Research On Theory And Application Of Evaporative（Condensing） Air Handle Unit

China has always advocated energy conservation and environmental protection policies.Evaporative cooling technology has the advantages of low carbon,energy saving,economy,and health,but it is greatly affected by meteorological conditions and has certain limitations in application.The condenser part of the air-conditioning unit is air-cooled,while in this unit,a plate-and-tube type evaporative condenser is used,which can make its heat exchange efficiency higher,reduce floor space and save water resources.Based on the above characteristics,an evaporative（condensing）air handle unit was proposed.First,the technical forms of evaporative and mechanical refrigeration are compared and summarized,and the current engineering is introduced.By comparing the existing domestic and foreign air handle units combining evaporative with mechanical refrigeration,and considering the characteristics of China’s climate,the experimental prototype structure of the subject was determined,and its operating process was reasonably designed.Based on the general operating mode,The load characteristics of the data center and indoor and outdoor parameters provide four modes of operation of the prototype in the data center,namely:natural cooling mode,IEC,IEC+DX,DX mode.According to the indoor and outdoor design parameters,design calculation and equipment selection for the unit,and then analyze its optimal operating efficiency through experiments.The test conditions are:dry bulb temperature:29.1℃,dry bulb temperature:18.7℃for testing.1)The best water-to-air ratio of DEC mode is measured.It is found that when the water-to-air ratio reaches Y=0.37,the DEC stage efficiency can reach 97.22%;2)Determination of the best water-air ratio and secondary air volume ratio in the IEC mode,it was found that when the water-air ratio reaches 0.28 and the optimal secondary air volume ratio is X_m=0.62,the efficiency of the IEC section can reach about 65%;3)Compared with IEC+DX and DX operation modes,it is concluded that opening the IEC section to pre-cool it can effectively increase the temperature drop by 15.9%.For the direct evaporative cooler packing,the bulk coefficient and characteristic number fitting of the oblique corrugated PVC packing were carried out.The indirect evaporative cooling section was optimized,and the test analyzed that the efficiency of the plate and tube indirect evaporative cooler was about 65%.Aiming at its operating mode,according to the regional dryness,10 sample cities were selected,and their annual application in the data center was partitioned.The method of discrimination was given,and the annual operating hours were counted.It is concluded that in a dry area like Urumqi,the time without mechanical cooling can reach more than92.2%;in a hot and humid city like Guangzhou,the time without mechanical cooling can reach more than 59.7%.According to theε-NTU algorithm,the current multi-purpose plate-fin cross-flow heat exchangers in data centers are used as an example to analyze the problem that when the outdoor temperature is too low due to the low side temperature during the winter operation,the primary side channel condensation affects the unit performance,but its operation Hours were counted.In cold regions such as Xinjiang,the primary dew condensation time can reach more than 50.4%,and in warm regions such as Guangzhou,there can also be 7.5%condensation time.Finally,taking a 160k W load data center in Xinjiang as an example,compared with the operating energy consumption of traditional mechanical refrigeration,it is concluded that it can save 145,000 yuan in electricity costs per year,and the energy saving rate is51.4%.The research shows that the functional efficiency of each functional section of the evaporative（condensing）air handle unit is high,and the direct and indirect operating efficiency is 22%and 9%higher than the general efficiency parameters of 75%and 55%.Applying it to data centers,in some dry areas,it is almost unnecessary to turn on mechanical cooling to meet operating requirements.In medium and high humidity areas,only auxiliary mechanical cooling is required to meet the load requirements.The application and promotion in wet areas provided a certain reference.