[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

GBlist: Re: windows in FLA

Beverly A. Weiter WROTE:
>Here in S. Florida were are "tropical" : no cold or even
>much cool - mostly just hot and hotter and very humid.
>I am getting conflicting info from local contractors - double vs. single,
>argon filled vs reflective coating vs.
>.....  The main problem seems to be condensation in double paned windows
>resulting from the extreme heat vs the excessive use of air conditioning
>and the extreme humidity.  I have a client who needs to change windows and
I need a fast answer.  Please note that the house is sited N/S but there is an
>added problem with a child who is severely asthmatic and sensitive to dust.

Carmody, Selkowitz and Heschong's book IS a great source.  On some of the
other acvice that Alex gave, I'm afraid I have to disagree {no offence Alex).
If the problem that you are trying to avoid is condensation IN the windows,
then what you need is a high quality dual glazed system.  Neither argon,
low-e coatings nor any other "add-on" will prevent condensation within the
insulated galss unit.  That is done by using quality spacer material and
installing it correctly in the factory.
As far as energy efficieny from windows in the So Fla environment, if the
windows are not adequately shaded by building elements (overhangs, awnings,
etc.) then you should go for glazing that has a low solar heat gain
coefficient (SHGC).  Achieving a low SHGC is not strictly the purpose of
low-e coatings.  The low emissivity slows down heat LOSSES.  Most of the
heat gain due to windows is not from conduction, but from direct solar
radiation.  Some low-e coatings also provide a low SHGC, but now all.  Two
glazings, both with a low-e coatings whose emissivity is ~0.20, can have
SHGCs of 0.40 and 0.84.  The latter would be best for the great frozen North
(maximizing solar gains) and the former would be best for your climate
(assuming that you want a low-e coating).
There are other ways to achieve the energy efficiency benefits of a reduced
cooling load.  You should consider some of them: shade screens, awnings,
deciduous trees, etc.  I realize that not all of these would be appropriate
for the client right now.  I also realize that the windows need replacing so
which winodw is the right one is really the question.  However, consider
that once you install a window with a very low SHGC, you cannot take
advantage of the winter heating of the sun.  If the house has a N/S
orientation, this is a potential that it might be a shame to waste.  For
cooling purposes, I recommend glazings like Low-e squared for east and west
facing windows.  I recommend a high SHGC glass for the south windows and
some means of taking advantage of the changing sun angle from winter to
BTW, for cooling, argon gives you NOTHING.  It is a waste of your money to
pay for it.  With all but one technology that I know of, it is highly likely
that most of it would escape within a few years anyway.

Nehmiah Stone
California Energy Commission

p.s.  You have a GREEEAT source os information on this topic in your
backyard.  You might want to give Florida Solar Energy Center a call;
specifically Ross McCluney.

This greenbuilding dialogue is sponsored by CREST <www.crest.org>
Environmental Building News <www.ebuild.com> and Oikos <www.oikos.com>
For  instructions send  e-mail to  greenbuilding-request@crest.org.