Relative Humidity means relative to saturation at that temperature. At saturation, when the air has "absorbed" as much water vapor as it can hold, condensation takes place, which may happen as dew. At 100% RH, anything slightly lower in temperature will "sweat," meaning water from the air will condense on it. When you lower the temperature, the air can't hold as much water vapor, so the RH goes up, even without adding any moisture. And vice versa when you raise temperature. Another way of looking at it is "dew point." This has to do with what temperature will cause condensation for the water vapor content of the air. It can be measured by taking polished stainless steel and lowering its temperature. At the point when it fogs up, that is the dew point. Or you can get an idea by putting a glass of ice water out and seeing how much and how fast it "sweats." If it doesn't sweat at all, your dew point is below freezing, and your RH is probably pretty low (how low depends how warm or cold the temperature is). Does that help? Regards, Fred Sturm University of New Mexico fssturm at unm.edu On Dec 9, 2008, at 10:30 AM, Jim Busby wrote: > List, > > The recent post on relative humidity has me wondering what RH really > means. Don Ms funny post about “death” with humidity being too low > shows that many (myself included) don’t understand RH. > > For instance, when I heard that the RH was 100% in Louisiana I > figured the whole state was under water. > > And, obviously life can be sustained when RH registers at near zero, > as is does occasionally in our music building. (Interestingly the > static electricity in such low humidity makes it essential that you > “discharge” the charge in your body before touching an ETD, or > before pumping gas, as multiple fires at gas stations have shown.) > > Any scientifically minded tech out there care to enlighten me? > > Thanks. > Jim Busby -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut_ptg.org/attachments/20081209/6717e20e/attachment.html>
This PTG archive page provided courtesy of Moy Piano Service, LLC