Two governing laws which are important in understanding the relationshipships between psychrometric properties are Dalton's Law and the Ideal Gas Law . The most commonly used terms to describe air-water vapor properties are temperature and humidity. The moisture content in air is often described by relative humidity . Other terms that relate to moisture content are humidity ratio , degree of saturation , vapor pressure and wet-bulb depression . The heat energy content or enthalpy of air includes sensible and latent heat.
Specific heat relates the change in temperature and the change in heat energy content.
A final air property that is important in the study of environmental control is specific volume . The relationships of these properties may be described by equations or depicted by a psychrometric chart. Changes in air-water vapor properties are brought about by psychrometric processes. Frequently these individual processes do not occur alone, but rather in combination. Livestock in a confined space add heat and moisture or cause the combined heating and humidifying processes.