Performance Analysis of a Direct-Expansion Solar-Assisted Heat Pump Using a Photovoltaic/Thermal System for Water Heating

This work presents the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) to supply 60 L per day of domestic hot water. The operating values in tests, such as refrigerant pressure and temperature, were taken in a built prototype every five minutes. The weather data measurements were obtained with a WS-1201 meteorological weather station and a CMP3 pyranometer. Boiling took place in a bare flat-plate solar collector using ambient temperature and the solar radiation intensity, with an emissivity value of 0.10. The system used a photovoltaic panel to turn on a variable speed compressor with 95 W of maximum power at 3600 rpm using R134a as working fluid. The measured condensation average temperature was 41.2 °C, meanwhile boiling temperature was 5.5 °C, gaining 252.8 W in the collector/evaporator and allowing releasing 335.8 W in the condenser while water reached a maximum temperature of 39.7 °C. In Test 1, when solar radiation had an average daily value of 607.5 W/m² with an average ambient temperature of 25.5 °C, water raised its temperature from 17.5 to 39.3 °C in 35 min. The maximum coefficient of performance (COP) of the system was 5.75 under rainy conditions in Test 2. Results showed that while the solar radiation intensity or ambient temperature were increased, the water heating time decreased. The environmental study also showed that by the implementation of the DX-SAHP, it could stop emitting 1065.6 kg of CO₂ per year due to the system using renewable energy for its working.