Well, after all, it is hot air, so perhaps it deserves a lot of discussion.  I really didn't expect so many people to come to the defense of poor old "hot air" but the debate has been vigorous.  See: http://homeenergypros.lbl.gov/forum/topics/the-science-of-hot-air-r...

I posted some more comments on that thread and invited those who still object to my debunking of this myth to post over there, not here.

Here, I would like to address the problems that pop up in explaining just what is behind all of that hot air we see moving up in so many places.  For example, if the hot air inside a chimney isn't moving up on its own and creating our draft, what is?

Beyond the descriptions that will change is a very simple method to visualize air pressures caused by different temperatures.  My worksheet at: http://myenergyworkshop.homestead.com/hot-air.html will walk you through how air stacks up to create the pressures we see inside our homes.  Once you understand this stacking process, you can apply it in many places, like a chimney, to explain draft. 

A simple example is a chimney chase.  We have all experienced the upward flow of air in the winter from basement to attic, but, if it isn't "warm air rising" and the basement is at a negative pressure wrto, then what is moving the air up?  By stacking up the air inside that chase and comparing it to the air stacked up inside the house you will discover that the positive 'ceiling to attic' stack pressure is actually the pressure from bottom to top of that chase.  A positive pressure moving the air from basement to attic.

But I'm getting ahead of myself.  First, what concerns do you have in explaining the air flow as we know it, without "hot air" being a moving force?

Note: John Brooks has another thread on Fun With Neutral Pressure Planes", it adds well to this topic.

Bud

Views: 273

Reply to This

Replies to This Discussion

Bud, I do NOT object to your Debunking of the Hot Air Rises Myth

I believe the "Hot Air Rises" Dogma has led to much confusion and some bad thinking.

here is a quote from a very recent GBA Q&A posting:

"Recessed lights in a cooling climate with insulation above them (non-cathedral ceiling) are not the problem they are in a heating climate and stuffed into a cathedral ceiling. Use your head folks. Cold air in the home drops (does not want to go through the light). Warm air above the light rises and does not want to drop into the home."

here is a link to the posting

http://www.greenbuildingadvisor.com/community/forum/green-building-...

and here is my comment:

"When a home is air conditioned ... Cold dense air can spill out thru openings in the lower part of the house.... reduce the pressure in the house and allow/induce attic air to spill into the living area."

John, you are braver than I.

A DIYer with no money trying to invent solutions to a disaster, wow it can't get much worse than that.  As for your comment and the snippy reply you got, his advice was trumped by several posters so I think he was looking for someone to bite and he picked you.  But you were correct.

He objected to you stirring the pot, but for many, that will be all we can do.  Present the information, whether they agree or not, and let that pot simmer a year or two until something clicks and and they finally accept it. 

Since I have the floor, I will introduce the next myth I want to debunk.  I mentioned it on the other thread, ye-old short-circuit theory.  Since each topic I introduce may take on its own lengthy discussion, I will open a new topic for each.

Bud

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

Profile IconWes Anderson, Jean-Paul and Bryan joined Home Energy Pros
yesterday
Dennis Heidner commented on Dale Stephens's blog post LED Lighting 24-month update 18,240 hours & counting
"Dale, good write up. For the landscaping bulbs,  if they had been T3 12V wedge bulbs,  I…"
Friday
Brett Little commented on Tom White's video
Thumbnail

The Future of Housing - And How Airtightness Can Help

"It's very true! So many people and contractors have tons of insulated attics but no air seal…"
Thursday
Chris Leach replied to Richard Beyer's discussion "The Dangers of Using Spray Foam Insulation"
"The problems will surface soon enough . Why don't we take a second look at this over rated…"
Thursday
Don Fitchett commented on Tom White's video
Thursday
tedkidd replied to Bob Blanchette's discussion How does Cycles Per Hour affect real world AFUE?
"Want to spot a simpleton? It's a guy who thinks EE and comfort are disconnected.  Want…"
Thursday
tedkidd commented on Tom White's blog post Clean Energy Works Oregon: Total Home Performance
"Nice post Tom! I really like how he puts that. Leveraging interests so they can optimize…"
Thursday
Kent Mitchell commented on Tom White's blog post Clean Energy Works Oregon: Total Home Performance
"As a contractor in the region - we frequently wonder how/why you can be a non-profit?  Oregon…"
Thursday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service