[Greenbuilding] Condensation on windows

[nick pine]

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