Air Conditioning
Authors: Cooper Kenneth W. 
Published: July 2004

Thermodynamic principles govern all air conditioning processes particularly, applications to equipment performance which influences the energy consumption of a system and to the properties of moist air which determine air conditioning capacity. The concentration of moist air defines a system's load. Definitions of laws of thermodynamics that apply best to air conditioning are theFirst Law, the law of conservation of energy, which states that the flow of energy into a system must equal the flow of energy out of the same system minus the energy that remains inside the system boundary, and theSecond Law, which defines the maximum theoretical performance for air conditioning equipment and provides a means of identifying energy losses in a system. It states that no heat engine operating in a closed cycle may produce work when communicating with a single temperature source. Air conditioning is the result of a heat engine operating in reverse. This means that work is added to the system and there must always be at least two temperatures, a low temperature source from which heat is received and a high temperature sink to which heat is rejected. Fundamental to the design of any air conditioning system is the determination of the operating conditions of temperature and humidity. Worker comfort must also be considered. Local areas of thermal discomfort, ie, one part of the body warmer or cooler than preferred, may cause a person to be uncomfortable when the overall temperature and humidity would normally produce a sensation of thermal comfort. Some causes of this are nonuniform thermal radiation, such as hot or cold windows, walls, panels, floors, and ceilings. In some instances of industrial inside‐design, the conditions have been compromised for the sake of worker comfort and do not represent the optimum for the product. In others, the conditions have no effect on the product or process other than to increase worker efficiency. Determining the proper size of air conditioning and heating equipment requires detailed study and calculation. A comprehensive statement of requirements and allowable variations must be supplied so that the best comfort conditioning system choice can be made. An analysis of the building structure must be conducted to determine the effects of heat gain from the sun. Air conditioning may involve heating or cooling air, humidifying or drying it, and the control of chemical impurities to maintain the desired space conditions. Two broad categories of air conditioning systems exist, unitary and applied. Unitary systems are self‐contained units that are “off the shelf.” They use electricity for cooling, and may use electricity, natural gas, fuel oil, or propane for heating. More flexibility is obtained with applied equipment, usually part of a “field erected” system, normally used to condition a relatively large area of a plant. Many industrial processes require accurate environmental control. Examples include chemical reactions and processes that are affected by atmospheric conditions; biochemical reactions; quality, uniformity, and standardization of certain products; odors and fumes; conditions in storage and packaging; quality of painted and lacquered finishes; and productivity and comfort of workers. Controlled atmospheric conditions are especially important to the textile, pharmaceutical, food processing, explosives, and photographic materials industries.