Definitions
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Dew point (wet bulb temp.): Temperature at which humidity in the air reaches 100% relative humidity and will condense from that air to form condensation or "dew."
Grains of Moisture : Term used to express the weight of moisture per pound of air (14 cubic feet). 7000 grains is the most that can be held in one pound of air. Since water weighs 8.34 pounds per US gallon and since there are 8 pints in one gallon, 7000 grains is equal to about 1 pint of water. Air cannot hold much moisture as far as poundage of water.
Psychrometric chart: Shows the relationship between air volume, temperature, and relative humidity and is used to calculate specific humidity (gpp), dew point (wet bulb temp.), and vapor pressure. Click Here to see an example.
Psychrometry: The study of the relationship between air, humidity, and temperature, and their effect on various materials and comfort levels.
Relative humidity: The relationship between air volume and the amount of moisture it holds at a specific temperature expressed as a percentage of that air's total moisture holding capacity. Amount of moisture in the air at a certain temperature.
Specific humidity (gpp): The weight of suspended moisture in air expressed in grains per pound. GPP is the term used to express the weight of moisture per pound of air (14 cubic feet). 7000 grains of moisture equal one pound.
Temperature (dry bulb temp.): Measured in degrees (°F) or degrees (°C).
Vapor pressure: The pressure exerted by a saturated vapor above its own liquid in a closed container. This is the pressure caused by water molecules in the air.
