Study on performance of storage tanks in solar water heater system in charge and discharge progress

Experiment was carried out to investigate the influence of position of immersed coil heat exchanger inside a storage tank on the charging and discharging performance of hot water tank. Discharging efficiency and charging efficiency were introduced to evaluate the performance of hot water tank. The experiment results showed that the discharging efficiency increased with the rising of the coil position. When the flow rate was 5L/min, the discharging efficiency of the tanks with top-coil was higher 5% and 13.1% than that of the middle-coil tank and bottom-coil tank respectively. The gap of the discharging efficiency of tank with different position HX (heat exchanger) reduced with the increasing of the flow rate. However, the charging efficiency reduced with the rising of the HX position. Numerical simulation was carried out to analyze the annual performance of SWHS (solar water heating system) with different position HX by TRNSYS. The simulation results indicated that the SWHS had the lowest annual solar fraction and annual collector efficiency when the HX was on the top level of tank. The annual performance of SWHS was greatly affected by charging performance. So the solar fraction had the same trend with charging efficiency.