Heat pump, Cascade, Compression ratio, Water heater
Single stage air source heat pump has been widely used around the world. However, it has some drawback, for example, deteriorated heating capacity and COP in cold ambient temperature. To overcome these disadvantages, cascade cycle has been suggested and shows better performance at low ambient temperature. Cascade cycle has smaller compression ratio at each cycle and shows higher compression efficiency compared to that of single stage cycle. Intermediate pressure is most critical parameter which decides the system performance. There have been many research studies about cascade heat pump system using NH3/CO2 and C3H8/CO2 as refrigerants at high and low stage, respectively. Most studies conducted on system optimization, finding the optimal intermediate pressure. However, little information has given about the experimental optimization results. In this study, AWHP (air to water heat pump), which is composed by two single stage cycle, was studied experimentally. AWHP high and low cycle adopts R134a and R410A as refrigerants, respectively, because critical temperature of R134a is higher than R410A. Since there are two single stage cycles, each cycle has a different compression ratio. In this research, by introducing numerical analysis, system optimization was studied. Characteristics of cascade cycle with respect to each compressor have been also studied. Experiment was conducted with various operating conditions; ambient temperature, water inlet temperature.