Theoretical And Experimental Research On Fresh Air Handling Units With Large Temperature Difference

In recent years, the Radiation cooling,because of its energy saving> comfortable and so on, have been extensively applied and rapidly developed. But in the actual using process, it also exposed the faults that its surface is easily knot dew, and its cooling ability is insufficient. So many experts and scholars put forward a variety of solutions, such as:(1) using cold air distribution technology to solve the problem of the condensation in radiation cooling; (2) combine the radiation cooling with the displacement ventilation (3) applied to radiant cooling system of the two-stage heat pump desiccant air conditioning system. To solve this problem, the author studied the corresponding direct evaporation of the large temperature difference fresh air handling which was used in radiation cooling.As an common fresh air conditioning system, the direct evaporative fresh air handling has a lot of advantages:piping system can adopt single pipe air supply, indoor pipeline is simple, take up the space is small, easy installation; Through controlling the supply air temperature and humidity and speed, we can control the air quality indoor; unit handling the fresh air by the, pattern of direct evaporation, so its heat exchanging efficiency is high. But in radiation cooling system, as fresh air assume the task of dehumidification, so it needs to deal with the higher temperature outdoor air to lower temperature and then send into indoor, in such cases, this paper proposed large difference temperature fresh air handling units with two evaporators in parallel ways to cool fresh air:outdoor high temperature fresh air was cooled in the high temperature evaporator and then entry into the low-temperature evaporator for further cooling.For better studying the operating performance of large temperature difference fresh air handling units, this paper compared and analyzed the economy and operation process between two-stage large temperature difference units and single units through theoretical calculations and exergy analysis method. And analyzed exergy losses of each operation process, which provided theoretical basis for further optimal design of the unit. In order to verify the reliability of theoretical analysis, designed and manufactured a large temperature difference fresh air handling unit,and had laboratory experimental study in different inlet air conditions. According to the collected data, analyzed the operating characteristics of two-stage unit and the single stage in different inlet conditions.As the fresh air handling component, evaporator is quite important in the large temperature difference fresh air handling units. The numerical simulation analysis of the heat transfer and flow process of fresh air in the evaporator with CFD software provides theoretical basis and reference for the optimal design of the two-stage evaporator.