Study On The Influencing Factors Of Heat Exchange Efficiency Of Plate Heat Exchange Core Of Fresh Air Unit

At present,the plate type fresh air unit can not only achieve the effect of conveying fresh air,but also meet the functions of filtering fresh air and realizing heat recovery.It also has the advantages of no transmission equipment,long service life and high heat exchange efficiency.For the plate type fresh air unit,its heat exchange efficiency in winter and summer is still affected by many factors,especially the operation analysis under the actual operating conditions has not been studied,such as the impact of outdoor air temperature,outdoor air humidity and wind speed on the heat exchange efficiency of the heat exchange core is not clear;After the heat transfer core dews and frosts,the effect on heat and mass transfer is not clear.Therefore,in order to enhance the energy conservation and applicability of plate-type fresh air generator in actual working conditions,this paper studies the factors affecting the heat exchange efficiency of plate-type fresh air generator in winter and summer by combining numerical simulation and experimental analysis.The main research contents are as follows:Based on the theoretical study of the sensible heat exchange,total heat exchange and phase change heat transfer of the plate type fresh air unit,the thermal and mass resistance in the process of heat and mass transfer are analyzed,and the change process of dew-frosting during total heat exchange is also analyzed.Using FLUENT software to analyze the temperature exchange process inside the plate heat exchange core during the operation of the total heat exchange fresh air unit.Under the condition of the indoor design air parameters of passive low energy building,the temperature change process and gas flow process of the heat exchange core under the winter and summer conditions are simulated,and the temperature change cloud chart and wind speed change vector chart inside the heat transfer core are obtained.The simulation results show that the new and return air outlet temperature and temperature exchange efficiency decrease with the decrease of outdoor air temperature,and the temperature exchange efficiency decreases with the increase of wind speed.According to GB/T 21087 “Standard of Air-Air Energy Recovery Device”,a two chamber test system for measuring the performance of fresh air units is established.Combined with the design standards of passive low energy buildings in winter indoor environmental conditions,The effect of the heat transfer efficiency of the plate heat transfer core was studied by simulating the actual operation conditions of heating in winter and cooling in summer.The experimental results show that under the experimental conditions,the changes of outdoor air temperature,humidity and wind speed have a great impact on the heat transfer core of the plate fresh air unit.The temperature exchange efficiency,humidity exchange efficiency and enthalpy exchange efficiency of the plate fresh air unit decrease with the increase of wind speed.When the outdoor air temperature is between-10? and 10?,the temperature exchange efficiency of the plate heat exchanger core decreases with the decrease of the outdoor air temperature,and the humidity exchange efficiency decreases with the increase of the outdoor temperature,and the enthalpy exchange efficiency tends to be stable.When the outdoor air temperature decreases from-10? to-15?,the temperature exchange efficiency of the plate heat exchanger core increases with the decrease of the outdoor temperature,the humidity exchange efficiency decreases with the decrease of the outdoor temperature,and the enthalpy exchange efficiency tends to be stable.Under the condition of extremely low outdoor temperature(below-15 ?),the exchange efficiency of temperature,humidity and enthalpy of the plate fresh air generator is significantly reduced.The main reason for the inflection point between-10? and-15? of outdoor air temperature is the effect of thermal resistance of frost formation.The suggestions are as follows: when the outdoor air temperature is less than-15 ? in winter,it is advisable to take preheating or defrosting;When the outdoor air humidity is less than 20% in winter,humidification measures should be taken;When the outdoor air temperature is less than 28 ? in summer,the unit should be stopped;When the outdoor air humidity is more than 60% in summer,dehumidification measures should be taken.Small volume plate type fresh air unit should operate at low wind speed.