(Definitions, Terminologies and Psychrometrics) Before we proceed further, let us familiarise ourselves with some of the often used terminologies and their definitions. Relative Humidity or RH Relative humidity is the actual amount of moisture in the air compared to the total or maximum moisture the air can hold at a given temperature. Dew Point Temperature Dewpoint temperature is the temperature at which moisture condenses on a surface.   Grains of Moisture Grains of moisture is the unit of measurement of the amount of moisture in the air. Dry Bulb Temperature - °C or °F The dry-bulb temperature is the temperature of the air as measured by an ordinary household thermometer. Wet Bulb Temperature - °C or °F The Wet-Bulb temperature is the temperature of the air as measured by an ordinary thermometer whose glass bulb is covered by a wet wick/cloth. Airflow around the wick causes the evaporation of moisture thus lowering the temperature and producing a reading lower then that on the dry bulb thermometer.

Desiccants
Can either be solid or liquid. A desiccant is a material that posses affinity for water vapor greater than that of air. Desiccants are of 2 types.

Absorbents
Absorbents are generally liquids or solids which become liquid as they absorb moisture, i.e. they undergo a physical or a chemical change as they collect moisture. Lithium Choride (LiCl) and Sodium Choride (NaCl) are typical examples of absorbents.

Adsorbents
Adsorbent do not under go any physical or chemical change when they come in contact with moisture. Water is adsorbed or held on the surface of the material and in the pores, Adsorbents are mostly solids. Typical examples of Adsorbents used for dehumidification are silica gel, molecular sieve and activation alumina.
The ideal desiccant would have an infinitely high surface area for collecting moisture, and an infinitely low mass, since the required heating and cooling energy is directly proportional to the mass of the desiccant and the mass of the machinery which presents the desiccant to the air-stream. The heavier the desiccant assembly compared to its capacity, the more energy it will take to change its temperature-which accomplishes dehumidification.