Optimal Charge Amount for Different Refrigerants in Air-to-Water Heat Pumps

This paper describes an experimental study on the heat pump performance and compressor suction pressure, in order to find out the optimal refrigerant charge amount for different refrigerants. Independent of the choice of refrigerant, environmental and safety problems can be reduced by detecting the optimal amount of refrigerant charge in the heat pumps or refrigeration systems. In this investigation, a laboratory air-to-water heat pump was built to find out the charge effects on the coefficient of performance and heating capacity for three different gases including R22, R134a and R404a. Gas injection was done gradually into the system, and results were obtained and recorded at each stage. It was shown that refrigerant overcharge and undercharge decrease performance of the unit. Although heating capacity increases gradually, compressor work increases with additional charge and there must be an optimum charge amount to obtain the maximum coefficient of performance.