| The dissertation investigates the coefficient of performance (COP) of heat pump with natural refrigerants and operating characteristics of the ground source heat pump theoretically and experimentally. The study considers the influence of refrigerants and heat source from the view of point of sustainable development. The work focuses on the research on the basic characteristics and performance of the heat pump using CO2 and R22 as working fluids. And the main contents are as following.1. Research of the coefficient of performance of the heat pump with natural refrigerants The properties of natural working fluids such as carbon dioxide, ammonia, hydrocarbon and water as heat pump refrigerants are analyzed and evaluated. The further analysis on basic properties of the coefficient of performance of CO2 transcritical cycle heat pump and the main effect factors are presented. The methods and the principles to confirm the main operation condition of CO2 transcritical heat pump cycle are proposed. Through comparisons on the coefficients of performance of heat pumps with different refrigerants based on the equivalent condensation temperature, the analysis indicates that there are some advantages for CO2 heat pump to compete to the conventional refrigerant heat pump in the condition of the middle and high temperature application. Two-stage compression CO2 transcritical heat pump cycle with an expander is studied in order to find the ways and measures to improve the efficiency of the CO2 heat pump. Meanwhile the compression type heat pump cycle with water as a refrigerant is analyzed theoretically and the results indicate that the three-stage or multi-stage compression type may be a good option when the heat pump with water as a refrigerant is applied. The properties of coefficients of performance of heat pumps with propane and isobutene are summarized. 2. Analysis of the Operating Performance of the Ground Source Heat PumpAccording to the characteristics of the soil as the heat source and sink, the operation rules are studied on the ground source heat pump with scroll compressor and R22 as a coolant and the one with CO2 as a refrigerant based on the thermodynamics. The methods are brought forward and discussed to make certain the type of the CO2 ground source heat pump unit, the operation parameters and the control maneuvers of performance of the ground source heat pump. The analysis shows that the capacity regulation and the pressure control based on the inlet temperature of the gas cooler can be a better control method for CO2 ground source heat pump and the pressure formula for operation control is also proposed. According to the experimental results of CO2 heat pump, the correlation of isentropic efficiency of the CO2 compressor is given and the main factors that affect the efficiency of the prototype of the CO2 heat pump are analyzed.3.Experimental Research of the Ground Source Heat PumpThe experimental ground source heat pump system has been set up, which consists of two wells with U-tubes inserted into 120m deep boreholes and four assistant wells for temperature test. The cooling capacity of the heat pump unit with R22 scroll compressor is 21.8kW at the ARI standard condition. The technical maneuvers of the experimental system, the data acquisition and manage systems can meet the demands of the ground source heat pump experiments at different seasons and various operation conditions. Experiments on operation property of the ground source heat pump with R22 were conducted at the winter condition and the summer condition respectively. The experimental results on the change of ground temperature profile, the characteristics of U-tube ground heat exchanger and the coefficient of performance of the ground source heat pump cycle are analyzed and summarized in special. 4. Establishment and Validity of the Ground Source Heat Pump System ModelAccording to the column source theory and with the help of existing theoretical and experimental researches of the ground source heat pump, the simulat...
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