Performance Study On Spray Solution Defrosting System For Air-source Heat Pump

In order to solve the problem of defrosting of air source heat pump,the current methods mainly include reverse cycle defrosting,hot gas bypass defrosting,energy storage defrosting,etc.,but all have shortcomings such as low efficiency and poor system stability.In addition,some scholars have proposed a variety of technical solutions for the use of hygroscopic media for frost suppression or defrosting,but there are also various shortcomings.Aiming at the shortcomings of existing defrosting methods for air source heat pumps,this paper proposes an air source heat pump solution spray defrosting system.The system uses the antifreeze solution without hygroscopic ability to spray defrosting the outdoor heat exchanger of the air source heat pump;because the antifreeze solution does not have the ability to absorb moisture,the partial pressure of water vapor is large,and the system adopts the method of air type solution regeneration.The spray antifreeze solution is in contact with air to achieve regeneration of the dilute solution.In this paper,the mechanism of solution defrosting and solution regeneration is analyzed from the perspectives of water vapor partial pressure and chemical potential.The air source heat pump solution defrosting system and its operation mode are designed.According to the characteristics of the system,ethylene glycol solution is selected as the system.Antifreeze solution,and according to the meteorological parameters of Qingdao area,the lower limit of the antifreeze solution concentration is determined to be 20%.Based on the growth mechanism of the frost layer,based on the thermodynamic theory,the mathematical model of the evaporator frost layer growth is established.The frosting process and performance of the air source heat pump are studied,and the frosting experiment is carried out.The thickness of the frost layer measured by the experiment is measured with time.The change verifies the accuracy of the mathematical model.Based on the law of frost growth,this paper proposes that the evaporation temperature can be used as the indicator parameter of the air source heat pump frosting state,as the key criterion of the system defrosting control,and based on the evaporation temperature change with the frosting time,it is applicable to the system itself.Features a defrost control strategy.According to the characteristics of the system and the needs of the experiment,the experimental platform of the air source heat pump solution spray defrosting system was designed and built,and the feasibility of the system was verified by experiments.In the case where the indoor temperature is 18 ° C,the outdoor ambient temperature is 0 ° C,and the relative humidity is 80%,the defrosting method using the solution spray after the last defrosting and the "frosting" stage before the next defrosting The effect of suppressing frosting on the unit is very obvious;the heating capacity is maintained at a high level;the average COP of the heating operation of the unit is 2.92,which is significantly higher than the average COP of the reverse cycle defrost of 2.72.Under the above conditions,the solution defrosting effect is good.When the power consumption of the fan and the solution pump is not considered in the case of defrosting and reheating of the solution,the average COP of the frosting-defrosting cycle is 2.90.The cycle average COP was 2.65,which was 9.4% higher than that of the reverse cycle defrost mode.In this paper,it is also verified by experiments that the regeneration of ethylene glycol solution can be achieved by means of air-type solution regeneration.Because the system does not intervene in the refrigerant circulation of the air source heat pump,the antifreeze solution spray defrosting has no effect on the air source heat pump unit,compared with the air source heat pump reverse circulation defrosting system,the solution spray defrosting new system inhibits The frosting effect is good,the unit operation is more stable,the indoor thermal comfort is good,the heating effect and energy efficiency are better than the reverse circulation system,and the solution regeneration energy consumption is small,and the continuous high-efficiency heat supply of the air source heat pump can be realized.