Humidity 101
6 videos • 248 views • by Condair USA/CA Humidity is defined as the amount of water vapor in air. Absolute humidity is a measurement of the actual water vapor in a given volume of air, usually expressed in grains of water per cubic foot or pound of air. Relative humidity is the amount of water vapor in a given volume of air compared to the amount of water vapor the same volume of air will hold at saturation (100% RH) at a given temperature. When a volume of air at a known % RH is heated, the % RH decreases as the volume of air increases. The absolute humidity or total moisture available in the air remains the same. In order to increase the % RH of the air once it has been heated, it will be necessary to add moisture. Example: One cubic foot of air at 0°F holds 0.48 grains of water at saturation. One cubic foot of air at 70°F holds 8.10 grains of water at saturation. When the 0°F air is heated to 70°F, the absolute humidity remains at 0.48 grains per cubic foot. The relative humidity of the 70°F air will be 6% RH, (0.48 grains divided by 8.10 grains) the amount of water in the 70°F air relative to the amount it can hold at saturation.