Mission-Critical Cooling Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A 
Air-cooled system A type of air conditioning system that uses freon as a refrigerant and air as a condensing medium. Typically, the air-cooled condenser is located outside and refrigerant lines are piped to it from the indoor unit.
ASHRAE Standard 52.2-199 Method of testing general ventilation air cleaning devices for removal efficiency by particle size.
ASHRAE Standard 90.1-2001 Energy standard for buildings except low-rise residential buildings.
ASHRAE Standard 127-2001 Method of testing for rating computer and data processing romm unitary air condtioners.
Auto-changeover A control package that provides for automatic switching from a primary air conditioning system to a backup in the event of a failure of the primary system.
B
BTU/hr The abbreviation for British thermal units per hour. The amount of heat required to raise one pound of water one degree fahrenheit per hour, a common measure of heat transfer rate.
C
CFM The abbreviation for cubic feet per minute, commonly used to measure the rate of air flow in an air conditioning system.
Chilled water system A type of air conditioning system that has no refrigerant in the unit itself. The refrigerant is contained in a chiller, which is located remotely. The chiller cools water, which is piped to the air conditioner to cool the space.
Comfort air conditioning Comfort air conditioning systems are designed for the comfort of people, not the protection of computer-based electrical systems. Unlike people, computers generate dry (sensible) heat, but not humidity. Only about 60-70% of a comfort system's total capacity is dedicated to the removal of sensible heat, while 30-40% is for dehumidification. With a large percentage of their total capacity devoted to the removal of moisture, comfort systems can lower room humidity far below acceptable standards. A larger comfort system is required to obtain the same sensible capacity as a precision cooling system.
D
Dehumidification The process of removing moisture from the air within a space.
Direct expansion systems One of two types of basic cooling media (the other is chilled water). Direct expansion systems utilize freon for cooling and dehumidification. The three most common methods of heat rejection are air cooled, water cooled and glycol cooled.
Downflow Refers to a type of precision air conditioning system that discharges air downward, directly beneath a raised floor, commonly found in computer rooms and modern office spaces.
E
F
Free Cooling System Typically a water cooled or glycol cooled system with an additional coil that provides chilled water cooling when the outdoor ambient is cold thereby reducing or eliminating compressor operation. Provides efficient system operation in Nothern climates.
Freon A general term used to identify, any of a group of partially or completely halogenated simple hydrocarbons containing fluorine, chlorine or bromine, which are used as refrigerants.
G
Glycol-cooled system A type of air conditioning system that uses freon as a refrigerant and a water/glycol solution as a condensing medium. Typically, the glycol-cooled condenser is located inside the air conditioner with the rest of the refrigeration components. Water/glycol is piped to the unit from a drycooler or other suitable source. The glycol keeps the solution from freezing during winter operation.
H
Humidification The process of adding moisture to the air within a space.
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L
Latent cooling capacity An A/C system's capability to remove moisture from the air.
M
Microprocessor controls A control system that uses computer logic to operate and monitor an air conditioning system. Microprocessor controls are commonly used on modern precision air conditioning systems to maintain precise control of temperature and humidity and to monitor the units operation.
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P
Precision air conditioning Precision A/C systems are primarily designed for cooling electronic equipment, rather than people. These pre-packaged systems offer excellent reliability and typically have a high ratio of sensible-to-total cooling capacity and a high CFM/ton ratio.
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S
Sensible cooling capacity An A/C system's capability to remove heat from the air. (lower the temperature)
T
Tonnage The unit of measure used in air conditioning to describe the cooling capacity of a system. One ton of cooling is based on the amount of heat needed to melt one ton (2000 lbs.) of ice in a 24 hour period. One ton of cooling is equal to 12,000 Btu/hr.
U
Upflow A type of air conditioning system that discharges air into the conditioned space via a top-mounted discharge plenum or through an overhead duct system.
V
Vapor seal A vapor seal is an essential part of preventing moisture infiltration into or migration out of a critical space, such as a data processing center or other room that contains sensitive electronic instrumentation. Essentially, a vapor seal is a barrier that prevents air, moisture, and contaminants from migrating through tiny cracks or pores in the walls, floor, and ceiling into the critical space. Vapor barriers may be created using plastic film, vapor-retardant paint, vinyl wall coverings and vinyl floor systems, in combination with careful sealing of all openings (doors and windows) into the room.
W
Water cooled system A type of air conditioning system that uses freon as a refrigerant and water as a condensing medium. Typically, the water-cooled condenser is located inside the air conditioner with the rest of the refrigeration components. Water is piped to the unit from a cooling tower or other suitable source.
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