[Bldg-sim] 90.1 G3.1.3.13 and eQuest

[Paul Riemer]

90.1-2010 has removed the 0.4 cfm/ft2 criteria, leaving the 30% or ventilation air minimum flow criteria.

Paul Riemer, PE, LEED AP BD+C
Associate / Mechanical
DUNHAM

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Monday, July 08, 2013 3:58 PM
To: James Hansen; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] 90.1 G3.1.3.13 and eQuest

Hi James,

I'm no doctor, but I think your gut checks out =).

The minimum 0.4 cfm/ft2 is going to be more than necessary for some spaces, and will in turn cause reheat that wouldn't otherwise occur for such spaces.  If this is causing issues of unmet hours or other related headaches, I think you could turn the minimum down in select spaces and stay within the intent of the requirement.

It's my sense the intent of this requirement is to set a "floor" of sorts, (however arbitrary) to pick up the realities of VAV system minimum airflows to maintain ventilation requirements, minimize/prevent stratification, and to avoid cool air "dumping" from registers when velocities get too low.  This sets a bar so that actual designs addressing these realities/issues aren't put at an immediate disadvantage.

Regards,

~Nick


[cid:image001.jpg at 01CE7BF5.E6B86050]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of James Hansen
Sent: Monday, July 08, 2013 9:37 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] 90.1 G3.1.3.13 and eQuest

Hi everyone,

I wanted to do a gut check of whether I'm interpreting ASHRAE 90.1-2007 Section G3.1.3.13 correctly.

That section says:

G3.1.3.13     VAV Minimum Flow Setpoints (Systems 5 and 7). Minimum volume setpoints for VAV reheat boxes shall be 0.4 cfm/ft2 of floor area served or the minimum ventilation rate, whichever is larger.

I have a number of System 5s for a warehouse facility with very low heating/cooling loads.

If I set the minimum flow for all zones to 0.4 in this screen, it ends up substantially over-supplying the baseline zones.

[cid:image002.png at 01CE7BF5.E6B86050]

Since there are maximum cooling supply temperatures (60 degrees), I end up overcooling the zones even at minimum load, so there is reheat.  There is also cooling energy to get the supply temps down to 60.

Am I doing anything "wrong"?

I seem to be following the requirements of 90.1, just want to make sure there isn't an exception somewhere that I'm missing.

Thanks!

GHT Limited
James Hansen, P.E., LEED AP
Senior Associate
1010 N. Glebe Road, Suite 200
Arlington, VA  22201-4749
703-243-1200 (office)
703-338-5754 (cell)
703-276-1376 (fax)
www.ghtltd.com<http://www.ghtltd.com/>

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