Energy-efficient windows

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ChrisGreaves
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Energy-efficient windows

Post by ChrisGreaves »

Edited on 29th April, five days later:-
I was wrong in most of my beliefs about Windows. This post from "stuck" got me unstuck.


Subject: Meeting software
PJ_in_FL wrote:
23 Apr 2022, 13:39
...Going with energy efficient windows really made a difference in our house, cutting our utility bill by more than half when combined with an up to date AC system.
Hello PJ.
I am confused, especially about the energy-efficiency.
In my case (snow and freezing rain again, today, ...) I am trying to convert my residence into a greenhouse, with as much glass as possible. The largest three windows are planned at 93"x70"; each of the six existing apertures will be enlarged and eight new apertures cut. My glass area will go from 13,000 square inches to 52,000 square inches.
I have learned that my energy consumption is already the lowest among all my friends (I live SOLO, program in my little study; read books in my little living-room, sleep in my little bedroom).
Despite its title, there IS no "unbearable heat of summer" in this town, but in the depths of winter, the 3'x2' window in my bedroom lifts the temperature to 22c some days, so large windows along the south wall ought to bring much-needed heat energy into my porch, kitchen, bedroom and study.

Herein lies my confusion: I am not so much worried about heat emigrating during the cold months as much as I want heat to immigrate from sunshine.

If one buys energy-efficient windows to defeat heat-transfer, then I don't want energy-efficient windows; I want windows that leak heat like a sieve.

In summer time ( check out the LOW maximums) the breezes cool the house down, but in winter time I need all the heat I can get! Coming in from the houtside.

Thanks for any advice
Chris
Last edited by ChrisGreaves on 29 Apr 2022, 09:57, edited 1 time in total.
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John Gray
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Re: Energy-efficient windows

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ChrisGreaves wrote:
24 Apr 2022, 11:56
Herein lies my confusion: I am not so much worried about heat emigrating during the cold months as much as I want heat to immigrate from sunshine.
If one buys energy-efficient windows to defeat heat-transfer, then I don't want energy-efficient windows; I want windows that leak heat like a sieve.
In which case you don't want even a single pane of glass - remove the glass and just let the heat enter or escape... :thumbup:
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Re: Energy-efficient windows

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John Gray wrote:
24 Apr 2022, 12:47
In which case you don't want even a single pane of glass - remove the glass and just let the heat enter or escape... :thumbup:
Oh John! You are transparently a pane :evilgrin:
I need at least one sheet of glass to assist in the conversion of the the shorter-wavelength rays from the sun into infra-red rays (roughly, "heat").
in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat
As a kid I lived in a house with practically no windows, it was awful in mid-winter when the temperature dropped to about 10ºc.
2022_20220326_144656_HDR.jpg
Back to heat: I suspect that the main loss of heat is from warm air escaping through the gaps in the sliding-windows. Note the strips of scrap toweling which reduce the airflow between two panes.
The Green tape is a rough outline of one of the new window apertures.
Cheers, Chris
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Re: Energy-efficient windows

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Knowing you, Mr. Greaves, this information is probably redundant; but in case it is not, you might consider a missive to this company and pose your question about heat absorbing windows for colder climes.
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Re: Energy-efficient windows

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BobH wrote:
24 Apr 2022, 18:23
Knowing you, Mr. Greaves, this information is probably redundant; but in case it is not, you might consider a missive to this company and pose your question about heat absorbing windows for colder climes.
BobH, you surely don't know me that well (grin)
The link suggested my nearest dealer at Clarenville 90 minutes drive south from my home.

Home Depot in St John's (3.5 hours) apparently supplies Andersen windows; this is the Home Depot with a Virtual Consultant who sent me links to six Farley products (they of the "energy efficient" fame)

I will take a look at comparable windows by Andersen, and then call their toll-free number tomorrow.

You are smarter than I, choosing as you do to live in a place well-suited to normal human activity. On 16th April last year I had 200 crocuses in bloom.
Last Friday (22nd) just two blooms to date. Two centimetres of :snow: this morning ...

This discussion has been good for me; :yep: my thoughts crystallize. The main aim of the new windows it so eliminate strong draughts that pump heat (hot air) out of my home.

Cheers
Chris
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Re: Energy-efficient windows

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ChrisGreaves wrote:
24 Apr 2022, 18:52
my thoughts crystallize.
Are you sure that that isn't because of the snow?
Best wishes,
Hans

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Re: Energy-efficient windows

Post by GeoffW »

Could you just get energy efficient windows (double glazed or low-E glass) that you can open? Or did I miss something?

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Re: Energy-efficient windows

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GeoffW wrote:
25 Apr 2022, 08:47
Could you just get energy efficient windows (double glazed or low-E glass) that you can open? Or did I miss something?
Opening the windows in mid-winter is not a good way to heat the house.
Opening the windows in mid-summer is to my mind a good way to cool the house (I don't use air-conditioning).

Basically, forget about summer(1) and focus on the Winter.
In wintertime I want to harvest heat from the sun's rays, by the sun's short-wave radiation shining through the glass, striking some object in the room, and then being converted to a lower-frequency wave length that cannot escape through the glass. Ultra-violet and blue light waves losing frequency and becoming infra-red, which, the books say, cannot travel as well through glass, and so the heat stays trapped inside the house.
The same argument should hold for the energy generated by my base-board electrical heaters: that heat should not be able to pass through the glass as infra-red (or infrarer(?)) waves.

Based on what I know of glasshouses (I note that we still don't have a Gardening Conference :evilgrin: ) a single pane of glass works wonders for raising the temperature within, and I rather suspect that single-pane windows would do the trick, as long as they were air-tight.
But where in Newfoundland are you going to find someone selling window kits that are not double-glazed?

(1) Here in Bonavista the unbearable heat of summer is like that mid-day in mid-winter in Perth or Adelaide. Indeed, I have often commented to my son on the temperature in readings in all three locations being equal at a specific time.
Cheers, Chris
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Re: Energy-efficient windows

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HansV wrote:
24 Apr 2022, 19:11
ChrisGreaves wrote:
24 Apr 2022, 18:52
my thoughts crystallize.
Are you sure that that isn't because of the snow?
No, Hans, I am sure that that is not why it isn't. Snow on the day before St George's Day (April 25th here in Newfoundland(this year)) focuses my attention even more on loss-of-heat to the outside! :grin:
Cheers, Chris
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Re: Energy-efficient windows

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Well, Chris, it is a cool 64° F as I type this and raining (prayers answered) here. Windows and doors are open to enjoy the pitter patter.

Glass alone has a high thermal transfer attribute. I wonder if heat gained during the day would not all be lost at night if used alone. I wonder, too, if there might be a glass, or combination of glasses and gases in windows, that exists that would allow the gain inside and deter the loss going the other way.

Have you considered a trombe wall to absorb solar heat?
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Re: Energy-efficient windows

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BobH wrote:
25 Apr 2022, 17:15
Have you considered a trombe wall to absorb solar heat?
No Bob, I hadn't, until now. Are you suggesting I rebuild my South Wall completely? Am I correct in assuming that you will come up here and help me next summer?
I thought as much!
Glass alone has a high thermal transfer attribute. I wonder if heat gained during the day would not all be lost at night if used alone. I wonder, too, if there might be a glass, or combination of glasses and gases in windows, that exists that would allow the gain inside and deter the loss going the other way.
I think of short wavelength light as being higher energy-content than long wave-length light.
So I think of a photon as an energy-particle of light, and photons of ultra-violet light as being more energetic than photons of infra-red light.

I think of glass like a piece of net/cloth that can trap particles that are moving slowly, as cloth will trap pieces of leaf debris or mist/fog, but cannot trap particles that are moving quickly, such as leaf debris in a hurricane, or such as particles of rain going pitter-patter.

So then I see glass as being capable of stopping the passage of slow-moving photons of infra-red radiation but allowing particles of the faster-moving ultra-violet radiation to pass.

Ultra-violet rays arrive from the sun and pass through both the first and second layers of glass without a problem, and then these ultra-violet photons collide with a bed or a book or a body or whatever and lose some of their energy in the collision, and with the lessened energy (as say infra-red radiation) are not able to pass back through the glass.

The glass acts as a regular filter that allows high-frequency sunlight radiation to pass into the room, but inhibits low-frequency radiation to pass out of the room.

Now I suspect that Mr. Puzey would point out that there is a broad spectrum of energy levels in sunlight, and a broad probability of electromagnetic waves passing through glass, so that this is all a matter of probability: that my infra-red rays have less chance of getting out of the room than do the ultra-violet rays of getting into the room in the first place.

I rest my case on the example of the air-leaky 3'x2' window heating my room to 22c in winter time.
That is, an air-tight sealed pane of glass is the single most effective mechanism for passive heating of an enclosed space.
Cheers, Chris
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Re: Energy-efficient windows

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What about simple convection heat loss?

In Canberra in winter, which does get cold, but not as cold as in Bonavista, we received good sun during the day. But the windows were very cold to the touch, and at night, they were a major source of heat loss in the room. Windows and doors were very well sealed, with a gap under the door being covered to stop air loss in the one gap. Thick curtains helped stop the heat loss, but I suspect that double glazing would have stopped a great deal of that heat loss. I understand that double glazing can cut heat loss by up to 30%.

I suspect that your hot greenhouse would have become extremely cold after sundown. I wouldn't like your chances of a good night's sleep overnight after a sunny winter's day.

You're talking about allowing for the sun only, which is great, but then you have around 8.5 hours of sun only in mid-winter, and that's only on clear days. So you have to allow for all those non-sunlight hours.

I don't think that double glazing stops much of the sunlight warmth at all.

Being in a cold climate, I assume that houses have good insulation. I suspect that your place in WA would perhaps not have been as well insulated. Houses in Australia, built in a largely warm client, are built to be cool in the heat, and often ignore a colder winter - hence your small windows, and possible not quite adequate insulation - though sometimes they are insulated against heat.

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Re: Energy-efficient windows

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GeoffW wrote:
25 Apr 2022, 21:56
What about simple convection heat loss?
I reduced that by using 12 wood screws to tack a sheet of Masonite over the ceiling hatch to the attic, after gluing strips of toweling around the sheet to provide a cushioned air barrier! Apart from closing the door there is not a lot else that I can do about convection; the ceiling has about a foot of insulation atop.
In Canberra in winter, which does get cold, but not as cold as in Bonavista, we received good sun during the day. But the windows were very cold to the touch, and at night, they were a major source of heat loss in the room. Windows and doors were very well sealed, with a gap under the door being covered to stop air loss in the one gap. Thick curtains helped stop the heat loss, but I suspect that double glazing would have stopped a great deal of that heat loss. I understand that double glazing can cut heat loss by up to 30%.
I don't mind windows being cold to the touch; when body heat is at 37c and the outside temperature is at 0c or -20c, there will always be a frontier of temperature change somewhere. And we must not confuse "temperature" with "heat movement". Computer-rooms haad air-conditioning ducts which could be at a cool room temperature (to the touch) but channeled frigid air inside the ducts.
I suspect that your hot greenhouse would have become extremely cold after sundown. I wouldn't like your chances of a good night's sleep overnight after a sunny winter's day.
Not at all. I do have baseboard heaters in each room (now). I am not trying to live without heating; I am trying to reduce the feeling of cold air wafting across my face when I am lying in bed! My maximum average daily electricity use over the past 12 months was $17 (heat, water, cooking, ...) and the minimum was $1. I am looking to reduce the spread of the two figures by reducing the maximum average. It is true that in a 10-day power outage my home will quickly become almost unbearable, but a great deal of heat (in any house) exists as a reservoir of heat in the walls and furniture.
You're talking about allowing for the sun only, which is great, but then you have around 8.5 hours of sun only in mid-winter, and that's only on clear days. So you have to allow for all those non-sunlight hours.
True. But gather ye rosebuds while ye may. I think that maximizing my glass area (13,000 sq in to 52,000 sq in) makes the best use of solar energy; and by trapping, as always, I mean the conversion of short- to long-wavelength electro-magnetic radiation. Remember, those glass-houses (green-houses) work! If the night-time temperature plummeted, those tomato plants would die. How does a glass house stay above freezing? Can it be a reservoir of heat energy, or auxiliary heaters (the equivalent of my baseboard heaters)? If the latter, then glass walls and roofs help to reduce, not eliminate, fuel bills.
I don't think that double glazing stops much of the sunlight warmth at all.
Well, OK, but why do you think that? I think that glazing works because I can read 22c off the room thermometer. I think that Double-glazing uses the trapped air as a conductive heat barrier; Single glazing suffices for blocking loss through radiation (infra-red waves).
Now I think of it, WA and SA are settling in for total electricty needs through solar cells. Solar cells work in a similar manner: they allow sunlight in (through the glass), but then convert it to another electro-magnetic form and store it somewhere else (in a battery cell as an example).
Being in a cold climate, I assume that houses have good insulation. I suspect that your place in WA would perhaps not have been as well insulated. Houses in Australia, built in a largely warm client, are built to be cool in the heat, and often ignore a colder winter - hence your small windows, and possible not quite adequate insulation - though sometimes they are insulated against heat.
New houses have insulation. This house is from 1955, and while we suppose it has insulated walls, no-one has looked inside yet! Our house in Gawler, and rented houses in Newcastle, Wollongong, and Perth were indeed cold in winter. In Gawler we burned mallee roots in one of the five fireplaces and the interior chimney warmed two rooms! Mind you, that house had 15" limestone walls.
The mining-house in SX had walls and roof of galvanized iron of course, and that meant that in winter-time the night-time temperature was close to the outside temperature.

{later)
... and then I waded through the local news:-
Bonavista Peninsula Farmer Concerned with Lack of Local Food Production
Note the harvested date on the label on the plastic container; 2022-Jan-10.
Then check the outdoors temperatures surrounding that date.
Assuming the operation is a commercial success, the data suggests that glass houses (either 98% glass; or 50% glass as in my case) are worth pursuing.
Cheers, Chris
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Re: Energy-efficient windows

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ChrisGreaves wrote:
25 Apr 2022, 18:21
I think of glass like a piece of net/cloth that can trap particles that are moving slowly, as cloth will trap pieces of leaf debris or mist/fog, but cannot trap particles that are moving quickly, such as leaf debris in a hurricane, or such as particles of rain going pitter-patter.
Don't, that's a bad analogy.
ChrisGreaves wrote:
25 Apr 2022, 18:21
So then I see glass as being capable of stopping the passage of slow-moving photons of infra-red radiation but allowing particles of the faster-moving ultra-violet radiation to pass.
That's not how glass works. Glass transmits infrared but absorbs ultraviolet. Which is why it gets hot in a green house and why you don't get a sun tan through glass.
ChrisGreaves wrote:
25 Apr 2022, 18:21
The glass acts as a regular filter that allows high-frequency sunlight radiation to pass into the room, but inhibits low-frequency radiation to pass out of the room.
No. Glass blocks high freq = UV light but allows low freq = IR to pass which is why:
ChrisGreaves wrote:
25 Apr 2022, 18:21
glass is the single most effective mechanism for passive heating of an enclosed space.
and why a single sheet of glass is rubbish at preventing the same enclosed space from cooling down once the sun is no longer shining on it.
Double, or triple, glazing introduces a static layer of air, which is a poor conductor of heat, as an layer of insulation thus slowing the rate of heat loss from the heated enclosed space to the outside.

Ken
Last edited by stuck on 26 Apr 2022, 17:35, edited 2 times in total.

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Re: Energy-efficient windows

Post by BobH »

Bravo, Ken! That is an excellent presentation. One thing I would add is that window frames also transmit or, rather, absorb and hold heat differently which is why wood windows are better than metal or plastic as they have a lower coefficient of heat transmission, I think.

Please correct me if I'm wrong. It has been a lifetime since I sold windows in the '60s.
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Re: Energy-efficient windows

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You're correct, Bob. If you've ever lived (as I have) in a house with metal window frames in a climate with cold winters, you'll know that such frames get immensely cold on the inside of the house.
Best wishes,
Hans

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Re: Energy-efficient windows

Post by HansV »

A relatively new development is vacuum glazing, i.e double glazing with a near vacuum between the layers of glass. It's expensive, but it has excellent insulation properties.
Best wishes,
Hans

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Re: Energy-efficient windows

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Further reading for you Chris, plucked more or less at random from a Google search on 'conduction convection radiation'
1) https://spark.iop.org/conduction-convec ... -radiation
2) https://www.animatedscience.co.uk/ks3-e ... -radiation

and from a search on 'heat loss from homes'
1) https://www.homebuilding.co.uk/advice/h ... in-a-house
2) https://www.buildwithrise.com/stories/home-heat-loss

In summary, if I lived where you live then I'd want a house where:
First: the walls are well insulated
Second: the walls are well insulated (no that's not a typo, it's emphasis)
Third: The loft is well insulated
Fourth: see 'Third'
Fifth: No outside door opens directly to the outside, there would have to be an enclosed porch between it and the big bad cold world, so that you can close the door from the house before you open the one to the outside and vice versa when entering the house.
Sixth: the windows are triple glazed windows and are completely draft proof
Seventh: there are thick curtains that can be drawn over the windows as soon as the sunsets

I could go on but I refer you the search on heat loss from homes I mentioned earlier.

Lastly, and forgive me if I've missed the point of this thread, but cutting holes in your (presumably) well insulated walls to let more light in is one thing but expecting that by so doing you will make your house warmer doesn't make any scientific sense to me. I'd expect more glass, even if it is triple glazed, to make your house colder.

Ken

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Re: Energy-efficient windows

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stuck wrote:
26 Apr 2022, 16:29
That's not how glass works. Glass transmits infrared but absorbs ultraviolet. Which is why it gets hot in a green house and why you don't get a sun tan through glass.
Thanks Ken for correcting my views. Since I can not fire my Physics teacher Mr. Puzey, I shall have to fire my own brain :stupidme: (grin)

I had the transmission/absorption back to front.
So how does this sound: UV light is absorbed by glass and the glass becomes warmer, and the glass then radiates IR to the room (heating the air and then the walls and fittings)?
and why a single sheet of glass is rubbish at preventing the same enclosed space from cooling down once the sun is no longer shining on it.
Double, or triple, glazing introduces a static layer of air, which is a poor conductor of heat, as an layer of insulation thus slowing the rate of heat loss from the heated enclosed space to the outside.
But then, but then ... incoming UV heats the outside sheet of glass which heats the trapped air which radiates onto both sheets of glass, the interior sheet being unable to transmit the IR to inside the room?

Double-glazing seems not to be effective at heating a room at all, as much as preventing room-heat escaping to the outside air.

That leaves me with three puzzles:-
(1) Glass houses (green houses as in Holland Tulips) must be using solar radiation to boost heat during the day, and using that trapped heat to offset fuel costs.
(2) Plants in glass houses are more tolerant of a range of temperatures greater than the range preferred by humans
(3) Why in mid-winter is my room shooting up to 20 or 22c on a sunny day?

My goal remains to replace the draughty sliding panes with air-tight casement windows, so the project goes ahead!

Thanks
Chris
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Re: Energy-efficient windows

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BobH wrote:
26 Apr 2022, 16:54
... which is why wood windows are better than metal or plastic as they have a lower coefficient of heat transmission, I think.
I agree with the thinking, but will stay with plastic frames. Throughout winter the high winds "sand-blast" painted wood with particles of icy rain (freezing rain), and fence posts and palings, as an example, soon degrade from a brilliant white to a grayish-white.
It is one thing to hire Tom Sawyer to repaint a fence; another to locate, let alone pay, a local contractor to repaint windows without painting spots on the glass.

FWIW The high winds here, from any angle, act like a pump to force cold air through the house; Since my first night here I have been aware of cold air being blown over my face, and have tried various solutions such as translucent plastic sheets to put a third barrier to air movement; tubes of transparent caulking (which has to be peeled off in the spring).

Cheers, Chris
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