Study On Defrosting Method Optimization Of Air Source Heat Pump In High Humidity Area

Air source heat pump is widely used because of its advantages of energy saving,high efficiency and cleanness.However,when heating in low temperature and high humidity areas,the surface of outdoor heat exchanger is prone to frosting.The growth of frost layer will lead to the decline of heating performance of the unit,so periodic defrosting is needed.At present,the most common defrosting method is reverse circulation method.In the defrosting process,the unit stops supplying heat to the room and takes heat from the room to melt the frost layer,resulting in poor indoor thermal comfort.In order to improve the defrosting performance of air source heat pump in low temperature and high humidity areas,this paper studies the defrosting methods and defrosting control strategies.In order to realize the continuous heating without shutdown of the unit,spray low freezing point solution for defrosting.Firstly,the mechanism of solution defrosting is analyzed from the perspective of chemical potential theory.Secondly,the theory of solution freezing point reduction and the physical properties of common low freezing point solutions are discussed.Then,after considering the advantages and disadvantages of each solution,ethylene glycol solution is selected as the defrosting solution.On this basis,a solution spray defrosting system was constructed,and an air source heat pump defrosting experimental platform was built.Through the conventional reverse cycle defrosting experiment of air source heat pump,the variation rules of the unit’s temperature,pressure,power and other characteristic parameters in the defrosting process are obtained.In view of the shortcomings of traditional defrosting control methods,a defrosting control strategy based on the temperature difference between the inlet and outlet of the indoor unit is proposed.Compared with the conventional operation mode of the air source heat pump,the defrosting start time of the prototype is 180 s earlier,the defrosting time is reduced by 30 s,the indoor energy absorbed during defrosting is reduced by 30.57 k J,and the average COP of the system is increased.For the constructed solution spray defrosting system,the concentration of the spray solution was determined according to the properties of the solution and the temperature characteristics of the outdoor heat exchanger when frosting,and the experimental study of the air source heat pump spray solution defrosting was carried out.The results show that the unit can achieve continuous heating without shutdown defrosting,and the discharge pressure of the prototype compressor is greater than 3.0MPa during operation The air outlet temperature of the indoor unit is higher than 40℃,and the heating capacity of the unit is more than 2000 W,which enhances the indoor thermal comfort.It is found that the surface temperature of outdoor heat exchanger is16.3% higher,the suction pressure is 12.2% higher,the maximum input power is 5.4% higher,and the maximum heating capacity is 21.3% higher in the solution spray defrosting operation than in the conventional operation under the same working conditions.