# Fun with Neutral Pressure Planes (NPP)

Greetings

First of all......

* As we upgrade and build new....

I think it is time to eliminate atmospherically vented appliances from the breathing zones of our homes

* I realize that the effects of wind and mechanical equipment can and often do overwhelm Stack Effect.

My current favorite online resources for visualizing "Stack Effect" are.....

*John Straube's Article

http://www.buildingscience.com/documents/digests/bsd-014-air-flow-c...

*John Klote's Article

http://fire.nist.gov/bfrlpubs/fire91/PDF/f91013.pdf

*Bud Poll's Worksheet

I plan to post some Illustrations and see if you folks agree with my current thinking about the location of Neutral Pressure Planes

Meanwhile...

Does anyone else have suggestions for online links concerning  "Stack Effect"?

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### Replies to This Discussion

An important element of the Klote report is that he uses a simplifying formula that only approximates the typical multiple vertical opening model.

"Analytic equations have been developed for the location of the neutral pressure plane for a few simple cases of leakage openings. However, the combinations of leakage openings in building shafts and compartments can be very complex... Analysis is simpler for horizontal openings, because the pressure difference across the opening does not vary with elevation. The analysis of this section is for horizontal openings…Vertical vents can be approximated by horizontal vents when the height of each vent is small compared to the height of the air column."

In a 2500 SF house with 1 ACH50 (about 350 CFM50), the Effective Leakage Area (ELA @ 4 Pa) is about 8 square inches. Since the blower door test is conducted with deliberate leaks sealed, this envelope leakage area is similar to what we might expect from dampered mechanical openings, making both deliberate and accidental leakage areas equally significant.

I'm still not sure what you're trying to accomplish by "controlling" the height of the NPP, especially given that - as you attest - the actual NPP will vary with both wind and mechanical effects.

Here's another link to an old article, CBD-23. Air Leakage in Buildings, from the National Research Council of Canada:

http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-23.html

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