[Greenbuilding] Condensation on windows
nick pine
nick at early.com
Mon Oct 29 14:32:16 CDT 2012
Corwyn <corwyn at midcoast.com> writes:
> The interior storm windows are a cheap way to do this, adding about R-2 to
> a window
With a single layer of glazing?
Bob klahn <Home-NRG at dnaco.net> writes:
>... 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.
Or use a $9 Casio fx-260 calculator. For example, 70 F air at 460+70 = 530 R
at 50% RH has a 530/(1-530ln(0.5)/9621) = 520.5 R (520.5-460 = 50.5 F
dewpoint.
Or stir a glass with some water and ice and measure the temperature when you
see condensation on the outside.
> (IR thermometers do not read accurately on glass, unless they can be
> adjusted for the reflectivity
They read close enough, even without adjusting for a 0.88 vs 0.95
emissivity.
> There are three driving forces involved in leakage across the window... 1)
> air pressure, 2) thermal pressure and 3) vapor pressure.
What's "thermal pressure" ???
Nick
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