| The moderate/high temperature heat pump technology has wide prospects inenlarging heat pump applications to achieve the higher delivery temperature andutilize waste heat. The object of moderate/high temperature heat pump technology ishigh-temperature and high-efficiency at present. The main factors for systemefficiency are conditions, working fluids, system components efficiency and thematch between working fluids and system; high-temperature mainly depends on theupper limit of suction temperature and exhaust temperature of compressor. As there isno high temperature compressor developed specifically for moderate/high temperatureheat pump system, compressors for room temperature heat pump system are utilized,and with environmental-friendly working fluids as well as confirmed COP, hightemperature and high efficiency can be achieved through optimizing the working fluid,solving technical issues on high temperature and the match between working fluidsand system.In this paper, theoretical performances of 5 fluids with excellent environmentaland thermodynamic characteristics were carried out with improved theoreticalanalysis methodology at condensing temperature from 75 to 95°C, and 2 mixturesmarked MB3 and MB4 were proposed. Meanwhile, they also were chosen as designworking fluids for experimental system.For practical application of moderate/high temperature heat pump system andrealization of high-temperature and high-efficiency, a new heat pump experimentalsystem was designed. There were plate-type evaporators, condenser, pistoncompressors for room temperature heat pump system in this system. In order tooptimize the match of system and analyze high temperature, the new experimentalsystem contained two evaporators, an electronic expansion valve and a thermalexpansion valve, a hermetic piston compressor and an open-type piston compressor.And the open-type piston compressor could be coupled with different motors.Experimental verifications for the performance of the new experimental heatpump system were carried out, and the results of the system performance of the newsystem as well as the load of evaporator and condenser caculated by parameters ofwater side and working fluid side were compared with the original experiment when R245fa was chosen as the working fluid. The results showed that the primary andsecondary system and the measuring system are stable and reliable: the performanceparameters of R245fa in the new experimental system were better compared with theoutcome of the original experimental system; the load of evaporator and condensercaculated by parameters of water side and working fluid side were consistent.In the new experimental heat pump system, comparative experimental study ofcycle performance on the pure refrigerants R245fa and non-azeotropic mixtures MB4were carried out at condensing temperature from 70 to 90℃, while experiments withhermetic piston compressor and open-type piston compressor were also conducted.The results showed that: (1) When MB4 was chosen as working fluid, the heatingcoefficient COPh and heat capacity were higher than the one when R245fa wasworking fluid.(2) Comprehensive efficiency of hermetic piston compressor was betterthan the efficiency of open-type piston compressor, but the exhaust temperature ofclosed piston compressor was higher. In all, it was appropriate to use the open-typepiston compressor in the moderate/high temperature heat pump system. |
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