Experimental Investigations of Transient and Daily Thermal Performances for a Balcony-Flat-Plate Solar Water Heater

Transient and daily thermal performances of the balcony-type solar water heater with a flat-plate collector were investigated under different weather conditions in Kunming. The results showed that the solar irradiance has a few influences on the thermal performance of the solar water heater. The system thermal efficiency is 50-57% when the daily total radiation varies from 5.3 to 22.2 MJ·m-2. The initial temperature of the water in the water tank has great effects on the thermal efficiency. The daily thermal efficiency decreases by 9% when the initial temperature increases by 10°C. The percentage (Useful energy/Energy need) exceeds 60% when the daily total solar radiation is more than 11.6 MJ·m-2. When the daily total solar radiation is larger than 21 MJ·m-2, the useful energy output of the solar water heater can meet the user requirement for hot water.