Experimental performance analysis on a direct-expansion solar-assisted heat pump water heater

摘要

A direct expansion solar assisted heat pump water heater (DX-SAHPWH) experimental set-up is introduced and analyzed. This DX-SAHPWH system mainly consists of 4,20 m{sup}2 direct expansion type collector/evaporator, R-22 rotary-type hermetic compressor with rated input power 0.75 kW, 150 L water tank with immersed 60 m serpentine copper coil and external balance type thermostatic expansion valve. The experimental research under typical spring climate in Shanghai showed that the COP of the DX-SAHPWH system can reach 6.61 when the average temperature of 150 L water is heated from 13.4 ℃ to 50.5 ℃ in 94 min with average ambient temperature 20.6 ℃ and average solar radiation intensity 955 W/m{sup}2,. And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 ℃. The seasonal average value of the COP and the collector efficiency was measured as 5.25 and 1.08, respectively. Through exergy analysis for each component of the DX-SAHPWH system, it can be calculated that the highest exergy loss occurs in the compressor, followed by collector/evaporator, condenser and expansion valve, respectively. Further more, some methods are suggested to improve the thermal performance of each component and the whole DX-SAHPWH system.