All, I am modeling a large research tower, 470,000 SF.? On past projects, all of the HVAC systems were 100% outdoor air with heat pipe energy recovery.? On this project, we will be returning part of the building, yielding 81% outdoor air.? I am trying to model the energy savings.? Equest is actually showing an increase in utility costs for going from 100% to 81%, both with and without energy recovery, which is the opposite of what I expected.? Both versions of the baseline have economizer.? If I compare the utility consumption, it looks as if the fan energy has increased significantly by decreasing the amount of outdoor air (entered as a fraction on the system outdoor air tab) and the cooling energy has increased a little.
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Does anyone have any idea what combination of inputs that I have that would lead to this problem?? It seems to me that these results couln't be valid.
?
Thanks,
Maria Ramos, PE
100% outdoor air system
Sep 24, 2012
Maria,
Do you now have a return air fan specified where you had no exhaust fan previously, or return fan kW that is greater than a previous exhaust fan? If so, that could explain your fan energy increase and cooling energy increase as well due to fan heat and maybe some duct heat gain.
Sorry, but that's all I can think of without knowing more specifics.
My best,
Mike Busman
I didn't make any changes to the return fan system when switching between 0.81 and 1.0.? Both have a return fan, sized similarly.? Although this is not entirely accurate, that's what I have at the moment.