Performance Study Of Direct Evaporation Fresh Air Handling Units

Direct evaporation fresh air handling units will transfer the cold energy directly from the refrigerant to the fresh air, avoiding the water transfer energy as an intermediate medium, mentioning the overall heat transfer efficiency of the unit, reducing the energy consumpution of cold water transport, reducing unit room area while transfering air at low temperature, operational efficiency of the unit is high and fresh air can be accurately handled. Relevant research of direct evaporation fresh air handling units was carried out through a combination of theoretical analysis and experimental research in this paper, Specific contents and conclusions are as follows:Direct evaporation fresh air handling units was designed based on regulatory requirements and the functional requirements that keep indoor air terminal running without condensation. A Performance Test Platform was designed and built according to the experimental needs, this platform contains the evaporator side closed air loop, the condenser side closed air loop, refrigerant circuit and data acquisition system.Analyzing the error of experimental data, the results show that the maximum error of the basic experimental data are less than 5%.The results show that increasing the head wind speed of evaporator, the supply air temperature and humidity ratio of the new air unit will increase first and then decrease and then increase; the cooling capacity, dehumidification capacity, latent heat cooling capacity, sensible cooling capacity, Energy Efficiency Ratio and evaporator surface equivalent heat transfer coefficient increase first and these parameters will fall when increasing to a certain value; the change of the temperature and pressure drop of condenser inlet steam and outlet steam, pressure difference of condenser import air and export air is very small; pressure drop of evaporator import air and export air increases linearly. Best evaporator face velocity of the direct evaporation fresh air handling units this article designed is 1.87m/s when the dry/wet bulb temperature is 30 ℃ /24 ℃ and compressor frequency is 60 Hz, maximum cooling capacity is 10.97 k W; the maximum amount of dehumidification is 8.67kg/h; maximum evaporator surface equivalent heat transfer coefficient is 64.41 W/(m2.K).Increasing the head wind speed of condenser, the supply air temperature and humidity ratio of the new air unit will decrease with decreasing trend gradually slowing; the cooling capacity, dehumidification capacity, latent heat cooling capacity, sensible cooling capacity, Energy Efficiency Ratio, evaporator surface equivalent heat transfer coefficient and condenser heat capacity will increase with increasing trend gradually slowing; the input power of compressor essentially unchanged; pressure drop of condenser import air and export air increases linearly.The refrigerant flow rate will increase when the operating frequency of the compressor increasing, while the supply air temperature, humidity, and Energy Efficiency Ratio will all decrease. However, cooling capacity, dehumidification capacity, compressor input power, import, import and export refregerant pressure drop of the evaporator increase. The sensible heat capacity first increases and then decreases, and import and export air pressure drop of the evaporator and condenser basically unchanged. The supply air humidity ratio of the new air unit and evaporator surface equivalent heat transfer coefficient trend to change like W and with small change ranges; Finally the best EER was found which equal to 2.89 when the compressor frequency is 40 Hz of the unit and the evaporator face velocity is 1.87m/s.The supply air temperature, humidity ratio and Energy Efficiency Ratio increase, while the cooling capacity, dehumidification capacity, latent heat cooling capacity, compressor input power decease, and evaporator surface equivalent heat transfer coefficient have no obvious change when increasing frequency of the compressor. However, The supply air temperature, humidity ratio, Energy Efficiency Ratio cooling capacity, dehumidification capacity, latent heat cooling capacity and evaporator surface equivalent heat transfer coefficient increase, while compressor input power essentially constant when frequency of the compressor remain unchanged but increase the evaporator face velocity instead. Finally the best EER was found which is 3.11 when the compressor frequency is 40 Hz of the unit and the evaporator face velocity is 2.07m/s.