The Performance Analysis Of A Two-Stage Air-Source Heat Pump

Nowadays Chinese economy and urbanization has been developed dramatically with serious energy-consuming issues. Fortunately, Air-source heat pump system, a highly effective, energy-saving and environmental heating device, is in accordance with the situation of Chinese energy and environment for future and has been widely used in South China, Southwest of China and Yangtze Plain. However, in terms of utilization in North China, owning to the lower temperature compared with South China, some problems have promoted in some extent, for instance, exhaust gas temperature of compressors is extremely high; displacement efficiency draws down dramatically; pressure ratio of compressors is too high, which contributes to weak performance and low heating capacity; and finally the system will be a frequent start-stop system. Thus this paper puts forward the two-stage air-source heat pump system with two stage throttling and midway incomplete cooling to construct theoretical circulation model and then draws some practical and theoretical conclusion.The background and improvement of two-stage compression heating pump system are introduced mainly. Construct single stage compression air-source heating pump system model and four types of two-stage compression heating pump systems models: two stage throttling and midway incomplete cooling, two stage throttling and midway complete cooling, one stage throttling and midway incomplete cooling, one stage throttling and midway complete cooling, relying on research of principle and processes of heating pump system. With comparison of the single stage system model and two stage system models, the two-stage compression system in reducing the compression ratio and exhaust temperature etc. is better than the single stage compression system. And comparison among the four type systems leads to a conclusion that two-stage air-source heat pump system with two stage throttling and midway incomplete cooling can be used as an ideal two-stage compression cycle used in northern area.Depending on the model constructed, the third part focuses on the essential parameters(such as COP, heat unit, refrigerant mass flow rate, shaft power of compressor, high pressure compressor exhaust temperature etc.) of two different working conditions. The two different working conditions refer to constant gas transportation quantity of compressors and variable gas transportation quantity of compressors. At the end of the chapter, In terms of the parameters, system pressure ratio, high pressure compressor exhaust temperature, specific volume of suction port of low pressure compressor, heat output and COP, the simulation value is forced to be compared with experimental value for these parameters in order to obtain that the simulation value is the same as actual value change trend.At last but not least, for the two-stage air-source heat pump system with two stage throttling and midway incomplete cooling, a multi-objective optimization method has been developed, which means the method uses optimization objects (unit heating power and COP) and optimization variable (intermediate pressure). As COP and unit heating power are important equivalently, COP will decrease slightly while unit heating power grows as a result of energy-saving and lightening pollution. Meanwhile thermal comfort of indoor space and hot water requirement will be met. When the evaporation temperature of-30℃, the condensing temperature is30℃, the unit heating power of system increases to3.1%while COP reaches at2.6with decreasing1.6%. When the evaporation temperature of-30℃, the condensing temperature is55℃, the unit heating power increases to3.6%while COP reaches at1.9with decreasing1.8%.Lastly, this study draws a major conclusion for the whole paper and put forward suggestions and prospects for the future research trend.