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

http://myenergyworkshop.homestead.com/hot-air.html

 

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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Concerning the Klote Article

No need to brush up on Calculus or Fortran....

Just try to follow the Illustrations and concepts

Hi John, glad to see the topic back at the top.  Your comment that atmospherically vented appliances need to be eliminated is correct and I would take the additional step and say that all auditors should have serious reservations about performing or recommending any wx work where these high risk appliances are in use. 

I have left my worksheet up but have newer pages in progress that will be added soon. 

I'll be following.

Bud

Good morning, great discussion. I have a question here in Chicago we have mostly atmospherically vented furnaces and boilers. When I look up at the chimneys some have no rain hat, some have a flat top with a grate around the perimeter(like chicken wire), and some have the standard b-vent top approved for combustion appliances. my question is what are the the  differences between each of these in overall stack affect on a house? I'm trying to resize photos will have them up later. Thank you in advance

Hi randy, I'll give this a try.  There can actually be several "stack effects" taking place in one house at the same time and they will each have their own pressure distribution and NPP.  A house that is rather open will have one.  Seal off the air flow between two floors and now you have two different stacks, each with a high and low and its own NPP.  Then look at your chimneys.  Each can be filled with different temperature air/gasses from cold to hot and each can have different exposure to outside temperatures.  The chase way around the chimney or vent pipes can have their own pressures which even though we will probably seal them, an initial complaint might be related to their air flow. 

As for the caps you mentioned, they would restrict the air flow through that path just a bit and thus a slight change in the total exfiltration of the house.  The result would be a slight shift in the NPP, less exfiltration and the NPP would move down slightly. As for one vs the other in regards to the house stack effect, probably no difference.

Bud

Hi Randy, thanks for the question

Hi Bud, thanks for your answer

I agree that there may be several chambers & flues(tubes) & Neutral Pressure Planes in a house.

 

This is just a Simple example of a theoretic "tight" house with only one open window.

My thinking is that the Neutral Pressure Plane would be near the middle of the only open window.

I say "near" based on the John Klote Paper.

The Klote Paper explains that the NPP is actually slightly below the center of the opening.

This is true for heating and cooling seasons.

I "think" that the pressure difference between Inside and outside will be Approx 1 Pascal at the floor and Aprox. 7 Pascals at the peak.

 

This Illustration is for the Cooling Season

the NPP is virtually in the same place as for the Heating Season

the pressures at the floor and peak are the same

only now....

Cold air is flowing OUT at the bottom and

Warm air is flowing IN at the top

Hi John,

In the heating season the pressure will be +7pa at the top and -1pa at the bottom, wrto (with reference to outside).  In the cooling season (just happens to be the same ▲T) it will be -7pa at the top and +1pa at the bottom, again wrto.  One of the keys to understanding how this comes about is introducing that outside pressure.  Our readings are wrto, but exactly what is that pressure.  We always think of it as 14.7 psi (101325pa) and most (myself included) never paid attention to the rate at which it changes (approx. 3.5pa per foot) as we go up or down in elevation.  My worksheet that John posted above goes into detail illustrating the pressure increments on the outside in cold air and then on the inside in warm (lighter) air.  It is the difference between those two columns of air that produces the total ▲T we call stack effect, in this case 8pa.  The next step is following the adjustment process that creates the NPP and ultimately determined the above and below pressures.

Making this connection between the atmospheric pressures outside and house the pressures inside has really helped me understand and predict air flow in many other applications.  Here are a few:  Attic venting, chimney draft, unintended duct drafting when not in use, convective heat transfer, and even predicting how tight a house is without running a BD (just an estimate for now).

Some may ask, "why do we need this new information?"  One of the answers is our new tighter approach to homes.  On a leaky home, opening a window might barely move the existing NPP.  But on a tight home, it could cause a swing of 10pa or more depending upon the outside temperature. 

One more detail that we will need to go over is that we cannot see this change in pressure between upstairs and downstairs with out trusty manometers.  A two story house from the ceiling at the top to the basement floor could have as much as 100 Pascals difference in pressure.  Seems like that is something they should have told us at training :).

Bud

Howdy Bud,

I totally agree that it helps to "Introduce" the outside pressure.

I know that it has helped me (Thank you Bud)

I actually have the outside pressures on my Drawings ....

I have turned them off for these early Illustrations.

I was just trying to keep things simple (and less cluttered) at first.

......And more like the John Klote example.

 

I think You and I are saying the same thing ... just with different words.

I will be adding the Outside Pressures in future Illustrations.

 

John

Except in this example the Delta-T is -35 and so the Delta-P would be -4 Pa.

Just like a Cold Climatist ..... assuming that "your" stack effect is the "positive" effect

And those who live in a hot climate experience "reverse stack effect"   ;--)

 

 

We all know that the Southland is "backwards". That's why we invaded it in 1861 and whooped it good.

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