Difference between AIRAH Gain and Summer

Question

Hi, I commonly use Hevacomp to calculate the maximum internal temperature for ventilated and non-ventilated enclosures as well calculating required cooling loads. 
 I am currently modelling a pump station (approximately 3m long x 2m wide x 2m high) in a metal enclosure and appear to have some conflicting information between summer method and AIRAH Gain. 
 What I am finding is: 
 
 When summer is used, internal temp reaches 76 C 
 When AIRAH gain is used and the set inside temperature is incrementally changed, the total load is 0 kW at approximately 55 C internal. 
 
 Can anyone please explain why there is such a significant difference between the maximum temperature calculated using the Summer Temperature method and the AIRAH gain method (when the internal temperature is adjusted until the Total Load is zero)? Zip file attached if needed. 
 Thanks 
 Pump Station Hevacomp.zip

Shane Regan · Answer

Hi Tim, 
 The design engineer would need to make the decision as to which calculation is most appropriate, however please note that the Summertime calculation's purpose is to find the peak temperature, while the AIRAH Gain (and CIBSE Gain) calculation is more designed to calculate Air Flow rates necessary to maintain room design conditions. With this in mind Summertime would give you more of a worst-case-scenario for peak temperature.

Difference between AIRAH Gain and Summer

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