Effect of Solar Irradiation Pattern on the Performance Test of Thermosyphon Solar Water Heaters

摘要

The performance of solar hot water heater is affected by design parameters, climatic conditions, and hot water load pattern. A Taiwan test standard was established in 1989 using outdoors daily efficiency test method. This test standard has been implemented for a long time with satisfactory results. However, it was also found from field applications that the pattern of solar irradiation would affect the result of the performance test. In the present study, we used a distribution factor Ri that is defined as the ratio of the total irradiation in the morning to that in the afternoon to characterize this effect. Ri reflects the asymmetry of solar irradiation distribution in the morning and in the afternoon. A field study is carried out. The data collected from the daily efficiency test results were screened using the criterion of Ri, in addition to the conditions defined in the Taiwan test standard. Two commercial products separately located in latitude 23°N and 25°N were tested. Data scattering occurs without using the criterion of Ri. If we adopt the test data using the criterion 0.5