Research And Development Of Low Temperature Air-Source Heat Pump Water Heater

This thesis mainly focus on the requirements for supply hot water in North market cold region and has designed for the heat pump water heater under low temperature conditions. It is proved that the circulating system useing scroll compressor with center supplement gas can take the air source heat pump water heater to be effective and to run reliability in low temperature environment.Generally, it is difficult for heat pump water heater to run when the ambient temperature is below -10℃. Low temperature operating conditions has a great influence on running efficiency, and it is easy to cause some problems on water heater. Working in low temperature, the compression ratio and the suction specific volume will increase, causing the higher exhaust temperature, reducing of heating capacity and COP, and leading to serious problems such as damage to compressor. So for the low temperature working condition, the system could use refilling and enthalpy increasing, two-stage compression and some other measures in order to improve the working efficiency. This paper analyzed the working process of the refilling and enthalpy increasing system with economizer in detail, and concluded the main performance of the system.Combined the practical case, the author made design and calculation of low temperature heat pump water heater in detail, including thermodynamic calculation of the system, selection of components, calculation of several variable operating conditions, cost-benefit analysis of variable economizer. It is improved that the refilling and enthalpy increasing system with economizer can further reduce the enthalpy of the refrigerant inlet evaporator and increase the cooling capacity of the system, with higher refrigerant mass flow rate, (higher) heating efficiency, lower temperature of the compressor exhaust and higher reliability.