caused by the combustion of fossil fuels (SDG 3.9).
— Solar thermal collectors and solar thermal technologies in water purification and desalination facilities to achieve universal and equitable access to safe and affordable drinking water for all (SDG 6.1).
— Solar thermal collectors and technologies as vital in developing countries' capacity-building programmes for water treatment activities (SDG 6.A).
— Solar thermal collectors to ensure access to affordable, reliable and modern energy for all (SDG 7.1).
— Solar thermal collectors to significantly increase the share of renewable energy for all (SDG 7.2).
— Solar thermal collectors in various applications to increase the overall global energy efficiency (SDG 7.3).
— International cooperation in solar thermal technologies to facilitate access to clean energy research and technology, especially in the fields of renewable energy, energy efficiency and fossil fuel-free technologies, as well as to facilitate investments in solar thermal-based energy infrastructure and clean energy technologies (SDG 7.A).
— Solar thermal collectors to develop infrastructure and technologies for modern and sustainable energy accessible to all in developing countries, particularly, least developed countries, small island developing states and landlocked developing countries, and to provide a sound basis for developing appropriate support programmes. (SDG 7.B).
— Solar thermal collectors and solar thermal technologies as well-suited technologies for local production, thereby achieving higher levels of economic productivity through diversification, technological upgrading and innovation, focusing on high value-added and labour-intensive sectors (SDG 8.2).
— Solar thermal collectors and solar thermal technologies as locally manufacturable devices with low requirements for production technologies and financial investments to promote and support productive activities, decent job creation, entrepreneurship, creativity and innovation, and to promote the formalisation and growth of micro, small and medium-sized enterprises, including through access to financial services (SDG 8.3).
— Solar thermal collectors and technologies to progressively improve the global resource efficiency of consumption and production, and to endeavour the decoupling of economic growth from environmental degradation. (SDG 8.4).
— Solar thermal collectors as part of high-quality, reliable, sustainable and resilient infrastructure, thereby supporting economic development and human well-being with a focus on affordable and equitable access for all (SDG 9.1).
— Solar thermal collectors to contribute to inclusive and sustainable industrialisation and to significantly increase the industry's share of employment and gross domestic product, particularly in least-developed countries, according to national circumstances. (SDG 9.2).
— Solar thermal collectors as a cost-effective means to increase the availability of energy and the predictability of energy costs by reducing dependence on fossil energy, thereby to facilitating the access of small industrial and other enterprises, particularly in developing countries, to financial services, including affordable credit, and to integrate these industries into value chains and markets (SDG 9.3).
— Solar thermal collectors to upgrade infrastructure and retrofit industries to make them sustainable, with increased efficiency in resource use and greater adoption of clean and environmentally sound technologies and industrial processes (SDG 9.4).
— Scientific research and technological capacity building in solar thermal technologies in all countries, particularly developing countries, including the promotion of innovation, research and development activities (SDG 9.5).
— Solar thermal collectors and solar thermal technologies to facilitate sustainable and resilient infrastructure development in developing countries and to provide financial, technological and technical assistance to African countries, least developed countries, landlocked developing countries and small island developing states (SDG 9.A).
— Solar thermal collectors as a way to enhance domestic technology development, research and innovation in developing countries. In addition, the standard supports the development of an enabling policy environment for solar thermal technologies for industrial diversification and commodity value addition (SDG 9.B).
— Solar thermal collectors for fossil and biomass-free production of heat and hot water to reduce the adverse per capita environmental impact of cities and, in particular, by contributing to better air quality. (SDG 11.6).
— Solar thermal collectors as an element of sustainable and resilient buildings, using local materials and local production capacity (SDG 11.C).
— Solar thermal collectors for local and affordable thermal food processing to reduce global food waste and food losses along production and supply chains, including post-harvest losses (SDG 12.3).
— Solar thermal collectors as a product that significantly reduces waste generation through its repairable designs and material reduction, by using recycled materials and reused components (SDG 12.5).
— Solar thermal collectors and solar thermal technologies to encourage companies to adopt sustainable practices and integrate sustainability information into their reporting cycles (SDG 12.6).
— Solar thermal collectors and solar thermal technologies as locally manufactured technologies, using mainly recycled materials, as part of sustainable public procurement practices. (SDG 12.7).
— Solar thermal collectors and solar thermal technologies to strengthen the technological capacity to move towards more sustainable patterns of consumption and production, not only in developing countries (SDG 12.A).
— Subsidy schemes for solar thermal collectors, and thus also the reduction and phasing out of inefficient fossil fuel subsidies, especially in developing countries, and minimising adverse impacts on their development in a manner that protects the poor and affected communities (SDG 12.C).
— Solar thermal collectors and solar thermal technologies to reduce the overuse of biomass for heat generation, thereby also supporting the implementation of sustainable management of all types of forests, halting deforestation and even enabling afforestation and reforestation worldwide (SDG 15.2).
— The transfer of expertise, dissemination and diffusion of environmentally sound technologies to developing countries on favourable terms (SDG 17.7).
Solar energy — Solar thermal collectors — Test methods
1.0 Scope
This document specifies test methods for assessing the durability, reliability, safety and thermal performance of fluid heating solar collectors. The test methods are applicable for laboratory testing and for in situ testing.
This document is applicable to all types of fluid heating solar collectors, air heating solar collectors, hybrid solar collectors co-generating heat and electric power, as well as to solar collectors using external power sources for normal operation and/or safety purposes. It does not cover electrical safety aspects or other specific properties directly related to electric power generation.
This document is not applicable to those devices in which a thermal storage unit is an integral part to such an extent that the collection process cannot be separated from the storage process for making the collector thermal performance measurements.
2.0 Normative references
The following documents are referred to in the text in such a way that some or all their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 9060, Solar energy — Specification and classification of instruments for measuring hemispherical solar and direct solar radiation
ISO 9488, Solar energy — Vocabulary
ISO/TR 9901:2021, Solar energy — Pyranometers — Recommended practice for use
ISO 14000 (series), on environmental management systems
ISO 14050, Environmental management — Vocabulary
ISO 14090, Adaptation to climate change — Principles, requirements and guidelines
ISO 50000 (series), on Energy management systems
ISO 59000 (series), on circular economy
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC/TS 62862‑1-1, Solar thermal electric plants - Part 1-1: Terminology
IEC 62862‑3-2, Solar thermal electric plants - Part 3-2: Systems and components - General requirements and test methods for large-size parabolic-trough collectors
IEC 62862‑5-2, Solar thermal electric plants - Part 5-2: Systems and components - General requirements and test methods for large-size linear Fresnel collectors
IEC 62817, Photovoltaic systems - Design qualification of solar trackers
3.0 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9488 and IEC TS 62862-1-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
4.0 Symbols
AA | Absorber area of the collector as defined in the ISO 9488 | m2 |
AG | Gross area of the collector as defined in the ISO 9488 | m2 |
Aa | Aperture area of the collector as defined in the ISO 9488 | m2 |
a1 | Heat loss coefficient | W/(m2K) |
a2 | Temperature dependence of the heat loss coefficient | W/(m2K2) |
a3 | Wind speed dependence of the heat loss coefficient | J/(m3K) |
a4 | Sky temperature dependence of the heat loss coefficient | — |
a5 | Effective thermal capacity | J/(m2K) |
a6 | Wind speed dependence of the zero-loss efficiency | s/m |
a8 | Temperature loss of 4th order | W/(m2K4) |
bu | Collector efficiency coefficient (wind dependence) | s/m |
C | Effective thermal capacity of the collector | J/K |
CR | Geometric concentration ratio (CR= Aa/AA) | — |
cf | Specific heat capacity of the heat transfer fluid | J/(kgK) |
cf,i | Specific heat capacity of the heat transfer fluid at the collector inlet | J/(kgK) |
cf,e | Specific heat capacity of the heat transfer fluid at the collector outlet | J/(kgK) |
cf,a | Specific heat capacity of the ambient air | J/(kgK) |
DNI | Direct normal irradiance as defined in ISO/TR 9901:2021 | W/m2 |
EL | Longwave irradiance (λ > 3 μm) | W/m2 |
Gb | Direct solar irradiance (beam irradiance), Gb = DNI·cos(θ) | W/m2 |
Gd | Diffuse solar irradiance, Gd = Ghem – Gb | W/m2 |
Ghem | Hemispherical solar irradiance | W/m2 |
Ghem,s | Hemispherical solar irradiance for the standard stagnation temperature | W/m2 |
Gs | Hemispherical solar irradiance for the calculation for the standard stagnation temperature | W/m2 |
H | Irradiation on collector plane for exposure test | MJ/m2 |
ki | Weighting factor for effective thermal capacity calculations | — |
Kb(θT,θL) | Incidence angle modifier for direct solar irradiance | — |
Khem(θT,θL) | Incidence angle modifier for hemispherical solar radiation | — |
KθL | Incidence angle modifier in the longitudinal plane | — |
KθT | Incidence angle modifier in the transversal plane | — |
Kd | Incidence angle modifier for diffuse solar radiation | — |
| Mass flow rate of the heat transfer fluid | kg/s |
| Minimum air mass flow by the performance test | kg/s |
| Maximum air mass flow by the performance test | kg/s |
| Downstream air mass flow rate | kg/s |
| Upstream air mass flow rate | kg/s |
| Leakage air mass flow rate | kg/s |
PPeak | Peak power | W |
pe | Static pressure of the heat transfer fluid (air) at the | Pa |
pi | Static pressure of the heat transfer fluid (air) at the | Pa |
pabs | Absolute pressure of the ambient air | Pa |
pD,max | Maximum design pressure | Pa |
| Power extracted from collector | W |
Qc,i | Computed energy yields Qc,I for sequence i of the validation procedure | J |
Qm,i | Measured energy yields Qm,i for sequence i of the validation procedure | J |
RD | Gas constant for water vapour | 461,4 J/(kgK) |
RL | Gas constant for air | 287,1 J/(kgK) |
T | Absolute temperature | K |
t | Time | s |
u | Surrounding air speed | m/s |
Vf | Fluid capacity of the collector | m3 |
| Volumetric flow rate | m3/s |
| Volumetric flow rate at the outlet of the solar collector | m3/s |
| Volumetric flow rate at the inlet of the solar collector | m3/s |
| Volumetric air leakage flow rate | m3/s |
XW,a | Water content of the ambient air | kgwater/kgdry air |
XW,e | Water content of the air at the exit of the solar collector | kgwater/kgdry air |
XW,i | Water content of the air at the inlet of the solar collector | kgwater/kgdry air |
Δp | Pressure difference between fluid inlet and outlet | Pa |
Δt | Time interval | s |
ΔT | Temperature difference between fluid outlet and inlet (ϑe - ϑi) | K |
α | optical absorption coefficient | — |
β | Inclination of the collector | ° |
γS | Solar azimuth angle | ° |
| Collector efficiency based on beam irradiance Gb | — |
| Collector efficiency based on hemispherical irradiance Ghem | — |
| Peak collector efficiency (ηb at ϑm − ϑa = 0 K) based on | — |
| Peak collector efficiency (η0,hem at ϑm − ϑa = 0 K) based on hemispherical irradiance Ghem | — |
| Collector efficiency, with reference to mass flow | — |
θ | Angle of incidence | ° |
θL | Longitudinal angle of incidence: angle between the normal to the plane of the collector and incident sunbeam projected into the longitudinal plane | ° |
θT | Transversal angle of incidence: angle between the normal to the plane of the collector and incident sunbeam projected into the transversal plane | ° |
ϑa | Ambient air temperature | °C |
ϑa,s | Ambient air temperature for the standard stagnation temperature | °C |
ϑe | Collector outlet temperature | °C |
ϑi | Collector inlet temperature | °C |
ϑm | Mean temperature of heat transfer fluid | °C |
ϑD,max | Maximum design temperature | °C |
ϑD,min | Minimum design temperature | °C |
ϑstg | Standard stagnation temperature | °C |
ϑsky | Atmospheric or sky temperature | °C |
ϑtrigger | Temperature at which the safety controls are activated for fail-safe operating condition | °C |
ϑm,th | Volume flow weighted mean temperature | °C |
ϑmp,e | Fluid temperate at the downstream air mass flow meter | °C |
ϑmp,i | Fluid temperate at the upstream air mass flow meter | °C |
ϑs | Measured absorber temperature | °C |
λ | Wavelength | µm |
ρ | Density of the heat transfer fluid | kg/m3 |
ρl | Density of air | kg/m3 |
σ | Stefan-Boltzmann constant | 5,670⋅10-8 W/(m2K4) |
τc | Collector time constant | s |
τ | Transmittance | — |
(τα)eff | Effective transmittance-absorptance product | — |
5.0 General
5.1 Test overview — Sequence of the tests
A complete test sequence for solar thermal collectors including durability test and thermal performance measurements is proposed in Table 1. This test sequence may be modified, or only single tests may be performed as required. For some tests, a certain preconditioning or a half-exposure test (see Clause 9) is mandatory. For all test sequences and single tests, the final inspection (Clause 17) is mandatory as the concluding test for the proper identification and description of the test sample and to identify problems or deficiencies.
Table 1 — Test list
Clause | Test |
Clause 6 | Internal pressure test for fluid channels A,C |
Clause 7 | Air leakage rate test |
Clause 8 | Standard stagnation temperature |
Clause 9 | Exposure test |
Clause 10 | External thermal shock test E |
Clause 11 | Internal thermal shock test |
Clause 12 | Rain penetration test A |
Clause 13 | Freeze resistance test A,B |
Clause 14 | Mechanical load test A |
Clause 15 | Impact resistance test A |
Clause 16 | Active self-protection mechanisms |
Clause 17 | Final inspection |
Clause 18 to 25 | Thermal performance test D |
Clause 26 | Pressure drop measurement |
A Half-exposure is required before the test. B For collectors claimed to be freeze resistant and collectors containing heat pipes. C Last test of the test sequence before final inspection. D Exposure is required before the testing if heat pipes are used in the collector. E Not required for collectors made with tempered or toughened glass covers. | |
The reporting forms in Annex A shall be completed for each test, together with the introductory form (see Table A.1) summarising the main results, including the test methods.
5.1.1 Design operating range
The design operating range (DOR) indicates the operating range for which the collector is designed to operate at without experiencing relevant degradation, damage or a reduction of the design life. The manufacturer defines the DOR, which shall be reported at least for the following parameters:
— Minimum design operating temperature range ϑD,min
— Maximum design operating temperature range ϑD,max
— Maximum design operation pressure pD,max at ϑD,max
— Minimum design installation inclination βD,min (measured from horizontal)
— Maximum design installation inclination βD,max (measured from horizontal)
— Maximum design positive mechanical load (snow load)
— Maximum design negative mechanical load (wind load)
— Maximum design impact resistance (ice ball diameter dD,max or steel ball drop height hD,max)
— Maximum design climate class
— Recommended heat transfer fluids
— Minimum design flow rate 
— Recommended flow rate 
— Maximum design flow rate 
— For tracking collectors: Angular operation range in all directions, as relevant
— Any other relevant design operating range
Additional safety factors must be considered depending on the use of a product and the applicable building code or certification scheme. These safety factors are not considered in this standard.
5.1.2 Testing of collectors with specific attributes
5.1.3 General
The general test procedures described in this document cover most current standard products. Some collector constructions with additional specific attributes shall be tested as indicated in this clause. Collectors can have one or several attributes. Attributes not mentioned in the test report shall not be considered as applicable for the tested collector.
5.1.4 Collectors using external power sources for regular operation
General
These collectors shall be tested to demonstrate suitable performance under normal operating conditions. All tests shall be performed using the intended original manufacturer’s equipment of the collector (tracking devices, pumps, sensors, etc.) and external power sources as specified by the manufacturer.
NOTE External equipment such as solar pumps or fans providing fluid flow for regular operation of the heat transfer and the thermal fluid loop are not considered part of the collector.
Reporting
The total energy consumption for the normal operation mode of the collector shall be assessed and indicated in the test report.
5.1.5 Collectors with active self-protection
General
Collectors may be equipped with active mechanisms for protecting the collector from damage caused by adverse operational or environmental conditions. Such active mechanisms (actuators, motors, pumps or other equipment) are activated at a specific threshold value (temperature, pressure, mechanical load, wind, etc.) to bring the collector into a safe operating mode.
These collectors shall be tested to demonstrate the ability to protect themselves from major failures due to adverse conditions that can arise in standard operation. All tests shall be performed using the intended original manufacturer’s equipment of the collector (tracking devices, pumps, sensors, etc.) and external power sources as specified by the manufacturer. The manufacturer shall provide the laboratories with all the necessary control set points and parameters.
Collectors with active self-protection against overheating
The functioning of protection mechanisms against overheating shall be verified as defined in Clause 16. If the verification is successful, the corresponding statements in Clause 8.1 (Determination of the standard stagnation temperature), Clause 9.6 (Exposure test), Clause 10.3 (External thermal shock) and Clause 11.3 (Internal thermal shock) apply.
Collectors with active self-protection against adverse weather conditions
The functioning of protection mechanisms against adverse weather conditions shall be verified as defined in Clause 16. If the verification is successful, the impact resistance test, the mechanical load tests and the ingress of rain test shall be carried out in the corresponding collector positions resulting from the protection mechanism.
5.1.6 Collectors co-generating thermal and electrical power
General
These collectors shall be tested as any other solar thermal collector for durability and thermal performance. All thermal performance tests shall be made under maximum electrical power generation conditions. For all durability tests, the electrical power generator shall not be connected to any load (open circuit) to prevent the collector from cooling and to simulate worst operating conditions.
Reporting
The electrical power generator shall be described in detail in the test report. The electrical operating mode shall be reported for all tests.
5.1.7 Tracking collectors
When testing collectors using any tracking mechanisms, the definitions of the ISO 9488 for gross- aperture and absorber area shall be used. The determination of these areas shall be reported in Annex A.2.5. using explanatory drawings or photos.
The gross area of parabolic trough collectors shall be determined according to the IEC 62862-3-2. The gross area of Linear Fresnel collectors shall be determined according to the IEC 62862-5-2.
For all the tests it shall be verified that the tracking mechanisms are operational with the precision as declared by the manufacturer. Tracking errors shall be characterized according to
— IEC 62862-3-2, part 6.4.5, Tracking error test, for parabolic trough collectors
— IEC 62862-5-2, Annex E, for linear Fresnel collectors
— IEC 62817, part 7, Tracking accuracy characterization, for other 2 axis-tracking collectors,
Alternatively, similar procedures can be used as defined by the testing laboratory.
5.1.8 Air and liquid heating collectors
General
Collectors that can be operated as liquid heating and as air heating collectors may be tested either with both functions active or only as liquid heating collector or only as air heating collector. In all cases a clear definition of the collector working conditions of both possible functions is required and shall be described in the test report.
These collectors shall be tested as any other solar thermal collector concerning durability and thermal performance. The function not being tested shall be operated in the conditions indicated below for thermal performance tests.
Conditions for thermal performance testing as liquid heating collectors
When testing the collector as a liquid heating collector, the part working as an air collector shall be operated with the working flow rate indicated by the manufacturer and with inlet temperature close to ambient temperature.
Conditions for thermal performance testing as air heating collectors
When testing the collector as an air heating collector, the part that works as liquid heating collector shall be operated with the working flow rate indicated by the manufacturer and with inlet temperature close to ambient temperature.
6.0 Internal pressure tests for fluid channels (liquid heating collectors only)
6.1 Objective
This test is intended to assess the capability of a collector to withstand the maximum design pressure in the fluid channels.
6.1.1 Fluid channels made of non-polymeric materials
6.1.2 Apparatus and procedure
The apparatus comprises a hydraulic or pneumatic pressure source, a safety valve, an air-bleed valve, and a pressure gauge. The pressure shall be measured with a standard measurement uncertainty of less than 5%. The air-bleed valve shall be used to empty the fluid channels of air before pressurization.
The fluid channels shall be filled with a liquid at room temperature and pressurized to the test pressure. After the pressure in the collector fluid channels has been raised to the test pressure, the fluid channels shall be isolated from the pressure source employing an isolating valve. The fluid channels shall remain isolated from the pressure source during the test period, and the pressure within the fluid channels shall be observed.
6.1.3 Test conditions
The fluid channels shall be pressure-tested at ambient temperature in the range 20 °C ± 15 °C, shielded from light. The test pressure shall be at least 1,5∙pD,max. The pressure shall remain stable at ±5 % of the test pressure before isolating the collector from the pressure source. The test pressure shall then be maintained for at least 15 min.
6.2 Fluid channels made of polymeric materials
6.2.1 Apparatus and procedure
The apparatus consists of either a hydraulic or a pneumatic pressure source and a means of heating the fluid channels to the required test temperature. The pressure shall be measured with a standard measurement uncertainty of less than 5 %. The fluid channels shall be maintained at the test temperature for at least 30 min prior to the test and for the full duration of the test.
One of the following methods shall be chosen to maintain the test temperature.
a) Submerging the fluid channels in a temperature-controlled water bath and using compressed air or inked water as the test medium.
b) Connecting to a temperature and pressure-controlled liquid circuit.
c) Heating the collector in a solar irradiance simulator or under natural solar irradiance and using a fluid as the test medium.
6.2.2 Test conditions
The test temperature shall be the maximum design temperature ϑD,max or the standard stagnation temperature ϑstg, whichever is higher. For systems that experience atmospheric pressure and are intended to drain while under stagnation conditions as tested per Clause 5.3.3, the test temperature shall be the maximum design temperature ϑD,max. The test pressure shall be at least 1,5∙pD,max. The test pressure shall be maintained for at least 1 h.
6.3 Results and reporting
If visible, fluid channels shall be inspected for leakage, swelling and distortion during the test.
For non-polymeric fluid channels, leakage is assumed for a pressure loss Δp > 5 % of the test pressure or 17 kPa, whichever is greater and/or if any leaking fluid droplets are observed.
For polymeric fluid channels, leakage is assumed if any droplets or loss of air is observed.
The results of this inspection shall be reported as in Annex A.4.
7.0 Air leakage rate test (air heating collectors only)
7.1 Objective
The test is intended to quantify the leakage volumetric flow rate.
The test is not applicable for open to ambient collectors and for collectors which, for design reasons, cannot be pressurized.
7.1.1 Apparatus and procedure
The air leakage rate test is performed using a volumetric flow meter, e.g. as shown in Figure 1 Leakage from sources other than the test object shall be quantified and deducted from the results of the collector test.
Key
1 | solar air heater change (SAHC) | 4 | temperature sensor |
2 | pressure gauge | 5 | fan |
3 | flow meter |
|
|
Figure 1 — Schematic of apparatus used for measuring air leakage rates
7.1.2 Test conditions
All pipe connections except one, shall be sealed. The remaining pipe connection shall be connected to a volumetric airflow measurement device and a variable speed fan. The pressure difference between the remaining pipe connection and the ambient shall be measured using a differential pressure measurement device.
The test consists of a positive and a negative air leakage rate test. The test shall be performed with positive and negative volumetric air flow up to 1,5 times of the maximum volumetric air flow used for the thermal performance measurement. The accuracy of the volumetric airflow measurement shall be better than ±2 % and better than ±10 Pa for the differential pressure measurement. The volumetric airflow shall be measured with a standard measurement uncertainty of less than 2 %. The pressure difference shall be measured with a standard measurement uncertainty of less than 10 Pa.
Note: The maximum operation pressure of the collector can be calculated by the maximum pressure between the remaining pipe connection and the ambient pressure at the maximum volumetric flow rate used during thermal performance measurement.
If the heat transfer medium is in direct contact with polymeric materials, the test temperature shall be the maximum design temperature ϑD,max or the standard stagnation temperature ϑstg, whichever is higher.
7.1.3 Results and reporting
The results shall be reported as required in Annex A.5.
8.0 Standard stagnation temperature
8.1 Objective
The stagnation temperature is the temperature that is reached in a collector during periods when no useful heat is extracted. The standard stagnation temperature ϑstg shall be determined for the standard stagnation conditions as defined in Table 2. This clause provides two methods (Clause 8.3 and Clause 8.4) for determining the standard stagnation temperature ϑstg.
Table 2 — Standard stagnation conditions
Standard stagnation conditions | |
| 850 W/m2 |
| 150 W/m2 |
| 30°C |
| −100 W/m2 |
| 0 m/s |
| 0 K/s |
The standard stagnation temperature is used in the following tests:
— internal pressure testing of collectors with polymeric absorbers (see Clause 6.3);
— air leakage rate test of air heating collectors with polymeric materials in direct contact to the heat transfer medium (see Clause 7);
— exposure test (see Clause 9).
For collectors equipped with self-protecting mechanisms against overheating, the stagnation temperature ϑstg is per definition the trigger temperature for safety activation ϑtrigger.
8.1.1 Testing under stagnation conditions
The term testing under stagnation conditions is defined as follows: the collector shall be mounted outdoors or in a solar simulator in such a way that it is reaching its maximum possible temperature with the available solar irradiance at least once per day. Liquid heating collectors shall not be filled with a heat transfer fluid. All connectors except for one shall be sealed to prevent from cooling by natural circulation of air. Unused connectors shall be insulated. If a temperature sensor is required, it shall be fixed firmly at the absorber location where the highest temperature relevant to the heat transfer fluid is to be expected. The sensor shall be shielded from solar radiation. If the collector is provided with a sensor tube, the temperature sensor shall be installed there using heat conductive paste to ensure good thermal contact. Otherwise, the following applies: For flat plate collectors and direct flow evacuated tube collectors, this position is defined at two-thirds of the absorber height and half the absorber width. For evacuated tube collectors with heat pipes, this position is found directly on a condenser of a heat pipe. For some evacuated tube collectors, the standard stagnation temperature may be measured on a single tube with appropriate insulation on top to reduce heat losses to simulate a complete collector. Where these definitions are not applicable, an alternative suitable location must be defined.
Collectors without backside insulation shall be mounted on a dark non-metallic surface (α > 80 %) to produce maximum temperatures consistent with worst-case conditions.
8.1.2 Measurement and extrapolation of the standard stagnation temperature
The collector is tested under stagnation conditions with a temperature sensor attached to measure the absorber temperature ϑs,m. The position of the sensor shall be described in the test report.
The collector is exposed for at least 90 min under stable stagnation conditions with an average surrounding air speed of less than 1 m/s. Stable conditions are given, if the measured irradiance Ghem,m is always within 1 000 W/m2 ± 100 W/m2 and if the measured ambient temperature ϑa,m is always within 30 °C ± 10 °C.
Based on the approximation that the ratio (ϑm − ϑa)/Ghem remains constant under steady-state collector stagnation conditions, the standard stagnation temperature ϑstg for the selected parameters (Ghem,s and ϑa,s) is then given by Formula (1):
(1)
where the index m indicates measured values. The standard stagnation temperature of the collector is defined as the average value of ϑstg over the measuring period of the last 60 minutes of the stagnation test period.
8.1.3 Determining standard stagnation temperature using efficiency parameters
Based on the definition that under stagnation no useful heat removal is possible, the stagnation temperature is also defined as the mean temperature under standard stagnation conditions (see Table 2) and is determined using Formula (2) and Formula (A.1):
(2)
For collectors with 
and 
, a safety margin of +20°C as in Formula (3) shall be added to the stagnation temperature determined in Formula (2).
(3)
This approach is based on extrapolating the collector efficiency formula to the stagnation condition, i.e. where the thermal output is zero. To ensure that the efficiency formula is still valid, some of the measured collector efficiency data shall have been measured with parameters ϑm, ϑa and Ghem resulting in a power output where 
with the additional condition that Ghem > 800 Wm-2. If this is not the case, the method is not applicable.
8.1.4 Results and reporting
Stagnation temperatures for other climatic conditions G′hem,s and ϑ′a,s shall be calculated using the standard stagnation temperature given in Formula (4):
(4)
The standard stagnation temperature is reported in an up rounded 10 °C resolution (see Annex A.6).
9.0 Exposure and half-exposure test
9.1 Objective
The exposure test provides a simple reliability test sequence, indicating (or simulating) operating conditions that are likely to occur during real service and allows the collector to settle, such that subsequent qualification tests are more likely to give repeatable results. To allow the collector to settle before performing certain tests, a half-exposure sequence test is defined. The exposure test always includes the half-exposure test.
One of the climate classes as defined in Table 3, shall be selected for testing. Climate class C is intended for special purposes and may be defined as required. For collectors without active mechanism to protect against overheating, three different procedures are available to perform the tests. The results of the three procedures are deemed comparable. Every exposure or half-exposure test is started with an initial outdoor exposure under stagnation conditions (see Clause 9.2) followed by either one of the three test methods described in Clause 9.3, Clause 9.4 or Clause 9.5 to fulfil the requirements of the selected climate class. For all exposure test sequences, the connectors shall be insulated according to the manufacturer’s instruction manual, and the inclination angle shall be within the specification of the manufacturer.
Collectors using active mechanism to protect against overheating shall be tested as described in Clause 9.6.
9.1.1 Initial outdoor exposure
The collector shall be mounted outdoors under any climatic conditions for testing under stagnation conditions (see Clause 8.2) for at least 30 days (or 15 days for half-exposure). If it is admissible to install the collector vertically, it shall be exposed for at least for 15 days in vertical position.
Any signs of damage as specified in Clause 17 shall be registered and reported with the test results.
9.1.2 Method 1 (Outdoor exposure)
The ambient air temperature shall be measured with a standard measurement uncertainty of less than 1 K. The hemispherical irradiance on the plane of the collector shall be measured with a pyranometer of class B or better, in accordance with ISO 9060. Irradiation and mean ambient temperature values shall be recorded at least every 5 min.
The collector shall be further exposed until the minimum irradiation H shown in Table 3 is reached. The initial outdoor exposure time may be included if ambient air temperature and hemispherical irradiance are measured accordingly.
The collector shall also be exposed for at least 32 h (16 h for half-exposure) at irradiance and ambient air temperature greater than the value shown in Table 3. Conditions resulting in the same collector temperature according to Formula (1) are acceptable. These hours shall be made up of periods of at least 30 min. The initial outdoor exposure may be included if the mentioned data are measured accordingly.
9.1.3 Method 2 (Heat transfer loop)
After the initial outdoor exposure, the collector is connected to a pumped heat transfer loop using a suitable heat transfer liquid, with the collector forming part of the loop. A suitable heat transfer fluid is one that will remain in its liquid state at the stagnation temperature and the maximum operating pressure of the collector. The collector is operated at a fluid temperature ϑm = ϑ′stg(G′hem,s,ϑ′a,s) + 10 °C using the highest possible flow rate, where ϑ′stg(G′hem,s,ϑ′a,s) shall be calculated as stagnation temperature for the selected climate class following Clause 8. Run the system at this flow rate and temperature for maximum 8 h and then turn the pump off for at least 4 h. Continue these cycles until at least 32 h (16 h for half exposure) of operation at stagnation temperature are reached.
The collector shall further be exposed until the minimum irradiation H shown in Table 3 is reached. (Method 1 or 3).
Visually inspect the collector daily and note any changes in its appearance.
This method is not applicable for heat pipe collectors.
9.1.4 Method 3 (Indoor exposure)
After the initial outdoor exposure, the collector is installed for testing under stagnation conditions (see Clause 8.2) in a temperature-controlled solar simulator. The solar simulator output is adjusted so that the average radiation measured at six uniformly distributed points on the collector is greater than indicated for the selected climate class in Table 3 with less than 20 % variation across the aperture. Conditions resulting in the same collector temperature according to Formula (1) are acceptable. Run the system under these conditions with the simulator being operated for maximum 8 h on and at least 4 h off. Continue this cycle of operation until the values for the selected climate class are reached.
Visually inspect the collector daily and note any changes in its appearance.
9.1.5 Exposure test for collectors using active mechanism to protect against overheating
Collectors with overheating self-protection mechanisms shall be operated for at last 30 days under normal operating conditions at temperatures in the intended operating range, and until the irradiation H for the selected climate class is reached. Furthermore, the collector shall be operated for at least 32 h at a temperature not lower than 0,95∙ϑtrigger but without triggering the protection mechanism. The 32 h shall be divided in at least four individual sequences of maximum 8 h duration. Between these sequences the collector shall reach ambient temperature or the minimum design temperature for at last 4 h, whichever is higher.
9.1.6 Test conditions
The set of reference conditions given in Table 3 shall be used. The values given are minimum values for testing.
Table 3 — Climate reference conditions for exposure test and thermal shock
Climate condition | Value for climate class | |||
Class C | Class B | Class A | Class A+ | |
Minimum hemispherical solar irradiance Ghem on collector plane during minimum 32 h (or 16 h in case of half-exposure) at minimum ambient temperature ϑa.a, b | Gx ϑa,x | 900 W/m2 15 °C | 1 000 W/m2 20 °C | 1 100 W/m2 40 °C |
Irradiation H on collector plane for exposure test during minimum 30 days. | Hx | 540 MJ/m2 | 600 MJ/m2 | 700 MJ/m2 |
Irradiation H on collector plane for half-exposure sequence during minimum 15 days. | Hx/2 | 270 MJ/m2 | 300 MJ/m2 | 350 MJ/m2 |
a For thermal shock tests, the values can be understood as 1 h average values. b Some collectors do not reach maximum temperature under perpendicular irradiation. The collector shall be installed such that during the 32 h the collector is reaching its maximum temperature. | ||||
9.1.7 Results and reporting
The results including the selected climate class, the measured irradiance and temperatures levels, and any observations shall be reported as required in Annex A.7.
10.0 External thermal shock test
10.1 Objective
Collectors can, from time to time, be exposed to sudden rainstorms on hot sunny days, causing a severe external thermal shock. This test is intended to assess the capability of a collector to withstand such thermal shocks.
10.1.1 Apparatus and procedure
The collector shall be operated under stagnation conditions or shall be connected to a fluid loop as in Method 2 of the exposure test. In case of air-heating collectors, the inlet and outlet shall be protected from water penetration.
An array of water jets shall be arranged to provide a uniform spray of water over the front of the collector.
The collector shall be subject to two external thermal shocks.
10.1.2 Test conditions
The collector shall be exposed to the selected climatic conditions as described in Table 3 or conditions resulting in the same collector temperature according to Clause 8 for a period of 1 h before it is sprayed with water for at least 5 min.
Collectors with overheating self-protection mechanisms shall be operated close to the self-protection trigger temperature for a period of 1 h before being sprayed with water for at least 5 min. The climate class for testing is considered as Class A+.
The water spray shall have a temperature always between 10 °C and 25 °C and provide a spraying rate of more than 0,03 kg/s per square meter of collector gross area.
10.1.3 Results and reporting
The results shall be reported as required in Annex A.8.
11.0 Internal thermal shock test (Liquid heating collectors only)
11.1 Objective
Collectors can, from time to time, be exposed to a sudden intake of cold heat transfer fluid on hot sunny days, causing an internal thermal shock, for example, after a period of shutdown, when the installation is brought back into operation while the collector is at its stagnation temperature. This test is intended to assess the capability of a collector to withstand such thermal shocks.
11.1.1 Apparatus and procedure
The collector shall be mounted either outdoors or in a solar irradiance simulator. Liquid heating collectors shall not be filled with fluid. All fluid channels shall be sealed except for one that is left open to permit free expansion of air in the absorber. One of the sealed fluid pipes shall be connected via a shutoff valve to a heat transfer fluid source.
The collector shall be subject to two internal thermal shocks.
This test is not applicable to those parts of the collector that are factory sealed.
11.1.2 Test conditions
The collector shall be exposed to the selected climatic conditions as described in Table 3 or conditions resulting in the same collector temperature according to Clause 8 for a period of 1 h before it is flushed with cold heat transfer fluid for at least 5 min.
Collectors with overheating self-protection mechanisms shall be operated close to the self-protection trigger temperature for a period of 1 h before being flushed with cold fluid for at least 5 min. The climate class for testing is considered as Class A+.
The cold heat transfer fluid shall have a temperature of less than 25 °C. The fluid flow rate shall be the maximum flow rate of the thermal performance test or at least 0,02 kg/s per square meter of collector gross area (unless otherwise specified by the manufacturer).
11.1.3 Results and reporting
The results shall be reported as required in Annex A.9.
12.0 Rain penetration test
12.1 Objective
This test is intended to assess the capability of a collector to withstand free-falling rain or driving rain without damage and without ingression of water to such an extent that a significant reduction of the thermal performance or lifetime is to be expected.
12.1.1 Apparatus and procedure
The collector shall be installed on an open frame at the minimum design installation inclination βD,min. Collectors designed to be installed exclusively into a roof structure shall be mounted in a simulated roof and have their underside protected. The positioning of the spray nozzles is defined in Figure 2, Figure 3 and Figure 4.
If this test setup is not applicable or deemed inadequate, a comparable configuration shall be set-up where all exposed points of the collector construction potentially susceptible to damage or ingress of rain (for example, the motor of a tracking parabolic trough collector) shall be sprayed using additional spraying nozzles.
During the whole test procedure, the collector shall be shaded from light (Ghem < 200 W/m2). Air heating collectors shall be left at ambient temperature without forced airflow. The collector is then sprayed for 4 h. After the spraying, the collector shall remain shaded until final inspection.
The penetration of water into the collector shall be determined by final inspection (see Clause 17) within 72 h after spraying, thus allowing for the impact resistance and mechanical load tests. The collector shall remain shaded from direct light but not being kept warm anymore until the final inspection. The collector shall be stored in such a way that the results are not influenced, and unnecessary transportation shall be avoided.
Alternatively, the mass of the collector can be determined before and after the test. If the mass of the collector is measured within 5 hours after the test and the total increase is less than 30 g/collector, the 72-hour period can be ignored. The mass of the collector shall be measured with a reading precision and reproducibility of equal or less than 0,005 kg.
12.1.2 Test conditions
The spray nozzles required are specified as follows:
— full cone spraying;
— mass flow of 2 kg/min ± 0,5 kg/min per nozzle;
— spray angle of 60° ± 5°;
— drop size >150 µm, according to technical information from spray nozzle manufacturer;
— the water pressure at every nozzle shall be maintained at 300 kPa ± 50 kPa.
If applicable, the positioning of the spray heads shall be such that:
— at least every corner and every side of the casing is sprayed directly as shown in Figure 2;
— at least every area shown in Figure 3 (flat plate collectors with middle bars) is sprayed directly;
— at least every area shown in Figure 4 (evacuated tube collectors) is sprayed directly;
— the spray nozzles are directed at an angle of 30° ± 5° onto the plane of the collector;
— the spray heads are at a distance of 250 mm ± 50 mm from the collector;
— the maximum distance between two spraying nozzles is 150 cm. Additional spraying heads shall be installed if this is not possible.
Middle bars and any other structural components where ingress of water is assumed possible shall be sprayed accordingly. Additional spraying heads shall be placed with a distance of 400 mm to 600 mm to the collector; the spraying angle of 30° is not required. Glazing and glass tubes do not have to be tested.
If there are additional points that could be exposed to rain and where ingress of water would be a problem (motor, drives, glass connections, electronic parts, etc.) these points shall also be tested if not already classified as IP65 according to IEC 60529.
Key
L | 250 mm distance of spraying nozzle to the collector. |
α | 30° angle of spray nozzle with respect to the collector surface |
γ | smallest tilt angle to the horizontal recommended by the manufacturer, if this angle is not specified, use 30° |
Figure 2 — Positioning of collector and spray nozzles for rain penetration test
Figure 3 — Spraying areas of flat plate collectors (including middle bar)
Figure 4 — Spraying areas of evacuated tube collectors
12.1.3 Results and reporting
The results shall be reported as required in Clause A.10.
13.0 Freeze resistance test
13.1 Objective
This test is intended to assess the capability of a collector to withstand freezing conditions without damage. This test is only applicable for collectors claimed to be freeze resistant and collectors containing heat pipes. For self-protecting collectors, Clause 5.3.3 applies. Collectors using additional liquids with the risk of freezing, e.g. in heat pipes, shall be tested for their freeze resistance.
Depending on the collector design, one or both of the following methods shall be used.
13.1.1 Freeze resistant collectors
13.1.2 General
The collector shall be mounted in a cold chamber. The collector shall be fitted correctly, shut completely and inclined at the smallest tilt angle to the horizontal recommended by the manufacturer.
Collectors with draindown or drainback freeze protection
Prior to every test cycle, the collector shall be filled with water for 10 min and then drained for 5 min using the device installed by the manufacturer. A temperature sensor shall be attached at the lowest point of the collector piping to monitor the temperature of any remaining water.
Freeze-resistant collectors
The collector shall be filled with water at the operating pressure. At the end of each cycle, the collector shall be refilled with water at operating pressure. The temperature of the water shall be monitored throughout the test.
13.1.3 Test conditions
The test temperature shall be set such that the temperature sensor indicates a temperature of maximum −20 °C (or as specified by the manufacturer) for at least 1 h per cycle. The collector is then thawed to at least +10 °C sensor temperature and kept warm for at least 1 h per cycle. This test cycle shall be repeated three times.
13.1.4 Results and reporting
The results shall be reported as required in Annex A.11.1.
13.2 Heat pipe collectors
13.2.1 General
This test shall be performed on all heat pipe collectors. A minimum of six heat pipes shall be selected to undergo a freeze resistance test. These heat pipes shall have undergone at least a half exposure as part of a full collector before testing. At least one heat pipe shall be retained as a control sample for comparison with the tested samples. It can be necessary to destroy part of the collector (evacuated tubes, collector housing, etc.) to extract the heat pipes. The test shall be performed in a suitable controllable climate chamber for the duration of a set number of freeze and thaw cycles. Alternatively, a low temperature fluid loop may be used for freezing. The test shall then be performed on a complete assembled collector.
13.2.2 Test conditions
A detailed initial inspection of all the heat pipes shall document the following:
— the shape (round, oval, cylindrical, conical, etc.) and outside dimensions of all parts of the heat pipe;
— photographic record of all test samples.
At least one heat pipe shall have a temperature sensor attached to ensure an accurate and average temperature is measured. The temperature sensor shall be attached mechanically and thermally to the lower end of a heat pipe near the fluid level when all the fluid inside the heat pipe is condensed and the heat pipe is held at the tilt to be used in this test. The temperature indicated by this sensor will be assumed to represent the temperature of the fluid inside the heat pipe.
Heat pipes that cannot be separated from the evacuated tube without damage may be tested with the evacuated tube in place. On one additional sample, the condenser shall be opened by drilling a hole so that a temperature sensor can be inserted and run to the location where the heat pipe heat transfer fluid rests.
The heat pipes shall be tested at the highest recommended tilt angle. The test temperature shall be set such that the temperature sensor indicates a temperature of maximum −20 °C (or as specified by the manufacturer) for at least 1 h per cycle. The collector is then thawed to at least +10 °C sensor temperature and kept warm for at least 1 h per cycle. This test cycle shall be repeated ten times.
A detailed final inspection including a photographic record shall be made for all samples.
13.2.3 Results and reporting
The results shall be reported as required in Annex A.11.2.
14.0 Mechanical load test with positive or negative pressure
14.1 Objective
The mechanical load tests are intended to assess the extent to which the collector and its attachment points can resist positive pressure load due to wind or snow and negative pressure or uplift forces caused by wind. The mounting hardware is not evaluated.
14.1.1 Apparatus and procedure
14.1.2 Mounting
The collector shall be installed using the manufacturers’ original equipment for mounting. The collector is attached to the mounting hardware at the collector attachment points (see Figure 5). The mounting hardware is attached to the test rig. The test rig shall be rigid. Flashings or sealing kits that are an integral part of the collector shall be included in the test.
Key
1 | Collector |
2 | attachment points (relevant for the test result) |
3 | mounting hardware to be used for testing (attached to the test rig, but not relevant for the test result) |
4 | stand (not tested) |
5 | roof hooks (not tested) |
Figure 5 — Definition of mounting hardware and attachment points
14.1.3 Methods for the application of the loads
Different methodologies may be used to apply evenly distributed positive and negative load to the collector such as follows.
— Foil and gravel, sand or water: The collector is placed horizontally covered by a flexible foil. A surrounding frame high enough to contain the required amount of gravel, sand or water is placed over the collector. The gravel, sand or water shall be distributed evenly in the frame so that everywhere the same load is created until the desired height is reached.
— Suction cups: Mechanically actuated suction cups are distributed evenly on the collector surface. The suction cups shall not hinder the movement of the collector cover caused by the mechanical load.
— Air pressure: The collector is installed in a test rig where a positive or negative air pressure can be applied from the front or rear side, for example, by using air cushions or by other methods.
— Loops in combination with tensile test facilities.
Other methods may be appropriate as well, as long as they provide a homogeneous pressure distribution over the whole collector gross area. The test method shall be described in the test report.
14.1.4 Particular specifications for tracking collectors or other specific collector types
If the methods described are not applicable (for example, for tracking parabolic trough collectors), the laboratory shall design specific and suitable procedures to test the resistance against mechanical load in accordance with Clause 5.3. When, according to the manufacturer’s instructions, controls are present to protect the collectors against wind or snow load, these control functions shall be checked accordingly. The test setup and procedure shall be clearly described together with the test results.
14.2 Test conditions
The pressures shall be increased in steps of maximum 500 Pa. The reference area to be used is the gross area of the collector. Each load step shall be maintained for a minimum of 5 min. A permanent deformation shall be assigned to a load value, while it is completely relieved after every load increment and the distortion is measured compared to the beginning of the test sequence.
14.2.1 Results and reporting
The results shall be reported as required in Annex A.12.
15.0 Impact resistance test
15.1 Objective
This test is intended to assess the extent to which a collector can withstand the effects of impacts caused by hailstones.
15.1.1 Test procedure
Two test methods are available either using ice balls or steel balls.
The test procedure consists in a succession of shot series on the collector. Each shot series consists in four shots of the same impact strength. For ice balls, the impact strength of a shot is determined by the ball diameter and velocity according to Table 4. For steel balls, the impact strength of the shot is determined by the height of drop according to Clause 15.4.
Increasing impact strengths shall be used in the successive shot series. For the first series of shots, the smallest ice ball diameter specified by the manufacturer, or the lowest height of drop specified by the manufacturer for the steel ball shall be used.
Impact locations shall be selected according to Clause 15.3.
For evacuated tube collectors, the following rule applies: If one tube breaks, the test shall be repeated with an additional tube. If this tube also breaks, the collector is considered as damaged at this impact strength.
If the fluid containing absorber can be hit directly by hailstones, the collector shall be filled with a fluid at atmospheric pressure.
15.1.2 Impact location
a) Glazed flat plate collectors: The points of impact shall be located inside a radius of 75 mm from the visible glass corner. For each series of shots of one specific ice ball diameter or test height, a different corner shall be chosen.
b) Evacuated tube collectors: For each ice ball diameter or height of drop, four randomly chosen tubes of the collector shall each be tested with one impact. Two tubes shall be tested at the upper end and two tubes at the lower end. The points of impact shall be located at a maximum of 75 mm from the upper visible end and from the lower visible end and impact the tube in the centre where the tube surface is normal to the impact. The shot direction shall be normal to the tube axis.
c) Collectors that cannot be clearly classified into the category a) or b): Four representative impact locations shall be defined by the testing laboratory. The coordinates of the points of impact shall be defined before the shots.
15.1.3 Method 1: Impact resistance test using ice balls
15.1.4 Apparatus
The collector shall be installed on a rigid frame. The support shall be stiff enough so that there is negligible distortion or deflection at the time of impact. The ice balls as defined in Clause 15.4.2 shall hit the collector in the locations defined in Clause 15.3 with the impact surface perpendicular to the path of the ice ball.
The mass of the ice balls shall be measured with a standard measurement uncertainty of less than 2 %. The velocity of the ice balls shall be measured with a standard measurement uncertainty of less than 1 m/s. The distance of the velocity sensor to the collector surface shall be at maximum 1 m.
15.1.5 Ice balls
The ice balls shall be made of water without any additive. They shall consist in clear ice entirely free of air bubbles and shall not have any crack visible to an unaided eye. The ball diameter shall be one of those listed in Table 4 with a tolerance of ± 5% for the mass and for the test velocity. The ice balls used for the shots shall have a temperature of less than −4 °C.
Table 4 — Ice ball masses and test velocities
Nominal diameter (mm) | mass (g) | test velocity (m/s) |
15 | 1,63 | 17,8 |
25 | 7,53 | 23,0 |
35 | 20,7 | 27,2 |
45 | 43,9 | 30,7 |
15.1.6 Specific aspects of the test procedure using ice balls
a) Place the balls in the storage container and leave them there for at least 1 h before use.
b) Ensure that all surfaces of the launcher likely to be in contact with the ice balls are near room temperature.
c) Install the collector at room temperature on the rigid frame.
d) The time between the removal of the ice ball from the container and its impact on the collector shall not exceed 60 s.
e) Fire the shot series on the collector as required. Inspect the collector at the points of impact and take notice of any sign of damage and visible effect of the shots.
15.2 Method 2: Impact resistance test using steel balls
The collector shall be mounted either vertically or horizontally on a support. The support shall be stiff enough so that there is negligible distortion or deflection at the time of impact.
Steel balls shall be used to simulate a hail impact. If the collector is mounted horizontally, then the steel balls are dropped vertically or if it is mounted vertically, then the impacts are directed horizontally by means of a pendulum. In both cases, the height of drop is the vertical distance between the point of release and the horizontal plane containing the point of impact.
If the test is carried out according to this method, the steel ball shall have a mass of 150 ± 10 g and drop heights from 0,4 m to 2,0 m with steps of 0,2 m shall be considered.
15.2.1 Results and reporting
The results shall be reported as required in Annex A.13.
16.0 Active self-protection mechanisms
16.1 Objective
The functionality of all active mechanisms which are protecting the collector from damage caused by adverse operational or environmental conditions shall be verified. These active self-protection mechanisms (actuators, motors, pumps or other equipment) are activated at a certain threshold value (temperature, pressure, mechanical load, wind etc.) to bring the collector in a safe operating or stow mode. Such safety modes are usually triggered by severe failures in the system and therefore the collector shall not go back automatically to normal operation mode without verification that the triggering problem is resolved. The collector shall therefore always remain in safe mode for at least one hour, or until a person is bringing the collector back to operation.
Collectors with any active protection mechanisms shall at least be tested for loss of power (Clause 16.3.1) and loss of communication (Clause 16.3.2).
Collectors with overheating protection shall also be tested according to Clause 16.3.3.
Collectors with protection mechanisms against adverse weather conditions shall also be tested according to Clause 16.3.4.
If these methods are not applicable or not appropriate, alternative test sequences shall be defined by the testing laboratory to verify suitable operation of all the active protection mechanisms.
16.1.1 Apparatus and procedure
The collector shall be operated under normal operating conditions. The sensors and controllers of the manufacturer shall be used for testing. The manufacturer shall submit to the laboratories the control set points and parameters. Depending on the test sequence, the relevant sensor triggering the self-protection mode shall be activated in a way that is as close to real operating conditions as possible.
16.1.2 Test conditions
16.1.3 Loss of power test
For all devices using external power sources for self-protection, it is assumed that power is available at the required level for normal operation and for at least the time required to bring the collector in a safe position after a self-protection threshold has been passed. To verify this, the collector is operated under normal operating conditions, then the main power connection is disconnected.
It shall be verified that the collector is going in a safe operating mode and remains there for at least one hour, or until a person is bringing the collector back to operation.
16.1.4 Loss of communication test
Collectors using controllers are usually operated from a central operating unit. If communication between collector and the central unit is interrupted, the collector shall go in a save operating mode. For this test, the collector is operated under normal operating conditions, then the main communication cable is unplugged.
It shall be verified that the collector is going in a safe operating mode and remains there for at least one hour, or until a person is bringing the collector back to operation.
16.1.5 Overheating protection test
Collectors using active overheating protection, shall go immediately in a save operating mode when the temperature ϑtrigger trespassed. For this test, the collector shall be operated such that it is trespassing the maximum allowed temperature ϑtrigger as indicated by the manufacturer.
It shall be verified that the self-protection mechanism is quick enough to protect the collector from damages caused by overheating.
It shall be verified that the collector is going in a safe operating mode and remains there for at least one hour, or until a person is bringing the collector back to operation.
16.1.6 Adverse climatic conditions protection test
The collector is operated under normal operating conditions. The sensors or signals used to trigger self-protection shall be activated to simulate adverse weather conditions (e.g. hail, wind, or snow). It shall be verified that the collector is going in a safe operating or stow mode until a person is bringing the collector back to normal operation mode. This safe position shall be used for testing of impact resistance, wind, or snow load as appropriate.
16.2 Results and reporting
The protection systems shall be described in the test report together with the control set points, threshold values and other relevant parameters. All results shall be reported as defined in Annex A.2.3.
17.0 Final inspection
17.1 Objective
The final inspection is intended to record the structure and materials of the collector and to assess the condition of the collector after completion of testing if it is not going to be used for other tests anymore. The final inspection shall also support the material efficiency assessment according to Annex G.
17.1.1 Test procedure
The collector shall be dismantled and inspected completely under laboratory conditions, i.e. in a non-operating condition, shaded from light and at room temperature. Final inspection shall be considered as a destructive test method and shall therefore be the concluding test.
The collector shall be described as required in Annex A.2. The information given shall be verified against the manufacturer’s information.
Following the list in Annex A.14, but not limited to, all defects and abnormalities shall be documented and rated where applicable according to the following key.
0 No problem:
Thermal performance, durability, safety and visual appearance are considered as not affected by the preceding tests and are deemed remaining stable over the expected lifetime.
No discolouration of the glazing due to outgassing is visible.
1 Minor problem:
Mainly visual appearance aspects, aesthetical defects. Durability and safety are considered as remaining stable over the expected lifetime. Slightly visible glazing discoloration due to outgassing.
Permanent condensation and continuously progressing deficiencies shall be rated as major problems.
2 Major failure:
Severe premature failure concerning thermal performance, durability, safety or visual appearance is found or is to be expected. Significant outgassing with visible glazing discoloration.
All findings rated as minor problem or as major failure shall be documented by photographs.
A “major failure” rating is mandatory (if applicable) in case of (but not limited to):
— breaking or permanent deformation of the cover or the cover fixing;
— liquid channel leakage;
— any deformation such that permanent contact between absorber and cover is established;
— breaking or severe deformation of collector fixing points or of the collector box;
— vacuum loss, loss of gas filling;
— dissolution of absorber coating;
— accumulation of humidity in form of permanent condensate on the inside of the transparent cover or permanent local accumulation of water excessing 30 g anywhere in the collector.
17.1.2 Results and reporting
The results shall be reported as required in Annex A.2 and using Table A.5 in Annex A.14.
18.0 Thermal performance testing
18.1 General
Thermal performance testing of solar collectors includes at least the assessment of the heat power delivered by the collector under various operating conditions (see Clause 23), the measurement of the dependence of the thermal performance on the incidence angle of the irradiation onto the collector (see Clause 26) and the determination of the collector heat capacity (see Clause 25). These three sets of parameters are required for the calculation of the collector heat output. For the test setup and the measurements, the provisions of Clause 19 to Clause 21 shall be followed.
This document also provides methods to determine additional important parameters such as the pressure drop and the time constant.
If the collector is supplied in fixed units of gross area smaller than 1 m2, then enough collector elements shall be linked together to give a test collector with a gross area of at least 1 m2.
Two methods are available for thermal performance testing: the steady-state method and the quasi-dynamic test method. Both methods are deemed to provide equivalent test results and methods for mutual converting the parameters sets are available. A combination of both methods is possible but shall always be clearly stated in the test report.
The validation sequence described in Annex I can be used to compare and verify the parameters measured with the two methods.
Thermal performance testing is possible on outdoor test facilities, as well as on indoor test rigs using a solar simulator. A combination of both methods is possible but shall always be clearly stated in the test report.
19.0 Collector mounting and location
19.1 General
The collector shall be mounted as specified by the manufacturer. Unless otherwise specified (for example air-brine collectors), an open mounting structure shall be used which allows air to circulate freely around the front, back and sides of the collector.
Collectors specified for roof/wall integration only, shall be installed according to the manufacturers’ instruction and using the original parts (e.g. flashing kits) on a simulated roof/wall structure where the rear side of the collector is protected from wind, but without additional insulation.
Collectors specified to be installed on an insulated structure (some wall collector designs, some swimming pool collectors, etc.) shall be mounted on an insulated backing with a quotient of the materials thermal conductivity to its thickness of 1 W/(m2K) ± 0,3 W/(m2K) and the upper surface painted matt white and ventilated at the back. The use of such insulation shall be described clearly in the test report together with a statement that the measured thermal performance results are possible only when using an additional back insulation with the thermal conductivity as used for the test.
NOTE Example material suited for the insulated backing is 30 mm of polystyrene foam.
For site-built collectors not supplied in a pre-specified size, it shall be checked that a realistic flow pattern and flow velocity is used during the thermal performance tests.
The collector shall be mounted such that the lower edge is not less than 0,5 m above the local ground surface. Currents of warm air, such as those that rise the walls of a building, shall not be allowed to pass over the collector. Where collectors are tested on the roof of a building, they shall be located at least 2 m away from the roof edge.
The type of installation, including the possible roof integration, the flashing kits, any additional protection of the backside or additional insulations, must be described and reported together with the test results in Annex A.15.3.1.
19.1.1 Shading from direct solar irradiance
The location of the test stand shall be such that no shadow is cast on the collector and the irradiance measurement instruments during the test.
19.1.2 Diffuse and reflected solar irradiance
For the purposes of analysis of outdoor test results, solar irradiance not coming directly from the sun’s disc is assumed coming isotropic from the hemispherical field of view of the collector. The collector shall be located where there is no significant solar radiation from surrounding buildings or surfaces reflected onto it, and where there are no significant obstructions in the field of view. Surfaces to be avoided in the collector’s field of view include large expanses of glass, metal or water. It is also important to minimize reflections to the rear side of the collector, especially for evacuated tube collectors. The reflectance of most rough surfaces such as grass, weathered concrete or chippings is typically low enough so that no problem is caused during collector testing.
In solar simulators, the simulated beam approximates direct solar irradiance only and it is necessary to minimize reflected irradiance. This can be achieved by painting all surfaces in the test chamber with dark low reflectance paint.
The solar reflectance of the background used during the thermal performance test of collectors being non-opaque from the back shall not exceed 20 %.
19.1.3 Thermal irradiance
The thermal performance of some collectors is particularly sensitive to the levels of thermal irradiance. The temperature of surfaces adjacent to the collector shall be as close as possible to that of the ambient air to minimize the influence of thermal radiation. For example, the outdoor field of view of the collector shall not include chimneys, cooling towers or hot exhausts. For indoor and simulator testing, the collector shall be shielded from hot surfaces such as radiators, air-conditioning ducts and machinery, and from cold surfaces such as windows and external walls. Shielding is important both in front of and behind the collector.
20.0 Instrumentation
20.1 Solar radiation measurement
20.1.1 Pyranometer
General
Pyranometers of Class B or better as specified in ISO 9060, shall be used to measure the hemispherical solar radiation following the recommendation given in ISO/TR 9901. Class B or better pyranometer(s) equipped with a shading ring or alternatively a pyrheliometer, together with a pyranometer, shall be used to determine the diffuse short-wave radiation.
For highly concentrating collectors (CR > 3) mounted on the original manufacturer’s solar tracking device, a pyrheliometer of Class B or better, as specified in ISO 9060, shall be used to measure the direct normal irradiance (DNI). The pyrheliometer field of vision shall be no more than 6° of arc. The tracking errors associated to the mounting on the tracker shall not exceed ±0,5°.
Mounting of the pyranometer
The pyranometer shall be installed such as to receive the same levels of direct, diffuse and reflected solar radiation as are received by the collector. The pyranometer shall be mounted such that its sensor is coplanar, within a tolerance of <1° with the collector plane. It shall not cast a shadow onto the collector area at any time during the test period. Care shall also be taken to prevent energy reflected from the solar collector onto the pyranometer. The body of the pyranometer and the emerging leads of the connector shall be shielded to minimize solar heating of the electrical connections.
Measurement of the angle of incidence of direct solar radiation
The incidence angles shall be determined by calculation or shall be measured with a standard measurement uncertainty of less than 1°.
In case of non-imaging stationary collectors such as CPCs, they shall be mounted so that the beam radiation from the sun falls within the angular acceptance range of the design.
20.2 Thermal radiation measurement
If required, the long wave irradiance, EL, shall be measured using a pyrgeometer mounted in the plane of the collector. The long wave irradiance shall be measured with a standard measurement uncertainty of less than 10 Wm-2.
The pyrgeometer shall be mounted to one side at mid-height of the collector.
20.2.1 Temperature measurements
20.2.2 Heat transfer fluid temperatures (Liquid heating collectors)
Required accuracy
The difference between the collector outlet and inlet temperatures ΔT shall be measured with a standard measurement uncertainty of less than 0,05 K. The inlet temperature shall be measured with a standard measurement uncertainty of less than 0,5 K.
Mounting of sensors
The sensor for temperature measurement of the heat transfer liquid shall be mounted at no more than 200 mm from the collector inlet and outlet, and insulation shall be placed around the pipe work both upstream and downstream of the sensor. If it is necessary to position the sensor more than 200 mm away from the collector, then a test shall be made to verify that the measurement of fluid temperature is not affected. To ensure mixing of the fluid at the position of temperature measurement, a bend in the pipe work, an orifice or a fluid-mixing device shall be placed upstream of the sensor. The sensor probe shall point upstream in a pipe where the flow is rising (to prevent air from being trapped near the sensor).
20.2.3 Volume flow weighted mean temperature ϑm,th (air heating collectors)
General
The volume flow weighted mean temperature describes the volume flow, heat capacity and density weighted temperature defining the mean temperature in an air duct.
If an airflow with temperature ϑ > ϑa is flowing through a ventilation channel, a certain temperature distribution is created and, consequently, a density distribution ρ(x,y) and heat capacity distribution c(x,y) due to heat losses of the ventilation channel and the given flow velocity distribution v(x,y) in the ventilation channel as described in Formula (5). The weighted mean temperatures ϑm,th,in and ϑm,th,out are the representative temperatures for the caloric balance of an air heating collector.
(5)
Due to the small influence of density and heat capacity, this may be reduced to Formula (6):
(6)
The flow distribution shall be homogenized constructively over the channel cross-section. The temperature measurement shall be designed in a way that temperature gradients are balanced over the channel cross-section. For example, the flow distribution can be homogenized by introducing fine-mesh nets in the ventilation channel. Using an averaging, evenly distributed (Archimedean spiral) temperature sensor in the channel, the thermal average temperature can be determined.
Required accuracy
The difference between the collector outlet and inlet temperatures ΔT shall be measured with a standard measurement uncertainty of less than 0,2 K. The inlet temperature shall be measured with a standard measurement uncertainty of less than 0,5 K.
Mounting of sensors
The sensor for temperature measurement shall be mounted at no more than 200 mm from the collector inlet/outlet and insulation shall be placed around the ducts both upstream and downstream of the sensor. If it is necessary to position the sensor more than 200 mm away from the collector, then a test shall be made to verify that the measurement of the fluid temperature is not affected; this can be done by a recalculation of the inlet and outlet temperature difference.
NOTE An example of a sensor configuration is given in Annex F.
20.2.4 Measurement of ambient air temperature
Required accuracy
The ambient air temperature shall be measured with a standard measurement uncertainty of less than 0,5 K.
Mounting of sensors
For outdoor measurements, the sensor shall be shaded from direct and reflected solar radiation by means of a white-painted, well-ventilated shelter, preferably with forced ventilation. The shelter itself shall be shaded and placed at the mid-height of the collector but at least 1 m above the local ground surface to ensure that it is removed from the influence of ground heating. The shelter shall be positioned not more than 10 m distance to the collector.
If air is forced over the collector by a wind generator, the air temperature shall be measured in the outlet of the wind generator and checks made to ensure that this temperature does not deviate from the ambient air temperature by more than ±2 K.
20.3 Flow rate measurement
20.3.1 Measurement of mass flow rate (liquid)
The mass flow rate shall be measured with a standard measurement uncertainty of less than 1 %.
20.3.2 Measurement of collector fluid flow rate (Air heating collectors)
Through the determination of pressure and temperature, the volumetric flow rate shall be converted to mass flow rate, as given in Formula (7)
(7)
Where the density ρl is calculated as in Formula (8):
(8)
To determine the flow rate, measurement methods using the differential pressure method (orifice plates, venturi tubes or laminar-flow-elements) or mechanical methods (turbine gas meter) shall be used. Thermal measurement methods are not applicable due to large measurement errors caused by the water content in the air.
Required accuracy
The mass flow rate shall be measured with a standard measurement uncertainty of less than 2 %. The absolute pressure of the ambient air pabs shall be measured with a standard measurement uncertainty of less than 50 Pa. The temperature of the airflow at the volumetric flow rate measurement unit shall be measured with a standard measurement uncertainty of less than 1 K. The volumetric flow shall be measured with a standard measurement uncertainty of less than 1 %.
20.4 Measurement of air speed over the collector
20.4.1 General
The relationship between the meteorological wind speed and the air speed over the collector depends on the location of the test facility, so that meteorological wind speed is not a useful parameter for collector testing. By using the air speed measured over the collector, it is possible to define clearly the conditions in which the tests were performed. The air speed shall be monitored during the test at a convenient point that has been calibrated relative to the mean air speed over the collector.
20.4.2 Required accuracy
The speed of the surrounding air over the front surface of the collector shall be measured with a standard measurement uncertainty of less than 0,5 ms-1. It shall be taken into consideration that most anemometers have starting limits which lie between 0,5 ms-1 and 1,0 ms-1. The surrounding air speed is usually not constant under outdoor conditions. The measurement of an average air speed is therefore required, either by an arithmetic average of sampled values or by a time integration over the test period.
20.4.3 Mounting of sensors for the measurement of air velocity over the collector
Surrounding wind or artificial wind generators may be used to provide the required wind speed parallel to the collector surface for testing. The uniformity of air speed in the field of collector area shall be checked as the air speed can vary from one end of the collector to the other. Air speed measurements shall be taken using a handheld anemometer. During these measurements, the surrounding air speed shall be close to zero. The measurements shall be taken at a distance of 50 mm from the plane of the collector, at points evenly distributed over the entire collector area. An average value shall then be determined.
During the test, the air speed shall then be monitored continuously at a convenient point that has been calibrated relative to the mean air speed over the collector, considering also surrounding air speed. The sensor shall not be shielded from the wind, and it shall not cast a shadow on the collector during the test periods.
If the backside of the collector is considered as wind sensitive, and if the backside is exposed to wind during testing, the air speed shall be adjusted and measured over the front and back surfaces. The average air speed on the front and back surface shall be used in the data correlation.
20.5 Elapsed time measurement
The elapsed time shall be measured with a standard measurement uncertainty of less than 0,2 %.
20.5.1 Humidity ratio (air collectors)
The humidity ratio XW shall be measured with a standard measurement uncertainty of less than 0,001 % (kgwater/kgdry air) at 25 °C fluid temperature.
20.5.2 Collector dimensions
The collector dimensions shall be measured with a standard measurement uncertainty of less than 0,3 %. Area measurements shall take place at a collector temperature of 20 °C ± 10 °C and under operating pressure if the absorber is made of polymeric material. If the resulting collector area is within 1 % of the manufacturer’s specification, then the manufacturer’s specification may be reported and used for efficiency calculation. If not, the measured collector area shall be used.
21.0 Test installation
21.1 Liquid heating collectors
21.1.1 General
An example of schematic test configurations for liquid heating collectors is shown in Figure 6.
Key
1 | solar collector | 7 | pump |
2 | temperature sensor (ϑi) inlet, downstream | 8 | artificial wind generator |
3 | temperature sensor (ϑe) outlet, downstream | 9 | anemometer |
4 | insulated pipe | 10 | radiation measurements |
5 | temperature controller | 11 | ambient temperature sensor |
6 | flow meter |
|
|
Figure 6 — Example of a closed test loop
21.1.2 Heat transfer fluid
The heat transfer fluid used for collector testing may be water or a fluid accepted by the collector manufacturer. The specific heat capacity and density of the fluid used shall be known to within ±1 % over the range of fluid temperatures used during the tests. Values for water are given in Annex D.
21.1.3 Pipe work and fittings
Pipe work shall be insulated such that the temperature gains or losses between the temperature sensing points and the collector inlet and outlet are reduced as much as possible under test conditions.
The collector pipe work shall be vented of trapped air and any contaminants shall be removed.
Unused connectors shall be insulated if this is required or recommended by the installation manual.
21.2 Air heating collectors
21.2.1 General
Several types of air heating collectors are distinguished.
— Air heating collectors working in a closed air circuit (closed loop).
— Air heating collectors sucking ambient air. Transpired collectors where ambient air is sucked through the absorber material, or through the perforated glazed collector cover.
— Open to ambient air heating collectors where ambient air is sucked in at defined inlet openings.
21.2.2 Closed loop test circuit
Closed loop collectors shall be measured in a test loop as outlined in Figure 7. Two flow meters shall be used, one at the inlet and one at outlet. The collector shall be measured at ambient pressure, which is realized by using two fans. Between the two fans, an area where the air can be conditioned may be installed.
Key
1 | fan | 9 | temperature sensor (ϑe) outlet, downstream |
2 | flow meter | 10 | flow meter |
3 | temperature controller | 11 | fan |
4 | temperature sensor (ϑi) inlet, downstream | 12 | pressure gauge (pi) |
5 | solar collector | 13 | differential pressure (Δp=pi – pe) |
6 | artificial wind generator | 14 | pressure gauge (pe) |
7 | anemometer | 15 | ambient temperature sensor |
8 | radiation measurements | 16 | barometer for ambient air (pabs) |
Figure 7 — Example of a closed test loop
21.2.3 Open to ambient test circuit
The mass flow for open to ambient air heating collectors can only be determined at the collector outlet. The collector inlet temperature corresponds to the ambient temperature. An example of a test configuration for testing open to ambient air heating collectors is shown in Figure 8.
Key
1 | solar collector | 6 | anemometer |
2 | temperature sensor (ϑe), downstream | 7 | radiation measurements |
3 | flow meter | 8 | pressure gauge (pe) |
4 | fan | 9 | ambient temperature sensor |
5 | artificial wind generator | 10 | barometer for ambient air (pabs) |
Figure 8 — Example of an open to ambient test setup
21.2.4 Heat transfer fluid
To determine the specific heat capacity of the air at each measurement point, the temperature and humidity are needed. This can be calculated with the air temperature as given in Clause 20.3.2. The density shall be calculated as described in Clause 20.4.2.
21.2.5 Pump and flow control devices
The fluid pump shall be installed in the collector test loop such that the heat that is dissipated in the heat transfer fluid does not affect either the control of the collector inlet temperature or the measurements of the fluid temperatures. The pump and flow controller shall be capable of maintaining the mass or volume flow rate through the collector stable to within 1 % despite temperature variations, at any inlet temperature chosen within the operating range.
21.2.6 Air ducts
Air leakage from the duct system shall not affect the accuracy of the measured collector thermal performance. Before the thermal performance measurement, the inlet and outlet test ducts shall be tested for leaks. The same method shall be used as described in Clause 7. No component shall have a higher leakage rate than 2 m3/h at 250 Pa.
21.2.7 Fan and flow control devices
The fan shall be installed in the collector test loop in such a position that the heat from it, which is dissipated in the fluid, does not affect either the inlet temperature or the measurements of the fluid temperature rise through the collector. The fan and flow controller shall be capable of maintaining the mass flow rate through the collector stable to within ±1,5 % despite temperature variations, at any inlet temperature chosen within the operating range.
21.2.8 Air preconditioning apparatus
The air preconditioning apparatus shall control the dry bulb temperature of the transfer medium entering the solar collector to within ±1,0 K of the desired test value at during the whole test period. The rate of energy collection in the collector is deduced by measuring instantaneous values of the fluid inlet and outlet temperatures. Even small variations of the inlet temperature lead to errors in the rates of energy collection deduced. It is particularly important to avoid any drift in the collector inlet temperature.
21.2.9 Humidity ratio
When air is the transfer fluid and the test panel is operated at a negative pressure, the humidity ratio of the test fluid shall be equal to the humidity ratio of the air surrounding the test panel. The humidity shall be controlled and measured at the different measuring points. Condensation in the testing loop shall be avoided.
22.0 Thermal performance test procedures
22.1 General
The thermal performance of the solar collectors shall be tested according to one of the methods described in the following subclauses.
For collectors co-generating heat and electric power, the thermal performance, the time constant, the incidence angle modifier and the heat capacity shall be measured in maximum peak power tracking mode, meaning with maximum possible electric power generation.
If the thermal performance of a collector is considered as not specifically sensitive to wind or long wave radiation exchange or upon request of the ordering party, a simplified testing procedure can be applied. Simplified testing means that the wind dependency and the long wave radiation exchange dependency are not assessed so that the parameters a3, a4, a6 are set to 0.
NOTE For wind- and infrared-sensitive collectors, the simplified test procedure leads to lower annual performance results compared to the full test.
For concentrating collectors with a transparent cover and a concentration ratio of CR > 3, wind speed dependency may be neglected. For concentrating collectors where the absorber is protected from wind (for example by using evacuated tubes), wind speed dependency may be neglected independent of the concentration ratio CR.
The thermal performance of highly concentrating tracking collectors is usually tested according to the quasi-dynamic test method. The steady-state method may be used if a distinction between beam and diffuse irradiance is considered. The requirements and parameters as described in Clause 22.4.3 for quasi-dynamic testing shall be followed.
For solar tracking collectors the tracking mechanism should not have a relevant influence on the thermal efficiency characterization. The tracking error should be less or equal to the theoretical acceptance angle of the concentrator (determination by geometrical calculation, optical simulation, or as specified by the manufacturer). In the testing report it should be registered if some data with incorrect tracking were rejected.
22.1.1 Preconditioning of the collector
The collector shall be preconditioned under stagnation conditions (see Clause 8.2) for at least 5 h at the level irradiation higher than 700 W/m2 and ambient temperature higher than 10 °C. Half-exposure or exposure test is sufficient to satisfy this preconditioning. Clause 5.3.3 and Clause 9.2 applies if the collector is equipped with means to prevent from stagnation.
The collector cover, reflectors and tubes shall always be thoroughly cleaned for all thermal performance measurements. If moisture is formed on the collector components, the heat transfer fluid may be circulated at elevated temperatures for as long as is necessary to dry out collector again. If this form of preconditioning is carried out, then it shall be reported with the test results.
22.1.2 Test conditions
22.1.3 General
The heat transfer flow pattern shall be selected as recommended by the manufacturer and shall be described in the test report.
22.1.4 Flow rates
If the recommended fluid flow rate is close to the transition region between laminar and turbulent flow, this can cause instability of the internal heat transfer coefficient and variations in the measurements of the collector efficiency. To characterize such a collector, it may be necessary to use a higher flow rate, but this shall be clearly stated with the test results.
The flow rate shall be held stable according to Table 6 (steady-state method) or to within ±2 % (quasi-dynamic method) of the set value during each test period and shall not vary by more than ±5 % of the set value from one test period to another.
Flow rate for liquid heating collectors
The fluid flow rate shall be set at approximately 0,02 kg/s per square meter of collector gross area. If this is not within the manufacturers’ specification, a reasonable flow rate within the specification shall be selected.
Flow rate for air heating collectors
The fluid flow rate shall be set as close as possible to the maximum, the minimum and the medium flow rate as specified by the manufacturer.
In case of a standalone collector (e.g. integrated PV for power supply for the fan and implicitly used as flow rate controller), the generated volumetric flow range dependence on the irradiance level shall be given.
22.1.5 Air speed parallel to the collector plane
When using the steady-state method, measurements shall be made at three average air speed ranges parallel to the surface of the collector: <1 m/s, (1,5 ± 0,5) m/s and (3 ± 1) m/s. The three wind speeds shall differ by at least 1 m/s from each other.
When using the quasi-dynamic test method, measurements shall be made over the entire range of wind speeds between 0 m/s and 4 m/s.
For simplified testing, the average value of air speed parallel to the plane of the collector, considering spatial variations over the collector and temporal variations during the test period, shall be ≥1.3 m/s.
Wind generators may be used if necessary to achieve sufficient wind speeds.
22.2 Test procedure
22.2.1 General
The collector shall be tested over the full range of operating temperatures specified by the manufacturer. The inlet temperature shall always be kept above the dew point so that condensation of water on the absorber is avoided. If possible, one inlet temperature shall be selected such that the mean collector temperature is within ±3 K of the ambient air temperature.
During a test, the measurements shall be made as specified in Clause 22.5.
22.2.2 Steady-state method
General
The angle of incidence of direct solar radiation at the plane of the collector shall be in the range in which the incidence angle modifier for the collector varies by no more than ±2 % from its value at normal incidence. The collector shall be tested at diffuse irradiance levels of always less than 30 %.
At the time of the test, the hemispherical solar irradiance at the plane of the collector shall always be greater than 700 W/m2.
Data sets shall be measured for the wind speeds given in Clause 22.3.3 and for at least four fluid inlet temperatures spaced evenly over the operating temperature range of the collector. If the distance between the inlet temperatures is less than 10 K the number of inlet temperatures may be reduced to three, but not less. A data set consists of at least four independent data points.
When testing in a solar simulator, at least two independent data points shall be obtained for each data set.
Steady-state testing of air heating collectors
For open to ambient collectors, all data points are measured for inlet temperatures equal to the ambient temperature.
22.2.3 Quasi-dynamic testing
Data points satisfying the requirements given below shall be obtained for at least four fluid inlet temperatures spaced evenly over the operating temperature range of the collector.
Weather conditions shall be as described in Clause 22.6.2, sequence day types 1 through 4. The second and third inlet temperature shall be selected so that the mean fluid temperature in the collector is evenly spaced between the lowest and the highest operating range of the collector.
The change in inlet temperature shall be done after each test sequence has been completed. Data recorded during this “step-change” period shall not be included in the test data. The inlet temperature shall be kept stable within ± 1 K during each test sequence.
22.3 Measurements
22.3.1 General
Depending on the chosen test method, the quantities that are needed for the measurement of the thermal performance shall be measured (see Table 5 as guideline).
Table 5 — Measured quantities during testing
Steady-state | Steady-state | Quasi-dynamic | |
Hemispherical solar irradiance at the plane of the collector | X | X | X |
Diffuse solar irradiance at the plane of the collector (only outdoors) | X | X | X |
Angle of incidence of direct solar radiation (alternatively, this angle may be determined by calculation) | X | X | X |
Air speed parallel to the plane of the collector | X | X | X |
Temperature of the ambient air | X | X | X |
Temperature of the heat transfer fluid at the collector inlet and outlet | X | X | X |
Flow rate of the heat transfer fluid | X | — | X |
Dew point temperature of the surrounding air | — | X | — |
(Relative) humidity of the heat transfer fluid at the collector inlet and outlet | — | X | — |
The mass flow rate of the heat transfer fluid at the collector inlet (only closed loop) | — | X | — |
The mass flow rate of the heat transfer fluid at the collector outlet | — | X | — |
Static pressure of the heat transfer fluid at the inlet and outlet of the solar collector | — | X | — |
Absolute pressure of the ambient air | — | X | — |
Long wave thermal irradiance in the collector plane (if not tested using the simplified method) | X | X | X |
22.3.2 Data acquisition requirements
Data shall be measured at intervals of 10 s or less. For the verification of the stability criteria average values shall be recorded at intervals of 30 s or less. For outdoor measurements, each data record shall contain a unique time stamp to calculate the angle of incidence of the solar radiation onto the collector.
22.4 Test period
22.4.1 Steady-state testing
A collector is considered to have been operating in steady-state conditions over a given period if none of the experimental parameters that are needed for the measurement of the thermal performance deviates from its mean value by more than the limits given in Table 6. The measurement period is at least four times the time constant of the collector (if known), or not less than 15 min for liquid heating collectors (if time constant is not known).
For air-heating collectors, the measurement period shall be more than 20 min.
Table 6 — Permitted deviation of measured parameters during a measurement period
Parameter | Permitted deviation from the mean value | |
Liquid heating collector | Air heating collector | |
Hemispherical solar irradiance | ±50 W/m2 | |
Thermal irradiance | ±20 W/m2 | |
Ambient air temperature | ±1,5 K | |
Fluid mass flow rate | ±1 % | ±2 % |
Fluid temperature at the collector inlet | ±0,1 K | ±1,5 K |
Fluid temperature at the collector outlet | ±0,4 K | ±1,5 K |
Surrounding air speed | ±1,0 m/s deviation from set value | |
22.4.2 Quasi-dynamic testing
General
The test period consists of four to five sequences (days). The number of days is dependent on the weather conditions on the test site. The data record shall contain data equivalent to all the important normal operating conditions (enough variability and dynamic range), to give decoupled collector parameters. This is done by varying the inlet temperature to the collector within its design range. If sufficient data has been recorded after four to five days, this data shall be evaluated following the guidelines outlined in Clause 23.1.3.
Description of test sequences
The minimum length of a test sequence shall be 3 h. The 3 h do not need to be consecutive and the test sequence may consist of several non-consecutive parts with a minimum length of 30 min.
Day type 1
The test sequence under η0 – conditions shall be conducted under mostly clear-sky conditions. It shall include values of the incidence angle from larger than 60° down to values where the difference of the incidence angle modifier of the beam irradiance differs not more than 2 % from the value at normal incidence (see Clause 25.2.2).
Day type 2
At least one test sequence shall be conducted under partly cloudy conditions, including broken cloud, as well as clear sky conditions. This can be a test sequence under elevated operating temperature or under η0 – conditions.
Day type 3 (1 day or 2 days)
Measurements under mean operating temperature conditions including clear sky conditions.
Day type 4
Measurements under high operating temperature conditions including clear sky conditions.
Day type 1 and day type 2 may be adapted for collectors with a concentration ratio CR > 20. These modifications of the procedure shall be described and explained in the test report.
Evaluation of test data
To ensure that the initial state of the collector does not influence the result of the parameter identification, a period of at least four times the time constant of the collector (if known) or 15 min (if time constant is not known) with the correct fluid temperature at the inlet and with the correct wind speed range across the collector shall not be included in the analysis. For clarity, the requirements are given in the form of idealized diagrams, showing important relationships between different test data, including the dynamic ranges that shall be in the data to achieve reliable and de-coupled collector parameters.
Figure 9 shows ϑm – ϑa versus Ghem to check if sufficient data has been taken under η0 – conditions and at higher inlet temperatures. This data will give all necessary information for the identification of η0,b and of the collector heat losses.
Figure 9 — ϑm – ϑa versus Ghem
Figure 10 and Figure 11 show if the data include enough data at high and low angle of incidence of the beam irradiance to identify Kb(θT,θL), and if enough data at high diffuse radiation levels is taken to identify Kd. Measurement data with higher Gb-values (upper curve), will give Kb(θT,θL). The lower values will give Kd.
Figure 10 — Gb versus θ
Figure 11 — Gd versus Ghem
If the wind speed is considered for the thermal performance measurement, Figure 12 is showing the ideal distribution of wind speed versus Ghem. The wind speeds as described in Clause 22.3.3 shall be considered.
Figure 12 — Wind speed versus Ghem
If long-wave radiation exchange is considered for the thermal performance measurement, Figure 13 is showing the ideal distribution of long wave radiation EL versus Ghem.
Figure 13 — EL versus Ghem
For all collectors tested under natural wind, Figure 14 shall be included showing the ideal distribution of ϑm – ϑa versus wind speed u.
Figure 14 — ϑm – ϑa versus u
22.5 Performance test using a solar irradiance simulator
22.5.1 General
The thermal performance of collectors is affected by the amount of direct and diffuse solar radiation. Therefore, only solar simulators may be used for thermal performance testing where a near-normal incidence beam of simulated solar radiation can be directed at the collector.
In practice, it is difficult to produce a uniform beam of simulated solar radiation and a mean irradiance level has therefore to be measured over the collector gross area.
22.5.2 Solar irradiance simulator for thermal performance testing
Simulators for thermal performance testing shall have the following characteristics.
The lamps shall be capable of producing a mean irradiance over the collector gross area of at least 700 W/m2. All measurements shall start only after reaching stable working conditions.
At any time, the irradiance at any point on the collector gross area shall not differ from the mean irradiance over the collector gross area by more than ±15 %. The collimation of the simulator shall be such that the angles of incidence of at least 80 % of the simulated solar irradiance lie in the range in which the incidence angle modifier of the collector varies by no more than ±2 % from its value at normal incidence. For typical flat plate collectors, this condition usually will be satisfied if at least 80 % of the simulated solar radiation received at any point on the collector under test shall have emanated from a region of the solar irradiance simulator contained within a subtended angle of 60° or less when viewed from any point.
The measured irradiance Ghem shall be presented in the test report as a table for a grid spacing of maximum 150 mm over the whole collector gross area. The irradiance Ghem shall be measured in the plane of the absorber.
The spectral distribution of the simulated solar radiation shall be approximately equivalent to that of the solar spectrum at optical air mass 1,5 (AM1,5). Measurement of the solar simulator's spectral qualities shall be made in the plane of the collector over the wavelength range of 0,3 μm to 3 μm and shall be determined in bandwidths of 0,1 μm or less.
The initial spectral determination shall be performed after the lamps have completed their burn-in period. The amount of infrared thermal energy at the collector plane shall be suitably measured (measurements in the wavelength range above about 2,5 μm but starting not beyond 4 μm).
A check shall be made to establish the effect of the difference in spectrum on the (τα)eff product for the collector. If the effective values of (τα)eff under the simulator and under the optical air mass AM1,5 solar radiation spectrum determined according to Formula (9) differ by more than ±1 %, then a correction shall be applied to the test results.
(9)
A correction shall be applied to the peak collector efficiency measured in the simulator as defined in Formula (10):
(10)
The correction factor shall not result in a correction of more than +/- 0,05. If correction is more than +/- 0,05, only the outdoor measurements shall be used.
Alternatively, the peak efficiency η0 may be determined in an outdoor measurement. If this value differs by more than ± 1% from the simulator measurement, then a correction shall be performed.
The major difference between indoor and outdoor testing is the long wave thermal irradiance. The long wave radiation in a simulator shall not be higher than 50 W/m2 (typically −100 W/m2 for outdoor conditions).
The fluctuation of irradiance shall be less than ± 1 % over the test period.
22.5.3 Additional measurements during tests in solar irradiance simulators
Measurement of simulated solar irradiance
The distribution of irradiance over the plane of the collector shall be measured using a grid of maximum spacing 150 mm. The spatial mean deduced by simple averaging shall be used for the data analysis.
Measurement of thermal irradiance in simulators
The thermal irradiance in a solar simulator is likely to be higher than that which typically occurs outdoors. It shall therefore be measured to ensure that it does not exceed the limit given in Clause 22.7.2.
The mean thermal irradiance in the collector test plane shall be determined whenever changes are made in the simulator, which could affect the thermal irradiance. The mean thermal irradiance in the collector test plane shall be reported with collector test results.
Ambient air temperature in simulators
The ambient air temperature ϑa in simulators shall be measured, taking the mean of several values, if necessary. Sensors shall be shielded to minimize radiation exchange. The air temperature in the outlet of the wind generator shall be used for the calculations of the collector performance.
22.5.4 Solar irradiance simulator for the measurement of incidence angle modifiers
For the measurement of the incidence angle modifier, only solar irradiance simulators fulfilling at least all requirements of Clause 22.7.2 shall be used. The collimation shall be such that at least 90 % of the simulated solar irradiance at any point on the collector under test has emanated from a region of the solar irradiance simulator contained within a subtended angle of 20° or less when viewed from the point.
The measured irradiance data and the measured collimation shall be measured with a grid spacing of maximum 150 mm over the whole collector gross area.
23.0 Computation of the collector parameters
23.1 Liquid heating collectors
23.1.1 General
The useful power extracted 
is measured as given in Formula (11):
(11)
A value of cf corresponding to the mean fluid temperature shall be used. If 
is obtained from a volumetric flow rate measurement, then the density shall be determined for the temperature of the fluid in the flow meter.
The extracted power is modelled as described in Clause 23.1.2 and Clause 23.1.3. If these models are not applicable, tables of measurements of the thermal collector performance shall be used.
The required surrounding wind speeds u during the thermal performance measurements (see Clause 22.3.3) are considered for modelling the extracted power.
23.1.2 Steady-state test method for liquid heating collectors
The extracted power is modelled as Formula (12):
(12)
23.1.3 Quasi-dynamic test method for liquid heating collectors
The extracted power is modelled as Formula (13):
(13)
For collectors with a concentration ration CR < 20, the use of η0,b, Kθ(θT, θL), Kd, and the coefficients a1, a2, and a5 are mandatory and they shall be identified and the parameter a8 may be set to 0.
For collectors with a concentration ratio CR > 20 or ϑm higher than 300°C, the parameters a3, a4, a6 and Kd may be set to zero, a5 is mandatory and shall be identified.
For the simplified testing option, the collectors are tested at wind speeds ≥1.3 ms-1 and the coefficients a3, a4, and a6 are set to 0.
23.1.4 Data analysis
The thermal performance parameters shall be determined by statistical least-square curve fitting of the measured data points. In the result sheet (Annex A), the fitted values of these parameters shall be indicated.
If one of these parameters is deduced with a negative value or if it has no statistical significance [i.e. the T ratio (parameter value/standard deviation of parameter value) < 2], this parameter shall be set to 0 in Formulae (12) and (13). If the parameter Kd is deduced with a T-ratio < 2, it shall be set to Kd = 1 for collectors with a low concentration ratio CR < 3, and to Kd = 0 if CR ≥ 3. If the parameter a5 is deduced with a negative value or with a T-ratio < 2, it shall be replaced by the heat capacity as determined according to Clause 24.4 divided by the gross area AG. If a parameter is set to a fixed value, the data analysis shall be repeated, and all other parameters shall be re-determined by statistical least-square fitting. In the result sheet (Annex A), the fixed values of these parameters shall be indicated.
23.2 Air heating collectors
23.2.1 General
The useful power extracted is measured as given in Formula (14)
(14)
A value of cf corresponding to the inlet and outlet fluid temperature and the ambient temperature shall be used. If 
is obtained from volumetric flow rate measurement, then the density shall be determined for the temperature of the fluid in the flow meter.
Where necessary, tables of measurements of the collector thermal performance are admitted.
NOTE Formula (14) has an uncertainty if the measurement is done under positive gauge pressure because the exact temperature of the volumetric leakage flow rate is not known. Under positive pressure, the temperature of the volumetric leakage flow rate differs depending on whether it occurs at the beginning or at the end of the collector.
23.2.2 Steady-state test method for closed loop air heating collectors
Closed loop air heating collectors shall be modelled as liquid heating collectors (see Clause 23.1).
23.2.3 Steady-state test method for open to ambient air heating collectors
The extracted power is modelled as Formula (15):
(15)
The collector efficiency 
is dependent on the mass flow rate 
and shall be measured and indicated at minimum, mean and maximum flow rate as specified by the manufacturer.
If the simplified testing option is chosen, this is reduced to Formula (16):
(16)
23.3 Standard reporting conditions (SRC)
The collector output (table and graphical presentation) shall be reported in a comparable form independent of the test method and for the same climatic standard reporting conditions (SRC) defined in Table 7. For all calculations, the model used for the analysis of the measurements shall be used.
Table 7 — Standard Reporting Conditions (SRC)
Climatic conditions | Blue sky | Hazy sky | Grey sky |
| 850 W/m2 | 440 W/m2 | 0 W/m2 |
| 150 W/m2 | 260 W/m2 | 400 W/m2 |
| 20°C | 20°C | 20°C |
| −100 W/m2 | −50 W/m2 | 0 W/m2 |
| 1,3 m/s | 1,3 m/s | 1,3 m/s |
| 0 K/s | 0 K/s | 0 K/s |
NOTE (
) normally has a negative value as the effective sky radiation temperature is lower than the ambient air temperature. A net long wave irradiance of −100 W/m2 corresponds to about a clear sky condition when ϑa = 20 °C and ϑsky = 0 °C.
For full compatibility, the parameters Kd and η0,b shall be determined, if not available, using the formulae given in Annex C.
Presentation of collector output shall be given up to the maximum temperature difference between mean heat transfer fluid and ambient for which the collector is tested plus a maximum of 30 K. Results down to the measured minimum temperature difference minus 10 K may be indicated. It shall be stated that the measured collector parameters are applicable only for calculations in this range.
The Peak Power 
shall be calculated using Formula (A.1) as the power output per collector, operated at the peak power conditions listed in Table 8 and at the incidence angle resulting in the maximum output.
Table 8 — Peak power conditions
Peak power conditions | |
| 850 W/m2 |
| 150 W/m2 |
| 20°C |
| 0 K |
| −100 W/m2 |
| 0 m/s |
| 0 K/s |
23.3.1 Standard uncertainties
The standard uncertainties of the measured collector parameters may be derived as outlined Annex E.
23.3.2 Reference area conversion
If, in addition to the standard representation, thermal performance parameters shall be indicated with reference to other areas than the gross area, the conversion rules given in Annex H shall be used.
24.0 Determination of the effective thermal capacity and the time constant
24.1 General
The effective thermal capacity and the time constant are important parameters describing the collectors’ transient performance. A collector can be considered as a combination of masses, probably at different temperatures. When a collector is operating, each collector component responds differently to a change in operating conditions, so it is useful to consider an effective thermal capacity for the whole collector.
It is evident that the effective thermal capacity and the overall time constant depend on the operating conditions and are not always simple collector parameters with a unique value. For this reason, one of the following methods including the indicated reference conditions shall be chosen. The measurement of the heat capacity and the time constant shall be performed using the flow rate for collector efficiency testing.
The effective thermal capacity a5 is equal to 
and is a mandatory part of the collector model.
24.1.1 Measurement of the effective thermal capacity with irradiance
The collector is installed and operated as defined in Clause 22.4. The collector area is shielded from the solar radiation (natural or simulated) by means of a solar reflecting cover. The fluid inlet temperature is set to ambient temperature ϑi ≈ ϑa until steady-state conditions are reached (ϑe ≈ ϑi). The inlet temperature is then kept stable at ϑa during the whole measurement.
The cover is removed quickly, and data are measured until the outlet temperature of the fluid varies by less than 0,5 K per minute, i.e. until steady-state conditions are achieved again. The radiation Ghem shall be set to zero for the time before the cover is removed.
Considering Clause 24.1 and Formula (A.1), the transient behaviour of the collector between the two steady states 1 and 2 is described by Formula (17):
(17)
Integrating over the period between the two steady states gives the following Formula (18) for the collector thermal capacity:
(18)
24.1.2 Measurement of the effective thermal capacity using the quasi-dynamic method
The test data shall include periods with high variability in solar radiation so that the thermal capacitance effects are significant. The required condition that dϑm/dt shall exceed ±0,005 K/s is usually met during partly cloudy days, type 2. If this is not the case, additional type 2 test days with partly cloudy conditions shall be added to the data set used for parameter identification.
24.1.3 Calculation method for the determination of the effective thermal capacity
The effective thermal capacity of the collector C is calculated using Formula (19), as the sum of the total thermal capacities mici of the constituent collector elements (glass, absorber, liquid contained, and insulation) weighted by a generic factor ki:
(19)
The weighting factor ki (between 0 and 1) consider that certain elements are only partially involved in collector thermal inertia. The values of ki are given in Table 9.
Table 9 — Weighting factors
Elements | ki |
Absorber | 1 |
Insulation | 0,5 |
Heat transfer fluid | 1 |
External glazing | 0,01·a1 |
Second glazing | 0,2·a1 |
All parts of the collector which are in direct contact with the heat transfer fluid (liquid or air) shall be weighted by ki = 1.
24.1.4 Determination of collector time constant
The measurements made for the determination of the thermal capacity (see Clause 24.2) shall be used for the determination of the time constant.
The measured difference between the temperature of the heat transfer fluid at the collector outlet and of the ambient air (ϑe − ϑa) are plotted against time, beginning with the initial steady-state condition until the second steady state has been achieved (see Figure 15). Steady-state conditions are met if the conditions listed in Table 10 are met for at least 10 minutes.
Table 10 — Permitted deviation of measured parameters
Parameter | Permitted deviation from the mean value | |
Liquid heating collector | Air heating collector | |
Hemispherical solar irradiance | ±50 W/m2 | |
Hemispherical solar irradiance | >700 W/m2 | |
Thermal irradiance | ±20 W/m2 | |
Ambient air temperature | ±1,5 K | |
Fluid mass flow rate | ±1 % | ±2 % |
Fluid temperature at the collector inlet | ±1 K | ±3 K |
Key
X | Time | 1 | Test start (ϑe = ϑi) and (ϑe = ϑa) |
Y | ϑe − ϑa | 2 | (ϑe − ϑa)final |
|
| 3 | 0,632 ∙ (ϑe − ϑa)final |
|
| 4 | Time constant τC |
Figure 15 — Time constant
The time constant τC of the collector is then defined as the elapsed time between the removal of the cover and the point where the collector outlet temperature reaches 
of the final temperature difference (ϑe − ϑa)final.
Alternatively, the time constant can be determined during a cool down period rather, i.e. by reversing the measurements described in Clause 24.2. The time constant of the collector is then the elapsed time between turning off the irradiance and the point where the collector outlet temperature reaches 1/e ≈ 0,368 of its initial steady-state value.
25.0 Determination of the incidence angle modifier (IAM)
25.1 General
The thermal efficiency parameters are determined for the collector at normal incidence conditions. A separate measurement shall be conducted to determine the incidence angle modifier to calculate the thermal performance of the collector under any incidence angle.
25.1.1 Modelling
The incidence angle modifier is defined as the ratio of the peak efficiency at a given angle of incidence and the peak efficiency at normal incidence according to Formula (20) and Formula (21), respectively.
(20)
(21)
For collector types where the thermal performance cannot be determined under normal incidence, other angles than normal incidence may be defined as reference angle. Such deviating models shall be described very clearly in the test report to prevent from miscalculations when using any simulation tools.
The longitudinal plane (index L) runs parallel to the optical axis of the collector and the transversal plane (index T) is perpendicular to the optical axis. The angles θT and θL are the projections of the incidence angles θ (given in a spherical coordinate system) onto the transversal and longitudinal planes, respectively, see Figure 16.
Key
1 | sun position | 4 | collector normal |
2 | transversal plane | 5 | collector plane |
3 | longitudinal plane | 6 | example vacuum tube |
Figure 16 — Symmetry planes and angles relevant for the determination of the IAM
For the correlation between θ, θT and θL, the Formulae (22) and (23) hold:
(22)
(23)
which are the projected angles of incidence onto the two symmetry planes, thus also Formula (24) applies:
(24)
For most collectors, the incidence angle modifier can be approximated by the product of two separate incidence angle modifiers in the perpendicular collector symmetry planes as defined in Figure 16:
(25)
These two incidence angle modifier functions shall be determined. For those collectors for which the incidence angle effects are deemed symmetrical with direction of incidence, it is sufficient to measure the incidence angle effects for one direction only to fully characterize the incidence angle modifier.
Several standard functions such as for example the Ambrosetti function described by Formula (26) are known:
(26)
Depending on the collector type, other appropriate functions may be used. For many collector constructions however, simple functions are not suitable to describe the incidence angle modifier. In these cases, lists of individual values, tabulated in steps of 10°, shall be used. Smaller steps than 10° may be added if deemed necessary.
Θ | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
K(θ) | K(0) | K(10) | K(20) | K(30) | K(40) | K(50) | K(60) | K(70) | K(80) | K(90) |
The incidence angle modifier for any incidence angle θ may then be interpolated using the lookup table and the linearized approximation shown in Formula (27):
(27)
where the open brackets denote rounded to next lower integer.
For most collectors, K(0°) = 1 and K(90°) = 0; however, for some specific designs, other fix points are possible. In case of asymmetric collectors, such table representation shall be extended to cover incidence angle from θ = −90° to θ = +90°.
25.1.2 Steady-state method
For steady-state measurements, Formula (12) is modified with the incidence angle modifier Khem(θT, θL) in Formula (28):
(28)
25.1.3 Quasi-dynamic method
The collector incidence angle modifiers, modelled as Kb(θT,θL) for direct radiation and Kd for diffuse radiation are mandatory parts of the collector model. Kd is modelled as a collector constant. These parameters are identified simultaneously together with all other collector parameters.
25.2 Test procedures
25.2.1 Steady-state liquid heating collectors
General
The collector shall be operated using similar conditions as for the thermal performance measurements (flow rate, wind speed, etc.). The mean temperature of the heat transfer fluid shall be controlled as closely as possible (preferably within ±1 K) to the ambient air temperature. The efficiency value shall be determined in accordance with Clause 22.4.2. The collector shall be tested at diffuse irradiance levels of always less than 30 %. During each test period, the orientation of the collector shall be such that the collector is maintained within ±2° of the angle of incidence for which the test is being conducted.
While measuring the incidence angle modifier in one plane of an optical unsymmetrical collector, the incidence angle within the other plane shall be kept to a value where the incidence angle modifier does not differ by more than 2 % from the one at normal incidence.
Care shall be taken that the measurement of the incidence angle modifier is not affected by inappropriate tilt angles. Particular care shall be taken that the pyranometer is placed exactly in the collector plane as small deviations induce considerable measuring errors.
The measurements shall be made at least at two different incidence angles between 30° and 70°, separated by at least 30°. For collectors with unusual optical performance characteristics, it is recommended that measurements are taken at more than two angles.
One of the following two methods shall be used for the determination of the incidence angle modifier (IAM).
Method 1
This method is applicable for testing indoors using a solar simulator with the characteristics specified in Clause 22.7 or outdoors using a two-axis movable test rack so that the orientation of the collector can be arbitrarily adjusted with respect to the direction of the incident solar radiation.
The collector shall be operated under stable conditions at different fixed angles for time periods required to reach stable instantaneous efficiencies.
Method 2
This method is applicable for testing outdoors using a stationary test rack on which the collector orientation cannot be arbitrarily adjusted except for the inclination angle.
The efficiency value shall be determined in such a way that one value of efficiency is taken before solar noon and a second value after solar noon. The average incidence angle between the collector and the solar beam for both data points is the same. The efficiency of the collector for the specific incidence angle shall be considered equal to the average of the two values.
25.3 Calculation of the collector incidence angle modifier
Regardless of which experimental method is used, values for the thermal efficiency of the collector shall be determined for each of the measured values of incidence angles. The measured collector efficiency ηhem(θT,θL) shall be recalculated using Formula (12) to match the η0,hem conditions and to give η0,hem(θT,θL). The incidence angle modifier is then deduced following Formula (29) by dividing by the thermal efficiency for normal incidence.
(29)
25.3.1 Reporting
The result shall always be presented as a table indicating the incidence angle modifier in steps of 10° (smaller steps than 10° may be added if deemed necessary) in longitudinal and transversal direction. The data that were not measured shall be calculated using the mathematical model used for the determination (see Clause 25.2), within the table the measured values shall be clearly marked to distinguish them from the calculated values:
θ | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
Kb(θT,0) | ||||||||||
Kb(0,θL) |
The mathematical model used for the calculation shall be described in the test report. The orientation of longitudinal and transversal axes shall be described to prevent misunderstandings.
For steady-state measurements, the diffuse incidence angle modifier constant Kd shall be determined as described in Annex C and shall be indicated in the test report.
26.0 Determination of the pressure drop
26.1 General
The pressure drop across a collector is an important parameter for designers of solar collector systems. Any fluid can be used for the measurement, but it shall be specified together with the test results. The recommended fluid temperature for the test is (20 ± 2) °C. Other temperatures are possible but shall be indicated together with the test results.
The heat transfer fluid shall flow as specified by the manufacturer. Particular attention shall be paid to the selection of appropriate pipefittings at the collector entry and exit ports to prevent inducing unwanted additional pressure drop. The collector shall be shielded from radiation during the whole test.
The pressure drop shall be determined for different flow rates, which span the range likely to be used in real operation. At least five measurements shall be made at values equally spaced over the flow rate range. At each operation point, the pressure shall reach steady-state conditions for at least 5 min.
26.1.1 Liquid heating collectors
26.1.2 Apparatus and procedure
The collector shall be coupled to a test loop conforming broadly to Clause 21. although less instrumentation is required than for collector efficiency testing.
The following data shall be measured in accordance with Clause 21:
— fluid temperature at the collector inlet;
— fluid flow rate;
— heat transfer fluid pressure-drop between the collector inlet and outlet connections.
The pressure drop across the collector shall be measured with a standard measurement uncertainty of less than 5% or less than ±10 Pa, whichever is higher.
26.1.3 Pressure drop caused by fittings
The fittings used to measure the fluid pressure can themselves cause a drop in pressure. A zero check on the pressure drop shall be made by removing the collector from the fluid loop and repeating the tests with the pressure-measuring fittings directly connected. The pressure drop caused by the test equipment shall be used to correct the measured pressure drop of the collector.
26.1.4 Test conditions
The test shall be carried out at a constant pressure corresponding to the intended operating pressure. The fluid flow rate shall be held constant to within ±1 % of the nominal value during test measurements.
26.2 Air heating collectors
26.2.1 Apparatus and procedure
Measuring devices shall be positioned upstream and downstream of the collector as illustrated in Figure 17. A zero check on the pressure drop shall be made by removing the collector from the fluid loop and repeating the tests with the pressure-measuring fittings directly connected. The pressure drop caused by the fittings shall be used to correct the measured pressure drop of the collector.
For open to ambient collectors, the inlet pressure is always the ambient pressure.
Pressure-measuring points shall have four external manifold pressure taps, as shown in Figure 17. The pressure in the test circuit and the pressure drop of the solar collector shall be measured using static pressure tap holes and either a manometer or a differential-pressure transducer. The edges of the holes on the inside surface of the duct shall be free of burrs. The hole diameter shall not exceed 40 % of the wall thickness or 1,6 mm. Provision shall be made for determining the absolute pressure of the entering heat transfer fluid.
The static pressure-drop of an air-heating collector and static pressure upstream or downstream of the collector shall be measured with a standard measurement uncertainty of less than 10 Pa.
Key
1 | air inlet test duct | 3 | differential pressure measuring device |
2 | solar collector | 4 | air outlet test duct |
Figure 17 — Measurement of pressure drop of air heating collectors
26.3 Calculation and presentation of results
The pressure drop shall be presented as table and graphically as a function of the fluid flow rate for each of the tests performed, using the format sheets given in Clause A.15.9.
For most collectors, the pressure drop can be approximated by a second order polynomial function as given in Formula (30):
(30)
The parameters a and b shall be derived by least-square curve fitting of the measured pressure drops at different flows. If this simple model is not applicable, a list of measured pressure drop data shall be presented in the test report.
Test reports may be issued on single tests or complete test sequences. Any deviations from the procedures as defined in this document shall be described including the technical reasons for such deviations.
For the identification of the solar collector, the description shall be as complete as possible and shall include at least the characteristics listed below, if applicable. Numbers shall be indicated with the indicated precision. Additional information can be important depending on the test sample. In case the information is given by the manufacturer, this shall be clearly stated. Manufacturer information shall be checked for plausibility by the test laboratory.
Name of manufacturer | |
Brand Name | |
Serial No | |
Collector Type (Flat-plate, ETC, PVT, Tracked, Evacuated, etc.) | |
Drawing(s) document No | |
Collector mounting possibilities (On-roof, In-roof, Façade, On Stand, etc.) | |
Description and technical data of all integrated electrical components (ventilator, pumps, PV-panel…) | |
Self-protecting collector (see Clause 5.3.3) | (Yes, No) |
If yes, a full description of the self-protection mechanism(s) together with their protection thresholds and set points, together with a full description of the modified test procedures and test results shall be given in the relevant result sheets of this annex. | |
Freeze resistant collector (see Clause 13.2) | (Yes, No) |
If yes, a full description of the mechanism(s) and/or collector properties guaranteeing freeze resistance shall be given in the relevant result sheets of this annex. | |
Freeze resistant heat pipes (see Clause 13.3) | (Yes, No) |
If yes, a full description of the mechanism(s) and/or heat-pipe properties guaranteeing freeze resistance shall be given in the relevant result sheets of this annex. |
Minimum design operating temperature range ϑD,max | °C |
Maximum design operating temperature range ϑD,min | °C |
Maximum design operation pressure pD,max at ϑD,max | Pa |
Minimum design installation inclination βD,min (measured from horizontal) | ° |
Maximum design installation inclination βD,max (measured from horizontal) | ° |
Maximum design positive mechanical load (Snow load) | Pa |
Maximum design negative mechanical load (Wind load) | Pa |
Maximum design impact resistance ice ball diameter dD,max | mm |
Maximum design climate class | |
Recommended heat transfer fluids | |
Minimum design flow rate | kg/s |
Recommended flow rate | kg/s |
Maximum design flow rate | kg/s |
For tracking collectors: Angular operation range (in all directions, as relevant) | |
Other limitations |
Gross length (from bottom to top, when oriented as tested) | mm |
Gross width (from left to right, when oriented as tested) | mm |
Gross height | mm |
Gross area, AG (as defined in ISO 9488, 2 digits precision) | m2 |
Aperture area, Aa (as defined in ISO 9488, 2 digits precision) | m2 |
Absorber area, AA (as defined in ISO 9488, 2 digits precision) | m2 |
For tracking collectors, the determination of the gross length, gross width, gross area, aperture area and absorber area shall be explained using descriptive illustrations. | |
Mass empty | kg |
Fluid content | l |
Enclosure material(s) | |
Joining methods, (pop rivets, screws, glued, etc.) |
Materials | |
Number of absorber elements (fins, tubes, etc.) | |
Absorber element length | mm |
Absorber element width | mm |
Absorber total length | mm |
Absorber total width | mm |
Absorber thickness (1 digit precision) | mm |
Solar absorptance α | |
Hemispherical emittance ε | |
Absorber Coating (type, brand name) | |
Bond between riser and fin/plate (mechanical, soldering, welding, laser welding, etc.) | |
Heat transfer sheets between heat pipe and tube (material, thickness, and shape) |
Flow pattern as tested (clear description and/or drawing) | |
Number of risers | |
Riser material | |
Riser length | mm |
Riser outer/inner diameter | mm |
Distance between risers | mm |
Manifold material | |
Manifold length | mm |
Manifold outer/inner diameter | mm |
Collector hydraulic connector type/size |
Absorber surface | m2 |
Type of absorber (overflow/underflow/flow through, etc.) | |
Absorber heat exchanger surface | |
Air filtration, description |
Material | |
Glass type (tempered, toughened, safety glass, etc.) | |
Thickness | mm |
Inner/outer diameter (for tube collectors) | mm |
Solar transmittance | % |
Glazing surface characteristics (clear, textured, coated, etc.) |
Location, material and covering | |
Thickness | mm |
Density | kg/m3 |
Thermal conductivity | W/mK |
Material | |
External diameter of pipe and condenser | mm |
Liquid type | |
Liquid mass | g |
Type of reflector (CPC, Flat, etc.) | |
Material | |
Length, width | mm |
Reflectance (hemispherical) | % |
Reflectance (diffuse) | % |
Photograph(s) of the collector | |
Comments on the collector design | |
Schematic diagram of collector mounting |
The materials used for the construction of the collector shall be listed using Table G.1.
A summary of all results shall be given using Table A.1. Full details shall be given in the individual test result sheets.
Table A.1 — Result summary table
Test | Date / Start-End | Summary of main test results | |
Delivery of test sample / Initial visual inspection |
|
| |
Air leakage rate test |
|
| |
Rupture or collapse test |
|
| |
Standard stagnation temperature |
|
| |
Exposure or half-exposure |
|
| |
External thermal | First |
|
|
Second |
|
| |
Internal thermal | First |
|
|
Second |
|
| |
Rain penetration |
|
| |
Freeze resistance |
|
| |
Internal pressure |
|
| |
Mechanical load | Positive |
|
|
Negative |
|
| |
Impact resistance |
|
| |
Thermal performance |
|
| |
Pressure drop measurement |
|
| |
Final inspection |
|
| |
Test method | |
Test fluid | |
Ambient temperature | °C |
Test fluid temperature | °C |
Test duration | min |
Maximum test pressure | Pa |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Test method | |
Volumetric flow | m3/s |
Ambient temperature | °C |
Fluid temperature | °C |
Intermediate pressure | Pa |
Test duration at each pressure | s |
Maximum test pressure | Pa |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
The results shall be presented as a table of values (Table A.2) and as a graph (Figure A.1) covering at least the specified operating range of the collector.
Table A.2 — Values of the volumetric pressure and leakage flow
Collector pressure over ambient pressure | Leakage volumetric flow rate (Vp.L) |
|
|
|
|
Key
X | collector pressure (Pa) |
Y | leakage volumetric flow rate (m3/h) |
Figure A.1 — Leakage flow rate curve of an air heating collector
Test location (indoor/outdoor) | |
Collector inclination | ° |
Average ambient temperature | °C |
Average hemispherical irradiance | W/m2 |
Location for temperature sensor | |
If a fluid was circulated: Fluid specifications, flow rate, fluid temperature | |
Method used to determine the standard stagnation temperature |
Standard stagnation temperature at 1 000 W/m2 and 30 °C | °C |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Test location (address and coordinates) | |
Collector tilt angle (measured from horizontal) | ° |
Collector azimuth angle (measured from south/north) | ° |
Test date (start/end) | DD/MM/YYYY |
Collector tested as façade collector | (Y/N) |
Number of days of initial outdoor exposure | days |
Location of temperature measurement (description/photos, if applicable) |
Location (address and coordinates) | |
Collector tilt angle (measured from horizontal) | ° |
Collector azimuth angle (measured from south/north) | ° |
Test date (start/end) | DD/MM/YYYY |
Collector tested as façade collector | (Y/N) |
Location of temperature measurement (description/photos, if applicable) | |
Number of days of outdoor exposure using method 1 | days |
Hemispherical irradiation on collector using method 1 | MJ/m2 |
Exposure time under stagnation conditions for the selected climate class | h |
Fluid used | |
Flow rate | kg/s |
Fluid temperature | °C |
Test date (start/end) | DD/MM/YYYY |
Location of temperature measurement (description/photos, if applicable) |
Average radiation on collector plane | W/m2 |
Average ambient temperature | °C |
Test date (start/end) | DD/MM/YYYY |
Location of temperature measurement (description/photos, if applicable) |
In Table A.3 and Table A.4, full details shall be given of the climatic conditions for all days during the test, including the initial outdoor exposure if irradiance and ambient temperature was measured.
Table A.3 — Climatic conditions for all days during the test
Date | H | ϑa | Location |
|
|
|
|
|
|
|
|
|
|
|
|
Table A.4 — Data record of fulfilled exposure test requirements
Date/Time | Ghem | ϑa | Time periods | Location |
|
|
|
|
|
|
|
|
|
|
Climate class tested (A+, A, B, C, indicate Ghem and ϑa for Class C) | |
Total days of outdoor exposure | d |
Total hemispherical irradiation on collector during the exposure tests | Ws/m2 |
Total exposure time under stagnation conditions for the selected climate class | h |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Test method (indoor simulator, outdoor, etc.) | |
Collector tilt angle (measured from horizontal) | ° |
Average irradiance during test | W/m2 |
Minimum irradiance during test | W/m2 |
Average ambient air temperature | °C |
Minimum ambient air temperature | °C |
Climate class tested (A+, A, B, C, indicate Ghem and ϑa for Class C) |
|
Problems, damages and failures according to Clause 17 (description and photos) |
|
Other observations and remarks |
|
Test method (indoor simulator, outdoor, etc.) | |
Collector tilt angle (measured from horizontal) | ° |
Average irradiance during test | W/m2 |
Minimum irradiance during test | W/m2 |
Average ambient air temperature | °C |
Minimum ambient air temperature | °C |
Climate class tested (A+, A, B, C, indicate Ghem and ϑa for Class C) |
|
Problems, damages and failures according to Clause 17 (description and photos) |
|
Other observations and remarks |
|
Description of collector mounting (in-roof, on-roof, open frame, etc.) | |
Collector tilt angle (measured from horizontal) | ° |
Number and description of position(s) of spray nozzles |
Problems, damages and failures according to Clause 17 (description and photos) |
|
Other observations and remarks |
|
Collector type (drain down, freeze-resistant when filled) | |
Collector tilt angle (measured from horizontal) | ° |
Problems, damages and failures according to Clause 17 (description and photos) |
|
Other observations and remarks |
|
Description of test method | |
Collector tilt angle (measured from horizontal) | ° |
Problems, damages and failures according to Clause 17 (description and photos) |
|
Other observations and remarks |
|
Description of the collector mounting kit used in the test |
|
Method used to apply positive pressure (water, suction cups, gravel, air pressure, etc.) |
|
Maximum test load without damage | Pa |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Description of the collector mounting kit used in the test |
|
Method used to apply negative pressure (water, suction cups, gravel, air pressure, etc.) |
|
Maximum test load without damage | Pa |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Test method (ice ball test, steel ball test) | |
List of all points of impact (description and/or illustrated by photos) | |
Maximum ice ball diameter without damage (if applicable) | mm |
Maximum ice ball diameter without damage (if applicable) | mm |
Maximum drop height (1 digit precision) without damage (if steel ball testing) | m |
Problems, damages and failures according to Clause 17 (description and photos) | |
Other observations and remarks |
Evaluation and rating of potential problems as described in Clause 17.
Table A.5 — Final inspection record
Collector component | Potential problem | Evaluation |
a) Collector box/fasteners | Cracking/warping/corrosion/rain penetration/permanent deformation/ |
|
b) Mountings/structure | Strength/safety/loosening/fatiguing/etc. |
|
c) Seals/gaskets | Cracking/loss of adhesion/elasticity/brittleness/etc. |
|
d) Cover | Cracking/breaking/crazing/buckling/delamination/ |
|
e) Absorber as a whole | Deformation/corrosion/buckling/etc. |
|
f) Absorber coating | Cracking/crazing/blistering/discolouration/peeling/ |
|
g) Reflectors | Deformation/cracking/crazing/blistering/discolourtion/buckling/peeling/flaking/etc. |
|
h) Absorber tubes and headers/ | Deformation/corrosion/leakage/loss of bonding/ |
|
i) Absorber mountings | Permanent deformation/corrosion/rupture/etc. |
|
j) Insulation | Water retention/outgassing/swelling/degradation/ |
|
k) Corrosion and other deterioration caused by chemical action. Anywhere in the collector | Corrosion shall be considered severe if it impairs the function of the collector or if there is evidence that it will progress |
|
l) Retention of water. Anywhere in the collector | Excessive retention of water anywhere in the collector |
|
m) Heat pipes | Loss of fluid/loss of pressure/severe deformation/etc. |
|
n) Self-protection systems | Any problem |
|
o) Safe installation and mounting | Sharp or cutting edges / loose connections / other potentially dangerous features endangering a safe handling and installation. |
|
p) Other components | Any other abnormality resulting in a reduction of thermal performance or service lifetime |
|
Summary (maximum of all ratings) |
| |
The reporting of the performance of a solar collector shall include
— description of the mathematical model used for calculating the thermal output and the collector coefficients determined by the measurements (Clause A.15.4.1);
— table of calculated thermal output data and graphical presentation of the thermal output under SRC standard reporting conditions (Clause A.15.4.2);
— for open to ambient air heating collectors, the thermal output shall be presented according to Clause A.15.5;
— incidence angle modifier (Clause A.15.6);
— collector heat capacity (Clause A.15.7).
For all results, the required unit and the precision for reporting are indicated and shall be used to provide comparable results that shall be used for further calculations and simulations using computer software and simulation tools.
Additional representation of the results in the test report are welcome but shall be presented such that they are separated from the standard reporting as outlined here to prevent confusion and unintentional misuse of the test results.
Full description of the required external power source (see Clause 5.3.2) | |
Estimation of the annual energy consumption for normal operation | kWh/a |
Test method (steady-state, quasi-dynamic) | |
Heat transfer fluid for testing | |
Wind generator | (Y/N) |
Orientation of the collector during test (landscape, portrait, tubes N-S, tubes E-W, ...) | |
Full description of the installation of the collector for the measurements |
Test location (latitude/longitude) |
|
Collector orientation (inclination, azimuth) |
|
Type of lamps | |
Minimum irradiance (measured over the collector surface) | W/m2 |
Mean irradiance (measured over the collector surface) | W/m2 |
Maximum irradiance (measured over the collector surface) | W/m2 |
Minimum collimation (measured over the collector) | W/m2 |
Mean collimation (measured over the collector) | W/m2 |
Maximum collimation (measured over the collector) | W/m2 |
Mean thermal irradiance (measured over the collector) | W/m2 |
Grid spacing for measuring irradiance, collimation and thermal irradiance | mm |
The collector coefficients listed in Table A.6 shall be used for all thermal output calculations.
For closed loop air heating collectors, the thermal collector performance coefficients shall be indicated for the three measured airflow rates.
Table A.6 — Thermal collector performance coefficients
Parameter | Result | Standard deviation | Unit | Decimal places |
η0,hem | — | 3 | ||
η0,b | — | 3 | ||
Kd | — | 2 | ||
a1 | W/(m2K) | 2 | ||
a2 | W/(m2K2) | 4 | ||
a3 | J/(m3K) | 3 | ||
a4 | — | 2 | ||
a5 | J/(m2K) | 0 | ||
a6 | s/m | 3 | ||
a8 | W/(m2K4) | 3 a | ||
C/AG | J/(m2K) | 0 | ||
NOTE | ||||
Flowrate during the measurement | ||||
Maximum temperature difference during thermal performance measurement | ||||
= _____ kg/s
= _____ KFormula (A.1) provides a mathematical model for the calculation of the thermal output of the tested collector:
(A.1)
The power output of a collector unit operated under SRC is listed in Table A.7 (unit for all data is W, indicated as integer value) and plotted as in Figure A.2. For closed loop air collectors, the information shall be indicated for the three measured airflow rates.
Table A.7 — Collector power output
| Standard reporting conditions | ||
| Blue sky | Hazy sky | Grey sky |
−10 | |||
0 | |||
10 | |||
… | |||
Max. tested | |||
Key
X | (ϑm − ϑa) (K) |
Y | power output per collector unit (W) |
Figure A.2 — Power output per collector unit for SRC
Peak Power per unit | W |
(indicate as integer)Gross Solar Yield figures shall be calculated in accordance with Annex B. By preference, the calculations shall be made for ISO reference locations (https://standards.iso.org/iso/9459/-4/Climate Data/), but any other data as required by the customer can also be used.
For open to ambient air-heating collectors, the thermal performance is presented as single data points measured as given in Formula (A.2) under different operating conditions as listed in Table A.8.
(A.2)
Table A.8 — Thermal performance of open to ambient air heating collectors
Data point |
|
|
|
|
|
| Measurement |
kg/s | W/m2 | °C | — | — | W | W | |
1 | |||||||
2 | |||||||
… | |||||||
9 |
If the simplified testing method is applied, the thermal performance is presented as single data points measured as given in Formula (A.3) under different operating conditions as listed in Table A.9.
(A.3)
Table A.9 — Thermal performance of open to ambient air heating WISC collectors
Data point |
|
|
|
|
|
|
| Standard |
kg/s | W/m2 | °C | m/s | — | — | W | W | |
1 | ||||||||
2 | ||||||||
… | ||||||||
27 |
Test method (tracked steady-state, fixed steady-state, quasi-dynamic, etc.) |
|
Location (indoor, outdoor) |
|
Definition/description of the longitudinal and the transversal axis |
|
Type of lamps | |
Minimum irradiance (measured over the collector surface) | W/m2 |
Mean irradiance (measured over the collector surface) | W/m2 |
Maximum irradiance (measured over the collector surface) | W/m2 |
Minimum collimation (measured over the collector) | W/m2 |
Mean collimation (measured over the collector) | W/m2 |
Maximum collimation (measured over the collector) | W/m2 |
Grid spacing for measuring irradiance, collimation and thermal irradiance | mm |
Model for the transversal incidence angle modifier KT(θ) |
|
Model for the longitudinal incidence angle modifier KL(θ) |
|
Incidence angle modifier for diffuse solar radiation Kd |
|
The results shall be presented as a table of values indicated with two decimal places (Table A.10) and as a graph (Figure A.3).
Table A.10 — Incidence angle modifier
θ | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
| ||||||||||
|
Key
X | incidence angle (°) |
Y | incidence angle modifiers (-) |
Figure A.3 — Incidence angle modifier
Test method (one of the methods of Clause 24) |
|
Effective heat capacity (including fluid) | J/kgK |
Fluid | |
Effective heat capacity (without fluid) | J/kgK |
Test method (See Clause 24.5) |
|
Time constant, τc | s |
Fluid used for the measurement | |
Fluid temperature | °C |
Pressure drop coefficient a as defined in Formula (30) | Pah/l |
Pressure drop coefficient b as defined in Formula (30) | Pah2/l2 |
The results shall be presented as a table of values (Table A.11) and as a graph (Figure A.4).
Table A.11 — Collector pressure drop table
Volumetric flow rate (l/h) |
|
|
|
|
|
|
Δp (Pa) |
|
|
|
|
|
|
Key
X | volumetric flow rate flow (l/h) |
Y | pressure drop (Pa) |
Figure A.4 — Pressure drop
For the direct comparison of collector performances or for performance rating requirements as needed for subsidy schemes and for other purposes of public interest, the use of the gross yield figures is recommended. The gross yield of a collector is defined as the energy provided by the collector operating at a constant temperature over a certain period under well-defined climatic conditions. The gross yield is therefore a measure for the possible energy supply of a collector without considering any specific system configurations.
Reference data representing the most important climatic conditions worldwide can be found at https://standards.iso.org/iso/9459/-4/Climate Data/ and shall preferably be used for collector ratings.
The following definitions and specifications are needed for the calculation of the gross yield figures:
| Time span for the calculation. The default value for |
| Sampling interval for the calculation, the default value is one hour |
ϑop | Fixed operating temperature equal to the mean temperature of the fluid; |
| Set of tabulated ambient conditions |
| Set of performance parameters |
| The incidence angle modifier shall be computed at the time stamp in the middle of the considered sampling interval, i.e. if |
| For co-generating collectors only: Peak electric power under standard testing conditions (STC). |
| For co-generating collectors only: Temperature coefficient |
is one year. 
= Jan, Feb,…;
at the geographic location 
adapted for the solar collector installed under azimuth and tilt angle 
. For fixed collectors, the default orientation is due south or north (
) with a slope defined by the geographical latitude - 15°, rounded to nearest 5°. 
for the electric power. If 
is not known, a default value of 0,5%/K shall be used.The reference ambient conditions are described by tables of climatic data with the required resolution.
The gross thermal yield GTY of a solar collector with performance parameters 
that is installed at the location 
operating at the collector temperature ϑop calculated for a time period Δt is defined as Formula (B.1)
(B.1)
where 
is the thermal power at the time stamp 
, calculated using Formula (A.1) with 
. The index "+" indicates that for the calculation
— only positive power outputs 
shall be considered;
— all negative temperature differences 
shall be replaced by 0.
The simplified presentation 
indicating only the operating temperature and the location can be used if the calculation is made for default boundary conditions.
For co-generating collectors the gross electric yield GEY is defined as Formula (B.2)
(B.2)
where
(B.3)
is the electric output of the collector corrected to the operating temperature.
The simplified presentation 
indicating only the operating temperature and the location can be used if the calculation is made for default boundary conditions.
NOTE For non co-generating solar collectors GEY=0.
The gross solar yield GSY is defined by Formula (B.4) as the sum of GTY and GEY to indicate in a generalized way the overall performance of a collector under specific operating conditions for a specific location.
(B.4)
This basic concept allows the definition of derived figures for simplified comparison of collector performances, for simplified calculation methods in legal applications and for similar purposes. For this purpose, weighted sums of gross solar yields for different operating temperatures and/or different locations are defined that are representative for the intended use.
A comparison of the parameters of the two basic models steady-state given by Formula (12) and quasi-dynamic given by Formula (13) and under the assumption that for steady-state only high irradiance and low diffuse levels are accepted, provides the following transformation keys given in Formula (C.1) and Formula (C.2):
(C.1)
and
(C.2)
To deduce Kd, the measured hemispherical incidence angle modifier Khem(θ,γ) is assumed to approximate Kb(θ,γ) which is then averaged and normalized over the hemispherical field of view of the collector. Under the assumption that the incidence angle modifier is symmetric with respect to the longitudinal and transversal axes, the calculations are reduced to a quarter sphere. For asymmetric incidence angle modifiers, it can be necessary to consider the whole hemispheric field of view. Kd is basically determined following Formula (C.3)
(C.3)
with
(C.4)
For most collectors, a simplified approach is considered appropriate, and the discrete averaging based on the tabulated IAM test results in steps of 10° is proposed. Kd is approximated as the averaged sum of the incidence angle modifiers over the quarter sphere using the tabulated incidence angle modifiers interpolated using Formula (C.5):
(C.5)
with W as reference for an IAM where Kb(θ,γ) = 1 for all angles of incidence as given in Formula (C.6):
(C.6)
Using the Kd as defined in Formula (C.5) and for full compatibility between QD and SS method, also η0,b is derived from the measured η0,hem for Blue Sky SRC as Formula (C.7):
(C.7)
Formulae (D.1) and (D.2) shall be used to calculate the density and the heat capacity of water in liquid phase in the range of up to 12 bars and 0 < ϑ < 185 °C[2].
(D.1)
with
y0 = 999,85 (kg/m3)
y1 = 5,332 10−2 (kg/m3K)
y2 = −7,564 10−3 (kg/m3K2)
y3 = 4,323 10−5 (kg/m3K3)
y4 = −1,673 10−7 (kg/m3K4)
y5 = 2,447 10−10 (kg/m3K5)
and
(D.2)
with
z0 = 4,218 4 (kJ/kgK)
z1 = −2,821 8 10−3 (kJ/kgK2)
z2 = 7,347 8 10−5 (kJ/kgK3)
z3 = −9,471 2 10−7 (kJ/kgK4)
z4 = 7,286 9 10−9 (kJ/kgK5)
z5 = −2,809 8 10−11 (kJ/kgK6)
z6 = 4,400 8 10−14 (kJ/kgK7)
The aim of this annex is to provide a general guidance for the assessment of uncertainty in the result of solar collector testing performed according to the present International Standard. Testing laboratories are often invited to provide a statement of uncertainty in test results in quantitative tests, in the framework of their accreditation or of application of product certification schemes. It is not the aim of this annex to define whether and in which cases the calculation of uncertainty in test results is necessary.
This guidance concerns only collector efficiency testing due to a) the importance of the result of this testing for the user, and b) the peculiarities of the calculations, since the final result of efficiency testing is not derived by a single measurement but by elaboration of a large number of primary measurements.
It is noted that the proposed methodology is one of the possible approaches for the assessment of uncertainty and other approaches can be implemented. It is the responsibility of each laboratory to choose and to implement a scientifically valid approach for the determination of uncertainties, following the recommendations of the accreditation bodies, where appropriate. For a more detailed review of the various aspects of determination of uncertainties in solar collector testing, see also References [3], [4], [5] and [6].
The basic target of solar collector thermal efficiency testing is the determination of the collector efficiency by measurements under specific conditions. More specifically, it is assumed that the behaviour of the collector can be described by a M-parameter single node, steady-state or quasi-dynamic model:
(E.1)
where
|
| is the collector instantaneous efficiency; |
|
| are quantities, the values of which are determined experimentally through testing; |
|
| are characteristic constants of the collector that are determined through testing. |
In the case of the steady-state model, for example, M = 3, c1 = η0, c2 = a1, c3 = a2, p1 = 1, p2 = (Tm − Ta) and p3 = (Tm − Ta)2.
During the experimental phase, the output, solar energy and the basic climatic quantities are measured in J steady-state or quasi-dynamic state points, depending on the model used. From these primary measurements, the values of parameters η, p1, p2,…, pM are derived for each point of observation j, j = 1…J. The experimental procedure of the testing leads to a formation of a group of J observations which comprise, for each one of the J testing points, the values of ηj, p1,j, p2,j,…,pM,j.
For the determination of uncertainties, it is essential to calculate the respective combined standard uncertainties u(ηj), u(p1,j), …u(pM,j) in each observations point. It shall be noted that, in practice, the uncertainties u(ηj), u(p1,j), …u(pM,j), are almost never constant and the same for all points, but that each testing point has its own standard deviation.
For the calculation of the standard deviation (squared standard uncertainty) in each point j, the following general rules can be applied (ISO GUM:2008).
a) Standard uncertainties in experimental data are determined by considering Type Α and Type Β uncertainties. According to the recommendation of ISO GUM, the former are the uncertainties determined by statistical means while the latter are determined by other means.
b) The uncertainty u(s) associated with a measurement s is the result of a combination of the Type Β uncertainty uB(s), which is a characteristic feature of the calibration setup, and of the Type A uncertainty uA(s), which represents fluctuation during sampling of data. If there is more than one independent source of uncertainty (Type B or Type A) uk, the final uncertainty is calculated according to the general law of uncertainties combination given in Formula (E.2):
(E.2)
c) Type Β uncertainty uB(s) derives from a combination of uncertainties over the whole measurement chain, considering all available data, such as sensor uncertainty, data logger uncertainty, uncertainty resulting from the possible differences between the measured values perceived by the measuring device. Relevant information shall be obtained from calibration certificates or other technical data related to the devices used.
d) By nature, Type A uncertainties depend on the specific conditions of measurement, and they account for the fluctuations in the measured quantities during the measurement. Type A uncertainty uA(s) derives from the statistical analysis of experimental data. In some cases (for example, in the case of the steady-state model), the best estimate of S is the arithmetic means s of the I repeated observations si (i = 1...I) and its Type A uncertainty is the standard deviations of the mean given in Formula (E.3):
(E.3)
where
(E.4)
In some other cases (for example, in the case of the quasi-dynamic model where no arithmetic mean of the repetitive measurements is used), uncertainty uA(s) can be equal to zero.
e) The term combined standard uncertainty means the standard uncertainty in a result when that result is obtained from the values of a number of other quantities. In most cases, a measured Y is determined indirectly from P other directly measured quantities X1, X2, ...XP through a functional relationship Y = f(X1, X2, ...XP). The standard uncertainty in the estimate y is given by the law of error propagation shown in Formula (E.5):
(E.5)
An example of such indirect determination in the case of solar collector efficiency testing is the determination of instantaneous efficiency η, which derives from the values of global solar irradiance G, fluid mass flow rate m, temperate difference ΔT, collector area Α and specific heat capacity cf. Thus, in this case, the standard uncertainty u(ηj) in each value ηj of instantaneous efficiency is calculated by the combination of standard uncertainties in the values of the primary measured quantities, considering their relation to the derived quantity η.
During analysing the data, least-square fitting of the model formula is performed, in order to determine the values of coefficients c1, c2,…,cM for which the model of Formula (E.1) represents the series of J observations with the greatest accuracy.
Since, in reality, the typical deviation is almost never constant and the same for all observations, but each data point (ηj, p1,j, p2,j,…,pM,j) has its own standard deviation σj, an interesting solution is the use of the weighted least-square (WLS) method, which calculates, on the base of the measured values and their uncertainties, not only the model parameters but also their uncertainty. In the case of WLS, the maximum likelihood estimate of the model parameters is obtained by minimising the χ2-function as shown in Formula (E.6):
(E.6)
where 
is the variance of the difference given in Formula (E.7) and Formula (E.8):
(E.7)
and
(E.8)
Finding coefficients c1, c2,…,cM and their standard uncertainties by minimizing χ2-functions is rather complicated, because of the nonlinearity present in Formula (E.5). A strategy is therefore to find these uncertainties numerically. Α method for the case of M-parameter model is presented below[6].
Let K be a matrix whose J × M components kj,m are constructed from M basic functions evaluated at the J experimental values of p1, …,pM weighted by the uncertainty uj:
or 
(E.9)
Let also L be a vector of length J whose components lj are constructed from values of ηj to be fitted, weighted by the uncertainty uj , as given in Formula (E.8):
or 
(E.10)
The normal formula of the least-square problem can be written as Formula (E.11):
(E.11)
where C is a vector, whose elements are the fitted coefficients. Given the fact that for the calculation of variances 
the knowledge of coefficients 
is needed, a possible solution is to use the values of coefficients calculated by standard least-squares fitting as the initial values. These initial values can be used in Formula (E.8) for the calculation of 
with J = 1…J and the formation of matrix K and of vector L. The solution of Formula (E.11) gives the new values of coefficients 
which, however, are not expected to differ noticeably from those calculated by standard least-squares fitting and used as initial values for the calculation of 
.
Moreover, Z = INV(KT·K) is a matrix whose diagonal elements zk,k are the squared uncertainties (variances) and the off-diagonal elements zk,l = zl,k, k≠l are the covariance between fitted coefficients:
for m=1,…,M (E.12)
(E.13)
It shall be noted that the knowledge of covariance between the fitted coefficients is necessary if one wishes to calculate, in a next stage, the uncertainty u(η) in the predicted values of η using Formula (E.1) and Formula (E.3).
A mean-value forming temperature sensor shall be evenly distributed in an Archimedean spiral of the whole cross-section (Figure F.1 and Figure F.2). This mean temperature ϑm can be determined in the air channel with a sensor. In front of the sensor, two fine-mesh nets are installed at a distance of 10 mm. The distance between the two nets shall be 10 mm. The average temperature ϑm is equal to the thermal mean fluid temperature ϑm,th if the flow distribution is homogeneous.
Key
1 | flow conditioner sieve |
2 | temperature sensor |
Figure F.1 — Arrangement in the sensor
Key
1 | temperature sensor (e.g. ϑi) |
2 | insulated pipe |
Figure F.2 — Example of a temperature sensor
Calibration recommendation: The sensor can be calibrated over the full range when it is installed in the air channel. The homogeneity of the temperature shall be at any temperature <0,2 K. This can be achieved and monitored in the flow channel by measuring at least 12 temperature points using an adequately positioned air swirler behind the mean-value forming temperature sensor. The measuring points shall be chosen so that each measuring point represents the temperature of an equal area.
Material efficiency aspect include the use of materials, the ability to reuse components or recycle materials at end-of-life, use of reused components and/or recycled materials, upgradeability, ability to extract key components for reuse, reparability, recycling, identifiability of the components, reusability, recyclability. For solar collectors, the main aspects are the amount of material, the reparability, and the recyclability. All materials with a total mass > 0,1 kg shall be listed as given in Table G.1. Flashing kits and mounting parts shall not be listed. Packing materials shall be listed if not reusable.
Table G.1 — Materials
Material | Description | Mass per | Identifiability | Separability | Replaceable parts | |
… | …. | |||||
Metals | … | |||||
… | ||||||
Glass | … | |||||
… | ||||||
Plastics | … | |||||
… | ||||||
Insulation | … | |||||
… | ||||||
Sealants | … | |||||
… | ||||||
Other | … | |||||
… | ||||||
Identifiability/marking: Is the material easily to be identified? Metals and glass are deemed identifiable; Plastics shall be marked for identification. Separability: Is the material at the end-of-life disassembly easily (that is, by simple mechanical operation using tools like screwdrivers and hammers and without using any specialized separation processes) separable from other materials such that the purity of the material is better than 95 %? Replaceable parts: Parts that can be replaced by non-professionals without specific manual skills in less than 30 min using standard household tools like screwdrivers or hammers only. Example: Double glass evacuated tubes. | ||||||
In previous standards and in some certification schemes, the thermal performance parameters are indicated in relation to absorber area AA or aperture area Aa instead of gross area AG. For all thermal performance parameters η0, η0,b, η0,hem, a1, a2, a3, a4, a5, a6 and a8, Formula (H.1) shall be used to convert between parameters measured in relation to area X to parameters measured in relation to area Y:
(H.1)
The parameters Kb(θL, θT), Khem(θL, θT), Kd, are independent of any area and do not need conversion.
To validate the collector parameters for liquid heating collectors derived according to Clause 23, the following validation procedure may be applied.
The solar collector is mounted on a fixed test rig facing the equator with a tilt angle resulting in an angle of incidence for the beam irradiance θ < 20° at solar noon. For the mounting and installation Clause 19 applies and for the instrumentation Clause 20 applies.
The same heat transfer fluid, heat transfer flow pattern and flow rate shall be selected as used for the thermal performance test.
The flow rate shall be held stable to ±2 % of the set value during the test.
The air speed parallel to the plane of the collector shall be in the same range as used for testing according to Clause 22.
The collector is tested from one hour before sunrise until the power output becomes negative around sunset. The collector inlet temperature ϑi shall be set in the starting phase 1 at about ambient temperature (ϑi ≈ ϑa) so that the resulting power output of the collector is close to 0. After the irradiance has reached 100 Wm-2, the inlet temperature shall be continuously increased to reach the maximum temperature ϑi,noon at solar noon ±30 min. The collector inlet temperature shall then be kept constant until the end of the test. The minimum irradiation during the test is 5 kWh/m2.
The inlet temperature at noon shall be selected such that the power at noon is about 75% of the peak power:
(H.1)
The maximum temperature difference shall also be limited to maximum temperature difference during thermal performance testing
(H.2)
The smaller of the two inlet temperatures defined by Formula (H.1) and Formula (H.2) shall be taken for the validation procedure. The validation is only valid for the temperature range.
Depending on the requirement of the customer, also other inlet temperature conditions may apply.
The testing day is made up of four periods as shown in Figure I.1. Period 1 starts 1h before sunrise and ends when the irradiation in the collector plane exceeds 100 W/m2. The duration of periods 2 and 3 is the same and is half the time between the start of the overall evaluation period and the time when the maximum temperature is reached. Period 4 lasts from the moment the maximum temperature is reached until the collector output becomes negative.
Figure I.1 — Temperature and radiation during the validation sequence
The energy yields Qc,2, Qc,3, Qc,4 are computed for the sequences i=2,3,4 and Qc,tot for the total sequence length (tot=2 - 4), using Formula (H.3)
(H.3)
where
is the set of collector parameters determined in Clause 22, where for the effective thermal capacity a5 the value of the calculated effective thermal capacity according to Clause 24.1 divided by the gross area (C/AG) shall be used.
is the set of measured operating and environmental conditions during the sequence.
The measured energy yields Qm,2, Qm,3, Qm,4, Qm,tot shall be determined using Formula (H.4)
(H.4)
The computed energy yields Qc,i are then compared to the measured energy yields Qm,i. The thermal performance parameters are considered as confirmed, if the calculated and measured energy yield deviate by less than 5% for each of the three individual periods 2, 3 and 4 and for the overall evaluation period, as defined in Formula (H.5).
(H.5)
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[2] Wagner et al., The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam; ASME, Journal of Engineering for Gas Turbines and Power, Volume 122, 2000
[3] MATHIOULAKIS E., VOROPOULOS K., BELESSIOTIS V. Assessment of uncertainty in solar collector modelling and testing. Sol. Energy. 1999, 66 (5) pp. 337–347
[4] MATHIOULAKIS E. VOROPOULOS K., BELESSIOTIS V. Uncertainty in solar collector modelling and testing, Proceedings of ISES Solar World Congress, Jerusalem, June 1999
[5] MÜLLER-SCHÖLL, C., FREI, U. Uncertainty Analyses in Solar Collector Measurement, Proceedings of Eurosun 2000, Copenhagen
[6] SABATELLI V., MARANO D., BRACCIO G., SHARMA V.K. Efficiency test of solar collectors: Uncertainty in the estimation of regression parameters and sensitivity analysis. Energy Convers. Manage. 2002, 43 (17) pp. 2287–2295
