weather math

Figment · Post by **Figment** » Thu Apr 20, 2006 10:31 am

I think I have a handle on this, but I've been sucking a lot of fumes lately, so someone back me up....

If the air is 55 degrees and 65% relative humidity, but I heat the inside of the shed to 75, then the relative humidity of that 75degree air should be LOWER, right?
Because the warmer air has the capability to hold more moisture, etc.

I'm trying to dredge up memories of 7th grade science class, but it's a slow dredge.

Post by **dasein668** » Thu Apr 20, 2006 10:35 am

Living up to your title once again!

I'm not sure the answer... it makes sense for the reasons you outline, but then again, the RH is usually much lower during winter, though that might just be due to other meteorological factors...

Post by **dasein668** » Thu Apr 20, 2006 10:44 am

Some australian website cited below wrote:Relative humidity (RH):

The ratio of the actual amount of water vapour in the air to the amount it could hold when saturated expressed as a percentage OR the ratio of the actual vapour pressure to the saturation vapour pressure expressed as a percentage.

The amount of water vapour the air can hold increases with temperature. [emphasis mine] Relative humidity therefore decreases with increasing temperature if the actual amount of water vapour stays the same.

Australian Government Bureau of Meteorology (Hey, it was the first hit, what can I say?)

jollyboat · Post by **jollyboat** » Thu Apr 20, 2006 12:01 pm

I thought Relative Humidity was the sweat behind my . . . never mind, I save that one for the 'anchor out'

bcooke · Post by **bcooke** » Thu Apr 20, 2006 5:35 pm

If the air is 55 degrees and 65% relative humidity, but I heat the inside of the shed to 75, then the relative humidity of that 75degree air should be LOWER, right?

The short answer for your fume damaged brain is:

YES

As the temperature rises and the amount of water in the air remains the same, the relative humidity (the ratio of the amount of water the air is capable of holding compared to what it is actually holding) will fall.

-Britton

Figment · Post by **Figment** » Fri Apr 21, 2006 7:55 am

Thanks guys. Just wanted to make sure that it wasn't going in the other direction.

Might be moot anyway. The primer wasn't sandable yesterday, which means I'm not laying topcoat today and through the somewhat-humid weekend.

Post by **Tim** » Fri Apr 21, 2006 12:58 pm

Just paint already! Some of us are anxiously awaiting this transformation.