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

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(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 in 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 degrees C to 50.5 degrees C in 94 min with average ambient temperature 20.6 degrees C and average solar radiation intensity 955 W/m(2). And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 degrees C. 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. (C) 2006 Elsevier Ltd. All rights reserved.