Terminology and Links

Terminology and Links

Here Carrier has summarised the most frequently used terminology to help the customer and supplied information on energy efficiency issues with guidance and dates on pending or already implemented legislation and regulations that affect the air conditioning industry.

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


In an absorption cycle, the vessel in which a lithium bromide solution absorbs low-pressure refrigerant water vapour produced in the evaporator.

Absorption Cycle

Absorption chillers differ from mechanical vapour compression chillers in that they utilize a thermal or chemical process to produce the refrigeration effect necessary to provide chilled water. There is no mechanical compression of the refrigerant taking place within the machine as occurs within more traditional vapour compression type chillers. Most commercial absorption chillers utilize lithium bromide (a salt) and water as the fluid pair; lithium bromide being the absorbent, water being the refrigerant. In order to produce the refrigeration effect necessary to make, for example, 44F chilled water, the shellside of the machine must be maintained in a deep vacuum to allow the refrigerant (water) to boil at approximately 40F. The lithium bromide solution absorbs the vaporized refrigerant, diluting it before it is pumped to the generator section of the machine where heat is added to reconcentrate the dilute solution. The water vapour boiled off in the generator is then condensed, returning to the evaporator as liquid. The reconcentrated lithium bromide returns to the absorber section as strong solution to begin the cycle again.


The metering (flow control) device inside a Carrier centrifugal chiller. Its unique design always feeds the cooler with liquid refrigerant, which has a much greater cooling capability than a gaseous refrigerant. Carrier patented design.


Allowable Exposure Limit.


Anti-Friction Bearing Manufacturers Association.


Annual Fuel Utilization Efficiency. The annualized average efficiency of a fuel-fired appliance, taking into account the effect of on-off operation. The higher the AFUE the lower the operating costs for the end user.

back to top


American Gas Cooling Centre.

Air Conditioning

The treatment of air temperature, humidity, cleanliness and circulation so as to achieve a controlled, desired result.


American National Standards Institute.


Air Conditioning and Refrigeration Institute.

ARI 550

Air Conditioning and Refrigeration Institute Standard 550-1992: Standard for Centrifugal and rotary screw water-chilling packages. The purpose of the standard is to establish , for centrifugal chillers and rotary screw water-chilling packages: definitions and nomenclature; a description of what constitutes such a package; published rating conditions; standard requirements for testing and a basis for published ratings; and proper refrigerant designations in systems.


American Society of Heating Refrigeration and Air Conditioning Engineers,

back to top


American Society of Mechanical Engineers.

ASME Construction

Strict design, manufacture, and testing standards set forth by the American Society of Mechanical Engineers. It involves independent inspection of every chiller built.

Atmospheric Pressure

The pressure exerted on all things on the Earth's surface that are a result of the weight of our atmosphere.

Bolt-Together Construction

Allows a chiller to be taken apart into modules and brought into buildings through standard doorways.


British Thermal Unit. The amount of heat required to raise the temperature of 1 pound of water by 1 deg F. A quantity of heat.


BTUs per hour. The basic small unit for measuring the rate of heat transfer.


In a direct-fired absorption chiller, the device that is used to combust natural gas or fuel oil to provide the heat necessary to reconcentrate the solution.


The measure of the amount of heat removed by a chiller, measured in tons of refrigeration (English units) or kilowatts of refrigeration (SI Metric units).


Carrier Comfort Network. A complete system for the management of HVAC building operations. CCN includes operator interfaces (ComfortWORKS, ComfortVIEW and Building Supervisor), product controls (Product Integrated Controls [PICs]), system managers Chillervisor, Digital Air Volume, and Flotronic System Manager), and controls for other HVAC and non-HVAC building components (Comfort Controllers).


Represented as degrees "C". The scale of temperature measurement most commonly used worldwide.

Centrifugal Compressor

A type of compressor used in vapour compression refrigeration cycles where a rotating impeller is the device which compresses the refrigerant vapour. The vapour is drawn into the impeller axially, and is discharged radially after energy is added to the vapour within the impeller.


Cubic Feet per Minute. The unit of measure of the volume rate of airflow, as in a heating or cooling system.

Chlorine-Free Refrigerant

A refrigerant containing no chlorine. The presence of chlorine in refrigerant compounds contributes to the depletion of ozone in the atmosphere.

back to top


Having less heat energy than the object against which it is compared. A relative term for temperature.


In a vapour compression cycle, the device that increases the pressure and temperature of refrigerant vapour. It continuously draws low pressure refrigerant vapour from the cooler, adds energy to increase the refrigerant pressure and temperature, and discharges the high pressure vapour to the condenser.


The process by which a gas is changed into a liquid at constant temperature by heat removal.


A heat exchange coil within a mechanical refrigeration system used to reject heat from the system. The coil where condensation takes place.

Condensing Furnace

A high-efficiency, gas forced-air furnace that uses a second condensing heat exchanger to extract the latent heat in the flue gas.


Heat transfer within a fluid by the movement of heated molecules from one place to another.

back to top


A device for absorbing unwanted heat into a refrigeration system. This heat exchanger typically consists of a hollow steel shell with copper tubes running through it. The fluid being chilled (relatively warm water) is pumped through the tubes. Heat is transferred from the chilled fluid to the refrigerant liquid inside the shell, boiling it and changing its state to a vapour.

Cooling Load

Heat which flows into a space from outdoors and/or indoors.


Coefficient of performance. This is a measure of the energy efficiency of a chiller.


Canadian Standards Association.


A bladed device used to vary the volume of air passing through the air outlet, air inlet, or duct.


The condensation of water vapour from air by cooling the air below the dewpoint or the removal of water vapour from air by chemical or physical methods.

Demand Limiting

Limits the power draw of the chiller during peak loading conditions.

Design Cooling Load

The rate at which heat flows into a space on a design day. The design day usually presents the space with 95% or more of its highest possible load.


1) Part of a centrifugal compressor that transforms the high velocity, low pressure gas exiting the impeller into higher pressure, low velocity gas discharged into the condenser.

2) Air Terminal device that evenly distributes air to a space.

Dry Bulb Temperature

Temperature measured using a standard thermometer. A measure of the sensible heat of the air or surface being measured.

back to top

Dynaglide Transmission

Transmission design on the Carrier Evergreen Chillers. It features AGMA class 11 gears, tilting pad thrust bearing, and single piece design, which assures alignment, even after disassembly. Carrier patented design.

ECA - Enhanced Capital Allowance

A scheme in the UK devised by the Government to encourage the use of energy efficient products. Tax can be reclaimed for certain parts.


In a chiller with a two-stage centrifugal compressor, the discharge from the first stage impeller and the inlet to the second stage impeller is at a pressure level approximately half way between the cooler pressure and condenser pressure. With this arrangement, an economizer may be used. This is a shell within which refrigerant liquid from the condenser drops down to the interstage pressure, flashing off some of the refrigerant which is drawn directly into the second stage impeller. This reduces the amount of refrigerant which has to be compressed by the first stage impeller, improving the refrigeration cycle efficiency. A similar arrangement may be used with a screw compressor when the compressor is equipped with an intermediate inlet port.


Energy Efficiency Ratio. The ratio of the rated cooling capacity in BTUs per hour divided by the amount of electrical power used in watts at any given set of conditions.


The process of removing air, moisture, and other gases from the inside of a refrigeration system.


A heat exchange coil within a mechanical refrigeration system used to absorb heat into the system. The coil where evaporation takes place.


Represented as degrees "F". The scale of temperature measurement most commonly used in the United States of America.


Federation of Environmental Trade Associations.


Flash SubCooler. This is a section of some Carrier condensers in which the pressure of condensed refrigerant liquid is reduced, which causes some of the liquid to flash into vapour, cooling the remaining liquid. The vapour is then re-condensed at the lower pressure, which improves the energy efficiency of the chiller.

Flue Gas

Products of combustion plus excess air plus dilution air (on natural-draft appliances) that pass through the vent.

Forced-air Furnace

Any furnace that uses a fan to circulate heated air.


In an absorption cycle, the vessel in which the lithium bromide solution is reconcentrated by boiling off the previously absorbed water.


Used as a refrigerant in a wide range of refrigeration equipment from room air conditioners to large centrifugal chillers. HCFC-22 has an ozone depletion potential of 0.05 and a global warning index of 0.34. The threshold limit for exposure is 1000 ppm.

As HCFC-22 contains 41% chlorine and has an atmospheric life of 15 years, this refrigerant is subject to phase-out in 2030 under the international Montreal Protocol. The U.S. Clean Air Act will prohibit the use of this refrigerant in new equipment in 2010, along with prohibiting new production after 2020.


A form of energy. The least organized form of energy. The form of energy into which other forms deteriorate.

Heat Exchangers

The parts of a chiller which exchange heat between two physically separated fluids. In a chiller, the heat exchangers are the cooler and the condenser, which exchange heat between the refrigerant and water or brine. Typically the heat exchangers used in chillers are of shell-and-tube design, where the water or brine flows through a number of tubes inside a containment shell, and the refrigerant is either boiled or condensed on the outside of the tubes.

Heat Pump

A comfort system in which the refrigeration cycle is reversed by using a four-way valve to supply heating as well as cooling.

Heat Recovery Ventilator (HRV)

HVAC equipment that saves energy by using a heat exchanger to transfer heat from the building exhaust air to the cold ventilation air entering the building.

Heat Transfer

The movement of heat from one place to another, between two substances, or within a substance.

back to top

Heating Capacity

The rate at which a device can add heat to a substance, expressed in BTUH.

Hermetic Motor

A motor which is sealed within the refrigerant atmosphere inside a chiller, and which is therefore isolated from the atmosphere outside the chiller. A hermetic motor is efficiently cooled by liquid refrigerant sprayed directly on the motor windings, and is smaller and lighter than a comparable air-cooled motor. A compressor driven by a hermetic motor has the advantage that the compressor shaft does not have to pass through a seal between the outside atmosphere and the refrigerant atmosphere inside the chiller.


A positive pressure, chlorine-free refrigerant having zero ozone depletion potential. HFC-134a is the refrigerant of choice for automotive and appliance applications, which will assure a plentiful supply at reasonable prices.

High-Stage Generator

In an absorption cycle, the vessel that performs the first stage of reconcentration of the lithium bromide solution by boiling off the water contained in the solution. The hot water vapour boiled off within the high-stage generator is used as the heat source for the low-stage generator.


Heat Pump Association


Rotating part of a centrifugal compressor which increases the pressure of refrigerant vapour from the cooler pressure to the condenser pressure.

Induced-draft Furnace

A furnace in which a motor-driven fan draws air from the surrounding area or from outdoors to support combustion.

Inlet Guide Vanes

Movable blades at the inlet of a centrifugal compressor which are used to control the capacity of the compressor. The guide vanes also provide rotation to the refrigerant vapour entering the compressor, which improves the efficiency of the compressor.


A material which inhibits heat transfer by conduction.

ISO 9000

The International Organization of Standards (ISO) 9000 standards define a Quality System which ensures the quality of a product.

ISO 9001

The model for Quality Assurance in Design, Development, Production, Installation and Servicing. ISO registration is just one of the building blocks for achieving world-class products. Currently, 29 Carrier manufacturing and service sites are registered, with 13 soon to follow.

back to top

Isolation Valves

Valves used for the transfer and isolation of refrigerant charge in the cooler or condenser, allowing refrigerant to be stored inside a chiller during servicing.


No entries

Kingsbury-Type Thrust Bearing

Self-levelling type of thrust bearing which equalizes bearing loading over the entire circumference of the bearing, and providing an optimum oil film shape. This design reduces bearing wear and provides high reliability and long bearing life.

Latent Heat

The energy of molecular separation and arrangement. It cannot be measured with a thermometer. Associated with change of state of a substance.


Liquid Crystal Display.


A control system process that automatically starts and stops a lag or second chiller in a two chiller water system.


Local Interface Device. Mounted in the control centre, this allows the operator to interface with the Processor Sensor Input/Output Module or other Carrier Comfort Network devices.


In a vapour compression cycle, the lift on the compressor is the difference between the high side (condenser) conditions and the low side (cooler) conditions, measured as either a temperature or pressure difference.

Limit Switch

A protective device used to open or close electrical circuits when temperature or pressure limits are reached.

back to top

Low-Stage Generator

In an absorption cycle, the vessel that performs the second stage of reconcentration of the lithium bromide solution. The heat source for the low-stage generator is the steam created in the high-stage generator.

Lubrication System

System in a chiller, consisting of an oil pump, oil cooler, and associated tubing and oil passages, which provides the oil needed to lubricate the compressor bearings.

Marine Water box

A type of water box in which the nozzles are oriented at right angles to the axis of the heat exchanger shell, and are connected into the sides of the water boxes, rather than into the covers. This allows the covers to be removed, for inspection or cleaning of the heat exchanger tubes, without disturbing the external pipes.

Metering Device

A component of a refrigeration system that controls the flow of high- pressure liquid into the evaporator.

Natural-draft Furnace

A furnace in which the natural flow of air from around the furnace provides the air to support combustion. It also depends on the pressure created by the heat in the flue gases to force them out through the vent system.


National Fire Protection Association.



Nozzle-In-Head Water box

A type of water box in which the nozzles enter through one or both of the water box covers, with the nozzles oriented parallel to the axis of the heat exchanger shells.

Oil Separator

In a chiller utilizing a screw compressor, an oil separator is often used to remove lubricating oil from the refrigerant vapour at the discharge of the compressor, in order to keep the oil from collecting in the heat exchangers.

Open-Drive Motor

A motor which is located outside the refrigerant containment of a chiller. An open-drive motor requires that the rotating compressor shaft pass through a seal between the outside atmosphere and the refrigerant atmosphere inside the chiller.

Packaged Unit

A self-contained heating and/or air conditioning system.


In a shell-and-tube heat exchanger, the number of passes is the number of times the fluid flowing inside the tubes flows the length of the heat exchanger. For example, a two-pass cooler has the cooled fluid inside the tubes flowing from the inlet end of the cooler to the opposite end, and then back to the inlet end, where the fluid exits the cooler.

Perfect Vacuum

The absolute absence of any pressure, even atmospheric (O PSIA or O In. Hg. Abs. or about 30 In. Hg. Vac).


Product Integrated Control. PICs are used in conjunction with the Carrier Comfort Network to control and monitor the operation of Carrier products.


A sealed chamber at the inlet or outlet of an air handler. The duct attaches to the plenum.

Positive Pressure Design

A chiller design using a refrigerant which operates above atmospheric pressure in all parts of the system. These chillers are typically smaller than negative pressure design chillers at similar capacities, and air and water vapour are kept out of the system by the positive pressure difference.

back to top

Power Panel

Houses all 230 or 115 control voltage components.


Force per unit of area.


Processor Sensor Input/Output module.

Pump down Unit

System which transfers refrigerant from a chiller to a storage tank, or into an isolated section of a chiller, for service. The pump down unit is also capable of evacuating a chiller prior to re-introducing the refrigerant, for minimum contamination of the refrigerant by air or water vapour.

Purge Device

A device which removes air and water vapour from the refrigerant inside a chiller. A purge is a necessity in negative pressure designs, but is not necessary in positive pressure designs where air and water vapour are kept out of the system by the internal pressure.


No entries


A fluid (liquid or gas) that picks up heat by evaporating at a low temperature and pressure. It gives up heat by condensing at a higher temperature and pressure.

Relative Humidity

The ratio of the amount of water vapour contained in the air to the greatest amount the air could hold at that temperature. Normally expressed as a percentage.

Reversing Valve

A valve that changes the direction of refrigerant flow in a heat pump.

Roof top Unit

A heating and/or cooling unit that conditions a structure; it is mounted on the roof after adequate reinforcement has been built into the roof.

Screw Compressor

A type of compressor used in vapour compression refrigeration cycles where two intermeshing helical rotors create pockets of continuously decreasing volume, in which the refrigerant vapour is compressed and its pressure is increased from cooler pressure to condenser pressure.


Seasonal Energy Efficiency Ratio. The total cooling of an air conditioner or heat pump in BTUs during its normal annual usage period for cooling divided by the total electrical energy input in watt-hours during the same period.

Sensible Heat

The energy of molecular motion. Measured with a thermometer. Associated with a change in temperature.


A condition in which a compressor or furnace is restarted immediately after it has been turned off.

Single Stage Centrifugal Compressor

Type of centrifugal compressor having one impeller.

Slide Valve

In screw compressors, this is the capacity control mechanism.

back to top


Starter Management Module. This implements Processor Sensor Input/Output module commands for starter functions.

Solenoid valve

In screw compressors, this is the mechanism that controls the movement of the slide valve through signals from the Processor Sensor Input/Output module.

Solid State Starter

Provides smooth, stepless acceleration of a chiller's motor from stop to full speed. The "soft start" reduces the mechanical stress on the compressor.

Split System

A refrigeration or air conditioning system in which the condenser and evaporator are in separate locations, joined by refrigerant piping.

Storage Tank

A steel shell in which the refrigerant charge for a chiller may be temporarily stored while the chiller is serviced.


This is a section of some condensers in which the temperature of the condensed refrigerant liquid is reduced. This improves the energy efficiency of the chiller.

back to top


The measure of the intensity of heat that a substance possesses.


A device that connects or disconnects a circuit in response to a change in the ambient temperature.

Thrust Bearing

A bearing which absorbs the axial forces produced in a centrifugal compressor by the refrigerant pressure differential across the impeller.


The basic large unit for measuring the rate of heat transfer (12,000 BTUH).

Total Cooling Load

Expressed in BTUH or tons. The rate at which total heat enters a space.

Total Heat

Sensible plus latent heat.

back to top

Two Stage Centrifugal Compressor

Type of centrifugal compressor having two impellers. The first stage impeller raises the pressure of the refrigerant vapour approximately half way from the cooler pressure to the condenser pressure, and the second stage impeller raises the pressure the rest of the way. With a two stage compressor, an interstage economizer may be used to improve the refrigeration cycle efficiency.


Underwriters' Laboratories.

Vacuum Pump

A pump used to remove air and moisture from a refrigeration system at a pressure below atmospheric pressure.

Vapour Barrier

A moisture-impervious layer applied to the surfaces enclosing a humid space to prevent moisture travel to a point where it may condense due to lower temperature.

Vapour Compression Cycle

A refrigeration cycle consisting of a cooler, a compressor, a condenser, and an expansion device. In the cooler, heat is removed from the fluid being cooled by the boiling of liquid refrigerant into vapour. The compressor continuously draws this low pressure vapour from the cooler, and adds energy to the refrigerant, increasing its pressure and temperature, and discharges the high pressure vapour to the condenser. In the condenser, the cooling fluid removes heat from the refrigerant, which is condensed into liquid. The expansion device, which may be a float valve or an orifice, drops the pressure of the refrigerant liquid back down to cooler pressure.


The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned.

Volume Index (volume ratio)

For screw compressors, this is the trapped volume existing at the beginning of the compression process divided by the reduced volume at the point of initial exposure to the discharge port.


For a shell and tube heat exchanger which has the water or brine flowing through the tubes, the water box is a chamber on each end of the shell into which all of the tubes empty. At the inlet end of the heat exchanger, an inlet nozzle (pipe) connects to the water box, and the fluid flows from the nozzle into the water box and into the first pass of the tubes; at the outlet end of the heat exchanger, an outlet nozzle connects to the water box, and the fluid flows from the last pass of the tubes into the water box and into the outlet nozzle.

Wet Bulb

A device used to measure relative humidity. Evaporation of moisture lowers the temperature of the wet bulb compared to the dry bulb temperature of the same air sample.


No entries


No entries


The practice of providing independent heating and/or cooing to different areas in a structure.

back to top