Experimental Study On The Performance Of The Two Stage Direct Expansion Fresh Air Anding Nit

The humidity of the air is very low after the treament of the direct expansion fresh air handing unit,handing by surface evaporator.And it can meet the requirement of temperature and humidity independent control system in most cases.The problems of load shedding and the stability in low load level restrict its application.Under the full year,temperature and moisture content of fresh air changing greatly,the load change greatly.It is of great significance to promote the wide application of the direct expansion fresh air handing unit to explorie the way of satisfy the requirements of dehumidification and cooling under high temperature and humidity conditions,stable and efficient in low load level condition.A kind of two stage direct expansion fresh air handing unit is designed,using two independent refrigeration systems,regulating the temperature of the supply air by condenser of the second refrigeration system.Then,the affect of different factors on the performance of the fresh air handing unit and the performance under the extreme wet condition and air conditioning period in Guangzhou are studied by experiments.Firstly,the effect of inlet air dry bulb temperature,wet bulb temperature and intermediate temperature(temperature after the first evaporator)on the performance of the two stage direct expansion fresh air handing unit are studied by experiments in the paper.Experiment results show: The cooling capacity of the first stage refrigeration system is 3.4 times of the second,so the performance of the first system has a great affect on the overall performance of the fresh air handing unit.The regularity of the affect of inlet dry bulb temperature,wet bulb temperature and intermediate temperature on the performance of the first stage refrigeration system is consistent with that of the fresh air handing unit.Under the dry bulb temperature conditions,the dry bulb temperature has little affect on the cooling capacity,SHR,input power,EER,reheating capacity and supply air moisture content.Dehumidification,sensible cooling capacity and latent cooling capacity are greatly affected by the dry bulb temperature.When wet bulb temperature is 25?,the dry bulb temperature increased by 3?,the dehumidification decreased by an average of 0.87g/s,with an average drop of 14.6%;the sensible cooling capacity increased by an average of 3.08 kW,with an average increase of 16.8%;latent cooling capacity decreased by 2.15 kW,with an average drop of 14.3%.Under the wet bulb temperature conditions,the wet bulb temperature has little affect on the cooling capacity,sensible cooling capacity,Sensible heat Ratio(SHR),Energy Efficiency Ratio(EER),reheating capacity and supply air moisture content.Dehumidification,latent cooling capacity and input power are greatly affected by the wet bulb temperature.When the air volume is 3000m3/h,wet bulb temperature increased by 1 ?,the dehumidification increased by an average of 1.19g/s,with an average increase of 21.4%;latent cooling capacity increased by an average of 2.99 kW,with an average increase of 21.2%;input power increased by an average of 1.07 kW,with an average increase of 12.2%.Under the intermediate temperature conditions,the affect of the intermediate temperature on every performance parameters of the fresh air handing unit is relatively larger,especially the input power,reheating capacity,and supply air moisture content.When the air volume is 3000m3/h,intermediate temperature increased by 2?,input power decreased by 3.18 kW,with an average drop of 28.2%;reheating capacity decreased by 3.65 kW,with an average drop of 31.3%;supply air moisture content increased by an average of 2.09g/kg dry air,with an average increase of 37.5%.Secondly,the performance of the two stage direct expansion fresh air handing unit under the extreme wet condition and air conditioning period in Guangzhou are studied by experiments in the paper.Under the extreme wet condition,the air volume is 2000m3/h,intermediate temperature is 14?,supply air temperature is 22?.The EER of the fresh air handing unit is between 2.32~2.62,the supply air moisture content is between 7.92~8.55 g/kg dry air.Limitations due to heating and humidifying capacity of the test platform,the experiments of air conditioning period is divided into two parts.Low enthalpy of level,the air volume is 3000m3/h.High enthalpy level,the air volume is 1000m3/h.During the low enthalpy level,the EER of the fresh air handing unit is between 3.45~4.16,and the supply air moisture content is between 7.74~8.01g/kg dry air.During the high enthalpy level,the EER of the fresh air handing unit is between 3.09~3.46,and the supply air moisture content is between 8.92~9.14g/kg dry air.At the same air volume,the EER and the supply air moisture content increase with the increase of inlet air enthalpy.