Theoretical analysis of excessive outdoor air in air conditioning system of underground railway stations

The actual outdoor air rate of the air conditioning system in the public area of underground railway stations is generally greater than the designed outdoor air rate, which increases the outdoor air load during the cooling season, resulting in an increase in energy consumption. The air conditioning system of underground railway stations usually adopts a coupling design scheme of supply fan, return/exhaust fan and small outdoor air fan. The problems such as the selection deviation of fans, the poor tightness of air valves and the unblocked bridge passing through the mixing room will cause a large deviation between the actual outdoor air rate and the designed outdoor air rate. However, the previous research lacks theoretical quantitative analysis of its influence. This paper takes a standard underground railway station as an example, establishes a theoretical calculation model of the air system, quantitatively analyses the influence of different factors on the outdoor air rate of the air conditioning system of underground railway stations, finds the key factors affecting the outdoor air rate, and puts forward some suggestions on the measures to be taken in the design and operation stages.