Study On The Performance Of High Temperature Air Source Heat Pump With13kW Heat Capacity

When normal air source heat pump is producing high temperature hot water, thedischarge temperature and pressure may be too high, heat capacity and coefficient ofperformance may decrease rapidly. If this problem can be solved to improve the outlettemperature to more than80℃, the application range of air source heat pump will begreatly expanded.In this thesis, in order to realize the goal of producing high temperature hot waterwith air source heat pump stably and efficiently, theoretical and experimental researcheson refrigerant injection system and cascade system have been made. The best qualityratio of binary mixed refrigerants is determined based on the refrigerant injection heatpump prototype platform. A single-double stage cascade heat pump system has beendesigned, which can ensure stable operation while more economic and energy saving.Using refrigerant injection structure in low temperature ambient may effectivelyreduce the compressor load. In this thesis, the refrigerant injection structure is used inhigh temperature heating section, not only makes the discharge temperature and pressuredecrease, increase the security and stability of system, but also effectively avoid thedecrease of heat capacity caused by turning down the main electronic expansion valvewhich decreases the refrigerant circulating volume. Experimental results show that, whenthe quality ratio of R134a and M is9:1of the new developed binary mixed refrigerants,the heat pump can get higher heat capacity and temperature under the condition that theoutlet water is more than80℃and the discharge pressure is less than2.7MPa. The heatcapacity is relatively stable in the whole heating process, the system can produce about13kW heat under normal conditions, and the discharge temperature is less than106℃.Theoretical study on the temperature distribution of single-double stage cascade heatpump system shows that, if the evaporation temperature is5℃, and the condensation temperature is80℃, the system may get largest coefficient of performance when thecondensation temperature of low stage is45℃. But the condensation temperature of lowstage should not be more than40℃considering that the limitation of suction pressure ofcompressor. Considering both ambient temperature and outlet water temperature todetermine the switch temperature of single-double stage system, results show that whensystem is running under double mode, the middle temperature should be regulated bycontrolling the electronic expansion valve to make system run with maximum efficiency.