# [Bldg-sim] Negative pressure for EQ cr 5

Cheney chenyu73 at gmail.com
Fri Oct 8 09:27:57 PDT 2010

```Hi Johannes,

I am sorry for my typo error. The equation can be found in ASHRAE Handbook
- HVAC Applications. My version is 2003, page 52.5. It is actually under
Fire an Smoke Management.

Cheers,
Cheney
On Fri, Oct 8, 2010 at 4:38 AM, Hopf, Johannes <johannes.hopf at dreso.com>wrote:

>   Cheney, can you post the chapter in the ASHRAE Handbook of Fundamentals
> where I can find the equation
>
>
>
> Johannes
>
>
>
>
>  *Von:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *Im Auftrag von *Cheney
> *Gesendet:* Mittwoch, 6. Oktober 2010 22:43
> *An:* creations.deepa at gmail.com
> *Cc:* Bldg-Sim
> *Betreff:* Re: [Bldg-sim] Negative pressure for EQ cr 5
>
>
>
> Hi Deepa,
>
>
>
> My two cents.
>
>
>
> For your question, you need to know:
>
>
>
> 1. the air volume in room and its pressure
>
>
>
> 2. To achieve 5Pa, how much more air should be introduced -
>
>
>
> Higher pressure x air volume in room/atmospheric pressure
>
>
>
> Now you get the number for the  static condition... ;)
>
>
>
> to maintain the pressure in a leaky room you have to pump in more air,
> right?
>
>
>
> 3. from the ASHRAE Handbook of Fundamentals:
>
> Q = 2610 x A x (DP)1/2
>
> • Q is the room leakage flow rate in cfm,
> • 2610 is a conversion factor,
> • A is the net open crack area of the room (generally not measurable), and
> • DP is the differential pressure.
>
> 4. If you'd like to maintain certain pressure in the room, you need to
> supply 2+3 first. When the pressure is established in dynamic condition,
> you need to supply only 3 to maintain the pressure you want.
>
>
>
> This is only the theoretical calculation for your reference.
>
> Cheers,
> Cheney
>
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