Experimental Study On A Combined Double Heat Sources Cascade High Temperature Heat Pump Under Variable Working Conditions

According to the situation that the single stage vapor compression high temperature heatpump required for relatively high temperature heat source, cascade high temperature heat pumpsystem required for relatively low temperature heat source but low efficiency, and utilization in anarrow temperature range of low grade energy, a type of combined double heat sources cascadehigh temperature heat pump traited for a key heat exchanger of condenser-evaporator has beenadopted, so as to realize the complex utilization of primary energy and secondary energy. Thissystem was able to product high temperature hot water to meet the heating processes and improvedthe efficiency of high temperature heat pump. In this paper, work principle, working mode,variable working condition features of this system are first theory analyzed. On this basis, theexperiment platform of cascade high temperature heat pump system is designed and constructed.The heating performance of different work modes including the single low temperature heat sourceand the dual heat sources is tested in various experimental conditions. The system performance isobtained in various work modes. The main research results were as follows:In the single low temperature heat sources mode, through the study on the heating propertiesof variable working conditions, the influence of temperature and flow rate on the performance ofthe system was quantitative analysised; In the low temperature heat source, while the flow rate oflow temperature heat source maintained0.7m3/h, and the inlet temperature changed from10℃to25℃, theheating capacity improved by28%and the COP improved by15.3%; while the inlettemperature maintained15℃，and the flow rate of low temperature heat source changed from0.35m3/h to1.05m3/h, the heating capacity improved by22.2%and the COP improved merely by15.4%; while the flow rate of users heating medium maintained1.05m3/h, and the inlettemperature changed from57℃to77℃, theheating capacity improved by10.5%and the COPimproved by17.5%; while the inlet temperature of users heating medium maintained72℃，and the flow rate changed from0.53m3/h to1.58m3/h, the heating capacity improved by0.8%and theCOP improved merely by12.6%; In the dual heat sources mode, through the study on the heatingproperties of variable working conditions, the influence of temperature and flow rate on theperformance of the system was quantitative analysised; As to medium temperature heat source,while the flow rate maintained, and the inlet temperature changed from42℃to53℃, theCOP andheating capacity improved by18.6%、8.9%; while the inlet temperature maintained, and the flowrate changed from0.4m3/h to1.165m3/h, the COP and heating capacity improved by1.2%、4.3%.Experimental results show that in the single low temperature heat sources mode, lowtemperature heat source’s temperature and flow rate significantly affect the performance of cascadeheat pump system, and the flow rate of users heat medium have obvious influence on the system’sperformance, but the temperature of user heat medium reduces the cascade heat pump system’sperformance; In the dual heat sources mode, the temperature of medium temperature heat sourcesignificantly affect the performance of cascade heat pump system, and the influence of flow ratechanged little; The analysis of variable working condition performance shows that in order toimprove the efficiency of this system, low temperature heat source’s temperature and flow rate, theflow rate of users heating medium, the temperature of medium temperature heat source should beimproved.