Dylanb
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« Reply #30 on: March 16, 2009, 05:30:06 PM » |
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I haven't peeked yet at the blog so here goes my stab. Heat rises with convection. However, the way heat moves INTO the dwelling is based on several forms of transfer. We as humans are typically the greatest source of heat in a house (radiation). Windows also transfer heat from direct sun (emittance & conduction & radiation). You also have certain materials in a house (walls & stained concrete floors for example) that have heat storage capability. The walls and floor will store heat all day, and eventually release it at night when the house cools down (once again, radiation & convection). Think of it as the walls and floors as batteries that get charged all day by direct light, then release the charge when the source stops. When the sun rises the next day, the recharge continues.
As far as WHY heat rises (other than convection), my guess is that heat is an energy that looks for and moves to the cooler areas. It also has to do with high and low pressure?
I have a great book about all this called; heating, cooling & lighting design. I'll mail it to anyone who wants to tackle it, just return the favor and send it to the next guy. Chapters & chapters on heat transfer.
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Dylanb
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« Reply #31 on: March 16, 2009, 05:31:51 PM » |
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By the way I absolutely love this subject and could go on all day....right or wrong. Great thread.
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Carl Brown
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« Reply #32 on: March 16, 2009, 08:32:16 PM » |
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A lot of variables.
Thank you guys very much.
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If it was your house wouldn't you want it done right!
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Jay Markanich
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« Reply #33 on: March 17, 2009, 06:06:31 AM » |
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Sorry to be late to this post! This is terrific Dr. Dave!
The sun radiates heat. It heats the earth, and everything in it heat somewhat by conduction. I think the materials of the house, particularly the attic, conduct heat from the sun's radiation. That's why when we are in attic spaces it can burn to touch the wood! These materials then radiate the heat they have acquired.
The heat from that radiation expands the air around it as it gets hotter. That's why attic spaces need to be ventilated! That's also why collar ties are recommended to help quell the expansion of the wood as the volume of air in an attic expands. The heated air seeks cooler, less compressed, air. Heat can radiate in any direction, up or down, depending on where the cooler, less compressed, air is. This compressed air has to find room to expand as it heats - higher pressure seeking lower pressure essentially. Isn't that why planes can fly? The wings causing movement toward lower pressure? Convection causes that movement of hot toward cold.
Surely things that are hot radiate heat. But it is convection that encourages heat to move toward cold, or rise, as in the example of the question.
The question is kind of narrow - so I think the most appropriate answer is convection. A whole lot of processes need to happen before that convection can occur however!
When should we go to that link? At the same time, and then come back to class to discuss? Lemmino!
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« Last Edit: March 17, 2009, 07:24:53 AM by Jay Markanich »
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Jay Markanich Real Estate Inspections, LLC Based in Bristow, serving all of Northern Virginia www.jaymarinspect.comFestina Lente - Make Haste Slowly |
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Wendell Cook
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« Reply #34 on: March 17, 2009, 07:19:19 AM » |
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[quote author=Dylanb link=topic=446.msg7872#msg7872 date=1237242606
As far as WHY heat rises (other than convection), my guess is that heat is an energy that looks for and moves to the cooler areas. It also has to do with high and low pressure?
[/quote]
Heat (actually hot air relative to its surroundings) rises because it is less dense, and therefore lighter than the cooler air. Heat is energy (duh, we know that!), which is simply increased molecular movement. The warm lighter air rises, and the heavier cool air sinks.
excellent question and discussion, Dave!
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Dylanb
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« Reply #35 on: March 17, 2009, 12:07:08 PM » |
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[quote author=Dylanb link=topic=446.msg7872#msg7872 date=1237242606
As far as WHY heat rises (other than convection), my guess is that heat is an energy that looks for and moves to the cooler areas. It also has to do with high and low pressure?
Heat (actually hot air relative to its surroundings) rises because it is less dense, and therefore lighter than the cooler air. Heat is energy (duh, we know that!), which is simply increased molecular movement. The warm lighter air rises, and the heavier cool air sinks. [/quote] My apologies Wendell. I shall refrain from mentioning the obvious from now on. How dare me. |
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Don Belmont
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Location: Barre VT
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« Reply #36 on: March 30, 2009, 07:47:38 AM » |
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A trick question right?
Conduction: External heating of the shell which conducts through the wall material. How much? it depends on the wall of course.
Convection: Outside air warms and is drawn into home by chimney effect. Again how much depends on the building.
Radiation: Sunlight and heat energy through the windows. How much you get depends on the windows.
So my answer 1-2-3
Don Belmont
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David A. Andersen
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« Reply #37 on: March 30, 2009, 04:43:31 PM » |
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Corrent.
The correct answer is "none of the above"!!!
The point is that we should "consider" everything berfore jumping off the bridge, as many of my "other board friends" try to do...
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Bill Warner
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« Reply #38 on: March 30, 2009, 05:04:04 PM » |
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What??? You mean there's more to this than just "dark spot baaaadddd"   I figured all this cavity radiator effect, accounting for wind speed, field emissivity settings, etc mumbo jumbo was just nonsense!!! No one said we actually need to think about what we're looking at. And they told me that any monkey could operate one of these things!!! |
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David A. Andersen
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« Reply #39 on: March 30, 2009, 08:01:12 PM » |
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We better be nice Mr. Bill! We'll get a scolding!  I'm being bad.... Don't do what I do, do what I say! |
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Carl Brown
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« Reply #40 on: March 30, 2009, 08:53:14 PM » |
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Yes you guys are a bad influence  |
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If it was your house wouldn't you want it done right!
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Chris Duphily
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« Reply #41 on: April 01, 2009, 07:04:05 PM » |
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Corrent.
The correct answer is "none of the above"!!!
The point is that we should "consider" everything berfore jumping off the bridge, as many of my "other board friends" try to do...
Thanks for the lesson David.  |
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Dale Duffy
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« Reply #42 on: April 01, 2009, 09:52:09 PM » |
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Corrent.
The correct answer is "none of the above"!!!
The point is that we should "consider" everything berfore jumping off the bridge, as many of my "other board friends" try to do...
Thank You David..!! Every question and response is great, if a person lacks common sense and building science knowledge I doubt an IR Cam or Thermography would be a good choice of professions-;) There are many variables involved even in Basic Thermography, personally I love the "Make you think questions" Thanks to everyone of you guys who are Thermographers for the feedback, I learn a little more with each question and answer...!!! |
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