Discussion on design and selection of direct-expansion air conditioning unit

Based on the design practice, analyses the characteristic and applicability of a direct-expansion air conditioning unit. Points out that it is different from the common water-cooled air conditioning unit. The supply air rate of the direct-expansion air conditioning unit must match its cooling capacity. The suitable range of air rate-cooling capacity ratio is 170 to 200 m3/(kW·h）. The air parameter in an air conditioned room should be checked if there is a great deviation between the actual air rate and design parameter. Based on the data comparison of a design case, analyses the effect of several factors on the design of air rate-cooling capacity ratio, such as indoor air design conditions, outdoor air design conditions and load characteristics of air conditioned room. It shows that the relative humidity of indoor air has a greater impact on the air rate-cooling capacity ratio than that of the indoor air temperature. And the cooling load of outdoor air is a key factor impacting on the operation effect of direct-expansion air conditioning units.