| Air source heat pump has been widely used in the vast area of China for its advantages of convenience,high energy utilization and no environmental pollution.But China has a vast territory and a complex and diverse climate.In consideration of it's complex and diverse climate,there are some problems in the application of air source heat pump in winter.First of all,in the middle and lower reaches of Yangtze river,commonly considered to be hot summer and cold winter,frosting on evaporator is more serious because of high humidity,leading to the reduction of the heat transfer of the evaporator,resulting in the overall reduction of thermal efficiency and heating capacity;secondly,in cold regions of northern China,due to the low temperature in winter the evaporation temperature and pressure will drop sharply and the exhaust temperature of the compressor will increase greatly which 'will decrease the system functional stability.Aiming at the problems of the most commonly used single stage compressed air source heat pump system in heating applications in cold regions,a two-stage compressed air source heat pump system with intercooler is studied.Based on the second laws of heat transmission and thermodynamics,a finite thermodynamic simulation model of single and double stage compressed air source heat pump system is established.The characteristics of two-stage compressed air source heat pump is prpved to be better than that of single stage compressed air source heat pump.This study is of great significance to the renewal of air source heat pump and the popularization and application of the air source heat pump in cold regions.This study is mainly focused on the following aspects:A two stage compressed air source heat pump with an intercooler and a single compressed air source heat pump are selected as the research objects,and their thermodynamic simulation models are established respectively.The model integrates the performance parameters of air,thermodynarmic parameters of refrigerant,and the type of components.It can truly reflect the working principle and practical operation of air source heat pump.With regard to the method of establishing the model,the dynamic distribution parameter method is adopted to make the calculation precision of the model higher.At the same time,the PID control algorithm is introduced to build up a distributed parameter model of the whole system based on PID control algorithm,which greatly improve the calculation speed of the model.In the selection of state parameters of air and refrigerant,on the one hand,after comparing with existing experimental data,the empirical formula based on previous studies are used;on the other hand,based on the existing experimental data,some calculating formula are put up by MATLAB.Based on the thermodynamic simulation model of the single and double stage compressed air source heat pump,different ambient temperature and evaporation temperature are act as the input of the mode[l to calculate the output results.By comparing the performance parameters of single and double stage compressed air source heat pump,such as COP,compressor exhaust temperature,condenser heat transfer and air outlet temperature,we can find out the advantages and disadvantages of single and double stage compressed air source heat pump.By adjusting some parameters like the intermediate pressure,heat exchanger tube length of evaporator,intermediate heat exchanger tube length,operation model of two stage compression air source heat pump again,operation results of two stage compression heat pump are obtained.Finally,the intermediate pressure,the length of heat exchanger tube of the evaporator and the intermediate heat exchanger which make the heat pump in the best condition are find out.A new type of air source heat pump system is proposed,which can adjust the operation mode of air source heat pump according to different ambient temperature.When the outdoor environment temperature is high in summer,transitional season or in winter,the single stage compression mode is used.When the outdoor environment temperature in winter is very low,the two-stage compression mode is used.The modified operation mode can solve the problem of poor adaptability of air source heat pump to the environment.The research on the problem of air source heat pump running in low temperature environment,establish a reliable thermodynamic simulation model,put forward a kind of convenient and reliable operation method and solve the problem of poor adaptability,which will be of great help.This study has important guiding significance for the renewal and replacement of the air source heat pump,and will also have a positive impact on the continued application of the air source heat. |
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