Simple “Super Insulated” Window?
Sorry, I wish I had an answer to share with you all. But I’m fishing for ideas instead.
I’ve been trying to brainstorm ideas for very well performing windows (and doors) for a house that will be very well insulated elsewhere. Minimizing glazing is not an option in this somewhat scenic area where winter averages around 15 degrees overall. It’s my home, so I’m willing to work with somewhat unconventional solutions.
Yes, I know there is lots of new space-age window technology out there (with NASA-like price tags) that give impressive r-ratings, but I’m more likely to go for something less high-tech, inexpensive, and unconventional. I’ve even built some windows in the past with pre-made double glazed panels.
Among other hair-brained scemes, I’ve considered having an inner window sash (perhaps removable, perhaps not – single or double glazed) that would work in conjunction with the double glazed outer window and 4-8″ air gap in between during the cold months.
Also, I would like to know if the following bit of math/logic is correct:
If 3/4ths of all wall area is R-30 (insulated wall) and the other 1/4 is R-5 (window/door) is it fair to say that the overall wall envelope of the home will perform at about R-23.75? If not, how do you calculate this?
Thank you.
Replies
Having 4 - 8" of air between panes of glass would be nearly worthless. The convection currents between the panes would facilitate drastic heat exchange.
I visited a home in Montana once that had a solar wall with panes about 3 - 4" apart and had a vacuum setup that pumped beads of styrofoam into the space at night and sucked it back out in the morning. It left a kind of static electric film that wasn't to great, but the owner thought he was really onto something.
I'd suggest that you consider fabric covered foam panels on hinges that would act as inside shutters to keep heat in at night or during extreme weather. Make sure the panels are VERY snug fitting though, or the chimney effect will negate most of the benefit. The best thing I've seen to snug up interior shutters or thermal curtains was small slats of wood screwed to spring loaded cabinet hinges. You simply snapped the slat shut over the edge of the thermal barrier and had a really tight fit.
Maybe you know this, but if you're going to set glass units into wood jambs that you build, set the units on neoprene blocks and be sure that the sealant you use is compatible with the sealant used to seal the units. Otherwise, one can ruin the other.
There is some good info in The Passive Solar Heat Book by Edward Mazria if you want to take the time to sift the good stuff out of the outdated stuff.
Any jackass can kick down a barn, but it takes a carpenter to build one.
" Having 4 - 8" of air between panes of glass would be nearly worthless. The convection currents between the panes would facilitate drastic heat exchange."
Would it be less beneficial than the 1/2" of air space in a 3/4" double glazed panel? If so, why? I had envisioned a typical double glazed sash on the outer edge of the wall and a seasonal double glazed sash on the inner wall. I figured the air space in between would help too. Am I wrong about that?
The vaccumed styrofoam beads story made my smile. I'm not that partial to unconventional solutions.
Fabric/foam/shutters of some combination have ocurred to me too. The thing I was hoping to avoid though is the feeling of being shut in by taking away the visual connection with the outside (also the hassle of having to open and close them each day). It would be a great solution for a vacation/seasonal home where you might be gone for weeks at a time but wanted to keep the place above freezing.
Thanks.
Sounds like you could benefit from doing some more reading on the topic.
My understanding is that still air is a good insulator, moving air is not. Thus, after a certain distance apart the air between panes begins to set up its own convention currents (down on the cold side, up on the warm side...). When such action is ging on, whether in a wall, in the living space, or between panes of glass, it continually brings the cooler air into contact with the warmer surfaces and the warmer air into contact with the cooler surfaces: heat loss.Any jackass can kick down a barn, but it takes a carpenter to build one.
Asl long as you keep the space between glass at 1/2 in there are no convection currents. You can keep adding glass panes and get increased efficiency. Dont know how much.
There used to be (2o yrs or so) sombody in New Mexico, name like zomeworks, who sold the styrofoam pellets system, think it was used in skylights, where fuzziness wouldn't be a problem. dickd
visited a home in Montana once that had a solar wall with panes about 3 - 4" apart and had a vacuum setup that pumped beads of styrofoam into the space at night and sucked it back out in the morning. It left a kind of static electric film that wasn't to great, but the owner thought he was really onto something.
Steve Baer of Zomeworks invented that; it was called a BeadWall. I don't think that he ever got the kinks out of the system, but it has a lot of merit. The big downside was all the piping, and that you had to store the beads someplace, like 50 gal drums in the basement, and that takes up a lot of room. But if you like inventing stuff, and have the room for storage, perfecting the BeadWall would be fun.
PaulBen
Hey NannyGee,
I believe the insulation value you are looking for is the U value.
R value is the insulation value of a component or wall or ceiling system. If you want to know how effective it is going to be in helping you insulate your house you need to look at the U value.
U value is the insulation value of the entire structure or house. In other words, it may not make economic sense to spend a lot of money on a certain R value component for a wall if you are loosing most of your insulation value in a structure through the ceiling do to poor insulation in the attic.
As to determining R and U values, and finding all about convection etc... just do a Google on "insulation manufacturers", and click the link to Owens Corning, Guardian, etc...
If I remember right Owens used to have great info on insulation specs.
Lots of Luck, Stay warm this Winter,
Cork in Chicago
U, referred to as the thermal transmittance coefficient, when inverted, becomes R. Thus a material or product with an R=2 has a U of 1/2 or .5. And R=7 equals U 1/7 or .14, etc. The lower the U-value, the higher the corresponding R-factor.
Most all window companies list the insulating values of their products by U-value, and the number is developed from testing a certain size window, say 36 x 60, and applying the value to the entire product line. Go to the fine print in the specification section of Andersen or Pella's catalog and you will see.
The superinsulated windows I know of are usually made in and for the Canadian market. Triple glazing, the use of heat mirror film, warm edge air spacers, and superior gasketing designs, all contribute to the performance.
One stateside window maker that I know of, Hurd, used to make some window products with high performance glazing options, including heat mirror film (one of the best performance-enhancers), but I am not sure whether they still do.
U-Value - difference between U and R values
Or U-factor - A measure of the rate of non-solar heat loss or gain though a material or assembly. It is expressed in units of Btu/hr-sq. ft- degrees Fahrenheit. Values are normally given for NFRC/ASHRAE winter conditions of 0 degrees F or 18 degrees C outdoor temperature, 15 mph wind, and no solar load.
http://www.energy.state.or.us/code/respub/res11.pdf
Mr Micro,
I agree with what you posted. I should have been clearer when I shifted thought from strictly discussing glass, and instead shifted topic to a total building or structure envelope.
What I was trying to convey is sometimes it is best to look at the "macro" or overall picture of your house, before you start spending a lot of time and money looking at super insulated windows.
The above link does a much better job at this than I, and shows you how to calculate the U-value for your entire house.
As it is the U value for the entire house that most effects you and your comfort and heating bills, sometimes it makes a lot of sense to calculate this value for your house.
A good link for figuring thermal properties " heat flow" is the following:http://www.squ1.com/index.php?http://www.squ1.com/thermal/resistance.html
I hope this clarifies what I was trying to state and may help others out there in BT.
Now I need to go back to stuffing my face with turkey day leftovers "sister-in-law" packed me a monster size load of these and I hear them calling me "cork, Cork, CORK!! You must feed NOW!! We are in fridge. Come hither and feed thy Face NOW!
Have a good one,
Cork- feeding his face in Chicago
You forgot to mention the argon gas.
"You forgot to mention the argon gas."
We got into that big time on BT about 3 or 4 years ago. Basically, why stop at Argon? Why not Krypton (which also prevents Superman from flying through your windows), Xenon, and Radon? Radon would radioactively decay so fast that the windows would implode in a week or two. Kr goes pretty fast too.
But Xenon is defintely better than Argon for all the same reasons Ar is better than Helium. Big atoms have a shorter mean free path than small molecules. Deep divers can tell you He/O2 mixes transfer heat out faster. (And make you sound like Mickey Mouse).
And, He, Ar, and Xe all have advantages in being monatomic noble gases. Molecules (like O2, N2 and especially CO2) have higher heat capcities because than can spin in two or three axis')
In transferring heat, O2 and N2 are bigger buckets that carry more heat.
Xe, Ar, and He are smaller buckets and Xe travels much less far in each step. Followed by Ar and He.
Summary: Xe is the best. Ar is good and predominates because it is plentiful - 1% of the atmosphere.David Thomas Overlooking Cook Inlet in Kenai, Alaska
>> Xe is the best. Ar is good and predominates because it is plentiful ...
I surmise that xenon costs quite a bit more.
David,since you have a lot of radiant heat experience, I was wondering what you would think of putting a double loop of finned copper tubing behind the backer board, on three sides, at the base of a tiled shower stall (new construction). I would use the hot shower water to heat the fins, which I would cover with sand , about a foot deep. The purpose is to provide a heat sink that would give up heat to help dry the stall. Even with A/C, and bathroom exhaust fans, we still get shower stall mildew.Is this too radical? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
"Is this too radical?"
You're asking someone who designs and builds (and carries) hot tubs for backpacking trips?!
First, on your concept: The heat transfer will be slow (you know that) but since it only needs to get dry eventually, that is not a problem. The timing of the heat delivery is perfect and automatic. It gets hot only when/after a shower.
To the the extent you do get heat out of the incoming hot water, it will be cooler at the mixing valve. Which is probably fine, you don't want a 120-130F shower. But the new "anti-scald" valves sometimes constrain the % of hot that can be used. A pity to have to crank all the HW in the house just for the shower. But, quick guess, it won't get a lot of heat out since air and sand are not super conductive.
Too bad you can't use waste shower water to heat the shower pan/surround. Oh you could, but it would need a pump, controller, etc.
Any way to use staple-up aluminium heat fins onto the back of the backer board? Epoxy? I fear the sand would be so massive as to only yield low-grade heat.
Pouring a foot of concrete would increase the mass and significantly increase the heat transfer. But I'd worry a lot about reduce HW temps at the shower valve.
Wouldn't just insulating the back of the backer board help? Then it would get hotter and not lose heat to the wall cavity. Leaving more of its mass (warmed by shower spray) for evaporating water.
My mom just kept a squegee (so?) in the shower. Wipe down the walls and you get 85% of the water drops down the drain. And prevent water spots from hard water from developing.
At car washes, they blow a LOT of air to dry off cars. Not sure if want that racket in your bathroom, but evaporation in all settings is a strong function of air speed.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Thanks for the input. I may build a test panel with an aluminum plate glued with thinset to the backer board, some copper water line with hose connections to the laundry tub, and see what kind of temp and how long it lasts at the tile face. I will put some foil faced insulation behind the glue up panel. I want all the heat to move through the tile to help evaporate the water. Will let you know if I ever do this. Are the bears bedded down yet? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
"My mom just kept a squegee (so?) in the shower. Wipe down the walls and you get 85% of the water drops down the drain. And prevent water spots from hard water from developing."
My DW didnn't have another kid I don't know about did she??? <G>
(2e's before the g?)
PS: Forget to wip'em down for a lecture on mildew??
David, Re: "too bad you can,t use waste shower water heat..."
In a way I can by installing a gravity film heat exchanger (GFX). A 40 " unit will recover about 50% (specs not in front of me ) of the heat from the draining shower water, and just a WAG, that should let me re-center the mix valve due to the warmer cold water side.
The squeegee is good, it's like that aspirin a day thing.
To NannyGee, sorry to drift from your original question, but I felt we had the subject surrounded. If you want more input, please post.
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
I liked the idea of the gavity film HX. I don't have the specs here either. I think they were claiming 40%-ish. I'd estimate 25-30% is more likely. But still - no pumps, no moving parts, it's an elegant approach. I'd wish I'd heard of the idea before building my place. City water comes in at 35-38F so the shower mixing valve is pretty touchy. Boosting cold water to 55-60F would save btu's AND make the valve easier to adjust. And with essentially ice water coming into my house, I'd get the highest possible HX efficiency.
But I'd probably wind my own. I was thinkin 2 or 3 parallel wraps* of 1/4 or 3/8** soft copper around 2" copper DWV pipe. Tack it in place. Then off to the radiator shop to dip it in there tank of solder.
*by parallel wraps I mean like the red, white, and blue on a barber pole.
**Need to check where you get turbulent flow (good in this case) at 0.8-1.3 gpm of cold divided among 2 or 3 pipes. Turbulent flow for the better HX.
My, but we have hijacked this thread to some obscure topics, haven't we?
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Yes, we have jumped the tracks with this train, apologies to NannyGee.
I found some GFX specs. 1/2" type L spiral wrapped around 3" or 4" copper pipe. Looks like one continuous run of 1/2". The 3" claim is heat rec at 49% and same size using 4" core pipe is 56%. Priced in $200 to 300 range.
I think I can buy some soft L, 100', and 48" of 4" copper for a good bit less. Clean, flux, tack, wrap, tack and dip.
Their chart (went to Google with GFX)shows drain water at 95 deg, incoming cold at 41 deg, and recovered heated water at 75 deg, which would be balmy warm to you. I down loaded their pdf quite a while back, have it somewhere.
If all the hype is true, and, I have a barrel where I keep the BIG grains of salt, then they are truly worthy devices. I think a shower is the best application due to run time, volume and immediate use of the heat. HMMMMM.... Paul
Energy Consultant and author of Practical Energy Cost Reduction for the Home
Yes, the shower is about the only fixture that drains as it fills. Clothes and dish washers cycle. Bath tubs more so.
95F outgoing is reasonable, I'll check.
41F is maybe Portsmouth or Syracause or Boise. I'm lower but obviously an outlyer. San Francisco, ST Luois or Norfolk would be about 51-52F. 60F or more in the sunbelt. So 41F seems unreasonably to their advantage and far from any population-averaged US water temp.
It is truly counter-current. The thin film inside the 3" is great for HX and efficiency. Seems to me though, they have to go turbulent in the 1/2" to really well. Which I believe (eyeballing a friction loss chart) starts over 2 gpm. But a 3-4 gpm shower head won't use quite that much cold water. Wait, you said it's type L! Smaller ID. Don't have a chart for that. Maybe they've got it right?
Edited to ask: Does anyone else follow or care what we're blathering about here?
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Edited 12/7/2003 2:04:37 AM ET by David Thomas
Yeah I'm curious. Would be interested to hear how much verticle drop you need for max effect vs how little you could get away with
Reinvent, if you Google for GFX, you can pull up their whole product line. They may have a 24", something in the 30s, a 40" and 60" for sure.
The heat gain falls off the shorter you go, but so does the cost. Vertical installation is key to keeping the water film well dispersed and migrating around the inside of the drain pipe.
For David, they had other temperature comparisons, I just posted the one closest to you. 55 incoming gained to 80 deg, and deep south 77 gained to 88 deg. I checked the shower out-flow last night and had 96-99 deg water heading south, with 108-110 at the shower head. Granted, I like hot showers; recouping part of that 20,000+ Btu shower would be satisfying.
Suggest we move to a new thread after this post in any further needed. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Type L does make a difference (thicker wall, smaller ID gets turbulent at a lower gpm). The laminar/turbulent transition comes at 0.89 gpm. That is a reasonable amount of cold water. Especially because it would be warm water (60-80F) to mix with 120-130F to make 3.2 gpm of 105F.
Let's say 0.89 gpm of 60F from the HX. Total of 3.2 gpm of 105F. Needs 2.31 gpm of 123F water. So it adds up. If it does better than 60F; or you run the HWH above 123F; or if it isn't a low-flow showerhead; you move more fully into the turbulent regime.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I considered making a home-made GFX as well. I don't think a home-made unit would match the GFX performance figures because, IIRC, the manufactured unit has a flattened tube wound around its perimeter, so the surface area for HX is much greater than a home-made one, which would have a more circular cross-section (depending on how beefy your forming facilities are). Also, the reduced thermal conductivity of a soldered joint would futher retard heat flow.
I still plan on making one myself using possibly two concentric, (coaxial) copper tubes, but it's now farther down the list in priorities.
If the vessel for the incoming water is large, then you have the advantage of not requiring the simultaneous use and drainage of water in order for the thing to work. (The GFX requires simultaneous usage and drainage such as a shower to be effective). ie dishwasher, laundry, etc. are less effective unless you have a larger reservoir for the incoming water.
Regards - Brian.
Meanwhile, back to the discussion...
No one has mentioned yet the "Super spacer".
Most thermalpane windows have an aluminum strip separating the two panes at their perimeter. ALUMINUM? ...Huh? Aluminum is one of the most thermally-conductive metals, and in a window where you want minimal heat loss.
The "Super spacer" is one brand name among many for the thermal break which is made at the perimeter of the panes to prevent/ minimize this heat loss. The dessiccant is contained within this spacer.
A good feature which enhances the thermal performance of a window with not a great increase in cost.
Regards - Brian.
hey guys, i remember reaserching this somwtime ago when I was think about building some of double paned windows myself....
The problem I ran into was that if you go over 3/4 of an inch in seperation of the two window panes you run into convection currents. The point of super insulated windows would be to minimize the convection currents because they help move the heat into or out of the building faster.
But if you put a double pane window with another single pane toward the inside of the house about 3/4 of a inch away.... cover over with thick multi layered drapes..... now your talking... this would stop all convection currents from happening.
But I am really enjoying the heat recovery discussion... would this be worth the $$ to put it in?Christmas is coming..... should I buy the wife that new tablesaw ....hmmmm
"cover over with thick multi layered drapes"
Someone had mentinoed drapes or coverings early and I had forgotten to reply.
If you can make them essentially airtight, great. But in general, insulation inside the windows makes for more condensation. Insulation or blocking air flow outside the windows (e.g. external shutters, storm windows) make for less condensation.
Puddles on the windowsill are to be avoided, IMO. But in a mild climate with good (double pane or better), some additional benefit could definitely be had with drapes or fitted quilts or panels. In my climate, the indoor air is already too dry. I'd humidify it more but for the condensation.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Airtight isn't good enough to avoid condensation. The material used must also have a very low permeability or the vapor goes right thru and condenses.
Considering that an outside shutter is impractical, here's a halfway solution: Use something like a cellular blind, but leave it raised at least 2 inches at all times. The blind does a good job of stopping the radiant heat transfer from your body to the window. In terms of personal comfort it's probably stopping about 50% of the window heat loss. The gap allows enough convective airflow to keep the window dry.
I've tried using mylar coated cellular blinds with a special track to seal around the edges (nowhere near airtight, but low permeability). The windows were just as wet as with a standard cellular blind and no track.
This really is a widespread problem with no commercially available solution.
I agree blinds would help with the radiant effect (or is it an anti-radiant effect?). I feel the cold by the five 4' x 6' window on the volcano/ocean side of our living room. Technically, I feel the lack of radiant heat the R-40 walls, 69F walls offer.
I disagree about "outside shutter is impractical", since every New England house over 150 years old has them. Helped a bit during Indian attacks and could be locally built way to control solar input (no expensive cloth drapes). But they would help a bit on winter nights, too.
What really bugs me are the "shutters" that are screwed to the house, too small to cover the windows, and sloped the wrong way (shedding rain when open instead of when closed). Gone from a functional component to a trim detail that is disfunctional in three ways.
Edit: But I agree that there is not a good commercial solution. Triple pane, argon- or xenon-filled fixes it for most instances. Or at least reduces condensation to the window frames.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Edited 12/9/2003 1:51:00 AM ET by David Thomas
Hey all, thanks for the continued responses.
(no problem with the topic diversion either...)
I recall many years ago when double-pane glass became the standard, it didn't take long for triple-pane (and even more) to get pushed, too. Yet I notice almost all the modern windows now are just doubles. Has it been established that the third pane of glass isn't worth the trouble?
BTW, I've long considered the shutter idea (inside, not outside) though I'm not excited about cutting off views or having to run around every morning and night, nor am I exited about the "look" either opened or closed. But it may be the most practical solution. Condensation worries me, too.
Triple-glazing also makes for one heavy honkin' window.
Most triple glaze windows these days use a plastic film in the center. Its lighter and cheaper and is almost always low e coated. Gas extra.
I made some thermalpanes ,acculy it was triple pane . I used windsheild tape for my spacer . This was a good 20 years or more ago and they have yet to fog up .
you asked did we understand?
i do - it a device to raise the value of the dollar v the euro- right?
I am interested /following both sides of this one (glass and shower)
OK so I have my shower all plumbed and drains in plastic running horizontal . No way to make a straight drop ,will it work here?
One other thing if the storm window was a thermal pane and gasketed all around and only 2" away from the main window (also a thermal pane) would you still have the turbulance?
You could run 1/2" INSIDE the ABS (if the building inspector doesn't look too close). Sealing up the ends is trick what with different rates of thermal expansion. You quickly arrive at U-tube solutions so common in reinferies. So the enter and exit are made at the same point and the U-bend can have freedom to move a bit. But the efficiency would be much less than these vertical gravity-film units. Both because of a shorter length of 1/2" and also because on the waste-water side the GFX is a thin film. In 3" horizontal ABS, the waste water is not thin film or turbulent so HX eff% drops a lot.
I'm in the same boat and have resigned myself to thinking, "In my next house. . . " Vertical GFX; north window in the bedroom for the auroras; etc.David Thomas Overlooking Cook Inlet in Kenai, Alaska
For the kind of heat transfer device you're considering, there might be some relevant experience to draw on from the moonshine booze community.... ;-)
-- J.S.
"experience to draw on from the moonshine booze community"
How true. My uncle operated a (legal) distillary producing European fruit brandies from fruit wine (peach, plum, etc). And the reflux chamber had random-dump packing. So much simpler and cheaper than the distillation trays used in oil refineries. And since it is cheaper, you can make it taller and get a finer "cut" There were some off-tasting aldehydes and ketones that preceeded and followed the ethanol during distillation and those were shunted aside.
An example of a two-man operation using 90-year old copper equipment from German Weimar Republic that was a better design that what Exxon uses today.
A co-worker of mine had stopped by with me. My uncle was trying to demonstrate the off-tastes he was discarding, but my co-worker found the waste product to taste better than what he usually drinks.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
My mom just kept a squegee (so?) in the shower. Wipe down the walls and you get 85% of the water drops down the drain. And prevent water spots from hard water from developing.
Then there's Arm & Hammer Clean Shower, which breaks the surface tension of the water, allowing it to run down the shower surround and into the drain. Keeps soap scum from building up, too. "Better living through chemistry," if you don't count the cost of dealing with the surficants downstream.
read the thread about storm windows here
Be warm
andy
My life is my practice!
http://CLIFFORDRENOVATIONS.COM
One thing I would recomend is to have a thermal scan done on your house after you have done some of this work. It can be very educational on exactly how your house is performing.
You are correct on the combined or average performance of the wall at 23.75, based on those R-val and areas, not considering the studs themselves. Obviously, a thermoscan will show the window to be dumping heat compared to the insulated R-30 wall section.
Hasbeen has described the air circulation effect of a wide spacing between glass, or any two surfaces. The only way for that space to be beneficial ( if empty) is if it was a vacuum, (like the old thermos bottles), and I don't think you can get there easily. Somewhere around an inch gap, additional space becomes a negative.
The foam bead walls I have seen have two problems:
A. the beads cling to the glass from static ele, and the wall does not fully evacuate. Looks pretty tacky, no pun intended.
B. the blower/vacuum system lets in enough moisture to condense and fog the glass...once again not the pristine view you are seeking.
Thermopane glass, insulated interior shutters or thermal drapes are about the solutions for viewing and cost survival in your climate. Let us know what you decide. Paul
> Somewhere around an inch gap, additional space becomes a negative.
I'd be interested in more precise documentation of this. For hundreds of years casement windows with two sets of sash, one inswing and one outswing, have been used throughout Scandinavia and central and Eastern Europe. I've seen them in Vienna, Moscow, Oslo, and Stockholm. The distance between them when closed is usually in the 3" - 6" range. Is there an optimum distance that the Europeans have been overshooting?
In Scandinavia it's traditional to hang a small light in the middle of each window maybe a foot from the glass. There's something magical about the look of that little light through parallel panes of wavy old glass in the long Northern twilight.
-- J.S.
I was curious about that, too. I've never been there but I've seen lots of pictures & movies.
NG,
I don't have time right this minute to read through all of the messages, so this has probably already been answered, but having 4" between the windows is a waste of one window and will end up being more expensive. That is the arrangement in my house in UT and it has several negatives. First, there is negligible insulating going on between the 2 windows - the space needs to be much less. Secondly, because normal air can get between the windows, you get condensation there (yes, even in the desert) when it's really cold outside and warmer inside. If they were single pane, we'd still get condensation, which shows you how little that second window helps. Thirdly, talk about a fly and spider factory - they love that space. The most comfortable rooms in my home are in the addition that my husband and I put on. We used double glazed clad casements in the sunroom ($$$), and double glazed vinyl sliders ($) in the bedroom, all low-E. We looked at a lot of windows before making our decision and one thing that we found was that you pretty much get what you pay for. Casements are more expensive, but they have the advantage of being able to open all the way to enjoy a breeze, as well as being the best windows for sealing up in inclement weather. Triple glazing is entering into the realm of diminishing returns, not giving as much bang for the buck. Insulating Window treatments can give a lot of bang for the buck, as long as they are easy to open and close so you do it when the time is right and not just twice a year.
My guess is that the places in Europe with the arrangement of two casements predate the double glazed, argon filled, low-E windows available today. You are looking at the progression of technology.
> My guess is that the places in Europe with the arrangement of two casements predate the double glazed, ....
Yes, by hundreds of years. The palace of the King of Norway has them, so does the Cathedral of the Intercession in Moscow, built in 1461.
> Triple glazing is entering into the realm of diminishing returns,
I saw some triple glazed in Stockholm and Oslo, but mostly double glazed.
-- J.S.
the low e argon filled units better really pay off energy wise, cause when the seal blows you just have more expensive junk.
John, I have also seen the double sash arrangement in many different countries, but as I recall,the doubling was often to get better air sealing. A step ahead of our typical storm windows as far as air infiltration goes. As you know, triple glazed windows are available, but the space is still close, and inert gas filled. I have also stayed in hotels with double thermal (inert gas filled) sashes, and a few inches between. The convection loop loss would be reduced by virtue of the R-value doubling.
If you look on page 51 of Dec '03 FHB, they diagram the convection loops that become established in a wall with free air movement. The same happens between two layers of glass that have air between them. Paul
.Energy Consultant and author of Practical Energy Cost Reduction for the Home
For those of you who want to get definitive answers on convection/heat transfer, etc., there is a Maxwell 2D SV (Student Version) FEA (finite element analysis) tool for free download on the web that is an excellent tool considering it is free. It has both conduction and convection (including the effects of film coefficient) in the calculations. The thermal part of the program is small, it is mostly an electric field strength and eddy current tool, but the thermal part of the program is excellent.
John, sorry I left off a printed reference. Page 31 of Consumer Guide to Home Energy Savings by Wilson, Thorne and Morrill.
Thickness of air space..."If the air space is too wide, however,convection loops between the layers of glazing occur. Beyond about 1", you do not get any further gain in energy performance with thicker air spaces." PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Ah, no further gain. But there isn't an optimum point beyond which it starts getting worse. Glad to hear that because I love the look of the parallel panes. Mine will be 4 - 5" apart if I live long enough to build them.
-- J.S.
whats needed also is research on how to keep the seals from blowing out every 10 years negating all or a lot of the energy savings!!!!!!!!!!
A-men, my friend. I just replaced 1 thermo pane in one of 10 windows in our sunroom, and it cost $105, and I did the labor. Did it save $105 plus 6% compounded over the last 12 years? Or, a fairer question, since I had to have a window, only the upcharge for the thermo pane over single glass should be considered. Still might be a reach to justify, but we do these things sometimes because it just feels right. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
John, If you like the look, then go for it. There is a value to satisfication.
I built some Japanese sliding paper panels to cover our windows in our Oriental sunroom.They pocket at each end of the room, one window width on each side of the windows. They serve as our "curtains" and help with heat loss in the winter.We first experienced them while staying in a hotel in the mountains south of Tokyo. They let in a very soft light, when closed.
With the wood grid, 12 panels, wooden tracks, real Japanese paper that I replace every three years, it can't be cost effective, but we love the look and the authenticity they give the room. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
I've done the math in the upper division course on heat and mass transfer. Between 1/2" and 1", depending on temperature and temperature gradient (which effect viscosity of the air and mean free path of the air molecules).
David Thomas Overlooking Cook Inlet in Kenai, Alaska
I have also done research on this topic for a personal project. There was/is on the 'net, somewhere if you do a search, a graph which shows the curve which results from the change in R-value as the airspace between two panes of glass changes. I came across it a couple of years ago, and IIRC, 1" was about the ideal distance according to that research. It may have been done by NRC Canada(?). The data are out there, so the proof has been done in the real world.
Regards - Brian
Edited 12/5/2003 12:44:14 AM ET by MARKLS8
Cork alluded to it. Mr. Micro explained a bit more but Paul got it wrong (this time, he?s often right).
U values are 1/R. R-values are 1/U.
R is in units of BTU/(hour sq-ft deltaT) and is a measure of insulation. An R-30 wall, 300 square feet at a 100 delta T (e.g. 70F to ?30F) loses 300 x 100 / 30 or 1,000 BTU/hour. R-values are additive when stacked on each other. The R-values of ext dead air, siding, insulation, sheetrock, interior dead air, etc add up: 0.2 + 1.5 + 19 + 1.0 + 0.5 = 22.2 R-value. Those particular examples are SWAGs.
R-values don?t average arithmetically when adding different areas like the walls and windows.
For that, you need U-values. In your example, you have 3/4 R-30 and 1/4 R-5. Which equates to 0.75 parts U=0.033 and 0.25 parts U=0.2. For an average U of 0.075 or an average R of 13.4
U is a measure of thermal conductivity ? the size of the pipe carrying heat out of the house. You CAN add the those pipe sizes to arrive at a total effective pipe size (total heat conductance). Than do 1/U to get average R-value.
So it is 13.3 effective R-value for that wall, not 23.75! If you have a big heat loss (windows), you can?t make up the difference by doubling the R-value of the walls. You?ve got to fix the windows. Note, however that truly R-5 windows are quite good.
I stand corrected, the window is really a breach in the wall heat wise, and all the insulation around it won't make up the difference. Tks, PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Thanks all.
Very interesting stuff. I did not know of U-values and I did not know that a wider air gap was a negative.
This is a great way to learn stuff (and it's comforting to watch the teachers learning stuff too)
Any other suggestions, observations, examples seen, etc. would be appreciated.
Here is a link to a disscussion we had about affordable super windows after I designed and ordered mine. I had some pretty specialized specs and a couple of added expense mull combinations that drove the cost up a bunch but I still averaged around $400 per window. Not bad for casements with a total U-value of .149!
http://forums.taunton.com/tp-BREAKTIME/messages?msg=35243.1
There is a formula in the thread for area weighting that will help you calculate the total u-value of the wall and windows combined and a link to the free software I used to do the window design and annalysis. Good Luck!
Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -
Unless I missed it, your question about just what is going on hasn't quite been answered. Not that I really know, but what the heck...
When you get a large area, convection currents are pretty understandable - you have hot air going up in one area as it is heated, over a little bit, and then down as the air becomes cooler and more dense. However, in a small area, there are surface boundary effects - the air near the wall sort of "sticks" to the wall. Probably a little beyond that you get weird types of turbulence that impede the air flow. Only after you get some distance between the two panes of glass do you have enough space for the air gaining heat from the pane on the inside of the house to rise in a relatively unimpeded fashion and then enough space to allow for the descending flow some small distance from the cooler outside glass. I am guessing somewhat as I haven't actually seen a description of what happens, but I have seen some good research on the boundary layers and turbulance that occurs when air moves over a surface such as a car fender when one attempts to minimize air drag, and I am guessing that they are somewhat related...
Yeah, roughly, qualitatively: When the boundary layers (from each side) overlap, air movement is slowed enough by friction against each surface so as to preclude convective circulation loops.
"Unless I missed it, your question about just what is going on hasn't quite been answered."
Casey: Come on! We were only up to 32 replies! Isn't that a little early in the process to answer someone's question? :-)
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Where I live the insulation problem is often one of keeping the heat out. Triple glazing (ie two air gaps), heat reflecting films (as used on cars), glass that is opaque to thermal radiation are all options. You want to keep the heat in so how about you put the heat reflecting film where it will reflect heat back into the room.
A low tech solution would be insulated shutters you close over the windows when you go to bed.