This standard specifies the test methods and calculation procedures for the steady-state and quasi-steady-state thermal performance of flat-plate solar collectors. The test methods include tests under outdoor natural solar radiation and tests under indoor simulated solar radiation. This standard applies to flat-plate solar collectors with pressure drop, glass cover, and liquid heat transfer medium. This standard does not apply to heat storage solar collectors with integrated heat storage and collector, nor does it apply to solar collectors without glass cover and tracking focusing. GB/T 4271-2000 Test method for thermal performance of flat-plate solar collectors GB/T4271-2000 Standard download decompression password: www.bzxz.net

ICS27.160
National Standard of the People's Republic of China
GB/T4271—2000
Test methods for the thermal performance offlatplatesolarcollectors
Published on 2000-02-16
Implemented on 2000-08-01
Published by Baojia Quality and Technical Supervision Bureau
GB/T4271—2000
This standard is a revision of GB/T4271—1984 with reference to the international standard ISO9806-1:1994 "Test methods for solar collectors - Part 1: Thermal performance of liquid collectors with glass cover with pressure drop" published by the International Organization for Standardization. The structure, test method, formula expression, parameter symbols, specified parameter data and table format are kept consistent with ISO9806-1:1994 as much as possible.
The main technical differences between this standard and GB/T4271-1984 are as follows: a) The 1984 version of the standard mainly refers to the American standard ASHRAE93:1977, while this standard refers to ISO9806-1:1994. b) According to the actual situation in my country, some technical requirements and parameters have been appropriately adjusted and modified on the basis of ISO9806-1:1994.
c) The provisions of this standard on the accuracy of instruments, test methods, test conditions and test equipment are stricter and more specific than those in GB/T4271-1984.
Appendix A, Appendix B and Appendix D of this standard are standard appendices, and Appendix C is a reminder appendix. This standard replaces GB/T4271-1984 from the date of implementation. This standard is proposed by the State Economic and Trade Commission and the China Institute of Standardization and Information Classification and Coding. This standard is under the jurisdiction of the New Energy and Renewable Energy Subcommittee of the National Technical Committee for Energy Foundation and Management Standardization. This standard was drafted by China Institute of Standardization and Information Classification and Coding, Beijing Institute of Solar Energy, and Institute of Electrical Engineering of the Chinese Academy of Sciences.
The main drafters of this standard are Zhao Yuejin, He Zinian, Fu Xiangdong, and Mi Yaowei. This standard was first issued in 1984 and revised for the first time in 1999. 1 Scope
National Standard of the People's Republic of China
Test methods for the thermal performance of flat plate solar collectors
GB/T4271—2000
Replaces GB/T4271—1984
This standard specifies the test methods and calculation procedures for the steady-state and quasi-steady-state thermal performance of flat plate solar collectors. The test methods include tests under outdoor natural solar irradiation and tests under indoor simulated solar irradiation. This standard applies to flat plate solar collectors with pressure drop, glass cover, and liquid heat transfer medium (hereinafter referred to as solar collectors or collectors).
This standard does not apply to heat storage solar collectors with integrated heat storage and collector, nor does it apply to solar collectors without glass cover and tracking and focusing.
2 Referenced standards
The provisions included in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid, all standards will be revised, and the parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T12936.1—1991 Terminology of solar thermal utilization Part 1 GB/T12936.2—1991 Terminology of solar thermal utilization Part 2 GB/T17683.1—1999 Solar spectral irradiance standard for different ground receiving conditions Part 1: Normal direct solar irradiance and hemispherical solar irradiance of air mass 1.5 (eqvISO9845-11992)
3 Definitions
In addition to the relevant definitions in GB/T12936.1 and GB/T12936.2, this standard also adopts the following definitions. 3.1 Absorber area absorberarea
The maximum projected area of ​​the absorber.
3.2 Daylighting area aperturearea
The maximum projected area of ​​the daylighting opening of the collector where unfocused solar radiation enters. 3.3 Collector gross area grosscollectorarea The maximum projected area of ​​a complete solar collector, excluding any fixed parts and parts connected to the working fluid pipeline. 3.4 Collector efficiency collectorefficiency Under steady-state conditions, the ratio of the energy taken away from a specific collector area (total area, lighting area or absorber area) by the heat transfer medium in a specific time interval to the solar energy incident on the collector area in the same time interval. 3.5 Solar radiation simulator solarirradiancesimulator An artificial radiation energy source that simulates solar radiation, usually consisting of a stack or a group of lamps. Approved by the State Administration of Quality Supervision, Inspection and Quarantine on February 16, 2000, and implemented on August 1, 2000
4 Symbols and units
GB/T4271:2000
The symbols and units used in this standard are listed in Appendix A (Appendix to the standard). 5. Collector installation and location
5.1 Overview
The way the collector is installed will affect the test results of thermal performance. The collector should be installed in accordance with the provisions of 5.2 to 5.8. The actual size of the collector should be used for testing, because the edge heat loss of a small-sized collector will seriously reduce the thermal performance of the collector. 5.2 Collector test bench
The collector test bench should not block the collector's lighting surface and should not significantly affect the insulation of the back and sides of the collector. The bench should adopt an open structure, and the air in front and behind the collector can flow freely. The lowest edge of the collector should not be less than 0.5m from the ground. The hot air rising along the wall of the building should not be allowed to pass over the collector. When testing on the roof, the distance between the bench and the edge of the roof should be greater than 2m.
5.3 Inclination
In order to make the test results internationally comparable, the collector should be installed so that the angle of inclination of the lighting surface to the horizontal plane is: local latitude ±5°, but not less than 30°.
Collectors can also be tested according to the manufacturer's requirements and the actual installation inclination. 5.4 Collector orientation
The collector should track the azimuth of the sun by manual or automatic methods. 5.5 Blocking of direct solar radiation
During the test, there should be no shadows cast on the collector. 5.6 Diffuse and reflected solar radiation
During the test, there should be no significant solar radiation reflected from the surfaces of surrounding objects onto the collector, nor should there be severe blocking within the collector's view of the sky.
When using a solar radiation simulator, all surfaces in the test room can be painted dark to minimize reflected radiation. 5.7 Thermal radiation
The surface temperature of objects close to the collector should be consistent with the ambient air temperature as much as possible to avoid the influence of thermal radiation from surrounding objects on the collector. During indoor tests, the collector should be isolated from the surfaces of surrounding cold and hot objects. 5.8 Wind
The collector should be installed where the wind can pass freely through its lighting surface, back and sides, and the average wind speed parallel to the lighting surface should be kept within the limit range specified in 8.3. If necessary, a fan can be used to achieve this wind speed. 6 Instruments and measuring disks
6.1 Solar radiation measurement
6.1.1 Total pyranometer
A first-level total pyranometer should be used to measure all shortwave radiation from the sun and the sky. 6.1.1.1 Prevent the influence of temperature gradient
The total pyranometer should be placed in a typical test position for at least 30 minutes before data collection to achieve temperature equilibrium. 6.1.1.2 Prevent the influence of moisture
Appropriate measures should be taken to prevent moisture from condensing on the pyranometer and affecting its readings. The pyranometer should be equipped with a verifiable desiccant, and the desiccant should be observed before and after each measurement. 6.1.1.3 Prevent the influence of infrared radiation
When using a pyranometer to measure the irradiance of a solar simulator, the influence of infrared radiation with a wavelength above 3um emitted by the simulator light source on the reading should be minimized.
6.1.1.4 Outdoor installation of pyranometer
GB/T4271—2000
The pyranometer sensor should be installed parallel to the collector daylighting port, and the difference in parallelism between the two planes should be less than ±1°. During the test, the pyranometer shall not block the collector daylighting port. The pyranometer shall be installed in a place where it can receive the same direct, indirect and reflected solar radiation as the collector.
During outdoor testing, the pyranometer shall be installed in the middle of the collector height. The pyranometer base and its exposed wires shall be protected to prevent them from being heated by the sun. The reflection and re-radiation of the pyranometer by the collector shall be minimized. 6.1.1.5 Use of pyranometer under solar simulator The pyranometer can be used to measure the distribution of simulated solar radiation on the collector daylighting port and its changes over time. The installation and protection of the pyranometer shall be the same as for outdoor testing.
6.1.1.6 Calibration cycle
The total pyranometer should be calibrated within 12 months before the collector test. If any change exceeds ±1% during one year, the calibration frequency should be increased or the instrument should be replaced.
6.1.2 Measurement of direct solar radiation angle
The direct solar radiation angle can be measured with a sunshade, which should be installed on one side of the collector plane. The direct solar radiation angle () can also be calculated by the solar hour angle (), the collector inclination angle (β), the collector azimuth angle (y) and the latitude of the test site (). The calculation formula is as follows:
coso=(sinosingcosp)-(sindcospsincosy)+(cosdcosdcoscosw)+(cososinpsinβcoscosw)+(cosasinβsinYsinw) In the formula, the solar declination 3 of the nth day of the year is calculated as follows: 8=23.45sin[360(284+n)/365]
6.2 Thermal radiation measurement
6.2.1 Outdoor thermal irradiance measurement
·（1）
The change of outdoor thermal irradiance is generally not considered in the collector test. The pyrheliometer may be installed in the middle of one side of the collector skylight plane to determine the thermal irradiance on the collector skylight. 6.2.2 Indoor thermal irradiance measurement when using a solar simulator 6.2.21 Measurement
Thermal irradiance may be measured using a pyrheliometer. To reduce the effects of simulated solar radiation, the pyrheliometer should be ventilated. For indoor tests, the thermal irradiance should be measured with an accuracy of ±10 W/m. 6.2.2.2 Calculation
When all thermal radiation sources and absorbers within the collector field of view are determined, the thermal irradiance on the collector skylight may be calculated from the temperature measurements, the surface emissivity measurements and the radiation angle coefficient. The thermal irradiance from a hot surface (represented by 2) to the collector surface (represented by 1) is given by e,F12T1. The more commonly used additional thermal irradiance (compared with the thermal irradiance of a black body at ideal ambient air temperature on surface 2) is given by the following formula: aFeT-Tt)
6.3 Temperature measurement
6.3.1 Measurement of heat transfer medium inlet temperature (t)6.3.1.1 Measurement accuracy
The measurement accuracy of the heat transfer medium inlet temperature should be ±0.1K. 6.3.1.2 Sensor installation
The temperature sensor should be installed within 200mm of the inlet, and the pipes before and after the sensor should be insulated. .(2)
An elbow or mixer should be installed at the front end of the sensor. In order to prevent the gas in the medium from gathering around the sensor, the flow direction of the medium in the pipe where the sensor is located should be upward, and the sensor probe should face the flow direction of the liquid, as shown in Figure 1. 3
Temperature sensor
GB/T4271—2000
Overflow sensor
(te,AT)
Solar collector
Elbow or mixer
Figure 1 Sensor placement for measuring the inlet and outlet temperatures of the heat transfer medium 6.3.2 Measurement of the inlet and outlet temperature difference (AT) of the heat transfer medium The accuracy of measuring the inlet and outlet temperature difference of the collector should be ±0.1K. 6.3.3 Measurement of ambient air temperature (t)
6.3.3.1 Measurement accuracy
The accuracy of measuring the ambient air temperature is ±0.5K. Elbow or mixer
6.3.3.2 Installation of the sensor
During outdoor testing, the ambient thermometer should be placed in a white louvered box within 15m of the collector to be tested. The installation height of the louvered box should be the height of the middle of the collector, but the height from the ground should not be less than 1m. If a fan is used to force air to flow through the collector, the difference between the fan outlet temperature and the ambient temperature should be within ±1K. 6.4 Working fluid flow rate (m) measurement
The mass flow rate can be measured directly or calculated by converting the measured volume flow rate and temperature. The accuracy of measuring the working fluid flow rate should be ±1.0%. 6.5 Wind speed measurement
6.5.1 Measurement accuracy
For indoor and outdoor tests, the accuracy of measuring air flow rate should be ±0.5m/s. In outdoor tests, the air flow rate is rarely constant, and the average wind speed during the test should be taken. 6.5.2 Sensor placement
For indoor tests, measurements should be taken point by point at several evenly distributed points 100mm above the collector and their average value should be taken. Measurements should be made under stable wind speed conditions before and after the performance test. For outdoor tests, if the average wind speed is less than 3m/s, artificial air supply should be used, and the anemometer should be used in the same way as for indoor tests. In places with natural wind, wind speed measurements should be made at the height of the midpoint of the collector and as close to the collector as possible. During the test, the wind passing through the sensor should not be blocked, and the sensor should not block the collector. 6.6 Pressure measurement
The accuracy of measuring the pressure drop caused by the heat transfer medium passing through the collector should be ±3.5kPa. 6.7 Time interval (△t) measurementWww.bzxZ.net
The accuracy of measuring the time interval should be ±0.2%. 6.8 Measuring instruments and data recorders
The minimum scale of the measuring instruments and measuring systems should not exceed twice the specified accuracy. 4
GB/T4271—2000
The accuracy of data processing technology or electronic integrators should be equal to or better than ±1.0% of the measured value. The accuracy of analog and digital recorders shall be equal to or better than ±0.5% of the total range, and the time constant shall be equal to or less than 15. The peak signal indication shall be between 50% and 100% of the total range. 6.9 Measurement of collector area
The accuracy of measuring collector area (absorber area, total area or lighting area) shall be ±0.1%. 6.10 Measurement of collector working fluid capacity
The collector working fluid capacity is represented by the same mass of the heat transfer working fluid used in the test. The measurement accuracy shall be ±10%. It can be obtained by measuring the mass of the collector when it is empty and the mass when it is filled with working fluid, or by measuring the mass of working fluid required to fill the empty collector.
7 Test bench
7.1 Overall structure
Figures 2 and 3 show the schematic diagram of the structure of the solar collector test bench with liquid as the heat transfer working fluid in the test pan. 7.2 Heat transfer medium
The heat transfer medium used in the collector test process can be water or a liquid recommended by the collector manufacturer. Ambient temperature sensor
Anemometer
Pyranometer
Earth radiation meter
Temperature sensor (t)
Secondary temperature regulator
Flowmeter
Observation glass
Temperature sensor (ta)
Insulation pipe
Solar collector
Bypass valve
Flow control valve
Filter||t t||(200um)
Figure 2 Closed test loop
Exhaust hook
Primary for heating and cooling
Temperature controller
Pressure sensor
Safety valve
Expansion tank
GB/T4271—2000
The change of specific heat and density value of heat transfer medium shall be within ±1% within the temperature range of heat transfer medium during the test. Appendix C (indicative appendix) gives the specific heat and density values ​​of water. The mass flow rate of heat transfer medium shall be kept constant throughout the test in order to determine the thermal efficiency curve, time constant and incident angle correction factor of the collector.
7.3 Pipeline layout and assembly
The pipeline of the collector working fluid circuit shall be corrosion-resistant and able to operate at a temperature of 95C. If non-aqueous working fluid is used, it shall be determined whether the working fluid is compatible with the system materials.
The length of the pipeline shall be as short as possible. In particular, the pipeline from the outlet of the working fluid temperature regulator to the inlet of the collector should be kept as short as possible to reduce the impact of the environment on the inlet temperature of the working fluid. This section of the pipeline should be insulated to ensure that the heat loss rate is 0.2W/K, it should also be protected by a sun-proof reflective coating.
The pipes between the temperature measurement point and the collector inlet and outlet should be protected by heat insulation and sun-proof reflective coatings so that the temperature drop in the pipe does not exceed 0.1K. The mixer should be installed above the liquid flow close to the temperature sensor (see 6.3). Ambient temperature sensor
Temperature sensor (TE)
Anemometer
Total pyranometer
Earth radiation meter
Temperature sensor (T)
Secondary temperature sensor
Flow meter
Observation glass
Flow control valve
Solar collector
Insulation pipe
Pressure sensor
Flow control room
Weighing gear
Exhaust valve
Primary temperature controller for heating and cooling Filter
(200μm)
Figure 3 Open test loop
Constant pressure box
A short section of transparent glass tube should be installed on the working fluid loop pipeline to observe bubbles and impurities in the working fluid. The transparent tube should be installed close to the collector inlet, but should not affect the temperature control or temperature measurement at the working fluid inlet. Air separators or exhaust devices should be installed at the collector outlet and other places where air is likely to accumulate. Filters should be installed upstream of the flow measurement device or pump. 6
7.4 Pumps and flow control devices
GB/T4271-2000
The working fluid pump should be installed in the collector test loop and should not affect the collector inlet temperature control or the position of the measuring working fluid. For general pumps, bypass and manual needle valves should be installed to adjust the appropriate flow. Flow controllers can also be used to stabilize the mass flow.
At any inlet temperature selected within the working range, the pump and flow controller should be able to maintain a stable mass flow rate, and the variation range should be within ±1%.
7.5 Heat transfer working fluid temperature regulation
The collector test loop should have the ability to maintain a constant collector inlet temperature, and its temperature range is the temperature range during operation. In particular, drift of the collector inlet temperature should be avoided. The test circuit shall have two-stage working medium inlet temperature control, as shown in Figures 2 and 3. The primary temperature controller shall be installed upstream of the flow meter and flow controller. The secondary temperature regulator is used to adjust the working medium temperature before the collector inlet. The working medium temperature adjustment range of the secondary regulator shall not exceed ±2K.
8 Outdoor Steady-State Efficiency Test
8.1 Test Apparatus
The installation of the collector shall comply with the provisions of Chapter 5, and the connection of the test circuit shall comply with the provisions of Chapter 7. The heat transfer medium shall flow from the bottom to the top of the collector.
8.2 Preparation of the Collector
Before the test, the collector shall be visually inspected and the degree of damage shall be recorded. The cover of the collector daylighting port shall be thoroughly cleaned. If there is moisture on the collector components, a heat transfer medium at about 80°C shall be circulated in the collector for a period of time to dry the insulation material and the collector casing. If this treatment is performed, it shall be stated in the test report. If necessary, an exhaust valve should be used or the working fluid should be circulated at high speed in the pipeline to discharge the gas accumulated in the collector pipeline. The transparent tube in the loop should be used to observe whether there are gases or impurities in the working fluid. If there are, they should be discharged. 8.3 Test conditions
During the test, the total solar irradiance on the collector lighting surface should not be less than 800W/m. The direct solar incident angle on the collector lighting port should be within the angle range of ±2% of the incident angle correction factor value when vertically incident. For single-layer glass collectors, the above conditions can be met if the direct solar incident angle on the collector lighting port is less than 30°. For collectors of special design, smaller incident angles are required. In order to indicate the collector performance at other incident angles, an incident angle correction factor can be used to determine it (see Chapter 11).
The average wind speed around the collector should be between 2 and 4m/s. Unless otherwise stated, the working fluid flow rate should be set at about 0.02 kg/ms based on the total area of ​​the collector. In each test cycle, the flow rate should be stable within ±1% of the set value. The flow rate variation between different test cycles should not exceed 10% of the set value. Due to the accuracy of the instrument, the measurement results of the working fluid temperature difference less than 1.5K may not be recorded. 8.4 Test procedure
In order to determine the efficiency characteristics of the collector, the collector test should be carried out within the operating temperature range of the collector under clear weather conditions. For the selection of data points, at least four evenly spaced working fluid inlet temperatures should be taken within the collector operating temperature range. In order to obtain no, one of the inlet temperatures should make the difference between the average working fluid temperature and the ambient air temperature within ±3K (if the heat transfer working fluid is water, the maximum temperature is generally 70℃).
At least four independent data points are taken for each working fluid inlet temperature, giving a total of 16 data points. During the test, measurements should be made according to the items specified in 8.5. 8.5 Measurement
The following measurements shall be made:
GB/T4271--2000
a) Collector total area Ac, absorber area Aa and daylighting area Ab) Working fluid capacity;
c) Total solar irradiance on the collector daylighting port; d) Diffuse solar irradiance on the collector daylighting port; e) Direct solar incident angle;
f) Ambient air velocity;
g) Ambient air temperature;
h) Collector inlet working fluid temperature;
i) Collector outlet working fluid temperature;
i) Working fluid flow rate.
8.6 Test cycle (steady state)
The test cycle for steady state data points shall include a preparation period of at least 15 minutes and a steady state measurement period of at least 15 minutes. In any case, the steady-state test period shall be greater than 4 times the ratio of the effective heat capacity C of the collector to the heat flow mct of the working fluid (for the determination of effective heat capacity, see Chapter 10).
If the test parameters deviate from their average values ​​during the test period within the range specified in Table 1, the collector can be considered to be in steady-state conditions during the given test period.
Table 1 Permissible deviation range of measured parameters during the test period Parameters
Solar irradiance
Ambient air temperature
Working fluid mass flow
Working fluid temperature at collector inlet
8.7 Representation of test results
Permissible deviation range of average value
±50W/m
The measurement results should be collated to generate a set of data points that meet the steady-state operation test conditions. These data points should be expressed using the data table given in Appendix A (Standard Appendix). 8.8 Calculation of Collector Efficiency
The instantaneous efficiency of a solar collector operating under steady-state conditions is defined as the ratio of the useful power actually obtained by the collector to the solar radiation power received by the collector.
The useful power actually obtained, Q, is calculated by the following formula: Q-mcAT
wherein the value of c corresponding to the average working fluid temperature should be used. If m is measured by volume flow, the density should be determined by the working fluid temperature in the flowmeter. 8.8.1 Solar Energy Received by the Collector
For single-layer glass flat-plate collectors, if the incidence angle is less than 30°, the incidence angle correction factor does not need to be used. When the total area of ​​the collector is used as a reference, the solar radiation power received by the collector is AcG: Therefore Q
When the daylighting area of ​​the collector is used as a reference, the solar radiation power received by the collector is AcG; Therefore Q
When the area of ​​the heat absorber of the collector is used as a reference, the solar radiation power received is AAG, Therefore 8
·（3）
·（4）
8.8.2 Normalized temperature difference
GB/T4271—2000
The instantaneous efficiency 7 (or 7) is expressed graphically as a function of the normalized temperature difference T*. When the average temperature of the heat transfer medium is used
ta-t+4
The normalized temperature difference can be calculated as
If the collector inlet temperature is used, the normalized temperature difference can be calculated as T
8.8.3 Graphical representation of instantaneous efficiency
(6)
· (8)
The graph of instantaneous efficiency (or) should be obtained by curve fitting using the least squares method, and the instantaneous efficiency curve is obtained by the following formula: nn-aT-aG(T)
(10)
(11)
The first-order or second-order curve should be selected according to the closeness of the fit. If the calculated value of α2 is a negative number, the second-order fit should not be used. The G value used for the second-order fit should be 800W/m2. The test conditions should be recorded in the data table given in Appendix A (Appendix to the standard). Data points measured under the condition that the diffuse solar irradiance is greater than 20% of the total solar irradiance should be corrected to the equivalent normal solar irradiance using the method given in Appendix B (Appendix to the standard). If the diffuse solar irradiance is less than 20%, its influence can be ignored. The following clauses provide instantaneous efficiency calculation formulas for four combinations of collector area (total area, absorber area) and normalized temperature difference (T:, T).
8.8.3.1 Instantaneous efficiency based on total collector area Using normalized temperature difference T:, the following two equations can be given: tm-t
%=70G-U
nG=700-diG
Where:
If normalized temperature difference T is used, the instantaneous efficiency formula is Q
= g -U4
NG=nG-
Where:
（12）
（13)
·（14）
（15）
（16）
（17）
GB/T4271--2000
8.8.3.2 Instantaneous efficiency based on lighting area The instantaneous efficiency equation with normalized temperature difference T: as reference is. = n0o - U, 4二
Where:
Su-Yuan—a.
Using normalized temperature difference T:, the instantaneous efficiency equation is az.G
n. = 70 - U, 4=
Where:
8.8.3.3 Instantaneous efficiency based on the area of ​​the heat absorber 6
The instantaneous efficiency equation based on the normalized temperature difference T: is Q
=700-UAm
Where:
TA= TOA-aA
Using the normalized temperature difference T, the instantaneous efficiency equation is Q
ZA = TOA-UF1
NA = ToA -
Where:
9 Steady-state efficiency test using solar radiation simulatoraa
（18）
（19）
（20)
（21）
（22）
（23）
·（24）
（25）
（26）
（27）
（28）
（29)
9.1 Overview
This test method is only applicable to simulators whose simulated solar radiation beam on the collector is approximately normal radiation. Since it is difficult to produce a uniform simulated solar radiation beam in practice, the average irradiance on the collector daylighting port should be measured. 9.2 Steady-state efficiency test using solar radiation simulator10
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