Performance Improvement And Experimental Research On A Direct Expansion Solar Assisted Heat Pump Water Heater

As an effective way of making use of solar energy, solar assisted heat pumps are becoming more and more popular. A prototype of a direct expansion solar assisted heat pump water heater (DXSAHPWH) has been patented by our teamExperiments were carried out on the prototype and data collected in typical working conditions during the four seasons. Data were analysed in order to determine the performance characteristics of DXSAHPWH. Analysis of data showed that although the total COP was higher than ordinary water heater, there was still much room for improvement in integration with building, performance of the solar energy collector, and the amount of power consumed during operation. A new solar collector was therefore designed and manufactured, and its performance tested on the DXSAHPWH. Data was collected for comparison with that of the previous prototype. Results showed that the new collector matched the system better, and the efficiency increased. Also another experiment unit was built to collect the specific parameters of new solar energy collector. Both experimental and theoretical analysis were adopted in the study of working principles of DXSAHPWH. A mathematical model for the designed DXSAHPWH system was established by steady and concentrating method. To validate the model,experiments were carried out and data were collected in typical weather conditions of Shanghai. Database of DXSAHPWH performance during variable weather conditions was obtained by running the program. The variable frequency operation control strategy for DXSAHPWH was found to be more reasonable and reliable and enhanced the performance. During June to August (when solar radiation was 700W/m2, temperature was 31 degree), the average COP reached 6.5, while equivalent collector efficiency was 110%.According to analysis of experiments data and simulation results, design of prototype of a DXSAHPWH was continued towards mass production, on condition that high system efficiency and good performance were preserved. After model was manufactured, continuous test for a month in winter followed. Then the effect to performance of DXSAHPWH from angle variation of solar energy collector was calculated, before a recommended installation angle of collector in Shanghai was finally obtained. Economic analysis of the DXSAHPWH was done with consideration of many many cities in China. Power consumed under different typical working conditions was generated with the model and average operation cost of DX-SAHPWH was compared with other traditional water heaters. Then performance of DX-SAHPWH was compared with the other key economic operational factors and analyzed by synthesis energy pricing method. It was shown that weather conditions, costs of energy and control strategy were crucial in energy conservation and for optimum operation of the DX-SAHPWH. In areas where solar radiation is abundant ranked as Class One or Class Two, DX-SAHPWH is far more economical and promising than traditional water heaters.