RE: [GBlist] dual pane glass for 450 f?

[Renewable News Network <rnn@rnn.com>]

correction on "heat mirror"

I forgot those words have a specific brand/design connotation.

the idea was to compare the performances of window a and b by sense
impressions within the comfort ranges, but pushing that envelope at times
with unacceptably low temperatures and draftiness.

WINDOW A

I meant to use the term, heat mirror, more generically as a window unit
acting to relect heat back to the inside with a low-e coating, probably
tin oxide (?).  This is a 46 inch wide by 96 inch high (nom. 4' by 8' or
nom. 30 SF solar Aperature) -- afixed insulated lite, installed
vertically and facing South.  With one inch overall thickness and two
1/4" low iron pieces of glass (I specified 5/8' space and 3/16" glass,
got an argument, and can't recall the upshot.)

A 5/8" air space is the minimum ideal, with 1-3 inches at 42 N. Lat. and
5,600 DD/YR about the same.  Over 4 inches of air insulation is counter
productive and creates a passive heat engine designed to deliver space
heat from inside out in a most natural and effective way.

WINDOW B

The West facing side lite is a recycled sliding glass door unit -- normal
glass, 5/8" thick overall, no particular coatings -- so I'd expect a few
confounding factors there for the persnickety.  (...not the least of
which is the fact that the West window looks out on bushes and a tree
enclosed area, whereas, the South windows have an unobstructed view up to
the sky, making the radiative loss to the universe a cool factor.

-ross@rnn.com

ps. visually, as I said, I could perceive no apparent difference.

On Wed, 9 Jan 2002, Ralph Bicknese wrote:

> Corwyn, Ross and other listers:
>
> < My sunspace now has a new insulated lite with heat mirror, which is warmer
> than an older insulated lite without any coating. Visually there's no
> apparent difference.>
>
> The Heat Mirror glass should feel warmer because it is a better insulator.
> But, Heat Mirror or any window with low e coating will allow less light to
> pass through the glass than standard double “insulated” glass.  In fact with
> Heat Mirror not only does the low e coating cut down on the light
> transmission, so does the layer of suspended plastic film.  But there are
> virtues of Heat Mirror for passive solar heating too.  One is that low e
> cuts down on heat loss, so does the extra layer of plastic film. But the
> plastic film makes a Heat Mirror window insulate like a triple glazed window
> without the weight and thickness of an added layer of glass.  Heat Mirror
> film also transmits more light than glass.
>
> Visually one can see only a very slight darkening of the window with Heat
> Mirror or a non-tinted low e coating verses one without.  Unless they were
> side-by-side one would not know the difference based on appearance.
>
> And yes, absolute temperature does have an affect on how well a window (or
> almost any product) insulates or does not.  Many window unit manufacturers
> publish winter and summer U and R-values because they vary from winter to
> summer based on the ambient temperature.  The  R-values published are based
> on testing at specific temperatures, not absolute temperatures.  Sometimes
> this is explained in the fine print at the bottom of the rating charts. I do
> not know what the effect on insulating qualities would be at 300 or 400
> degrees F ambient. I have not heard of multi-pane glazing being used at
> those temperatures. I would be concerned about seal failure and stress
> fracture due to differential expansion between the dividers and other unit
> components at those temperatures.
>
> I do not know what use is being considered at those temperatures but the
> studies I saw on thermal solar collectors in the late 70’s and early 80’s
> did not show double glazing to be cost effective or practical.  Most people
> used low iron (ultra clear), high solar transmittance, single-light glass
> and designed to extract the heat from the panel quickly to minimize heat
> loss.  Incidentally these studies also showed collection could be enhanced
> significantly by using a low emissivity (low e) coating on the collector
> plate (as opposed to the glass).  Studies at Los Alamos Labs and other
> places showed low e coatings installed on collection areas on passive solar
> Trombe Walls also created significant performance gains. It was not long
> after that we started to see the first trials of low e coatings on windows.
>
> Cheers,
> Ralph Bicknese
> -----Original Message-----
> From: Corwyn [mailto:corwyn@midcoast.com]
> Sent: Wednesday, January 09, 2002 11:43 AM
> To: Renewable News Network
> Cc: Y & L; greenbuilding@crest.org
> Subject: Re: [GBlist] dual pane glass for 450 f?
>
> On Wednesday, January 9, 2002, at 09:09 AM, Renewable News Network wrote:
>
> Ross Wrote:
> Can you run side-by-side tests?
> . . .
> My sunspace now has a new insulated lite with heat mirror, which is warmer
> than an older insulated lite without any coating. Visually there's no
> apparent difference.
>
> Did you run a side-by-side test for the second. I ask this only because the
> human eye is notoriously bad at determining light levels (in fact, it does
> the opposite, and adjusts so that most light levels within a large range,
> when viewed independently, look alike (this is light meters are necessary in
> photography)).
>
> Concerning the original question, I don't know any reason that absolute
> temperature makes any difference in performance characteristics of windows.
> Anybody?
>
> Thank You Kindly,
>
> Corwyn
>
> <?fontfamily><?param Times New Roman><?bigger>--
> Corwyn
> corwyn@midcoast.com<?/bigger><?/fontfamily>
>


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