Study On The Influence Of Cold Island Effect And Ambient Wind Field On The Performance Of Air Source Heat Pump Array

Air source heat pump is being used more and more widely as a kind of energy conversion device with high efficiency,energy saving and environmental protection.The heat source of the air source heat pump system comes from the surrounding air,so the state of the air around the evaporator will inevitably have a great impact on its operation performance,which directly affects the efficiency of the whole heat pump system and its low temperature adaptability.Modular air source heat pump has the advantages of flexible combination,simple installation and convenient use,but because of the small heating capacity of single module,it is usually necessary to use multiple modules in combination to meet the large load.Studying the influence of ambient wind field on the heat absorption performance of heat pump evaporator in modular heat pump array is of great significance for improving the energy efficiency of heat pump in use.Aiming at modular air source heat pump with V-type finned tube evaporator and using porous medium model,this paper establishes a numerical calculation model of single air source heat pump module and multi-module 3 X 5 combined array,compares and studies the flow field distribution around finned tube evaporator and heat pump array under different ambient wind fields,and analyses the effect of cold island and ambient wind fields on evaporation of air source heat pump array in the influence law and physical mechanism of heat absorption performance of the device.On this basis,the effects of transverse spacing of heat pump arrays,arrangement of arrays and installation of guide vanes around arrays on the inlet air temperature of evaporators,air suction capacity of fans and heat flux density of evaporators were studied.The main conclusions are as follows:The air flow field around the single module heat pump verified the existence of cold island effect.In the absence of ambient wind,the buoyancy caused by temperature difference becomes the power of cold air return after the air is heated by the evaporator and the temperature is lowered vertically by the fan,resulting in the decrease of the air temperature at the entrance of the evaporator,the deterioration of the heat absorption performance and the decrease of the energy efficiency of the unit under the condition of wind.Wind field will affect the air flow rate and inlet air temperature through the evaporator.When the ambient wind field is swept laterally,with the increase of ambient wind speed,the pressure rise of the fan decreases gradually,the suction capacity of the fan increases,and the average heat transfer coefficient increases.When the ambient wind field is swept longitudinally,the average heat transfer coefficient and heat flux density of the evaporator are higher than those of the non-wind condition.When the ambient wind speed is from 1m/s to 7m/s,the suction capacity of fan,the average heat transfer coefficient and the heat flux density of heat exchanger decrease with the increase of ambient wind speed.The existence of ambient wind field does not completely deteriorate heat transfer,appropriate wind speed improves the distribution of the external flow field of heat exchanger to a certain extent and helps to improve the uniformity of air distribution.Different ambient wind fields have different effects on the heat transfer performance of each evaporator unit in the air source heat pump array.The transverse spacing,arrangement and installation of guide vanes of the array have great influence on the heat absorption performance of the evaporator.Increasing the transverse spacing properly can increase the air suction capacity of the fan and improve the heat absorption performance of the evaporator.The staggered arrangement has obvious advantages when the wind speed of the X-direction wind field is larger,but in general,the forward arrangement is better than the staggered arrangement in resisting the deterioration of the environmental wind field.On the one hand,the arrangement of guide vanes around the unit reduces the air suction capacity and the average heat transfer coefficient of the fan,on the other hand,increases the average inlet air temperature of the evaporator in the array.The comprehensive effect of installing guide vanes is to increase the heat flux,but proper blade spacing should be selected.