RE: Fresh Air Having Large Effect on CIBSE Gain Results

Stephen Brown — Thu, 12 Dec 2019 16:47:36 GMT

Hi Simon,

You can find information on the calculations in the Help for the CIBSE Gain program. This explains how the Fresh Air is treated.
It's difficult to give a specific reason without seeing both hand calc and your project but my initial thought would be to check your Plant On and Off Time in the Building Data section. A Plant On and Off of 1-24 will give a lower result than if you run your plant during the occupied period only.

Best Regards
Steve