Because warm air can hold more moisture, relative humidity changes with temperature even when the amount of water stays the same: cool air without adding or removing water and RH rises. Comfort and building durability favor roughly 30 to 60 percent indoors. For load work and diagnosis, techs prefer dew point or humidity ratio, which don't move with temperature.
Relative humidity reads 65 percent in the classroom, but it's only 70 in there, so the dew point's about 58, not terrible.
Also heard as
- RH
Related terms
Dew point
The temperature at which air becomes saturated and water starts condensing out when it is cooled.
Humidity ratio
The weight of water vapor per weight of dry air, usually given in grains per pound.
Psychrometrics
The science of air and the water vapor mixed into it, used to design and diagnose heating, cooling and humidity control.
SHR
Sensible heat ratio: the share of a cooling load or coil capacity that is sensible rather than latent.