System Performance Research For High Temperature Cascade Heat Pump

Energy is the foundation and motive force of modernization,with the development of economy and society,energy and environment has become the most important problem to be solved in the world.In order to solve the problem of energy supply and demand and make full use of China's rich low-temperature heat sources,cascade high-temperature heat pump technology is the first choice.The heating temperature is the key index to measure the recovery of waste heat,the higher the heating temperature,the higher index of energy and quality allocation,and the more obvious the effect of energy saving.The present research of cascade heat pump could not meet the technical needs of energy allocation.To solve the above problems,the research object of this paper is the HTCHP system,which can realize heating temperature of 140? and can provide strong technical support to low temperature heat source quality promotion.Based on the present research status of the single stage and cascade heat pump,in view of the principle and method of the low temperature energy quality promotion technology,the selection of the working fluid,the coupling between the working fluid and the thermal machinery,the optimal design selection of the heat exchanger and the optimization of the operating parameters of the system was analyzed in this research,which is the theoretical foundation for the research work later.According to the basic principle of working fluid screening in HTCHP system,the optimum refrigerant model was established for the first time.BY differentiating the fitting formula to determine the maximum volumetric capacity of the working fluids within the operating temperature range of the system,the working medium suitable for the superimposed high-temperature heat pump system is optimized for BY-3 /R245 fa.The experimental data showed that the working fluids performed good with reasonable compression ratio and COP with the discharge temperature of150 ?.160 SZ and 320 SZ were selected as lubricants for low and high temperature refrigeration cycles,respectively.With the support of the national "973" project,a 20 kW cascade heat pump test rig was built to analyze the effect of operation parameters on the performance of HTCHP system.The test results showed that when the heating temperature of the HTCHP system reached 142 ?,the compression ratio of the high and low temperature refrigeration cycle is 3.84 and 4.13,respectively,and the COP of the system is 1.72.The exergy analysis of the HTCHP system showed that the equipment with the greatest exergy loss of HTCHP system were the high temperature end electronic expansion valve,the condenser and the cascade heat exchanger.So,the key point to improve the performance of the HTCHP system is to improve the exergy efficiency of the three parts.In this paper,the BP artificial neural network(BP-ANN)was introduced to predict the COP,heating capacity and the high temperature refrigeration cycle condenser water outlet temperature.The results showed that the BP-ANN has a high accuracy in predicting the data of the training group and verification group,with the prediction error of 4% and 6%,respectively.