Effect of refrigerant charge on the performance and environmental footprint of R32 heat pump water heater

R32 refrigerant represents an alternative option to be used in heat pump water heaters because of the low operative pressure, nontoxicity and minor flammability level (A2), along with zero ODP and low GWP (675). This study contributes to the optimal selection of the refrigerant charge for commercial heat pump water heater application with a rated heating capacity of 4 kW. Experiments and simulations are conducted by varying mass charge (0.52 kg, 0.56 kg, 0.59 kg and 0.61 kg) with constant air temperature and humidity and water temperature. Consequently, the heat pump water heater will be evaluated in terms of the energetic performance and environmental footprint based on the LCCP analysis. The results demonstrate a maximum COP of 5.62 occurs at a mass charge of 0.61 kg. The LCCP analysis demonstrates reduced emissions in this condition when a representative case of specific water demand is considered. Simulations show accurate agreement with the experimental with an average maximum relative error less than 5%.