Study On The Working Characteristics And Design Method Of An All-air THIC Air Conditioning System

All-air system is widely used in industrial and civil buildings at present.Its common forms are primary and secondary air return systems.However,there are many problems in these two systems,such as heat and cold offset,non-energy saving,non-flexible regulation,poor adaptability and so on.So far,many scholars have proposed improved schemes,and studied the performance and adaptability of the system,including all-air temperature and humidity independent control(THIC)system,but the existing all-air THIC system has been found to have limited application scope of fresh air ratio.Therefore,this paper presents an all-air THIC system with exhaust heat recovery,and studies it.The calculation method of air treatment process of the new system is put forward through research;the applicable range of heat-moisture ratio and fresh air ratio of the new system is discussed and compared with the existing THIC air conditioning system;the mathematical calculation model of the new system is established,and the influence of variable structure parameters of heat exchanger on the performance of the new system is studied by Matlab;and three kinds of new systems are simulated by Des T.Through the analysis and comparison of the whole air system,the components with the greatest loss rate in the new system are found out,and the influence of the change of the upwind area of different components on the heat transfer and dehumidification is studied.The results show that the new system has a larger range of heat-moisture ratio and fresh air ratio: the indoor design temperature is 25 ?,and the range of heat-moisture ratio can be expanded by 62.2%,55.9%,52.5% when the temperature of frozen water is 7,5 and 3 ?,respectively.The ratio of dehumidified fresh air increases from 24.5%,12.7%,9% to 69%,35% and 25% respectively;the temperature of frozen water is 5 ?,and can be treated at room temperature of 24,25 and 26%.The range of heat-humidity ratio was expanded by 67%,63.6%,51.7% respectively.The fresh air ratio of dehumidification increased from 26%,19%,16% to 46.2%,35% and 28%,respectively.The application scope of the system engineering was more and more extensive.In winter and summer,the efficiency of the new system is higher than that of the traditional primary and secondary return air conditioning system.The closer the outdoor dry bulb temperature or chilled water temperature is to the room temperature,the higher the efficiency of the system is,and the efficiency of the system increases with the increase of the air temperature difference.In winter and summer,the components with the highest loss rate are high temperature surface cooler and low temperature surface cooler.Under winter and summer conditions,increasing the total heat recovery windward area can greatly reduce the cooling capacity or heating capacity of cryogenic surface cooler and improve the system efficiency;increasing the windward area of sensible heat recovery device will increase the heat transfer capacity of high-temperature surface cooler,reduce the heat transfer capacity of low-temperature surface cooler slightly,and reduce the system efficiency;increasing the windward area of cryogenic surface cooler will reduce the heat transfer of high-temperature surface cooler.Increasing the heat transfer capacity of cryogenic surface cooler will reduce the system efficiency,and the range is not large.Total heat recoverer is the key component in the system.