[Bldg-sim] Negative pressure for EQ cr 5

[Deepa]

We have an exhaust rate of 1.31cfm/sf (or 75cfm per door) which exceeds the
minimum requirement greatly. According to what you have
mentioned, this should be good as far as creating a negative pressure.

Just to know, are there any equations to calculate this or is it best
determined by physical measurement?

Deepa



On Wed, Oct 6, 2010 at 12:57 PM, James Hansen <JHANSEN at ghtltd.com> wrote:

>  I’ve documented many EQc5s and have never been asked to prove anything.
> For what it’s worth, back when I used Contamw for stair pressurization
> calcs, even a modest airflow of about 200 CFM per 3 foot door created
> pressure differences of 0.1-0.15 in.  That’s on the order of 25-30 PA.  So
> as long as you’re in the range of 50 CFM per door, you’ll be OK (assuming
> the door undercut and crack are the only openings into the room).
>
>
>
> This is a major generalization, and there are a lot of parameters that
> would need to be included to accurately calculate, but it helps me sleep at
> night knowing 50 CFM / door usually meets this credit.
>
>
>
> And Karen, I don’t follow why you would steer clients away from this
> credit.  Putting full height walls around janitor’s closets and print shops
> and negatively exhausting them is a good thing, right?
>
>
>
> *GHT Limited
> **James Hansen**, PE, LEED AP*
>
> *Senior Associate***
>
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>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Karen Walkerman
> *Sent:* Wednesday, October 06, 2010 3:49 PM
> *To:* James V Dirkes II, PE
> *Cc:* creations.deepa at gmail.com; Bldg-Sim
> *Subject:* Re: [Bldg-sim] Negative pressure for EQ cr 5
>
>
>
> Obtaining a negative pressure difference also requires sealing the space.
>  Door seals, and sealing walls.  If you exhaust 0.5 cfm/sf from a room with
> chicken wire walls, you won't achieve any kind of measurable pressure
> difference.
>
>
>
> I usually steer clients away from this credit for this very reason
> (difficulty coupled with measurability)
>
>
>
> --
>
> Karen
>
>
>
> On Wed, Oct 6, 2010 at 3:36 PM, James V Dirkes II, PE <jvd2pe at tds.net>
> wrote:
>
> Personal opinion:
>
> ·         5 Pa is difficult to (accurately) measure
>
> ·         1 Pa is impossible outside of a lab
>
>
>
> I don’t know what they were thinking when making these requirements, since
> they’re not too clear, but I suspect that if you demonstrate .5cfm / sq.ft.
> and no recirculation you’ll be OK.
>
>
>
> *Error! Filename not specified.*
>
>
>
> *The Building Performance Team
> James V. Dirkes II, P.E., LEED AP
> *1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
>
>
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Deepa
> *Sent:* Wednesday, October 06, 2010 2:59 PM
> *To:* Bldg-Sim
> *Subject:* [Bldg-sim] Negative pressure for EQ cr 5
>
>
>
> Hello all,
>
>
>
> One of the requirements for EQ Credit 5 is to prove that the areas such as
> the janitor's closet need to be negatively pressurized to a minimum
> of 5Pa when doors are closed and 1Pa when doors are open. Generally, in
> mechanical drawings, the cfm values are mentioned for exhaust fans.
>
>
>
> I wanted some insight as to how this pressure difference information can be
> obtained for both cases. Is there a straightforward calculation?
>
>
>
>
>
> Thanks,
>
> Deepa
>
>
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