Dehumidification Glossary

 Dehumidifiers & Air Dryers

Actual vapor pressure — The partial pressure exerted by the water vapor present in a parcel. Water in a gaseous state (i.e. water vapor) exerts a pressure just like the atmospheric air. Vapor pressure is also measured in millibars.

Dehumidification — The process of removing moisture from the air or other materials.

Desiccant — A substance such as calcium oxide or silica gel that is used as drying agent.

Dew point — The temperature air must be cooled to in order for saturation to occur, producing water in the form of dew or condensation. The dew point temperature assumes there is no change in the air pressure or moisture content of the air.

Dry bulb temperature — The actual air temperature.

Evaporation — The change of liquid water into water vapor. Moisture evaporates due to differential vapor pressure—the larger the vapor pressure differential, the faster the drying.

Humidistat — An instrument that indicates or controls the relative humidity of the air.

Hygrometer — An instrument that measures atmospheric humidity.

Relative humidity — The ratio of the amount of water vapor in the air at a specific temperature to the maximum capacity of the air at that temperature. Relative humidity is expressed as a percentage and can be computed in a variety of ways. One way is to divide the actual vapor pressure by the saturation vapor pressure and then multiply by 100 to convert to a percent.

Saturation of air — The condition under which the amount of water vapor in the air is the maximum possible at the existing temperature and pressure. Condensation or sublimation will begin if the temperature falls or water vapor is added to the air.

Saturation vapor pressure — The maximum partial pressure that water vapor molecules would exert if the air were saturated with vapor at a given temperature. Saturation vapor pressure is directly proportional to the temperature.

Wet bulb temperature — The lowest temperature that can be obtained by evaporating water into the air at constant pressure. Wet bulb temperatures can be used along with the dry bulb temperature to calculate dew point or relative humidity.

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