Research Of Heating System Based On Transcritical CO₂ Heat Pump And Low Grade Heat Source

With the strengthening of global warming,the use of clean energy and energy conservation tends to focus more attention of international community.To realize the application of heat pump in cold area,two wastewater source heat pump hot water system with electricity-assisted heater and a solar assisted heater are proposed,and its optimization analysis and performance comparison are carried out.At the same time,the heating performance of the heat pump,the main energy consuming equipment in the system,is analyzed,and the influence of compressor frequency and throttle valve opening on the unit characteristics is explored.The main conclusions are as follows:(1)In the heat pump unit,the decrease of throttle valve opening will lead to the increase of power consumption of compressor,the heating capacity of the unit first increases and then decreases,and the corresponding comprehensive heating coefficient gradually decreases.At the same time,the total exergy loss of the unit increases,the exergy efficiency first increases and then decreases,but the exergy loss of per heat capacity is opposite to the exergy efficiency.The increase of compressor frequency will lead to the increase of other parameters except the comprehensive heating coefficient of the unit.(2)In the heat pump unit,among the four main equipments,the compressor has the largest energy loss.The isentropic efficiency is the key factor affecting the compressor efficiency and the comprehensive heating coefficient of the system during the operation of the heat pump unit.The improvement of isentropic efficiency is very important.The operation of the heat pump unit with low throttle valve opening should be avoided as far as possible,because the comprehensive heating coefficient of the heat pump unit is lower at this time,and the throttling loss is very large due to the gasification of the working medium at the outlet of the throttle valve.(3)The COP of the solar-assisted waste water source heat pump hot water system is significantly higher than that of with electrically-assisted heater.The increase of the heating capacity of the solar collector will reduce the comprehensive heating coefficient of the heat pump unit,and also reduce the heat load of the heat pump unit.Both of them affect the energy consumption of the heat pump unit,which makes the change of the energy consumption of the heat pump unit uncertain.Therefore,the influence of solar collector should be considered in the process of system design.(4)In the solar assisted waste water source heat pump system,the flow rate of the hot water circulating pump has the greatest impact on the system efficiency,followed by the volume of the hot water tank.The annual outlet water temperature of the system meets the demand of the end water temperature.Affected by the environmental temperature changes,the outlet water temperature is higher in summer.After optimization,the effluent temperature of the system is more stable in winter,the annual energy consumption of the system is reduced by 4.561×10~6k J,and the energy saving rate is 1.255%.The research of this paper provides a reference for the application of heat pump and renewable energy in cold regions,and clarifies the change rule of heat pump unit performance with some parameters,which can provide a reference for the design of heat pump parameters,so as to improve the performance of the system.