Anti-Frosting Operation And Regulation Technology Of Air-Water Dual-Source Heat Pump Evaporator

Building energy consumption accounts for an important part of total energy consumption,due to the accelerating process of urbanization in China and the continuous improvement of people’s living standards.Air energy has been applied to the field of building energy efficiency,which is the most widely distributed renewable energy source.In order to reduce building energy consumption and achieve the strategic goals of the "14th Five-Year Plan" energy-saving plan,it is of great significance to improve the efficiency of air energy utilization.Air source heat pumps are widely used in the field of building heating because of their low initial investment,clean and pollution-free advantages.However,there is frost formation in the air source heat pump in winter,resulting in problems such as high energy consumption for defrosting and unstable heating.At present,the main research hotspots of air source heat pump frosting focus on frost formation mechanism,fin shape,structure size and other aspects.Relevant scholars have found that the multi-heat source heating technology combined with other renewable energy sources such as solar energy has greatly improved the frost suppression and defrost energy consumption of evaporators.However,how to prevent the evaporator from frosting under cold climate conditions and improve the heat pump heating performance is still a technical problem that needs to be explored and solved.In this study,the conditions under which frosting begins on the surface of the evaporator are analyzed,and the relationship between the evaporation temperature of the refrigerant evaporation temperature and the absolute moisture content of the air under the critical frosting condition of the evaporator is fitted according to the 90%relative humidity line of the enthalpy moisture map.The thermal field and power field of the air-water dual heat source heat pump evaporator are analyzed,and the simulation model of the evaporator heat exchange unit is established.Under the conditions of cold season,the frost resistance of the evaporator under the working conditions of the double heat source was experimentally tested and simulated.Using the established model,the variation law of each parameter in the double heat source heat pump evaporator under the critical frost state is analyzed.The main influencing factors affecting the frost formation of the double heat source heat pump evaporator are: hot water temperature,inlet air speed,temperature and refrigerant evaporation temperature.In the low air temperature environment,increasing the hot water temperature can meet the evaporator operating temperature is not lower than its critical frosting temperature,improve its anti-frosting ability in winter.The higher the inlet air velocity of the evaporator,the lower the temperature of the hot water in the evaporator required under critical frosting conditions.When the outdoor air temperature is lower than 0 ℃,the refrigerant evaporation temperature is adjusted by adjusting the hot water temperature.Thus achieving the effect of anti-frosting.Taking Changsha as an example,the anti-frost regulation technology of air-water dual heat source heat pump is analyzed.In areas with hot summer and cold winter,the anti-frost operation of the dual heat source heat pump can be realized by supplying hot water at about 20 ℃ to the hot water pipe in the evaporator.The lowest temperature in Changsha area in winter is-2.5 ℃.When the double heat source heat pump evaporator does not have hot water,when the inlet wind speed of the evaporator is increased to 2.6 m/s,the surface of the evaporator can be prevented from frosting.When the outdoor air temperature is lower than 0 ℃,in order to prevent the air from absorbing heat from the evaporator,an adjustment method of adjusting the evaporation temperature of the refrigerant can be used.