90.1 VAV Baseline

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My baseline system is System 5: Packaged VAV w/ reheat, but 90.1 doesn't
specify the minimum airflow percentage and I'm not sure what to use.
Equest defaults the min VAV airflow at 40% in core zones and 30% in
perimeter zones. Increasing this number to 100% (cv) nearly doubles the
heating energy. Since this is such a sensitive number, it's accuracy is
critical, what do you think I should use?


Tobias, Mike's picture
Joined: 2011-10-02
Reputation: 0


Section G3.1.3.13 calls for a minimum of 0.4 cfm/ft2 of floor area
served. Use this number as your minimum flow.

Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

Addendum AM revised G3.1.3.13 to alternatively allow the zone minimum ventilation flow, but I get lost when I think about how that is supposed to be calculated.

Is the minimum ventilation air the same as the % OA at the system or is it the zone minimum OA without any multi-space impacts?
Remembering that Std 62's method for determining system level OA in a multi-space VAV system is dependent on
1) the zone design flow rate which you are now auto sizing
2) the zone minimum zone flow rate which you are trying to determine

G3.1.25 is clear that minimum ventilation rates should be the same between the models (excepting DCV) and that kind of makes sense at a system level. But potential collisions still exist when system supply air volume is lower than the minimum outside air volume or when you want to claim ventilation effectiveness impacts.

Whatever you come up, with eQUEST will accept a minimum cfm/sf in the detailed mode.
Paul Riemer

Paul Riemer's picture
Joined: 2011-09-30
Reputation: 0


I believe this is specified in Appendix G.


Carol Gardner's picture
Joined: 2011-09-30
Reputation: 0