Hello all,

I have a question regarding outside air input. For my design building I enter my outside air at the system level, as the minimum outside air ratio, which I get from my equipment schedules. 90.1 requires that the outside airflow be the same. To do this I take my summary report from my design building and enter the values from that report into the baseline model zones. When I run my baseline model the outside airflow rates from the summary report match those of my design model, and my unmet heating hours are good in both models, but the heating gas consumption in my baseline building triples. The result is I am getting great, but unrealistic, energy savings.

Does anyone know why this is happening? Why would entering the OA at the zone level cause such increased heating for the save total CFM entered at the system level? How are you folks typically handling your outside ventilation air.

Any help would be greatly appreciated, thank you.

Scott Tomlinson, PE, LEED-AP