Comparative experimental analysis of direct-expansion solar-assisted heat pump water heaters using R134a and R290

Abstract

To conduct a comparative evaluation on the performance of a R290 direct-expansion solar-assisted heat pump (DX-SAHP) system, two experimental set-ups of the DX-SAHP system have been designed, fabricated and tested for domestic hot water supply, using R134a and R290 as refrigerant, respectively. A micro-channel solar collector/evaporator was used in the R290 system. Based on them, numerous experiments were carried out under the meteorological winter conditions to compare the thermal performance of two systems. The results show that the average compressor power of the R290 system during the whole test days reaches 301.1 W, which is 7.04% lower than that of the R134a system. The corresponding average heating capacities of the R290 and R134a systems are 859.7 and 786.4 W, respectively. When 0.2 m3 water is heated from approximate 10 to 40 °C with average solar radiation intensity of 500 ± 3 W m−2, ambient temperature of −0.7 ± 0.1 °C and wind speed of 1.2 ± 0.1 m s−1, the average coefficient of performance (COP) of the R290 system reaches 2.72, which is 32% higher than that of the R134a system. In addition, under the same conditions, the average collector efficiency of the R134a system reaches 0.66 while that of the R290 system reaches 0.73 with the corresponding average compressor power of 405.9 and 291.4 W, respectively.