[Bldg-sim] Negative pressure for EQ cr 5

[James Hansen]

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

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

www.ghtltd.com <http://www.ghtltd.com/> 

 

 

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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