Baseline hvac system for data center

Based on the existing modelling guidelines, which should still be valid, the answer is: "Data centers in the baseline building will typically be served by a separate system because they trigger the exception to the HVAC mapping requirements having to do with abnormal internal heat gain and schedules of operation. When heat gain differences of more than 10 Btu/h or operation schedule differences of more than 40 hours/week trigger this exception, a separate system is required to serve the data center. Either system 3 (PSZ-AC) or system 4 (PSZ-HP) shall serve the data center (depending on the heating source for the building). See the PRM, G3.1.1, Exception b." However, I was wondering if an air-side economizer should be considered for the baseline, as this is process cooling and air-side economizers are not really applicable to large Data Centers.

Be careful when applying the G3.1.1 exceptions. The first step is to determine the predominant condition in the building. If the area of the data center is greater than the other areas with lower loads then it is the predominate condition and the exceptions get applied to the other areas and not the data center. I do not see an exception in 90.1-2010 however there is an exception in 90.1-2013 related to the economizers. You should look for an addendum to 90.1-2010 that contains this exception. If it is in a addendum you can use it in a v4 project. If it is not in an addendum you cannot use it.

The G3.1.1 exceptions are not optional. If they apply you must use them. With that said if you are a predominately a system 3 then applying the exception may not change anything.