Experimental Investigation on the Two-stage Compression Heat Pump Water Heater System with Refrigerant Injection

Nowadays heat pump water heater becomes a very hot topic in hot water industry. However it still has many problems such as higher condensing temperature, large-scale operation conditions and lower COP in cold regions. Based on these problems, the paper presents a prototype assembled with a two-stage rotary compressor which can be used in cold regions. The working principle and the basic feature are introduced in this paper. The operation performance was measured under different ambient temperatures especially -7 -15 , and it is also discussed about the performance, heating capacity and parameters of the system with the vapor injection. The influence factor and the trend of optimization design are also demonstrated. The experiments show that the prototype can provide much better energy performance than the conventional heat pump water heater especially in cold regions. The heating capacity can even increase 40% when the ambient temperature is -15 . The improvement rate of heating capacity varies with the water temperature, while the total heating capacity enhances obviously when the mid-pressure refrigerant injection is available. It is important to control the mid-pressure and injection refrigerant volume for the enhancement of all the heating periods.