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jolt wrote:

At 70 degree indoor temp. at 30% RH the window temperature would have to
reach 28 degrees or less for the moisture in the air to reach dew point.

No. Tdp = (70+460)/(1-(460+70)ln(0.3)/9621)-460 = 37 F...

20 TI=70'indoor temp (F)
30 TA=35'outdoor temp (F)
40 RIF=.67'R-value of indoor air film
50 FOR RV=1 TO 4'window R-value (ft^2-F-h/Btu)
60 TG=TI-RIF*(TI-TA)/RV'glazing and dew point temp (F)
70 RH=100*EXP(9621/(TI+460)-9621/(TG+460))
80 PRINT RV,TG,RH
90 NEXT RV

Window glazing Max Relative
R-value temp (F) Humidity (%)

1 46.55 43.15557
2 58.275 66.32038
3 62.18334 76.20583
4 64.1375 81.62463

Nick


Your right I should use my reading glasses when I use a Psychometric Chart.
At 37 degrees the glass temperature reaching dew point is more likely. Dry
bulb wet bulb temps with my background were use to calculate superheat or
subcool.