eQuest Users Group - Setting outside air minimum

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Hello folks,

Hopefully someone knows how to deal with outside air. I can't seem to figure out how to set my minimum outside air on my HVAC systems. When I set my OA minimum on my Air system , and adjust the minimum OA fraction in my schedule I still get ventilation results below my set minimum. It seems, no matter what I do to the outside air setting on the system side the program sizes the OA ventilation based solely on what my outside air ventilation rates of the individual spaces and ignores any setting I put in my system. Does anyone have experience on how to remedy this?

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- Thank you,

Scott Tomlinson, PE, LEED-AP

Tomlinson, Scott's picture
Joined: 2011-09-30
Reputation: 0

I thought this min. is for heating season. See below.


The minimum outside air flow divided by the supply air flow during
winter heating periods. You may alternatively, or additionally, specify
outside air quantities at the zone level using the ZONE keywords
OA-CHANGES, OA-FLOW/PER or OUTSIDE-AIR-FLOW. The default is calculated
from zone loads and ZONE input.

If you enter MIN-OUTSIDE-AIR as well as the ZONE keywords
values take precedence. If no zone-level values are specified,
MIN-OUTSIDE-AIR will be used. If MIN-AIR-SCH is specified,
MIN-OUTSIDE-AIR, or the corresponding ZONE values, should be entered.

The program will not allow MIN-OUTSIDE-AIR to be less than the sum of
the EXHAUST-FLOWs for all zones divided by the sum of all supply flows
for all zones. That is, the exhaust fan operation will override

The minimum outside air ratio reported on SV-A is based on the design
calculated supply air flow and not on the value input for SUPPLY-FLOW,
which overrides the design flow rate.

When evaporative cooling is in effect, the outside air dampers are 100%
open. When outside air is able to cool the building without the aid of
evaporative cooling, the outside and return air dampers modulate open.


Li, Lan's picture
Joined: 2011-09-30
Reputation: 0

I could be wrong, but I believe that specified zone OA rates/ratios
takes precedence over the system specification. Check the OA for each
zone, and see if there's anything there.

If that's not it, I don't have any other ideas.

Hope this helps.

-Adam A. Gonthier

Adam Gonthier's picture
Joined: 2011-09-30
Reputation: 0