Re: [GBlist] Low E glass

["L84Work" <m.tymoshuk@rogers.com>]

  From "Tap the Sun Passive Solar Techniques and Home Designs"  p.8."Windows
with the right low-e coathing are an excellent choise for solar passice
homes because the relative small drop in solar heat gain is more than offset
by the reduction of heat losses through long-wave transmission."

  For example, window #2 could have Low-e #3 instead of #2 and the SHGC
should be around .60 allowing the window to let more heat in while
preforming very well in all other aspects.

Matt


From: "Renewable News Network" <rnn@rnn.com>
To: "Richard Averett" <averettr@norwich.net>
Cc: <greenbuilding@crest.org>
Sent: Tuesday, January 01, 2002 3:58 PM
Subject: Re: [GBlist] Low E glass


> Hi Maureen/Richard,
>
> Corwyn's formulations are causing me some consternation. I did a
> google search and could not come up with a clear and straightforward
> definition of "solar heat gain coefficient" that could explain the low
> numbers (.30-.60).  I thought a double glazed lite allowed about 85
> percent transmission of sunlight normal to the surface.  If so, then the
> low SHGC must represent an averaging of the times of reduced gain due to
> increased angles of incidence (tilt and orientation.)  And if that's the
> case, then one wants to know the ranges for those variables.
>
> Most of the research on windows appears to deal with the space cooling
> issues in the more tropical climates.  Tinted glass and spectral coatings
> may offer benefits, but not so much in the North, I would guess.  If one
> needs to block the light, curtains work, and such extras only add costs
> for features that only reduce your Winter time performance, but that's
> neither here nor there.
>
> The analysis, also, appears confounded by the U-values of the window,
> which involves the peformance of the whole window, including what (?)
> other factors (?) -- when the point of the original question was, I
> think, about the impact of low-e coatings on solar gain.
>
> I get easily confused.  These matters can quickly evolve from a mix of
> apples and oranges to bananas and grapes in a veritable fruit salad of
> cause and effect confusion.  And then there's all the design issues --
> reflection, wind loading, space use, movable insulation, etc.
>
> I don't know that one can attribute a greater comfort to low-e alone,
> when a replacement window, with improved infiltration, and what all, can
> make for an improved overall situation.
>
> As a rule, its wise to use standard products.  And, in the North, as I
> understand things, low-e insulated lites are pretty much the thing to
> do -- warmer windows, less heat loss, little reduced solar gain, and no
> appreciable visual impact.  If you're installing fixed glass, you can
> more easily specify low iron glass, also, to maximize the solar gain.
>
> Have a merry happy, everybody!
>
> Yours truly,
> Ross@rnn.com
>
> On Mon, 31 Dec 2001, Richard Averett wrote:
>
> > We are building a house in Upstate New York,(42 North latitude).
> Does anyone have an opinion on whether Low-E glass on the South side
> will interfer with solar gain in the winter?  Thanks.
> >
> > Happy New Year!
> > Maureen
> >
>
> Date: Tue, 1 Jan 2002 11:45:34 -0500
> From: Corwyn <corwyn@m...>
> To: Richard Averett <averettr@n...>
> Cc: greenbuilding@c...
> Subject: Re: [GBlist] Low E glass
>
> On Monday, December 31, 2001, at 10:58 AM, Richard Averett wrote:
>
> I am struggling with the same question myself, and though I don't have
> many answers, I do have some thoughts (And in addition I am sure my
> thoughts (if wrong) will be quickly corrected (no way easier to get
> good information than to post bad)).
>
> Anyway, the simple answer is yes, it will interfere.  The question then
> becomes, is it still worth it?  The two attributes of windows that are
> relevant are U-value and SHGC (solar heat gain coefficient).  You can
> find these out for some windows by looking in <http://www.nfrc.org/>
>
> One tells you how much heat you lose, and the other how much you gain.
>
> I think the simplified equations are as follows
>
> Heat Loss (in BTU/Day) = U-value (whole unit not center of glass) *
> square feet of glass * temperature difference (in degrees F) * 24
> hours/day.
>
> Heat Gain (in BTU/Day) = SHGC * square feet of glass * Available Solar
> Energy * % sunshine.
>
> temperature difference = inside design temperature (probably 68-72) -
> the outside temperature (you might want to use average daily
> temperature for the coldest month)
>
> available solar energy  can be found using the PEC solar calculator for
> your latitude, orientation (degrees off true south)
> <http://arch.ced.berkeley.edu/vitalsigns/res/res_online.html>
>
> To take my situation on an average day in February for two (random)
> windows
>
> 1) Double Pane, No low-e, Air filled:  U-Value = .48, SHGC = 0.60
> 2) Double Pane Low-e #2, Argon filled: U-Value = ..31, SHGC = 0.34
>
> My house will face 7 degrees east of True South (10 W of Magnetic South).
> At my latitude a (almost) south vertical window receives 1842 BTU/ft^2
> on a sunny day.
>
> The average temperature in the nearest measured city (Portland ME) in
> February is 24.5 degrees F, the average % sunshine is 59%.
>
> Window 1 is therefore:
> Heat Loss = .48 * 10 * (68 - 24.5) * 24 = 5011.2
> Heat Gain = .60 * 10 * 1842 * 0.59 = 6520.68
> Difference = 1509.48
>
> Window 2 is
> Heat Loss = .31 * 10 * (68 - 24.5) * 24 = 3236.4
> Heat Gain = .34 * 10 * 842 * 0.59 = 3695.052
> Difference = 458.652
>
> So, in this example. the (probably cheaper) non low-e, air filled
> windows are better (all else being equal) than the argon filled low-e
> windows (on the south side).  Note that this assumes that you are able
> to benefit from all the solar gain (if you have to open the window to
> cool the house off...)  Thermal mass will help with that.
>
> Hopefully this will either help, or prod some more knowledgeable into
> helping,
>
> Corwyn
>
>
>
> <RNN>
>
>
> ______________________________________________________________________
> This greenbuilding dialogue is sponsored by REPP/CREST, creator of
> Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
> Environmental Building News and GreenSpec http://www.BuildingGreen.com
> ______________________________________________________________________
>


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________