Replies

1. Expert Member
   BILL WICHERS | May 07, 2019 08:38pm | #1

   Yes, the chart can help determine that info. Looks like you’d be around 58% at 80 degrees.

   You would follow the curve for 61% over to 78 degrees (or follow 78 degrees straight to the curve for 61%). This gives you the moisture content of the air at that temperature and relative humidity (RH). Go straight on the other axis to the 80 degree line and read off the humidity from the RH curve that intersects that temperature at the moisture content you found earlier. You’ll most likely have to interpolate a bit since the curves aren’t normally given in 1% increments, it’s usually 50%, 60%, 70%, etc.

   The chart let’s you determine the absolute moisture content in the air at specific temperature and humidity points. Once you have that info, it’s easy to move around on the chart to find what the RH would be for a given moisture level at another temperature. It’s a very handy chart, and not difficult to use despite how confusing it first looks.

   Bill

2. 
   Jon_R | May 07, 2019 08:38pm | #2

   It's easier to use http://www.dpcalc.com

1. Expert Member
   BILL WICHERS | May 07, 2019 08:53pm | #3

   Yeah, but that's cheating :-)

   Bill

3. GBA Editor
   Martin Holladay | May 08, 2019 05:55am | #4

   Charles,
   If you want guidance on using the psychrometric chart to answer the type of question you just posed, see this article: "How to Use the Psychrometric Chart."

4. 
   Peter Yost | May 08, 2019 09:20am | #5

   I find it really handy to have this app on my iPhone: PsyCalc. Screenshot attached. Same app is available for android phones.

   Peter