Outside airflow (eQuest Users group)

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Thank you to those who helped with my previous outside air question. I now understand how the outside air is controlled, I'm just not sure how I should be setting it. ASHRAE 90.1 - 2004 dictates that the minimum outdoor air ventilation rates should be the same for the design and baseline building, but one of our LEED review comments is that our baseline model should be modeled base on ASHRAE 62.1 - 2004 requirements. It seems that if I let eQuest size my OA based on ASHRAE 62.1 I won't match my design building OA rates (in this case, 100%). Also, if I let eQuest size my OA based on the 100% OA rate of my design building I will be over ASHRAE 62.1 requirements.
What method of outside air sizing have y'all been using for your models, and have you been approved by USGBC with the method?

- Thank you,

Scott Tomlinson, PE, LEED-AP

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

I have always sized the outdoor air to be the same in the proposed and
baseline buildings. There is a section in Appendix G that specifically
directs the modeler to do this. I have had a number of buildings approved
using this method.


No Username provide's picture
Joined: 2011-09-30
Reputation: 200

I agree with Karen. Appendix G is pretty clear that ventilation rates should be identical in both cases unless the proposed case is using DCV, and there is an implied understanding that the proposed OA rates meet code, whether that be 62.1 or the applicable local code. Some people make the mistake of using the same percentage of outside air in both cases, but it?s the flow rates that need to be identical, not the percentage. I find that this usually requires entering a CFM at the zone level, particularly for multi-zone systems, and the elevation factor needs to be applied if the project is not at sea level (that is, if you want output reports to match the design documents exactly).

With respect to the review comment, I would just hold your ground and follow your (correct) interpretation of Appendix G. I?ve had conflicting review comments on previous projects, too. Sometimes the reviewer is simply misinformed.


Dakota Kelley's picture
Joined: 2011-09-30
Reputation: 1