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"?

Views: 4094

Reply to This

Replies to This Discussion

Don't you also need to know elevation to know D-P since height within a structure is used? ... once it's opened to the outside the elevation matters to density over that height at any D-T.

I'm not sure which post you're responding to or exactly what your question is.

About the only atmospherically vented appliance left in most homes are tank water heaters. Most furnaces, tankless water heaters, and dryers use induced draft blowers.

Bob-------In my area your comment could not be further from what I see everyday. 80% and less are way more common than we would like. Condos on slabs are culprits. The furnace is either in the attic space or a closet. Other than the cheaper route by the builders you have the problem of routing the condensate drain through un-heated areas ( freezing ) In older housing stock built on slabs you have the same freezing problems as the CAZ is generally in the center of the home and the only route for the drain is up and out. The DWH is in a closet area with hi/low combustion air coming in from the attic. I see older homes everyday w/ furnace in basement that need replaced but the HO is not about to fork out until it fails. People don't generally plan on furnace upgrades until they fail. I wish your comment applied in my area ( OHIO )

We still see a few old furnaces, but they aren't common in Oklahoma. Most people replace the furnace when their A/C goes out. Sometimes we do see a few furnaces from the 80's where the A/C has been replaced multiple times. Moving a furnace is no small undertaking, they are rarely relocated when they are replaced.

Hello Bob and Ed.

I too only wish the situation that you have witnessed Bob was taking place in my area. I have now performed 30 audits in the last 3-4 months, and of these 5 folks had new furnaces\boilers installed. Each one is an atmospherically-vented appliance, and the homeowners all are upper-middle income. I did have one small win to get excited about, when a homeowner decided to go with a high-efficiency unit after I spent considerable time convincing them.

Ladies and gentlemen, I am so glad to see so much constructive conversation on NPPs and stack effect. At the same time, I wonder what this means when so many homes are like sives, with rapidly aging combustion appliances in them. And, remember, I mainly serve upper-middle income homeowners. My days in low-income really can get one down.

Patrick

Patric, Ed, my neighborhood is much like what you are describing and Patric, it does get depressing.  My market is primarily just above the low-income and a pellet stove addition would be far more likely than a new high efficiency.  

One of my concerns about many of these old leaky homes is that much of the easy savings involve air sealing.  I've seen chimney chases (plural) big enough to climb from basement to attic.  Easy fix, but what will that huge change in leakage do to everything else.  Add in a case of great stuff in the basement and attic and suddenly the old pot belly furnace in the basement is searching for combustion air.  Throw in a gas water heater and an old fireplace and these home owners need a serious education, before they start their DIY improvements.  And we are the ones that should know how to explain the "why" and stack effect becomes part of that discussion.

Bud

I am including some example outside pressures in this drawing.

Bud Poll's worksheet is based on an outside atmospheric pressure of 101,325 Pascals

(a common value for sea level)

I have decided to imagine that my "house" is at a slightly higher altitude.

I chose a round number... 100,000 Pascals

This example shows Two open windows.

I am thinking that the NPP would be about 10 feet above the floor.

(Approx midway between the two windows.)

The pressure WRTO would be + 5.5 pa at the top and -2.5 pa at the bottom.

again this a a theoretically tight house

 

I think Bud Poll knows the answer for this...

but first.....Anyone else?

Where is the Neutral Pressure Plane for this example?

(how high above the floor)

 

What are the pressures at the floor and the peak WRTO (with respect to the outside)?

I forgot to add something to my hypothetical question.....

Assume the the "House" will be heated and maintained at 70 degrees

John, I just found this thread. Good stuff!

I would say that this is identical to a single opening through the wall at 6', which would put the NPP at the vertical center of that opening, which in this case is right at the bottom of the flue.

But, because it's a vertical stack that terminates in a lower pressure zone, the CFM would be much greater than a similarly-sized horizontal opening (if the flue were 6" diameter, the flow rate would be 90 cfm) and so it would make the house below the flue entry strongly negative and mildly positive above it.

Correction: In doing some research to respond to other issues here, I stumbled across the answer to this puzzle and my first guess was incorrect. 

The open flue would serve as a passive exhaust "fan" and hence lower overall house pressure, reducing natural exfiltration (the positive pressure zone) and increasing infiltration (the negative pressure zone), thereby raising the NPP (see figure d).

error-file:tidyout.log

These illustrations are from a wonderful archived article at the National Research Center of Canada:

CBD-245. Mechanical Ventilation and Air Pressure in Houses

http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-245.html

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Jim Gunshinan commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"I had a revelation while attending Bruce Manclark's session of duct leak testing at the Energy…"
14 hours ago
George J. Nesbitt commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Blower Door; the 2007 test was a depressurization test, and the 2014 a pressurization test, which…"
14 hours ago
George J. Nesbitt replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Plan, plan, plan, plan. The 1st step to is to understand the house, how it's built, the…"
14 hours ago
George J. Nesbitt posted an event

High Performance Windows - A Panel of Experts at Pyramid Alehouse`

April 26, 2014 from 3pm to 5pm
Join a lively panel discussion on high performance windows. We'll cover some basics, as well as…See More
15 hours ago
Kaushal Bharath Raju replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi David, Thanks for pointing out Martin Holiday's article. I do not wish to engage in the…"
15 hours ago
Profile IconAdam Penberthy, Scot Davidson and j jarvella joined Home Energy Pros
16 hours ago
David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"More food for thought on this subject - read this (fairly) recent blog by one of the most respected…"
21 hours ago
Curt Kinder commented on Christopher Morin's blog post 5 Things New Energy Efficiency HVAC Contractors Need to Know
"You left out air distribution...Without at least a passing glance at how much air moves through the…"
yesterday
David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"I mis-spoke - I was referring to the Midori House in Santa Cruz. Have an in-depth discussion with…"
yesterday
Kaushal Bharath Raju replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi David & Bud, $400/sqf > $300 sqf. The latter is the minimum cost of new construction in…"
yesterday
David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Kaushal, There was a deep energy retrofit upgrade project (to Passive House standards) in San Jose…"
yesterday
Kim Tanner updated an event

Beyond Residential Testing at The Energy Conservatory

May 14, 2014 to May 16, 2014
The Energy Conservatory (TEC) is hosting a Beyond Residential Testing event. In addition we are…See More
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service