Theoretic Analysis And Experimental Study On Cascade Heat Pump System

From the view of energy and environment which is facing enormous challenge, to satisfy the requirement of higher temperature for heat pump---a sorts of saving energy equipment, the cascade heat pump project was put forward in order to realizing heating with large temperature difference and getting high temperature energy.Firstly, the cascade heat pump project was put forward based on the theory of mature cascade refrigeration which makes low temperature. After academic analyzing, the experiment status was designed —evaporator temperature is 0℃ and condenser temperature is 80℃. The largest pressure of the cascade heat pump system is under 25bar. We chose two sorts of familiar refrigerants—R22 and R142b. R22 was in low temperature class and R142b was in high temperature class. I decided the dimension of the cascade system and chose system parts, including compressor, thermostatic expansion valve, heat exchanger and so on.Secondly, the experiment system was designed, then the experiment stage was built and tested. Experiment was done after the working fluids were filled into the eligible system. The first experiment was not successful because the thermal quantity of the two stages was not suited. After improving the system we got the hot water above 70℃, then the experiment succeeded. An effective method was brought out which heat up water by two steps. The new way enhanced system performance greatly and this was a spark of the text. At the beginning, the high temperature stage working fluid was pure R142b then R22 was appended into R142b gradually. The mixtures were the new high temperature working fluids. Then experiments were done under the maximal allowable pressure and contrasted the experiment results to finding the best mixed proportion.Finally, the thermal economy of the cascade heat pump system was analyzed. Then conclusions were got: the system can make hot water above 70℃. Heating up water by two steps can improve performance of the system. Designing new system form and choosing high-powered working fluids are the accurate ways to upgrade the capability of cascade heat pump system.