I am working on a project where the mechanical specification allows for a 2degC temperature rise but when I try to apply this parameter in the CIBSE Gains Design Data Tab the project freezes at 0%.
I can make other design parameter changes but this one.
Hi Grant, my first thoughts would be that this could possibly be related to your room design and cooling supply air temperatures, however I can't be certain without seeing the project - could you please forward it? Upload link here.
Shane Regan | Senior Building Performance Support Engineer
Hi Shane, I've uploaded the project to the above link.
Thanks Grant. I notice that the units in this project are set to imperial, is that correct?
The issue is much as I suspected - the supply air temperature to cool the rooms has been set to 71.6F in CIBSE Gain:
Which is the same as the design temperatures for your rooms (for both Winter and Summer):
Please note for your room to be cooled the temperature of the supply air used to cool the room must be less than the design temperature. The additional affect of the 2degree temperature rise means that in effect your cooling supply air temperature is higher than your allowed room design temperatures - this is invalid so is leading to the crash.
Thanks for your reply, the SI units in my project are metric so not sure why imperial are being shown your end.
Reading through the documentation I believed that the supply air temperature should only be lower than the room temperature when "a central all air system" is used (page 84 of manual).
Hi Grant, that part may be referring to the temperature of Fresh Air loads. The relevant part about the supply air temperature can be found below.