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Thanks Bob, this isn't an argument. We use very different
definitions of the meaning of several words. In my little world, the
physics says air flows due to air pressure difference, but heat
'flows' to a different drummer, and that can be experienced
empirically. Sounds like life would be easier in your world. <br>
<br>
<blockquote cite="mid:508DEFCF.7090502@dnaco.net" type="cite">
Peter,<br>
<br>
I don't intend to start an argument but have to rise in defense of
my comments.<br>
There are three driving forces involved in leakage across the
window, or any other building surface, 1) air pressure, 2) thermal
pressure and 3) vapor pressure. All flows are created by a
differential in one or more of these. Both heat and moisture
ride on air movement. <br>
I rarely see simple explanations, or fixes, to this sort of
problem but physics rules all of them.<br>
<br>
Bob Klahn<br>
<div class="moz-cite-prefix">On 10/28/2012 10:37 PM, Peter Kidd
wrote:<br>
</div>
<blockquote cite="mid:508DEC01.6090108@shaw.ca" type="cite">
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<div class="moz-cite-prefix">Air flow through the window is not
the same as heat flow and in NO way will it always be in to
out, hot to cold. Within one window assembly air may even flow
in two directions, typically in such a case, in at the bottom
and out at the top. Your simple case is incomplete, but in any
case pressures do drive air flow, but not temperature
difference (although pressures can be established because of
temperature but that is not at all the same thing).<br>
<br>
I'd quibble with some other points you raise, but I can't pass
on the above.<br>
<br>
</div>
<blockquote cite="mid:508DD521.8060007@dnaco.net" type="cite">
Two points, in response to two of your posts (bearing in mind
that I am speaking on the assumption of a cold climate). <br>
<br>
In a cold winter, without extreme exterior humidity and wind -
in coastal Alaska, for example - the flow through any leaks in
the window assembly will be from warmer to colder. The
greater the temperature differential, the greater the pressure
driving the leakage. So, "cold' air should not be leaking
into the space between panes because the air between panes
will be somewhere between the interior air temp, at the inside
pane, and the air temperature against the outside face of the
outer pane. Therefore, the air/heat flow will be from inside
to out.<br>
<br>
Of course, that is the simple model. Solar loading and wind
will have their effects. Of course, the ideal is to have all
seams/joints in a window unit hermetically sealed, but that's
a hard thing to achieve and sustain over time. <br>
<br>
Adding appropriately sealed layers to the window units will
change the temperature of the air film under whatever
conditions are producing condensation, but any window can
condense, given the "perfect storm" of conditions. Look to
the RH/temperature/lifestyle conundrum for each "problem"
window.<br>
<br>
The solution is to determine the RH/temperature combination
that allows the problem, then locate the moisture source(s)
and change them or the actions/assumptions which are causing
the elevated RH.<br>
<br>
As Mr. Holladay points out, there are several ways to
calculate a given window's condensation likelihood ranges.
Unfortunately, these have to assume a standard set of
conditions, which may not match those at you home, for any
give window or any given time. For all of the complex factors
involved, whether or not you will have a condensation problem
on any given window finally comes down to the surface
temperature of the window (which as he points out varies for
different areas of the window) and the dewpoint of the film of
air actually in contact with that window surface.<br>
<br>
Recommendations and RH guideline for house temperatures are
useful as starting points but, if you have a condensation
problem, the two approaches are either to experiment or to
have an accurate RH gauge to measure the room air near the
window at any given time and to get an accurate measurement of
the window's surface temperature. You will need some form of
psychrometric chart to look up the dewpoint for that
temperature and RH. Someone will need to chart those factors
over the time the problem occurs, then go looking for the
excess moisture source(s).<br>
<br>
The chart can take a bit of practice to understand but there
are "slide rule' forms of the psychromatic chart, to more
easily find dewpoint. Bachrach makes a sling psychromometer
which has a slide rule built into the case, but it can be a
pain to use. Electronic psychrometers give dewpoint as an
automatic function, but are significantly more expensive.<br>
<br>
Reading the air film temperature or RH is difficult to
measure; better to use the room air near it and add a
cushion. Trial and error should show you a workable
adjustment factor.<br>
<br>
Reading the window surface temperature can also be tricky. I
have the best luck with a quick response contact thermometer.
Remember the edge of the glass at the frame is the most likely
spot for condensation to start. (IR thermometers do not read
accurately on glass, unless they can be adjusted for the
reflectivity, only possible on some expensive models. You
could use a "black body" target to get around the
reflectivity, but that is probably beyond what you need to get
into. <br>
<br>
I hope this is helpful.<br>
Bob Klahn<br>
<div class="moz-cite-prefix">On 10/28/2012 6:30 PM, Sacie
Lambertson wrote:<br>
</div>
<blockquote
cite="mid:CAM6L0t4GLPeOyYVJuDWCCvG9w9CS8LKAob67om8X4_x7ZdUjFQ@mail.gmail.com"
type="cite"><font><font face="verdana,sans-serif">thanks <font>for
the suggestion Cor<font>wyn but we have about 50
windows in this house, all of them 9 year old Pellas
(the only manufacturer who would make my custom
sized windows <font>within my time frame--a long
story here)</font>. I can't possibly imagine
building storms for the inside of these.<br>
<br>
<font>Our indoor humidity is within the <font>suggested
range.</font></font><br>
<br>
<font>S</font><br>
</font></font></font></font><br>
<div class="gmail_quote">On Sun, Oct 28, 2012 at 5:24 PM,
Corwyn <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:corwyn@midcoast.com" target="_blank">corwyn@midcoast.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On 10/28/2012 1:20 PM, Sacie Lambertson
wrote:<br>
Our windows are starting to condensate at the base on
the<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
inside. Many of you have suggested this is the
penalty of winter.<br>
Isn't there anything I can do about it?<br>
</blockquote>
<br>
</div>
See my previous suggestion for interior storm windows.<br>
<br>
Here's the basics of when you will get condensation.
When the dewpoint temperature of the inside air is a
the same as (or greater than) the temperature of the
inside surface of the windows (or anything else in your
house), that surface will condense water. So in order
to avoid condensation you need to either lower the
dewpoint of the air inside, by reducing the humidity, or
increase the temperature of the inside surface of the
windows.<br>
<br>
Whether the humidity is too high is a matter of
perspective and some controversy. Get a humidity gauge
and measure what yours is. Generally somewhere in the
40% - 60% range is recommended, but balance is between
being too dry (and the dry throat and colds that that
produces) and being too wet and the mold and mildew (and
the allergies that aggravates), so decide for yourself.
That said, lowering the humidity will reduce the
condensation (and vice versa). One of the things we
generally see is that as people increase the air
tightness of their house they need to go from worrying
about too low humidity to worrying about too high
humidity. At that point, you are probably in the place
where you will need to have supplemental ventilation
(for fresh air reasons), and an HRV will take care of
the humidity issue.<br>
<br>
The other way is to raise the temperature of the glass.
Traditionally this was done by putting the central
heating output right under the windows so that hot air
washed over the surface warming it up. Now, the
solution is generally to increase the insulation value
of the windows. The interior storm windows are a cheap
way to do this, adding about R-2 to a window for about
$1.50 per square foot (if you make them yourself), I
make them for around $4.00 per square foot. Raising the
temperature of the glass will also increase comfort
levels (even at the same air temperature.<br>
<br>
Thank You Kindly,<br>
<br>
Corwyn<span class="HOEnZb"><font color="#888888"><br>
<br>
<br>
-- <br>
Topher Belknap<br>
Green Fret Consulting<br>
Kermit didn't know the half of it...<br>
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<a moz-do-not-send="true"
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value="+12078827652" target="_blank">(207)
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