| We will basically achieve the energy conservation and emission reduction goal of reaching the peak of carbon by 2030,and implement the new development concept of green and environmental protection.With its efficient and environmental friendly operation mode,air source heat pump has gradually become one of the indispensable heat sources for people’s heating or hot water preparation in their lives.In northern winter,the outdoor side heat exchanger of the heat pump is easy to frost,which affects the service efficiency of the heat pump,so it needs to be defrosted.At present,most heat pumps still focus on the traditional reverse cycle defrosting and hot gas bypass defrosting.The former is easy to destroy the thermal comfort of the indoor environment,while the latter requires long-term defrosting operation.This topic proposes an air source heat pump system with partial defrosting.The system divides the heat exchanger outside the room into three sections for heat exchange.When it is necessary to defrost the heat exchanger outside the room,one section of the heat exchanger is defrosted through the switching control of the valve,and the other two sections of the heat exchanger maintain normal evaporation and heat absorption,so that the unit can make heat without interruption while defrosting.The theoretical analysis and conclusion of the unit performance are as follows:1)Unit equipment selection and test bench construction.Based on the segmented outdoor side heat exchanger,the equipment is calculated and selected,and the experimental environment,operating conditions,data acquisition mode and system commissioning process of the unit are described in detail.At the same time,by combing the parameter analysis methods such as unit performance evaluation index,it provides a basis for the theoretical calculation and experimental research of the unit in the future.2)The mathematical model of defrosting of segmented outdoor heat exchanger is established to study the relationship between defrosting time,average heating capacity and fan frequency of heat exchanger under different working conditions.The results show that increasing the wind speed of the outdoor side heat exchanger can improve the heating effect of the unit in the process of frosting and defrosting,but the increase of wind speed leads to the increase of convective heat transfer,which prolongs the time of defrosting process;The decrease of ambient temperature or the increase of condensation temperature will reduce the heating capacity of the unit during defrosting and prolong the defrosting time.3)The frosting defrosting experiment is carried out on the partial defrosting heat pump unit to explore the changes of parameters such as suction and exhaust pressure,suction and exhaust temperature,heating capacity,power consumption and cop in the defrosting process of the unit;At the same time,combined with different working conditions of ambient temperature,relative humidity,condensation temperature and fan frequency,explore the changes of defrosting performance of the unit.It is compared with the reverse circulation defrosting method.The results show that the subsection defrosting process can make heat continuously,but the suction and exhaust pressure fluctuates greatly;The defrosting time and heating effect of the unit are greatly affected by different working conditions.Among them,the defrosting time with fan frequency of 0Hz is the shortest.Compared with the reverse circulation defrosting mode,partial defrosting can make heat continuously and has better thermal comfort.To sum up,this topic studies a new partial defrosting mode,which provides a basis for the promotion of subsequent heat pump technology and the improvement of unit control strategy. |
