Experimental Study on Variable Speed Operation Characteristics of Photovoltaic Direct-drive Direct-expansion Heat Pump Water Heater
A direct-current direct-drive direct-expansion heat pump water heater system based on uninsulated micro-channel photovoltaic/absorber/heat collector(PV/T modules)was proposed.The photovoltaic of PV/T modules directly drives the direct-current compressor of the heat pump system through the maximum power tracking controller(MPPT),and the heat absorption of photothermal conversion is absorbed and upgraded by the evaporator of the heat pump system to heat the hot water in the heating water tank,thus realizing the system integration of solar energy and heat pump.To improve the operating efficiency and reliability of the system,the variable speed operation condition of the compressor which changes step by step with the change of solar radiation was designed,with experimental research done.The results show that the power generation of the system is greater than that of the heat pump,and off-grid operation can be realized.The temperature rise of PV/T components can be controlled by the operation mode of compressor speed increasing with the increase of solar radiation intensity,with the average electrical efficiency,thermal efficiency,and total efficiency of 19.65％,48.8％,and 68.4％respectively.It only takes 210 min for 90 L water to heat from 18.8 ℃ to 52.8 ℃.The average energy utilization efficiency and coefficient of performance of the system are 68.4％and 6.84,respectively.With the decrease of solar radiation intensity,the operation mode of decreasing compressor speed can maintain high energy utilization efficiency and coefficient of performance of the system.The average energy utilization efficiency and coefficient of performance of the system are 93.8％and 5.52 respectively.
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