Had Pella windows installed last year. I’ve noticed on very cold mornings that ice has formed around the bottom of the windows. Any idea what causes this? and how to stop it?
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Do you have forced air or radiant heat?
Lots of plants, pasta eaters?
Curtains or blinds?
New paint job, damp basement, lack of bath venting?
All these contribute to condensation which will appear as ice till the sun comes out or beads of moisture from lack of air movement.
A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Calvin,
Your assertion that forced-air heating systems or radiant-floor heating systems are a cause of window condensation has no basis in fact.Warm, humid interior air contacts cold surface. Condensation forms. Two possible solutions: (1) lower indoor humidity level. (2) raise the temperature of your glass. End of story.
M,
Your assertion that my assertion has no basis in fact.......
has no basis in fact.
I asked if one or the other heat source because:
Radiant heat has no air movement to wash the glass, which would tend to cause evaporation sooner.
The heat source doesn't cause it, but can limit it. Normal comfortable humidity levels in the high 30's will show moisture on the glass when there's no air movement.
No?A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Your assertion that his assertion that your assertion has no basis in fact, in fact has a basis in finding facts.
Wheeeeee! =)
I have nothing useful to contribute...................wait, that would make a great tagline wouldn't it ? Naive but refreshing !
I have nothing useful to contribute...................
when did that stop any of us here?A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Calvin,
Okay, now that I understand what you were driving at, I concede that it's possible that some homes with forced-air heat may have fewer condensation problems than some homes with radiant-floor heat. I apologize for my tone. You're right that it's technically possible. However, count me a skeptic that it is an important factor in the real world. There are just too many variables:
--Many homes with forced air heat have registers that are not directed towards the window glass.
--Homes with radiant-floor heating system do have convective loops.
--Air flow patterns in individual rooms are idiosyncratic and depend on many factors other than the heating system type.
--Finally, it's highly unlikely that anyone with window condensation problems is going to install a forced-air heating system and disable an existing radiant-floor heating system.
M, thank you for understanding my meaning tho I probably worded it crappy to begin with.
Here's my situation. We have older marvins='88. Metal division strips between the glass which might transfer cold quicker. Moderate plants. Passive solar/radiant in slab with tile throughout. In open LR-ceiling fan up high. Upstairs quite open to downstairs allowing a loop of moving air (somewhat enhanced by the fan).
At night and on very cold (near zero) days, frost (ice) will form on the bottom 1/4'' of glass on most every window. Usually Humidity running at 35%. During the day-ice will melt to beads of sweat and then evaporate.
In windows away from the ceiling fan wash we see this occur longer and more often.
There's my thinking.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
There IS a lot to Calvins statements.Over the past month, I just did some experiments at an uninhabited but heated house. One end has a sunroom full of single glaxed large casement windows. They wanted some advice on keeping them from frosting up.They originally had pull down roller shades and had added quilted curtains, which made the ice growth worse.I was stopping in to look every early AM at sunrise and trying various things such as leaving the curtains up, or the roller shades up or combinations of half and half.There were baseboard radiators immediately under these windows, so airflow was happening based on natural convection off them.With the shades and curtains drawn, there was massive ice build on the glass.
With them up and the glass cleared, there was almost no ice build.
with the curtains left down so they were only open 8-12" at bottom, there was also almost no frosting. My conclusion was that just the modest warm air flow across the glass from the radiators rising was enough to keep the frost off the glass.
Since the house is vacant for the winter, the daily humidity can be presumed stable and not affected by showers and cooking, etc.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
It is my considered opinion backed by much experience that people often think that ice should not form on the warm side of anything.but the warm side will not BE warm enough to prevent ice formation if heat cannot get to it.circulation circulation circulation....I got to go out and take apart my "porch" ceiling today because during my current project, I must had inadvertently shifted some insulation around my shower drain trap.so now I get no circulation of heat and the trap has frozed...just wish it would freeze during warmer weather...cuz I HATE farting around in 10∘ weather...br...
.
"After the laws of Physics, everything else is opinion" -Neil deGrasse Tyson
.
.
.
If Pasta and Antipasta meet is it the end of the Universe???
It is my considered opinion backed by much experience that people often think that ice should not form on the warm side of anything.
but the warm side will not BE warm enough to prevent ice formation if heat cannot get to it.
circulation circulation circulation....
Circulation is not the only way to "warm" the window.
There is a more passive way to warm the climate near the window.
Reduce conduction...reduce thermal bridges to the outside.
Also it seems to me that blowing air on cold glass will increase heat loss.
The guy was asking what caused the condensation. Radiant heat (not necessarily radiant FLOOR heat) will TEND to have less air flow/mixing throughout the room regardless of where the forced heat vents are (but they are often under/near the window). Therefore heating system type can easily CONTRIBUTE to the condensation situation.
And no, he wasn't suggesting or even implying that to solve it, he might suggest turning off the heating source or even altering it substantially. There aren't too many variables (unless you think a handful is too much). 3 or 4 conditions that occur simultaneously may be the culprit. Removing just one could solve the problem.
While condensation can be a bit of a brain twister, the basic science is pretty simple and if you look at the bits and pieces of the situation (including the heating system type and configuration), you can begin to get a handle on what is going on.
Clew,
If I am the "guy" you are referring to..........would you do me a favor next time? Please refer to me as "man". I've always longed to be "the man".
I hope you and Holliday have had the opportunity to come across the few other threads on the general frost on glass topic that have popped up in the last week. Amazing what a wide spread cold snap will do to this board.
In them you'll see a couple different variations on the theme. Interesting that the more things differ, the more they remain the same.
Merry Christmas.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
"the more things differ, the more they remain the same."I was reviewing a link in the archives from Rez the other day going back to '97Amazing ho w true that is. We keep on keeping on...
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Normal comfortable humidity levels in the high 30's will show moisture on the glass when there's no air movement. No?
No. A double-glazed lowE argon window should not condense at 0° outside until the indoor humidity is about 60%. The inside surface temperature of the glazing should be 55°, which would require 70° air at 60% RH for condensation to occur, let alone frost.
You MIGHT have a humidity problem (you have to measure it to be sure), but 70° indoor air at 25% RH will condense on a window that's cold enough to freeze.
The real problem you have is either
1. thick curtains or shades or shutters that effectively seal the windows from the indoor air, or more likely
2. significant air leakage around the window that's allowing the inside surface to drop below freezing.
There's no way a new efficient window should ever freeze on the inside.
Check weatherstripping and closing hardware, and make sure the rough openings were properly air-sealed.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/23/2008 9:53 pm ET by Riversong
Edited 12/23/2008 9:54 pm ET by Riversong
Edited 12/23/2008 10:05 pm ET by Riversong
Well then, next time you're in Ohio and it's 10 degrees out, stop on by and show how I'm wrong.
Bring all you testing equipment with you also.
thanks.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Well then, next time you're in Ohio and it's 10 degrees out, stop on by and show how I'm wrong.
I don't need to go anywhere to know that you and the OP have something more than a humidity problem.
Here in VT it has to get below zero before I get frost on my single-glazed clear-glass windows (indoor RH 28%).
Double-glazed clear-glass windows shouldn't condense at 35% indoor RH until the outdoor temperature drops to -10°. Anything with lowE or better should never condense at any outdoor temp if the indoor RH is 35%.
And this is condensation. Not frost. For a window to be freezing on the inside, if it's not thermally-isolated from the interior by curtains or shades, there has to be cold air leakage washing the glass.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Discussing anything with you is like talking to a cop.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Man, this is a pretty tough thread for you, huh. ;)
That'll learn ya not to go an' try to help someone out.
Feelin' better?
Remodeling Contractor just on the other side of the Glass City
Yeah, you'd think they'd take pity on an invalid perhaps under extreme mind altering medications.
I know for sure that they're lucky I'm not at full strength.
Merry Christmas.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Just say "Yes Sir" unless you want an attitude adjustment. LOLFigures from a book are fine, but they don't always work in the real world.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Figures from a book.
Paul, 20 yrs ago I built this place with good Marvins. I don't heat it with a candle, but in comparison to all but a rare few-this one uses minimal energy for maximum comfort.
I'm not stupid. I do things right-and you know I wouldn't take a shortcut on my own place.
I tell 'em that with upper 30's humidity (not done with astm equipment) and 10 degrees outside that there's condensation and maybe even freezing water on the bottom 1/2'' of glass. Didn't forget the airwash of the glass, radiant lack thereof (sure there's a convection movement......there's convective movement when the dog farts too).
There must be something wrong?
Merry Christmas!A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
I start getting frosting at around zero to five degrees, but only in the bathroom and the master bedroom - which wife likes to keep colder by closing the door, so less heat and convection there.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Ok, here's the latest offbeat non scientific window glass report.
34 degrees. 37% humidity. No Floor Heat on, masonry heater not burned since two nites ago..............
no ice, no water, no moisture neither on the bottom edge of glass.
However, 1-1/2 (estimated) of ice on all packed surfaces outside. Car tracks, foot paths.
ugh.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
> Double-glazed clear-glass windows shouldn't condense at 35% indoor RH until the outdoor temperature drops to -10°. Anything with lowE or better should never condense at any outdoor temp if the indoor RH is 35%.> And this is condensation. Not frost. For a window to be freezing on the inside, if it's not thermally-isolated from the interior by curtains or shades, there has to be cold air leakage washing the glass.Bullfeathers!!
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Perhaps you haven't gotten to post #78 yet, so I'll repost it for you:
The single-glazed wood awning windows in the little wood-heated cabin I live in have begun to frost now that the outside temperature has dropped close to zero (interior RH of 28% at 65°).
And so have the single-glazed aluminum storm windows in my mudroom (where the woodstove is and the air temperature is high and the humidity is lower).
This is to be expected. Frost on efficient wood-framed double-glazed lowE² Pella windows is not, unless there is major air leakage.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Bullfeathers!!
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
The mark of the immature man is that his only response to that which he can't understand is "bullfeathers".
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The thing is, I've learned that there's no point in arguing with you since you're always "right", no matter how wrong you are. So I'll leave it at "bullfeathers".
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
there's no point in arguing
Dan,
Question him...challenge him.
You may learn something and so may he.
Theodoric of York ............"Nah!"
http://www.nbc.com/Saturday_Night_Live/video/clips/theodoric-of-york/2888/
Edited 1/1/2009 6:39 am by homedesign
The thing is, I've learned that there's no point in arguing with you since you're always "right", no matter how wrong you are.
I'm always glad to be proven wrong. You've offered neither proof nor even logical argument.
Tossing invective only proves that you have nothing useful to say.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The charts you posted were for (unstated) laboratory conditions. In no real house do you achieve those laboratory conditions.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Awwww man.
You had it nailed, right on target.
Then you had to go and reply.
Why would you do this to yourself.
Good luck.
;)Remodeling Contractor just on the other side of the Glass City
The charts you posted were for (unstated) laboratory conditions. In no real house do you achieve those laboratory conditions.
And in no real house would the inside surface of a double-glazed lowE window with thermal breaks and a relatively non-conductive frame be anywhere near freezing.
Unless the inside air temperature was near freezing.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
> Double-glazed clear-glass windows shouldn't condense at 35% indoor RH until the outdoor temperature drops to -10°. Anything with lowE or better should never condense at any outdoor temp if the indoor RH is 35%.
> And this is condensation. Not frost. For a window to be freezing on the inside, if it's not thermally-isolated from the interior by curtains or shades, there has to be cold air leakage washing the glass.
Temp RH Dew point RH Dew RH Dew
70 35 39.2° 30 34.9° 25 29.7°
65 35 34.5° 30 30.2° 25 25.3°
62 35 31.7° 30 27.5° 25 22.8°
Window edge (sightline) temperature predictions based on LowE2 coating and 1/2" airspace at 0°F exterior and 70° interior (not argon filled):
Spacer:
aluminum 31.8°
U-steel 34.5°
Stainless Steel 38.2°
Foam 41°
Edited 1/2/2009 8:34 am ET by Oberon
All these computations overlook a simple fact: Cold air falls. As convection draws air down across a window it gets progressively colder. Given a large enough window, regardless of the technology, eventually the air will drop below freezing, if the outside temp is below about zero F.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
>>All these computations overlook a simple fact: Cold air falls. As convection draws air down across a window it gets progressively colder. Given a large enough window, regardless of the technology, eventually the air will drop below freezing, if the outside temp is below about zero F.Huh? All it means is that the falling film of air can approach more closely the temperature of the inside glass surface. There still will be conduction of heat from the bulk air adjacent to that falling film of air, making up the heat loss from air film to glass. Thus some steady state temperature profile will be achieved across the window assembly, according to the R values of the layers making up that assembly, including inside and outside air films. You just can't have the inside air film temperature approach the freezing point with a "large enough" window built as described if you have an adjacent air mass at 70 F.[Edited from "the outside air temperature" to what now appears in that last sentence.]I have to agree with other replies, that for frozen water (frost) to appear anywhere on the inside of the window, the local temperature must be 32 F or lower. Since the described assembly leads to a calculated temperature profile that makes the inside (center-of-) glass surface far closer to room temperature, the only explanation for frost occurring is something that invalidates the calculation local to that spot. And that would be high conductivity at the edge (improper window construction) or convective flow of bitter cold outside air (leak), bypassing the various layers comprising the window's insulative value.
Edited 1/2/2009 10:10 am ET by DickRussell
Certainly AT SOME POINT the transfer of heat from the room air mass counteracts the heat transfer from the window, and the air stops getting colder, but still it means that you can't simply factor room air temp into your equations. At the bottom of a reasonably large window the "effective room temperature" will be 20-30 degrees colder, easily enough to push the numbers into a zone where frost would be expected.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Edited 1/2/2009 12:03 pm by DanH
I have to agree with other replies, that for frozen water (frost) to appear anywhere on the inside of the window, the local temperature must be 32 F or lower.
A given - hopefully, no one disagrees with that statement!
Since the described assembly leads to a calculated temperature profile that makes the inside (center-of-) glass surface far closer to room temperature, the only explanation for frost occurring is something that invalidates the calculation local to that spot.
True, but it doesn't have to be something outside of the normal performance profile of the window (although it often is).
Keeping in mind that "center-of-glass" is the entire glass surface less the outer 2-1/2" closest to the edge of the sash/glass interface; lower temperatures at the edges are due to higher edge conductivity which does not invalidate the calculated temperature profile (local to that spot), as much as it is simply part of the overall calculation.
Standard windows, even those with LowE coatings, can see indoor surface temperatures below the freezing point of water along the edges given the right circumstances. Often those circumstances have less to do with the window than with installation, location, obstructions, etc. but (for example) if looking at the numbers that I posted earlier, and extrapolating from them, it is quite possible to see edge temperatures from normal, unobstructed windows fall below freezing in the right circumstances.
And that would be high conductivity at the edge (improper window construction) or convective flow of bitter cold outside air (leak), bypassing the various layers comprising the window's insulative value.
Again, higher conductivity at the edges is normal and unavoidable at the current common window technology level and it rarely indicates improper construction as much as it indicates different materials and material interfaces along the edge.
All these computations overlook a simple fact: Cold air falls. As convection draws air down across a window it gets progressively colder. Given a large enough window, regardless of the technology, eventually the air will drop below freezing, if the outside temp is below about zero F.
Cold air falls, but it cannot become colder than the surface it contacts. And, if there's nothing to create a "pool" of air at the sill, it's simply going to continue to fall to the floor.
But this is why heavy curtains or shades or shutters will facilitate wondow condensation by trapping the colder air.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
> Cold air falls, but it cannot become colder than the surface it contacts. But as the cold air falls, the surface becomes colder because it's exchanging with colder air. And when the cold air hits the sill (or just the lower sash frame) it IS going to create a "pool" of cold air.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
But as the cold air falls, the surface becomes colder because it's exchanging with colder air. And when the cold air hits the sill (or just the lower sash frame) it IS going to create a "pool" of cold air.
It's not the interior air which is cooling the surface of the glass, but the glass which is cooling the air.
Air is a fluid, just like water, it cannnot "pool" without a container. Which is why you can feel the cold air from windows falling down to the floor, and which is why radiators or FHA vents are placed under windows to counteract this.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
> It's not the interior air which is cooling the surface of the glass, but the glass which is cooling the air.Right, and it's the interior air that's WARMING the glass. Without that warming it would be the same temp as the outside air. Cooler interior air means cooler glass, which in turn means the air will get cooler still.Air won't literally "pool" a the bottom of the window, but it will change speed, creating turbulence. If you did a temperature profile of the air along a vertical slice of the window you'd see a bulge of cold air at the bottom.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Right, and it's the interior air that's WARMING the glass. Without that warming it would be the same temp as the outside air. Cooler interior air means cooler glass, which in turn means the air will get cooler still.
There is a steady-state heat loss from the inside air to each layer in the window. The only way to reduce the steady-state temperature of the inside of the window (outside temperature remaining the same) is the lower the temperature of the entire air mass of the interior.
You're making it sound as if the cooler air next to the inside of the glass can continue to cool the window indefinately (as if it's an air conditioner). It reaches a homeostasis as long as inside and outside temperatures and air speed don't change.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You make it sound like there's no such thing as a counterflow heat exchanger.The inside of the window will be colder if the air IT'S IN CONTACT WITH is colder -- it has very little to do with the temperature of the room as a whole. So the glass at the bottom of the window will be colder than the glass at the top, because it's in contact with colder air. And the air in turn will become colder because it's in contact with colder glass.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
You make it sound like there's no such thing as a counterflow heat exchanger.
With constant input temperatures at each side of the counterflow exchanger, it will quickly reach a steady-state in which the incoming air (in winter) will be at a constant temperature somewhere between indoor and outdoor temperatures.
The inside of the window will be colder if the air IT'S IN CONTACT WITH is colder -- it has very little to do with the temperature of the room as a whole. So the glass at the bottom of the window will be colder than the glass at the top, because it's in contact with colder air. And the air in turn will become colder because it's in contact with colder glass.
Yes there will be a temperature profile from top to bottom on a window, though it will be negligible on an efficient window and noticable on an inefficient window. This is why inefficient windows will condense of possibly frost first on the bottom and then progress upwards.
There is also heat stratification in any leaky or poorly-insulated house. A very efficient house - and very efficient windows - have very little stratification and hence very little internal convection.
What you're suggesting, however, is that a window can work like a heat pump and continue to cool by feeback between glass an air. The inside air film next to the glass will always be warmer than the glass (somewhere between glass and ambient air temperature, just like the crossflow example) and the heat transfer will be in one direction only. It is NOT a perpetual motion feedback loop.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
> With constant input temperatures at each side of the counterflow exchanger, it will quickly reach a steady-state in which the incoming air (in winter) will be at a constant temperature somewhere between indoor and outdoor temperatures.True, but the temperature of the barrier between the two flows will be much colder at one end than the other.> Yes there will be a temperature profile from top to bottom on a window, though it will be negligible on an efficient window"Negligible" is in the eyes of the beholder, I suppose, but regardless of the quality of the window the profile gradient will be there, and it can easily amount to 5-10 degrees.> What you're suggesting, however, is that a window can work like a heat pump and continue to cool by feeback between glass an air.No, I was not suggesting that. I was simply saying that, in steady state, the temperature near the bottom of the window will be significantly colder than at the top, due to the pattern of heat exchange. This is why you tend to see the condensation at the bottom of the window.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
I was simply saying that, in steady state, the temperature near the bottom of the window will be significantly colder than at the top, due to the pattern of heat exchange. This is why you tend to see the condensation at the bottom of the window.
On a cold winter night, if you put your hand below the sill of a single-glazed or double-clear window, you'll feel a cool breeze, though less so with the double-glazing.
On the same night, if you put your hand below the sill of a double-glazed lowE window with good thermal frame and spacer breaks, you will feel nothing.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Speak for yourself.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Speak for yourself.
Perhaps the laws of physics are different where you live.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
No, the laws of physics apparently work better here than there.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
You'll be doing good to change that same window from a single glazed to a double glazed on the same night!But I often see that cool breeze with double glazed units - even those that don't make frost. You just live in the fantasy world called denial.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I have dual pane clear, low-e with argon and aluminum spacers and low-e argon with SS spacers. All 3 drop a cold air breeze out the bottom. Some worse then others but the worst are the ones over my desk.... and they aren't the clear.
Go figure I have an anomaly never before seen and proven scientifically impossible.
I have dual pane clear, low-e with argon and aluminum spacers and low-e argon with SS spacers. All 3 drop a cold air breeze out the bottom. Some worse then others but the worst are the ones over my desk.... and they aren't the clear.
And what are the contributing factors? What is the exterior temperature when you feel the convective flow? What is the interior temperature? How leaky is the house? How much temperature stratification is normal on a cold day - warm at ceiling, colder at floor?
A leaky house with noticable thermal stratification is going to experience more natural convective flow at cooler surfaces, like windows, because of the warmer air at the top of the room (bigger delta-T, more flow).
A very tight house with very little thermal stratification will experience very little convective flow at windows, providing that they are efficient windows.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Riversong I gotta admit.... You continue to sell the sizzle on a steak that a hungry buzzard wouldn't touch..... And from your posts alone, all the condensation mysteriously vanished from all my different window glazings at the mention of your in depth knowledge.
Dan,
I wasn't that specific in my reply because I was only listing numbers.
My intention was to compare various RH readings with associated temperature readings; particularly at the prime location where condensation and frost will form on a window surface.
My contention in this and in my earlier posts is that making definitive statements about the potential risk of condensation (and frost) simply by quoting RH, without taking into account a number of other factors, isn't valid.
Edited 1/2/2009 12:15 pm ET by Oberon
I agree with you there.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
It appears that your data agree with my assertion: that only the worst-performing glazing system would be below freezing at the edge on a 0° day.
I said it would require -10° outside to cause frost on an efficient window.
Where did your data come from?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/2/2009 1:40 pm ET by Riversong
Since they actually pay me to do this same sort of stuff in my "day job", I happen to have a fair number of contacts in the glass and window industries as well as a number of references.
In this case I used an advance copy of Cardinal's new "Residential Glass Technical Guide" (where the specific numbers came from) that I often use for reference both here and in my day job.
I am guessing, but I would suspect that it is ultimately intended to be the follow up to the Red Book which is available on their web site.
http://www.cardinalcorp.com/technology/redbook.htm
Using RH as a guide in determining the potential for window condensation can be very useful, but when measuring RH in a home in order to try to determine the cause of window condensation or icing problems (or other issues as well), obviously the location of the RH measurement can be a very significant factor and in the right (wrong?) circumstances basing performance on RH in the home can be misleading.
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For example, an air temperature of 70°F with an RH of only 25% means that there is approximately 4½ grams/m³ of moisture in the air which means the dew point temperature is 29.7°F – cold enough for ice to form if the window temperature goes below the dew point.
However, as temperature goes down RH goes up just so long as the amount of moisture in the air doesn’t change. So, assuming the same 4½ grams/m³ of moisture in the air at 55°F, the RH would be a little over 41%, but at the same time the dew point remains constant at 29.7°F. And if the air temp drops to 32°F and the moisture level remains constant, the RH is now 92% but the dew point temperature is still 29.7°F.
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So if an RH reading is taken at some distance from a window, it could read as low as 25%, or lower, and there could still be sufficient moisture in the air to result in condensation on the glass surface despite the low RH reading in the home.
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Consider that a home kept at 80°F, with an RH reading of 25%, would have about 6.3 grams/m³ moisture and a dew point temperature of 39°F. Again, the home hygrometer correctly reads only 25% RH, but if the glass temperature is below 39°F, then there is a real likelihood of window condensation, although less likelihood of frost or ice unless the glass temp goes below freezing, of course.
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Also consider that the U-factor of a window changes as outside temperature changes. As the air temp goes down the R-value of the unit will decrease so that a window with a U-factor of .30 (for example) at +20°F might have a U-factor of .34 at -20°F. This doesn’t indicate a flaw in the window, it is simply physics. And it is important to remember that all windows can be a good bit colder at the edge than they are at center-of-glass (center-of-glass is defined as not just the exact center point of the window it is the entire glass area approximately 2â€-3†from the edge), so edge condensation is more likely.
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Hey Oberon,
Looks like you have a good Understanding of condensation and windows!
I enjoyed your explanation.
The issue here, however, is not simply condensation but frost. If the windows are performing so poorly that the interior surface is below freezing, then either the window unit or the window installation (or perhaps the use of heavy curtains) is the problem.
You could lower the indoor RH enough to prevent condensation in that case, but the wood floors would shrink, the furniture would fall apart, and the occupants woud have respiratory tract problems and nosebleeds.
No energy-efficient window should have any interior parts below freezing except in the most extreme (near-arctic) conditions.
Either the glazing has no lowE coatings or inert gas fill, or there is no thermal break in the spacers, or the frame is too conductive, or the poor quality or poor installation allows significant air leakage.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/24/2008 1:52 pm ET by Riversong
The pine in a sash has an R value of what?
It's not the center of the glass that's the problem.
The pine in a sash has an R value of what? It's not the center of the glass that's the problem.
THE NFRC label on all new windows is required to list the average unit U-value (not center of glass).
The R-value of the sash only tells you the rate of heat loss through that element. And the conductivity of the material will tell you how cold it would feel if you touched it. But the temperature of the inside surface (or more accurately, the inside air film on a surface) will be roughly the same as the indoor air temperature (just as the outside surface will be roughly the same as the outdoor temperature), unless there is air leakage.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
So then why do you quote center of glass numbers?
So then why do you quote center of glass numbers?
I quoted no glass U-value or R-value numbers. What I referred to was the average inside temperature of various glazing types under certain conditions.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"A double-glazed lowE argon window should not condense at 0° outside until the indoor humidity is about 60%. The inside surface temperature of the glazing should be 55°, which would require 70° air at 60% RH for condensation to occur."
These are the exact same numbers used by Andersen for "Center of glass"
http://www.andersenwindows.com/servlet/Satellite?blobcol=urldata&blobheader=application%2FpdfContent-Disposition%3A+inline%3B+filename%3DAndersen_Glass_Performance.pdf%3B&blobkey=id&blobnocache=false&blobtable=MungoBlobs&blobwhere=1201053567625&ssbinary=true
If you don't actually read what you write perhaps you can at least cite the reference. I may not know everything about thermodynamics but I do know the smell of BS.... ;-)
If you don't actually read what you write perhaps you can at least cite the reference. I may not know everything about thermodynamics but I do know the smell of BS.... ;-)
Put your sledgehammer away and go back to school.
Those are industry standard numbers. And the only thing that's BS is that it's completely irrelevant.
We're not talking about a condensation problem. We're talking about a freezing problem. It's physically impossible for the inside of an efficient window to freeze unless the indoor air temperature is extremely low, the window is isolated from the inside air, or there is a significant cold air leak.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/24/2008 10:57 pm ET by Riversong
"But the temperature of the inside surface (or more accurately, the inside air film on a surface) will be roughly the same as the indoor air temperature (just as the outside surface will be roughly the same as the outdoor temperature), unless there is air leakage."My experiments showed about a 3-4° diff
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My experiments showed about a 3-4° diff
And that's due to the temperature gradient through the inside air film (R-0.68).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
There are a number of factors that contribute to edge condensation and to the possibility of ice formation on the window. In addition to those that you already mentioned (all of which I agree with), the type of spacer or the width of the airspace may also affect the formation of window condensation as well. The use of an aluminum spacer, for example, can result in indoor glass edge temperature of ~32F when exterior temperature reaches 0F even if the IG was manufactured with the most efficient LowE coating currently available on the market.
"You could lower the indoor RH enough to prevent condensation in that case..." depends on how you lower the RH because you can lower it either by lowering the level of moisture in the air (which will affect dew point), or by raising the air temperature (which won't affect the dew point), and since it is the dew point temperature that determines the formation of condensation, in that sense RH is irrelevant.
The point of my post was simply to illustrate that even with an RH as low as 25%, condensation is still quite possible in the right circumstances. It is quite possible that a home with a measured RH of 50% would not have condensation while a home with a much lower RH can have condensation - even with identical windows in both homes.
Edited 12/25/2008 11:36 pm ET by Oberon
In addition to those that you already mentioned (all of which I agree with), the type of spacer or the width of the airspace may also affect the formation of window condensation as well.
This thread was about Pella windows installed last year. None of those can be contributing to frost.
depends on how you lower the RH because ...since it is the dew point temperature that determines the formation of condensation, in that sense RH is irrelevant.
Since no one is suggesting changing the indoor set point temperature, RH is the dterminant factor.
It is quite possible that a home with a measured RH of 50% would not have condensation while a home with a much lower RH can have condensation - even with identical windows in both homes.
Not in the same ambient conditions. With identical windows, properly installed and not isolated by curtains, shades or shutters what you suggest is not possible - unless you're suggesting something as absurd as one house at 50° & 50% RH and the other at 70° & 25% RH, which would have a slightly higher dew point.
And, again, we're not talking about condenstion but frost with new Pella windows. There's an installation problem with air leakage.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"we're not talking about condenstion but frost"What is the difference? Only one degree of temperature on the glass.
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""we're not talking about condenstion but frost""Yes. Frost is just frozen condensation.No condensation and no frost no matter what the temperatures are..
William the Geezer, the sequel to Billy the Kid - Shoe
In order to stop condensation from forming on the surface of a window, it is necessary to either lower the dew point temperature of the air to a level below the dew point temperature of the window surface, or to warm the window surface to a temperature above the dew point temperature.
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Relative humidity is a comparison of actual vapor density versus saturation vapor density at a particular temperature. Dew point is 100% relative humidity or the point where the air at a certain temperature is no longer able to hold any more moisture.
So, if the air has reached vapor saturation, or 100% relative humidity, then the air will release moisture that will show up as condensation on any surface that is at a temperature below the dew point temperature of the air or of the mateiral that condensation forms on.
If the surface is below freezing, then the condensation will form as frost or ice. <!---->
Increasing air temperature will lower relative humidity but it will not change the dew point temperature which is based on the amount of water vapor in the air and is not based on the temperature of the air. So while RH is lower with higher air temperature, it may not effect condensation on window surfaces at all – unless the rise in air temperature also results in a corresponding rise in window glass temperature to a level above the dew point temperature.
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But lowering the amount of water vapor or moisture in the air will also lower the dew point temperature as well. If the dew point temperature is lowered sufficiently to drop it below the temperature of the window glass there should have no more condensation issues.
It is quite possible that a home with a measured RH of 50% would not have condensation while a home with a much lower RH can have condensation - even with identical windows in both homes.
Not in the same ambient conditions. With identical windows, properly installed and not isolated by curtains, shades or shutters what you suggest is not possible - unless you're suggesting something as absurd as one house at 50° & 50% RH and the other at 70° & 25% RH, which would have a slightly higher dew point.
It's neither absurd nor impossible, but there does have to be mitigating circumstances such as you suggested - which goes back to my original and really only point - that it is necessary to examine all the details before simply suggesting that RH is the cause. A home with an RH of 50% can have no condensation trouble while a home with an RH of 25% can have all sorts of troubles - even if these homes are next door to one another.
If the homes have identical windows, then it is obvious that there are other issues involved, including blinds or shades blocking access of air to the glass, poor insulation around the windows, poor installation of the windows, whatever - there is something causing the windows to be cold, finding out what it is goes a long way in solving the problem. In this there is no disagreement.
I know that window and glass companies all have their charts detailing the recommended RH versus the predictability of condensation, but when it starts to get cold, it can be difficult to stay within the recommended guidelines. And staying with the recommended guidelines doesn't mean that there won't be occasional problems. Mother nature doesn't always do exactly what we want her to do. For example, at -20°F outdoor temp, a typical recommendation is no more than 15% RH in the home. In a home kept at 70°, that equals only 2.75 g/m³. That isn't very much, but if the homeowners drop the temp to 60° at night then RH jumps up to 21%. So does that mean that only because the RH is now outside of the recommended guidelines that they are going to have condensation problems where they didn't when the RH was "lower"? Or are there other issues to consider?
With the home at 70° and 15% RH, the dew point temp was 17.5°. Lower the temp to 60° and the RH rises to 21% while the dew point stays the same, still 17.5°. If lowering the home's air temperature by 10° at night also resulted in a lower window surface temperature then condensation may become more likely, but it wasn't specifically because of the rise in RH resulting from lowering the air temperature that the window may have developed condensation. It was specifically the lowered temperature of the window surface that resulted in condensation, and in this case ice, forming.
RH is not truly irrelevant. The factors involved in determining the causes of condensation can and often do relate directly to RH or visa versa. However, if presented simply as "X% RH means window condensation and Y% RH means no condensation" then I would still suggest that RH as presented is irrelevant.
Edited 12/26/2008 2:08 pm ET by Oberon
For example, at -20°F outdoor temp, a typical recommendation is no more than 15% RH in the home.
Nobody who considers the occupants of a house would suggest 15% RH, since that is nosebleed and significant respiratory distress territory.
The human body requires RH between 30% and 70%, while a house would prefer between 20% and 40%. Thus the compromise range that will satisfy all is 30% to 40%.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Thanks, Oberon. It's good to hear the facts laid out in a straight scientific way (without a forced helping of ego).Billy
Thanks. I really enjoy wide ranging discussions that have several opinions.
To quote Robert Heinlein (twice):
“I never learned from a man who agreed with me.â€
"Never worry about theory as long as the machinery does what it's supposed to do.â€
and since it is the dew point temperature that determines the formation of condensation, in that sense RH is irrelevant.
Oberon,
I would say that condensation becomes visible at the dewpoint temperature.
homedesign,
This is a better definition of condensation than I could give off-my-head:
condensation (kndn-sshn)
The change of a gas or vapor to a liquid, either by cooling or by being subjected to increased pressure. When water vapor cools in the atmosphere, for example, it condenses into tiny drops of water, which form clouds.
The American Heritage¯ Science Dictionary Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved
If I understand your post correctly, I think that what you are suggesting (in my words - sorry) is that nature doesn't like things out of balance so as air temperature changes there is the potential for both gain and loss of moisture?
If I misread or if I really didn't understand your post then ignore my comments, however, based on my interpretaion, I would suggest that while the capacity of air to "gain" moisture as it warms is certainly true, by definition it is only possible for air to "lose" moisture (condensation) when it falls below dew point temperature or when it reaches 100% relative humidity.
Edited 12/26/2008 2:27 pm ET by Oberon
Oberon,
Check out this video to see my point.
http://www.youtube.com/watch?v=ZBlTzkpMIoQ
Condensation is happening all the time.
Condensation is happening all the time.
Yes it is. And it's completely irrelevant because it's exactly balanced by evaporation.
What is relevant is the equilibrium RH of the air, its dewpoint temperature, the surface temperature of materials, and the equilibrium moisture content of materials.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
There's no way a new efficient window should ever freeze on the inside.
Never say no way... We can always find a way to screw up an energy efficient window.
By the way, all:
The single-glazed wood awning windows in the little wood-heated cabin I live in have begun to frost now that the outside temperature has dropped close to zero (interior RH of 28% at 65°).
And so have the single-glazed aluminum storm windows in my mudroom (where the woodstove is and the air temperature is high and the humidity is lower).
This is to be expected. Frost on efficient wood-framed double-glazed lowE² Pella windows is not, unless there is major air leakage.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
To add my 2 cents, if the humidity is so high that you get condensation on the glass, think of what's happening inside the walls or in the attic! I had a humidifier once, got rid of it because everything felt damp. Moist air goes into an unheated closet and you get damp clothing, etc. Normal human activity generates plenty of interior moisture, I wouldn't add any unless the air got really dry.
Ice is a bit extreme. Windows should be able to maintain at least a 30 degree difference between inside and out. Exactly how cold was it?
Edited 12/12/2008 12:47 pm ET by sledgehammer
It was very cold outside ~ 3degrees. The furnance Humidifier is set to 25%. I realize this doesn't relate to the exact inside humidity. Probably need to get something to measure it. The furnance is a forced air furnance. I'm a little worried about lowering the humidifier any lower. I've heard you can damage wood floors and wood furniture if it's set too low. On a similar topic, my sister had pella windows installed this summer and is having the same issue. Although they had a new addition added on to the house with Anderson windows that don't have the same issue. I wonder if putting a fan in front of the window/s may help. the windows were installed with low expanding foam instead of insulation.
The furnance Humidifier is set to 25%. I realize this doesn't relate to the exact inside humidity. Probably need to get something to measure it. The furnance is a forced air furnance. I'm a little worried about lowering the humidifier any lower.
DP,
Good idea about measuring the humidity.
You do not need a humidifier.. you need a DEhumidifier. Changing the settings for a humidifier will not remove water vapor. A humidifier adds water.
Opening the curtains if closed will help..you also may need to bring in and then heat more outside air when it is very cold. Perhaps get a DEhumidifier.
What the humidifer is set to is meaningless, you need to measure the interior humidity. Windows are basicly a hole in the side of your home, they will always be colder then a well insulated wall... and you will always be able to reach a point where moisture and freezing will be a problem no matter whos window you use. You can't use anyone elses house as a comparison because it's peoples living habits more then construction that causes this.
Best you can hope for is keeping it to a minimum, because everywhere else in the home air is exposed to the cold the same thing is happening.
You can't use anyone elses house as a comparison because it's peoples living habits more then construction that causes this.
Sledge,
I think it is the construction and the inhabitants.
25% is a bit high for 0F. Not definitely high, but marginal.You must reduce the indoor humidity based on the anticipated outdoor temp. I used to have a chart of suggested settings for typical conditions, but lost it somehow.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Measure the RH in the house. Measure at different times of the day. At night it might be higher (do you use night setback?) due to the colder indoor temp.
Maybe you need to run your ventilation system (i.e. bath fans) more frequently.
Piffin had some good notes about differences with window treatment positions and such. Window treatments can have a huge impact. If you have venetian blinds, even open (i.e. but not pulled up), they may cause a dead spot of air near the window.
What type of windows? Low-e?
Another thought ... installing these to replace old leaky windows has caused you to trap more moisture in the house. RH goes up. Condensation occurs. Maybe this is the leaward side of the house, too?
you said the installer used expanding foam?.......I'd pull the casing and check, at 3 degrees it only takes a small empty gap........
I've had condencing problems in the past with air tight houses, but I'd do the easy thing first and check to see just how well the foam is working..........
The only way I ever did a window was the old tried and true stuffed insulation (that I did myself to make sure it was done right)
Had Pella windows installed last year. I've noticed on very cold mornings that ice has formed around the bottom of the windows. Any idea what causes this? and how to stop it?
I do not think anyone has mentioned where the ice has formed.
I contend that there is a microclimate around this window.
Condensation is happening all the time.. we just do not see it until the dew point temperature. There is a concentration of moisture near the bottom of the window due to gravity. Evaporation occurs and thus cooling... making this area cooler than the calculated gradient temperature.
Of course .. I am only guessing.. water is so mysterious and fascinating.
Contributing to the extra cold condition around the window is likely a typical construction flaw...Thermal bridging of the rough framing.
Riversong's homes have a very elegant, minimilist amount of wood around the window openings. This event (the window edge frosting) would be much less likely in His home.
I say that it may not be an air leak... but rather typical/poor framing practices.
I do not think that we should all build with Larsen trusses...but we can sure learn something by observing what Riversong has done. And then think about why he did it.
View Image
Thanks for the tip to my framing technique.
I say that it may not be an air leak... but rather typical/poor framing practices.
But thermal bridging will only increase the rate of heat loss through part of the shell, not the temperature at the inside, which will be within a few degrees of room temperature regardless of the insulation value.
In a quality, efficient window, like a new Pella, with thermal breaks in the glass unit non-conductive sash and frames, and good air sealing - it's not possible for the interior to be below freezing if the indoor air is at normal room temperature unless:
the window is very well isolated from the interior space
there is an air leak, allowing sub-freezing air to infiltrate
or both
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/26/2008 5:01 pm ET by Riversong
Why do you have to keep asserting that it is not possible when there have been several statements that it has happened and that it does happen and you have a window/glass experts explanation of how the scientific principles work?Show your human side and say that it is unlikely or less likely. claiming that it is impossible in the face of the evidence undermines your credibility
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Why do you have to keep asserting that it is not possible when there have been several statements that it has happened
I have never said it is not possible. What I've consistently said is that it is physically impossible unless the conditions I specified were met.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Damn, you are one of the best BS artists I've ever met!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Damn, you are one of the best BS artists I've ever met!
If what you mean is Building Science, then thank you for the recognition.
Everything I've posted on this forum is documented science. You might try some sometime, its nourishing.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Wow
what a scrap
Well in the house I grew up in built in 1957 with pella windows up here in Cold Saskatchewan Canada the windows were frozen along the bottom just about all winter. Close the curtians = more ice. Dad would play with the humidistat to minimize icing. with little effect.
Now I live with a radiant floor ICF house with All Weather Windows with fiberglass frames and the triple argon low e glass. Proper overhangs for our south facing home on a lake. I know the RH is low. Air to Air heat exchanger on low.
I was running around with my new weather station from Lee Valley Tools I got as a present and we have about 20% RH great for drying wood in the shop but!! Last night when loving sweet wife was cooking big supper rh was about 25. No nose bleeds, I think we have got used to it. tried running a humidifier for years not much meaursuable luck.
So obviously we have no condensation issues even thru -35 c for the last 2 weeks with a bone chilling wind.
The condo project I am working on just had the new windows installed 2 weeks ago. and we are taping etc. new windows with insulation in the gaps minimal condensation. The one window that was not replaced as it was done about 6 months ago is wet to the top, frozen on bottom. so all thing equal in the envoirment and one window sweats like hell! So what gives?
If your Pella window is freezing I would call the rep and see what he thinks.
I have installed a few windows lately and some are just #### even with the big names. Some have flexed so much just lifting them into the hole, I thought they would fall apart before we got them in place, I wonder how much perfomance was lost to shipping and instalation damage. I really think about the stability of large PVC units period. You should have seen my niegbours PVC windows sag and blow out when the other neighbours house burnt. The people on the other side just lost the sealed units in fiberglass frames. ( scarrey afternoon).
Science is a wonderful thing. It especially helped my spiritual midwife moderating my rite of passage when I was in a transitional phase.....
Unfortuneately it wasn't covered by my HMO
Edited 12/26/2008 8:32 pm ET by sledgehammer
Edited 12/26/2008 8:33 pm ET by sledgehammer
Damn, you are one of the best BS artists I've ever met!
If what you mean is Building Science, then thank you for the recognition.
Sir Riversong,
I salute you. You are a Building Scientist/Artist.
After re-reading this thread from top to bottom I conclude that you are correct (or else I have been duped by your BS)
"Keep the outside air out" is even more important than I thought.
Yup, science is great stuff.But don't forget that it is not static and fixed. So when you rely 100% on what is known, so far, and say nothing else is possible, you are preventing yourself from learning more. So science has to be tested against the real world. You know that scientists proved that a bee can't fly don't you?
And that the sun circles around the earth?The fact is, that in a situation like this, there are at least a dozen variables that all play a part and nobody has written the formulae to prove which variable has the most impact on this situation. River only thinks he knows.OK, maybe I'm only an apothecary still working on turning lead into gold, but at least I know how much I don't know. He already thinks he knows it all. Don't fall into that trap, or your education is finished.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Yup, science is great stuff.
Science isn't "stuff". It's a method for turning crude observations into verifiable and repeatable explanations (theories). Great Stuff, on the other hand, is a messy and wasteful can of spray foam - a lot like personal observations of the untrained and non-methodical.
But don't forget that it is not static and fixed. So when you rely 100% on what is known, so far, and say nothing else is possible, you are preventing yourself from learning more. So science has to be tested against the real world.
Since it's not "stuff" it cannot be static. It's an evolving body of knowledge which, in fact, tests the real world to determine the validity of our observations. And it is the sicentific process which involves testing speculative theories about "what might be" and then either disproves them or expands our knowledge base.
You know that scientists proved that a bee can't fly don't you?And that the sun circles around the earth?
The "science has proved that bees can't fly" urban myth originated in a 1934 book by entomologist Antoine Magnan, who discussed a mathematical equation by Andre Sainte-Lague, an engineer. The equation proved that the maximum lift for an aircraft's wings could not be achieved at equivalent speeds of a bee. That is, an airplane the size of a bee, moving as slowly as a bee, could not fly. Although this did not mean a bee can't fly (which after all does not have stationary wings like the posited teency aircraft), nevertheless the idea that Magnan's book said bees oughtn't be able to fly began to spread. It spread at first as a joke in European universities, at Sainte-Lague's & Magnan's expense. But later it became a "fact" among the gullible or the uneducated not smart enough to get the joke.
And it was the Catholic Church that determined that the earth is the center of the solar system. It was science which disproved that piece of dogma.
The fact is, that in a situation like this, there are at least a dozen variables that all play a part and nobody has written the formulae to prove which variable has the most impact on this situation. River only thinks he knows.
And I've spelled out most of those. Yes, I do know the laws of physics and hygro-thermo dynamics. They're really not that difficult to apply in simplistic cases like this one.
OK, maybe I'm only an apothecary still working on turning lead into gold, but at least I know how much I don't know. He already thinks he knows it all. Don't fall into that trap, or your education is finished.
Since what you mean is an "alchemist", not an "apothecary", which is a pharmacist, it seems you don't even know how much you don't know. Because I, on the other hand, know exactly what it is I know, I also know where the limits of my knowledge are and either don't tread in those waters or take the time to educate myself about them. You might do well to do the same.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Blah, blah, blah.............Remodeling Contractor just on the other side of the Glass City
Don't fall into that trap, or your education is finished.
Piffin, Thanks for the reminder.. I question everything everyone says.
I am a practicing Architect.. I will continue to practice and never master.
You reminded me a while back that Dr. Joe was not god.
I know that Joe and Riversong and ALL make mistakes.
I regurgitate what I think I know even though it makes me look foolish when I get corrected.
I have learned a lot from ALL in this thread and I have so much more to learn.
Yep, been a good thread. It's where truth gets tested that we all learn.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I've known a good number of scientists over the years, both academic and real world. The best ones are open minded and humble. The best ones rarely talk in absolutes. As you point out, a good scientist puts forth a postulate based on his research and experience. Scientists also recognize that the laboratory must go to great lengths to eliminate variables, while the real world has an almost infinite number of variables that can't all be isolated or accounted for. Not only are they hard to account for, the interaction between these variables creates new unpredictable variables.........and so on. Conscientious scientists (anyone for that matter) should always watch out for hubris. It's kind of funny how much of that (hubris, that is) shows up in this forum. Especially in the Energy, Heating & Insulation folder. ;-)John Svenson, builder, remodeler, NE Ohio
it's like the preacher who preaches too hard on sin vs. perfection.I don't trust that one, because all the ones I ever heard get onto absolutes absolutely got in trouble. It's sad, but it happens.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Whole thing is waaay out of real world practices / earthly occurances.
I must be mellowing, it has entertainment value - funny.
After you been down the "river" once you know where it ends.
It'll run it's course.
Sad part comes when the preaching turns to mandates.
Remodeling Contractor just on the other side of the Glass City
good thing it doesn't ever show up in the pol discussions...
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"After the laws of Physics, everything else is opinion" -Neil deGrasse Tyson
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If Pasta and Antipasta meet is it the end of the Universe???
In a quality, efficient window, like a new Pella, with thermal breaks in the glass unit non-conductive sash and frames, and good air sealing - it's not possible for the interior to be below freezing if the indoor air is at normal room temperature unless:
the window is very well isolated from the interior space
there is an air leak, allowing sub-freezing air to infiltrate
or both
Riversong,
Just one more factor that we did not discuss...what about outside convection (the wind)? 3 degrees outside with a strong wind?
Just one more factor that we did not discuss...what about outside convection (the wind)? 3 degrees outside with a strong wind?
Wind has little effect on the insulating quality of any solid material. All it does is strip of the outer dead air layer (R 0.17). Wind chill effects only living things.
What wind will do, however, is increase the leakage of cold air through a poorly installed window (or one with damaged weatherstipping or that is misaligned).
Again: there has to be air leakage for frost to occur on an efficient window (unless the indoor temperature is close to freezing).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Wind chill effects only living things
My hot coffee is not alive?
Air is a fluid .. will it not cool the glass more as the speed increases?
Edited 12/31/2008 7:44 pm by homedesign
My hot coffee is not alive?
I don't know about yours but my coffee keeps me alive ;-)
Air is a fluid .. will it not cool the glass more as the speed increases?
Heat moves only from a higher temperature surface to a colder surface.
The outside surface of a window will be slightly above outside air temperature with no wind because of the insulating value of the still air film (R-0.17).
With a double-glazed lowE window (U-0.33), with 65° indoor and 0° outdoor air, the outer glass surface temperature will be 3.7° with a deltaT across the pane of about 3°.
The only thing the wind will do is move away (at a rate dependent upon wind speed) the insulative layer on the outside of the glass. This will bring the outer glass surface to the outside temperature (in this example, 0°) and decrease the overall R-value by 0.17 to 2.83 and increase the heat loss 5.6%.
So, if it was a large window with 15 sf of glazing, it's heat loss would increase from 325 BTU/hr to 344.5 BTU/hr, or an additional heat loss of 19.5 BTU/hr. Even if there were 10 such windows on the windward side(s), the additional 195 BTU/hr is not very significant for a whole house heat loss of perhaps 24,000-35,000 BTU/hr in an efficient house.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/31/2008 8:36 pm ET by Riversong
Edited 12/31/2008 8:37 pm ET by Riversong
Heat moves only from a higher temperature surface to a colder surface.
Heat can also transfer from a surface to a fluid like atmospheric air.
Heat can also transfer from a surface to a fluid like atmospheric air.
Of course. And if we're talking about radiant heat transfer, which occurs over a distance and in relation to the mean radiant temperature of each object, then it would be a gas volume's average temperature that would matter.
But even fluids - both liquids and gasses - conduct heat by surface contact, and because air has thermal resistance (R-5/in for perfectly stagnant air), there will be a layering of temperatures in air and it will be the temperature of its surface in contact with another surface which will determine conductive heat flow.
In reality, the very thin surface film of air on the outside of a thermal envelope offers only R-0.17 (on the inside, it's R-0.68 because of difference in density and turbulence).
So the primary mechanism for convective heat transfer is in the elimination of this stagnant air film and its thermal gradient, resulting in surface contact at ambient temperature. The faster the flow velocity, the more easily the air surface can remain at or near ambient conditions.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Robert,
I am trying to understand..but I am slow.
Are you saying that once the air film has been blown away..then there will NOT be an increase in heat flow(from the glass) as the wind speed increases?Or is it negligible?
I am still trying to visualize that?
It seems to me like the coefficients that you are using would change when outside conditions are not steady state.(forgive me I'm an Architect and may not have the terms correct)
Are you saying that once the air film has been blown away..then there will NOT be an increase in heat flow(from the glass) as the wind speed increases?Or is it negligible?
Convective currents "move" heat by two methods:
1. by rising or falling, they physically move the heat contained in the fluid to other zones
2. by stripping the surface air film from a stationary surface (or water film from a submerged body), they accelerate conduction.
Convective heat loss is a combination of conductive heat loss and fluid dynamics. Moving air doesn't strip heat any faster, except that by moving the warmed air away from a warmer surface it maintains a larger steady-state delta-T.
In other words, still or slow-moving air will warm next to a warm window and hence reduce the delta-T and reduce heat loss. Faster-moving air will not remain in contact with the warmer surface long enough to increase it's temperature significantly.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>>...and because air has thermal resistance (R-5/in for perfectly stagnant air),...From the thermal conductivity of air at 35 F (avg. of 0 and 70), I back out R 5.93/inch. The conductivity is about 11% lower at 0 compared to 70 F, meaning that the R is about 12% greater. Perhaps that accounts for the odd 10% apparent gain in R of the attic assembly in that (herein) famous ORNL paper comparing cellulose to loose chopped FG in an attic as temperature drops. The paper never said why the cellulose R would show a gain, only why the FG would show a loss.Source: AIChE/DIPPR Data Compilation Project. Agreed, this is for "dead" air. How would they keep a chunk of air from wiggling around long enough to measure it? But that's what it is, assuming some accurate technique was used to get it.
But even fluids - both liquids and gasses - conduct heat by surface contact, and because air has thermal resistance (R-5/in for perfectly stagnant air), there will be a layering of temperatures in air and it will be the temperature of its surface in contact with another surface which will determine conductive heat flow.
Robert, you are thinking of air as a resistor "r-5/in"
Perhaps we should think of it as a conductor instead.
I read somewhere that a flowing gas can CONDUCT from 3 to 50 times as much heat as a still gas.
I still agree that AIR TIGHTNESS is paramount... I am just trying to get a better understanding of convection.
I am not trying to beat this thread to death because of some frost on a window.
It is what is happening inside the wall.. the condensation and the frost that we do not see that seems most important to me.
Robert, you are thinking of air as a resistor "r-5/in"
Perhaps we should think of it as a conductor instead.
All things are thermal conductors. The poor conductors we call insulators. All residential insulation products work by trapping air, because air is an excellent thermal insulator. But all insulations conduct heat, just more slowly.
I read somewhere that a flowing gas can CONDUCT from 3 to 50 times as much heat as a still gas.
Conduction of heat from one material to another, or from one area within a material to another area, is linearly dependent upon delta-T. The only way to increase heat conduction is to change the delta-T.
Moving fluids (air, water) at a constant temperature cannot conduct heat any faster than still fluid at the same temperature. Heat loss is increased, however, because the colder fluid next to a warmer solid surface will remain at its ambient temperature only if the fluid that is picking up heat from the surface is moved away and replaced by more cold fluid. Slowly moving fluids will leave a layer of fluid at the surface of a solid because of the surface tension of the fluid, and this thin layer will warm and reduce the delta-T unless there is enough velocity or turbulence to strip it away.
Fluids with a high thermal conductivity, like water (4.2 BTU-in/hr-sf-°F) will strip heat much faster than air (0.156 BTU-in/hr-sf-°F). Air has a very low specific heat (0.0182 BTU/cf°F) as well as thermal conductivity, compared to the specific heat of water (1 BTU/lb°F).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/4/2009 3:05 pm ET by Riversong
Edited 1/4/2009 3:23 pm ET by Riversong
Moving fluids (air, water) at a constant temperature cannot conduct heat any faster than still fluid at the same temperature.
Robert, my textbook says that the Heat loss coefficient increases with velocity...the greater the velocity ..the greater the HLC.
What am I missing?
you aren't missing anything. YOUR text is right.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
my textbook says that the Heat loss coefficient increases with velocity...the greater the velocity ..the greater the HLC.
I thought I already addressed that. The increased velocity is more effective at removing the warm (insulative) air layer adjacent to the surface and hence decreases the outside air contact temperature and increases the delta-T. But all the heat loss is due to conduction to the (now colder) air.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
But all the heat loss is due to conduction to the (now colder) air.
I thought that convection was a combination of conduction and mass transfer.
Isn't that why we have a fan with a car radiator?
Can you explain how mass transfer plays into convection?
Edited 1/4/2009 7:23 pm by homedesign
Edited 1/4/2009 7:42 pm by homedesign
I thought that convection was a combination of conduction and mass transfer.
Can you explain how mass transfer plays into convection?
I've done that two or three times already in this thread.
It moves away the layer of warmer air and increases the conductive delta-T.
The faster the flow, the more effectively it maximizes the delta-T.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Sorry..was not tryin to irritate you.
I'm just here to learn.
I did some number crunching.
With 65° indoor temperature, 0° outside temperture, a 12 sf double-glazed lowE window will experience a heat loss rate of:
in (minimal) laminar flow - 228 BTU/hr
in "standard" outside conditions - 258 BTU/hr (13.18% more)
in fast, turbulent flow - 268 BTU/hr (17.59% more)
The convective heat transfer coefficient for air varies from 1.76 to 17.6 BTU/hr-°F, depending on velocity and turbulence. As you can see, the range of increase in heat loss is narrow because the thermal resistance of the window glazing limits the heat flux to the outer surface of the outer pane, and the moving air can do little more than thin out or remove the viscous layer of air in contact with the glass, thus reducing the effective R-value of that air film from a 0.57 in still air to 0.17 in slowly moving air to 0.06 in fast-moving turbulent air.
Edit: I used SI instead of Imperial units for the convective coefficient of air. So I've corrected the numbers.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/5/2009 4:57 pm ET by Riversong
Edited 1/5/2009 5:14 pm ET by Riversong
Robert, thank you for all the effort.
I understand your concept about the air layer.
It is what happens after the air layer is stripped away that concerns me.
When I google wind chill...First thing that comes up about wind chill is that it only affects living things.
Sort of like your first response.
Next they bring up the point that if you put a glass of warm water outside in the wind... then it Will Cool down faster than if put outside outside with no wind...but it will never cool below the outside temperature.
OK .. I get that part.
Once there is no delta-T then heat transfer stops.
I say our homes are "alive" and there will be a delta-t when conditions outside are different than inside.
Our homes will try to maintain temperature like our bodies do.
My twisted perception is that it does not matter what the r-value of the assembly is...as long as there is delta-T ....wind chill will transfer more heat from the assembly as the wind velocity increases.
zero degrees outside with no wind is not the same as zero with wind...the heat transfer coeffecients of the assembly will change when there is a pressure induced. Sort of like the heat is being sucked towards the BIG ZERO and the moving mass of the wind helps it to suck harder.
Once a creature dies and internal heat is no longer produced then wind chill will no longer matter.
As a matter of fact, the original wind tables were developed by placing a bucket of water outside in different conditions and measuring how long it took to freeze.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
As a matter of fact, the original wind tables were developed by placing a bucket of water outside in different conditions and measuring how long it took to freeze.
That was an antiquated measure of weather severity (which was useful knowledge in the Antarctic), but it was only roughly proportional to what we now use as the Wind Chill Index which is a measure of the perceived temperature of a human face in the wind determined by wind tunnel experiments on human beings.
A 2½" diameter plastic cylinder of water in no way resembles a human face, with its blood-rich skin and steady-state core temperature and evaporative cooling.
The perception of cold is dependent upon skin temperature, which is why it can feel sub-freezing in conditions in which it's impossible to get frost-bite.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Yeah, but the old scheme worked for decades, and may actually have been better at estimating the heat loss from a properly clothed person. When the wind chill approaches 50 below you cover your face.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Yeah, but the old scheme worked for decades, and may actually have been better at estimating the heat loss from a properly clothed person.
Actually, it never was intended to indicate actual heat loss from the body. Paul Siple, who created the original formula, quickly realized this so he ignored the original units (kCal/m²-hr) and made it a unit-less number to create some thresholds for various discomfort levels.
Which is why others later turned it into an (almost equally worthless) "equivalent temperature" and then eventually into the current (2001) wind chill index based on actual human testing.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Robert,
Ok ... So the only thing going on with convection is...
the insulating still fluid layer thins and
The HLC of the FLUID increases with velocity
this can have a significant effect on conductive assemblies(like a car radiator or human skin)
or negligible effect on a good window or whale blubber.
Am I learnin?
this can have a significant effect on conductive assemblies(like a car radiator or human skin)
or negligible effect on a good window or whale blubber.
That's right. A car radiator and human skin are not only relatively conductive, but they're also relatively hot - so the high delta-T will move a lot of heat without that insulating layer of air next to it.
The outside of a window is very close to outside temperature, and I imagine the outside of a whale's skin is very close to water temperature - so with or without the surface film they're not going to lose much heat.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
One thing you forget is that any large object (like a building) has a "cocoon" of warmer air around it -- not just a thin "skin", but a relatively thick blanket that may extend several feet in still air. A moderate breeze will strip this off the windward side of the object, but the layer will tend to be retained on the leeward side (depending on object shape and wind direction) until the breeze becomes fairly strong. This effect can up the surface temperature another 5-10 degrees in a "lossy" buiding.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Edited 1/7/2009 7:06 am by DanH
One thing you forget is that any large object (like a building) has a "cocoon" of warmer air around it
I can't forget something I never heard of ;-)
Do you have documentation for that?
Any vertical air space more than about 3/4" is subject to convection. Just like any fluid (water, e.g.) it is only the surface tension between it and the surface that maintains a "skin" of stagnant fluid. Anything beyond that skin is subject to convective forces and will quickly move up (or down) and away even in the absense of wind.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Sorry that your education has been so sorely neglected.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
In other words, No you don't.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
As a wise man once told me:"often thy wisest word is thy unspoken word"...in other words, if we all relax and step back this thread will go away..View Image
"...in other words, if we all relax and step back this thread will go away."Be Not The First On Which The New Is Tried, Nor The Last To Put The Old Aside....
As a wise man once told me:
"often thy wisest word is thy unspoken word"
...in other words, if we all relax and step back this thread will go away.
Oh Jocobe...you did it now ;-)
Was the purpose of your post Ironic humor or sarcasm?
I believe that Convection is more than a just a perception and more than just the reduction of an insulating air layer.
Here is my twisted mind experiment:
Take a canister of 65degree water...canister has an r-value...water has an r-value
place canister in 0degree environment
canister and water cool at rate A
blow on it until air film and r-value of air film are extremely small(negligible)
(one windchill source says 4 mph)
canister and water cool at rate B
Increase the velocity....and I believe the cannister/water will continue to cool more rapidly(depending on velocity) as they did in the early windchill experiments.
Did the r-value of the cannister /water change?...I say yes because a pressure greater than just delta-T has been induced.
R-values are not fundamental laws...they are coefficients that are derived from observations under certain conditions.
Edited 1/10/2009 9:51 am by homedesign
Did the r-value of the cannister /water change?...I say yes because a pressure greater than just delta-T has been induced.
No, the r-value does not change (other than by changing the material's temperature and hence density).
R-values are not fundamental laws...they are coefficients that are derived from observations under certain conditions.
R-values are based on fundamental laws of physics - the conductivity of particular materials at a particular temperature. The conductivity of a material does not change with pressure differentials (unless it's a gas and its density changes accordingly).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
R-values are based on fundamental laws of physics
Robert, My textbook says that heat transfer coefficients are related to Subsidiary Laws...Not Fundamental Laws
Consider this: 2 fluids are separated by a thin membrane
Fluid A is 65deg...Fluid B is 0deg..delta-T = 65
Fluid B starts to flow ...Heat flux increases with velocity of Fluid B
delta-T is still 65...yet more heat "flows" from A to B
Did the "resistance"(conductivity) of the membrane not change?
Edited 1/11/2009 11:23 am by homedesign
Consider this: 2 fluids are separated by a thin membrane
Fluid A is 65deg...Fluid B is 0deg..delta-T = 65
Fluid B starts to flow ...Heat flux increases with velocity of Fluid B
delta-T is still 65...yet more heat "flows" from A to B
Did the "resistance"(conductivity) of the membrane not change?
Absolutely not. The conductivity of any material will vary with temperature, which is why it is measured (and standardized for comparison) at a specific temperature. But that conductivity and that temperature variance curve are fixed qualities of the material, regardless of what's happening around the material.
For instance. By ASHRAE standards, a window (or any vertical thermal element) has an overall R-value which includes an interior air film of R-0.68 and an external air film of R-0.17. These are the test standards, which include natural convection on the room side and forced (weather) convection on the outside.
When there is fluid (air) flow outside the normative standards, the overall conductivity of the installed window assembly decreases, though the window unit (glass, spacers, frame) never changes its thermal conductivity.
The R-value of the exterior air film can vary between 0.68 and 0.06, so the overall R-value of an R-3 window could theoretically vary from 2.89 to 3.51 (about a 22% difference in heat loss). But the maximum difference between the ASHRAE design U-value and U-value at maximum outside convection is only 4%.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/11/2009 8:00 pm ET by Riversong
Edited 1/11/2009 8:16 pm ET by Riversong
And my truck windows never frost over because they are always at the same temp as the outside air....
Edited 1/11/2009 8:03 pm ET by sledgehammer
.View ImageView Image
fabulousJohn
I understand your concept about the air layer. It is what happens after the air layer is stripped away that concerns me.
The surface film of air can never be fully stripped away, only thinned. And then there's less insulation (air = R-5/in).
When I google wind chill...First thing that comes up about wind chill is that it only affects living things.
Right. Wind chill is perceived temperature and a measure of the rate of heat loss from exposed skin. Only sentient beings can perceive their own temperature.
Next they bring up the point that if you put a glass of warm water outside in the wind... then it Will Cool down faster than if put outside outside with no wind...but it will never cool below the outside temperature.
Once there is no delta-T then heat transfer stops.
Conductive heat transfer stops. Radiant heat loss is dependent, not on air temperature, but on the temperature (or rather difference in temperature) of other objects in line-of-sight.
I say our homes are "alive" and there will be a delta-t when conditions outside are different than inside.
Only when they're growing mold ;-), and there will be a delta-T when temperature conditions are different inside to out.
Our homes will try to maintain temperature like our bodies do.
Yes, that's the function of the central heating system and its control unit: thermostat. Like the human body, the house is homeo-thermic but with a very much less complicated technology.
My twisted perception is that it does not matter what the r-value of the assembly is...as long as there is delta-T ....wind chill will transfer more heat from the assembly as the wind velocity increases.
Conductive heat loss will occur at exactly the rate of (delta-T x area / R-value) no matter how fast or slow the wind is blowing. All the wind does is reduce the overall R-value by reducing the very small R-value of the outside air film. While this small change in R-value would be significant for an aluminum canister (which has almost no R-value to start with), it is almost insignificant to a wall that has a high R-value or even to an R-3 window (from about R-3.02 to R-2.91).
zero degrees outside with no wind is not the same as zero with wind...the heat transfer coeffecients of the assembly will change when there is a pressure induced. Sort of like the heat is being sucked towards the BIG ZERO and the moving mass of the wind helps it to suck harder.
Wind doesn't suck heat unless it creates infiltration. Ignoring leaks, zero degrees is still zero degrees to a window (give or take 3% or 4%)
Once a creature dies and internal heat is no longer produced then wind chill will no longer matter.
Neither will the air temperature. The creature will then be in thermal equilibrium with its environment ("Make me one with everthing", said the Buddhist to the hot dog vendor).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>>Air has a very low specific heat (0.0182 BTU/lb°F)I'm assuming that's a typo or something else, like incorrect units. Specific heat of air in the range encountered in heat loss calcs is roughly 0.24 BTU/lb/degF. Your number looks more like BTU/cu.ft/F. Ummm, 379 cu.ft/lbmol @60 F, divided by MW=29.0 (avg), gives 13.07 cu.ft per lb, times your 0.0182 gives 0.24. OK, that's it.
I'm assuming that's a typo or something else
Yup, BTU/cf °F
My mistake.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"With a double-glazed lowE window (U-0.33), with 65° indoor and 0° outdoor air, the outer glass surface temperature will be 3.7° with a deltaT across the pane of about 3°."
So are you saying that, with the interior & exterior conditions you stated, the inside of the glass would be 6.7°?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
So are you saying that, with the interior & exterior conditions you stated, the inside of the glass would be 6.7°?
The inside of the outer pane in the double-glazed window will be approximately that temperature.
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outer pane<!----><!---->
5.5<!----><!---->
3.8<!----><!---->
0.14<!----><!---->
4.67%<!----><!---->
94.33%<!----><!---->
6.72<!----><!---->
3.68<!----><!---->
outside air film<!----><!---->
<!----> <!---->
<!----> <!---->
0.17<!----><!---->
5.67%<!----><!---->
100.00%<!----><!---->
<!----> <!---->
0.00<!----><!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
TOTAL<!----><!---->
R-<!----><!---->
3.00<!----><!---->
100%<!----><!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
How cold is "very cold"? Below about -10F ice on the window panes is reasonably normal, depending on humidity levels, airflow, curtains, etc.
So, you still keeping up with this thread?
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http://www.quittintime.com/