ASHRAE Terminology

refrigeration is created by evaporating a refrigerant in a heat exchanger (evaporator) with the vapor then absorbed by an absorbent medium from which it is subsequently expelled by heating at a higher partial vapor pressure (in a generator) and condensed by cooling in another heat exchanger (condenser).

convector with integrated air supply where primary air plus induced air pass through the cooling coil(s). Cooling medium is generally water.

transportation of a specified airflow to or from the treated space, by ducts or plenums. Air-treatment devices can be added to the distribution system for the purpose of treating the air (e.g., cleaning, heating, cooling, humidifying or dehumidifying, etc.)

duct and dampers arrangement with an automatic control system that together allow a cooling system to supply outdoor air to reduce or eliminate the need for mechanical cooling during mild or cold weather.

(1) an air-distribution assembly consisting of inlet duct connection(s) and outlet duct connection(s) whose purpose fulfills (either manually or automatically) one or more of the following functions: controls the rate of the airflow, controls the velocity or pressure and/or temperature of the air, mixes primary streams of different temperatures or humidities, or mixes within the device primary air with air from the treated space. (2) an air terminal unit may be composed of automatic or manual dampers, filters valves, heating or cooling coils, sound attenuation, nozzles, or fan assemblies. See also diffuser terminal.

A unit spraying, atomizing, or down-flowing water (or any type of solution, e.g., dehydrating) into the air stream and capable of heating, cooling, humidifying, or dehumidifying the air according to the temperature, hygrometric, or concentration characteristics of the fluids present. Can be used for the purpose of removing particulate matter from the airstream See scrubber.

cooling by forced circulation of air at high velocity. Compare to jet cooling.

a refrigeration cycle consisting of four stages: compression of air, cooling the air down to ambient temperature, expansion of the air, and heating of the cold air by heat absorption in the space to be cooled.

a single number rating of the air-diffusion performance of a mixing system at specified supply-air delivery rate, temperature, moisture content, and space cooling load. ADPI is based on air speed and effective draft temperature.

Assembly consisting of sections containing a fan or fans and other necessary equipment to perform one or more of the following functions: air circulation, filtration, heating, cooling, heat recovery, humidifying, dehumidifying and mixing of air, and necessary control functions.

(1) process involving controlled heating and subsequent controlled, generally slow, cooling. Applied usually to induce ductility in metals. (2) treatment intended to remove internal stresses, alter mechanical or physical properties, produce a definite microstructure, and remove gases.

sensible-cooling load for the entire one-year simulation period (e.g., for hourly simulation programs, this is the sum of the hourly sensible cooling loads for the one-year simulation period).

(1) in a water cooling tower or evaporative cooling device, the difference between the average temperature of the circulating water leaving the device and the average wet-bulb temperature of the entering air. (2) in heat exchangers, the temperature difference between the leaving fluids.

(also called natural draft cooling tower), air movement through a cooling tower by aspiration or natural convection.

a heat exchanger for cooling brine with an evaporating refrigerant.

cooling of air by spraying brine into the airstream. Note: process discontinued in meat refrigerating plants because of salt corrosion of meat-carrying rails.

the cooling effect produced by the change in enthalpy between the refrigerant liquid entering the expansion valve and the vapor leaving the evaporator, generally measured in Btu per hour (kW or tons of refrigeration).

the rate, expressed in watts (Btu/h), at which the equipment removes latent heat from the air passing through it under specified conditions of operation.

the rate, expressed in watts (Btu/h), at which the equipment removes sensible heat from the air passing through it under specified conditions of operation.

the rate, expressed in watts (Btu/h), at which the equipment removes heat from the air passing through it under specified conditions of operation.

absorption of injected CO₂ into a liquid, usually preceded or accompanied by liquid cooling.

cooling degree day. See degree day.

(in a cooling tower) smallest tower subdivision that can function as an independent heat exchange unit. It is bounded by exterior walls or partitions. Each cell may have one or more fans or stacks and one or more distribution systems.

cooling efficiency ratio

(1) change from heating to cooling or vice versa. (2) change from one set of controls to another.

outdoor temperature the designer selects as the point of changeover from cooling to heating by the HVAC system.

Ceiling panels that are made up of elements that connect together and cool primarily through radiation. The cooling medium is usually water.

water used as a cooling medium (particularly in air-conditioning systems or in processes) at below ambient temperature.

Cooling of a substance without freezing it

cooling load factor

sequential production of either electrical or mechanical power and useful thermal energy (heating or cooling) from a single energy form.

cooling or heating element made of pipe or tube that may or may not be finned and formed into helical or serpentine shape.

the heat exchanger that removes heat from (cooling) or adds heat to (heating) the airstream being conditioned.

the heat exchanger that rejects heat to (cooling) or absorbs heat from (heating) a source external to the conditioned space. In the cooling mode, the coil operates as a condenser. In the heating mode, the coil operates as an evaporator.

process for assembling two precision-machined parts by cooling the inner member so that it can be inserted into the outer member, the members fit tightly together when both are at the same temperature.

an operating mode that occurs during either the cooling season or the heating season when the appliance operates to meet a water heating load along with a space conditioning load. With respect to seasonal performance calculations, this mode occurs when both a water heating load and a space conditioning load occurs simultaneously.

a complete ceiling panel that is designed and can be independently installed and operated for both sensible cooling and sensible heating of an indoor space through heat transfer between the thermally effective panel surfaces and the occupants and/or the indoor space by thermal radiation and natural convection.

the seasonal coefficient of performance of the combined appliance when used to meet both the space-cooling and domestic water-heating loads that occur during the space-cooling season. The quantity is dimensionless.

refrigeration for comfort, as opposed to refrigeration for storage or manufacture.

heating, cooling, or refrigerating system used in a commercial or business place.

a water cooler that, in addition to the primary function of cooling and dispensing potable water, includes a refrigerated compartment with or without provisions for making ice.

System in which refrigeration is affected by the vaporization at low pressure in a heat exchanger (evaporator) of a liquid refrigerant, the vapor thus formed being restored to the liquid state by mechanical compression to a higher pressure and subsequent cooling in another heat exchanger (condenser).

process whereby a side port in the compressor (usually a screw compressor or multiwheel centrifugal compressor) is used to provide refrigerant subcooling, resulting in an improvement in overall system efficiency.

a unitary air conditioner, for a computer and data processing room, consisting of one or more assemblies that include a DX evaporator or chilled-water cooling coil, an air-moving device, and air-filtering devices. The air conditioner may include a compressor, condenser, humidifier, or reheating device.

liquid formed by condensation of a vapor. In steam heating, water condensed from steam, in air conditioning, water extracted from air, as by condensation on the cooling coil.

a variation of solution heat exchangers, used on steam-fired, double-effect machines and on some single-effect, steam-fired machines. Uses the condensed steam to add heat to the solution entering the generator.

the fluid used as the condensing media in a liquid cooled, self-contained refrigerator.

number of degrees that a pressurized liquid is cooled lower than its saturated temperature at that pressure.

(1) an apparatus for processing low-pressure refrigerant vapor back into high-pressure liquid refrigerant to be used for cooling a refrigerator. (2) machine designed to condense refrigerant vapor to a liquid by compressing the vapor in a positive displacement compressor and rejecting heat to a cooling medium. A condensing unit usually consists of one or more positive displacement compressors and motors, condensing coils, liquid receivers, and other devices mounted on a common base.

rate of heat removal by the refrigerant assigned to the condensing unit in a refrigerating system. This is equal to the product of the mass rate of refrigerant flow produced by the condensing unit and the difference in the specific enthalpies of the refrigerant vapor entering the unit at a specified superheat and the refrigerant liquid leaving the unit at a specified subcooling.

cooling by direct contact with a cold surface.

technology or systems used to store cooling capacity. Normally applies to comfort or air-conditioning applications. Compare to cold storage and ice storage.

(1) Removal of heat, usually resulting in a lower temperature and/or phase change (2) Lowering temperature

(1) ambient air used to remove heat from a device, space, or system. (2) cooled air used to lower the temperature of a space or products stored in a space.

see heat pump, cooling, and heating.

(also known as total cooling capacity), design maximum rate at which equipment removes heat from a fluid under specified conditions of operation.

an arrangement of pipes or tubes, not enclosed in a pressure vessel, that can be used either with refrigerant or secondary coolant to provide cooling or cooling with dehumidification.

see degree day.

the outdoor dry-bulb temperature equal to the temperature that is exceeded by 1% of the number of hours during a typical weather year.

the outdoor wet-bulb temperature equal to the temperature that exceeds a stated number of hours during a typical weather year. The value is normally stated as a percent. This value is applicable to cooling systems where the main purpose is dehumidification and the prevention of mold and mildew.

the primary air dry-bulb temperature reduction divided by the primary air entering dry-bulb temperature less the entering secondary wet-bulb temperature.

a ratio calculated by using the formula: CER = (C+ FE)/E where: C = cooling capacity, Btu/h (W), FE = fan electrical input, W × 3.413 Btu/W (W), E = total electrical input (W).

the sum of all site energy in kilowatt-hours required to provide cooling via vapor compression, ventilation, dehumidification, humidification, evaporation, absorption, adsorption, or other means.

the site electric energy consumption of the mechanical cooling equipment including the compressor, air-distribution fan (regardless of whether the compressor is on or off), condenser fan, and related auxiliaries.

the flow rate of liquid refrigerant required for all cooling purposes in a compressor or condensing unit.

(1) amount of cooling per unit time required by the conditioned space or product. (2) heat that a cooling system must remove from a controlled system over time.

ratio of the cooling building load to the steady-state cooling capacity.

substance used, with or without a change of state, to lower the temperature of other bodies or substances. See coolant. See refrigerant.

that portion of the year that the outdoor air temperature is above 18.3°C (65°F).

apparatus for lowering the temperature of a space or product to a specified temperature.

a ratio calculated by dividing the net total cooling capacity in watts by the total power input in watts (excluding reheaters and humidifiers) at any given set of rating conditions. The net total cooling capacity is the total gross capacity minus the energy dissipated into the cooled space by the blower system.

heat transfer device, often tower like, in which atmospheric air cools warm water, generally by direct contact (evaporation).

unit that includes means for cooling and which may also include means for other air-handling-unit functions.

smallest tower subdivision that can function as an independent heat exchange unit. It is bounded by exterior walls or partitions. Each cell may have one or more fans or stacks and one or more distribution systems.

see cooling-tower packing.

fog condition created when the exhaust air or plume from a cooling tower, which is essentially a saturated air/water vapor mixture warmer than ambient air, becomes supersaturated so that part of the water vapor condenses into visible liquid droplets.

(also known as tower fill), that part of a crossflow, counterflow, or natural draft tower consisting of splash bars, vertical sheets of various configurations, or honeycomb assemblies, tile, or other materials which cause the water to break up into droplets to effect heat and mass transfer between the circulating water and the air flowing through the tower.

visible exhaust from a cooling tower. Compare to cooling-tower fogging.

total heat rejection capacity of a cooling tower, traditionally, 15,000 Btu/h. Note: this value is based on 25% compressor heat added to a ton of refrigeration. Current energy-efficient equipment may have lower values than traditional values.

(1) typically, a chemical agent that protects internal machine parts from the corrosive effects of the absorbent solution in the presence of an air chemical agent that slows corrosion of metal parts of a system. (2) substance added to a brine or other cooling medium.

cooling below –244°F (–153°C, 120 K).

represent the accumulation of dissolved minerals in the recirculating cooling water. Draw-off (or blowdown) is used principally to control the buildup of these minerals. Increasing the amount of minerals present in the water by cycling can make water less aggressive to piping; however, excessive levels of minerals can cause scaling problems. As the cycles of concentration increase, the water may not be able to hold the minerals in solution. When the solubility of these minerals has been exceeded, they can precipitate out as mineral solids and cause fouling and heat exchange problems in the cooling tower or the heat exchangers. The temperatures of the recirculating water, piping, and heat exchange surfaces determine if and where minerals will precipitate from the recirculating water. The use of water treatment chemicals, pretreatment such as water softening and pH adjustment and other techniques can affect the acceptable range of cycles of concentration. Concentration cycles in the majority of cooling towers usually range from 3 to 7. The water may also be filtered and dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water. In closed-loop systems, corrosion inhibitors may be used. 1. in boilers, the ratio of chlorides in the boiler water to the chlorides in the feedwater. 2. in cooling tower operation, the ratio of chlorides in the recirculating cooling tower water to the chlorides in the makeup water.

Outdoor air unit that provides ventilation directly to a space or sensible heating/cooling units. If equipped with an exhaust fan it can control building pressure. Can have an air-to-air recovery device to save energy . Other options include custom air cleaning, enhanced dehumidification devices, compressors, condensors. 2. Make up air unit.

duration of the off cycle of a refrigerating system sufficient to permit defrosting of a cooling coil.

equipment and controls designed to remove frost (ice) from cooling coils of a refrigerating system.

the difference in temperature between the outdoor mean temperature over a 24-hour period and a given base temperature. For the purposes of determining building envelope requirements, the classifications are defined as follows: (a) cooling degree day base 50°F, CDD50 (10°C, CDD10): for any one day, when the mean temperature is more than 50°F (10°C), there are as many degree days as degrees Fahrenheit or Celsius temperature difference between the mean temperature for the day and 50°F (10°C). Annual cooling degree days (CDDs) are the sum of the degree days over a calendar year. (b) heating degree day base 65°F, HDD65 (18°C, HDD18): for any one day, when the mean temperature is less than 65°F (18°C), there are as many degree days as degrees Fahrenheit or Celsius temperature difference between the mean temperature for the day and 65°F (18°C). Annual heating degree days (HDDs) are the sum of the degree days over a calendar year.

the difference in temperature between the outdoor mean temperature over a 24-hour period and a given base temperature, used in estimating heating and cooling energy use. For any one day, there are as many degree days (Kelvin-days) as there are degrees Fahrenheit (degrees Celsius) departure of the mean temperature for the day from the base temperature

mass of water condensed during cooling or the equivalent refrigerating capacity expressed in terms of the latent heat of the water condensed per unit of time.

direct formation of the solid phase by cooling a vapor below the triple point.

(1) system in which the cooling effect is obtained directly from the expansion of the liquid refrigerant into a vapor. (2) common term applied to an air-conditioning or refrigeration system that utilizes the vapor-compression refrigeration cycle. In a vapor-compression refrigeration cycle, the refrigerant removes heat in the evaporator by directly expanding the entering liquid refrigerant into vapor as it leaves the evaporator. The vapor is then compressed and piped to a condenser where the heat removed by the evaporator and the heat of compression are rejected to another medium so that the gaseous refrigerant is condensed to a liquid. The liquid is then piped to a pressure reducing device/metering device to be supplied to the evaporator.

withdrawing cooling or heating potential from thermal storage.

a type of air-distribution system, used only for cooling purposes, in which air at a temperature below room temperature is supplied to the floor level at a low discharge velocity [<100 fpm (0.5m/s)] and is returned near ceiling level. Thermal plumes, which develop over heat sources in the room, drive the overall floor to ceiling air motion, producing a stratified environment with cooler and fresher air near the floor and warmer and less fresh air near the ceiling.

(1) conveying means, such as ducts, pipes, and wires, to bring substances or energy from a source to the point of use. The distribution system includes auxiliary equipment such as fans, pumps, and transformers. (2) parts of a cooling tower, beginning with the inlet connection, that distribute the hot, circulating water within the tower to the points where it contacts the air.

ratio between the energy consumption by the equipment if the distribution system had no losses (gains for cooling) to the outdoors or effect on the equipment or building loads and the energy consumed by the same equipment connected to the distribution system under test.

concept of providing and distributing, from a central plant, cooling energy to a surrounding area (district) of tenants or clients (residences, commercial businesses, or institutional sites). Compare to district heating.

centralized facility for generation and distribution of the heating and cooling and/or power needs of a community, rather than individual heat or cold generators (i.e., furnace or air conditioner) at each residential, commercial, or institutional site.

concept of providing and distributing, from a central plant, heating energy to a surrounding area (district) of tenants or clients (residences, commercial businesses, or institutional sites). Compare to district cooling.

measure of cooling demand per unit area. Customary units are kW/hectare or tons/acre.

condenser that contains two separate tube bundles, allowing the option of either rejecting the heat to the cooling tower or to another building system requiring heat input.

condenser constructed of concentric tubes in which the refrigerant circulates through the annular space and the cooling medium through the inner tube.

piping arrangement for heating, air-conditioning, or refrigerating systems in which heating and cooling fluid is circulated through supply mains which are above the levels of the heating or cooling units they serve.

(1) current of air, when referring to pressure difference that causes a current of air or gases to flow through a flue, chimney, heater, or space. (2) current of air, when referring to localized effect (generally, the unwanted local cooling of the body caused by air movement) caused by one or more factors of high air velocity, low ambient temperature, or direction of airflow whereby more heat is withdrawn from a person’s skin than is normally dissipated.

vessel or tray placed under an evaporator coil or cooling coil to receive condensed moisture, melted frost, or ice. Also called a drip tray or a defrost pan.

(1) change in mechanical or electrical characteristics with the passage of time, change in temperature, or both. (2) change in output/input relationship over a period of time with the change unrelated to input, environment, or load. (3) in a cooling tower, water lost as liquid droplets entrained in the exhaust air. It is independent of water lost by evaporation. (4) movement of current carriers in a semiconductor under the influence of an applied voltage.

(1) leak in a liquid system. (2) liquid which appears on thawing frozen food, water melting from evaporator, or water droppings from a cooling surface. (3) pipe or a steam trap and a pipe considered as a unit that conducts condensation from the steam side of a piping system to the water or return side of the system.

vessel or tray placed under the cooling coil to receive the melt from frost or ice. Also called drain pan.

(1) deviation from the no-load control point that results from a change in the heating or cooling load. (2) linear term referring to the percentage decrease in output voltage for a square wave or rectangular wave as a function of time. Also can apply to voltage error caused by leakage in a sample and hold circuit. (3) (of an air jet in mixing air diffusion), vertical distance (hv) between the lowest horizontal plane tangent to a specified isovel and the center of the core of an air jet.

mechanical, refrigerated equipment using metal or plastic as a direct heat transfer medium and for reserve cooling capacity.

ice formed on a cooling surface, then removed to be stored in an insulated container (tank). Compare to ice harvester.

(1) a process employing heat recovery equipment or heat exchangers. (2) device that, on proper variable sensing, initiates control signals or actions to conserve energy. A control system that reduces the mechanical heating and cooling requirement.

a system by which the supply air of a cooling system is cooled indirectly with a fluid that is itself cooled by heat or mass transfer to the environment without mechanical cooling. Examples of commonly used fluids are water, glycol mixtures, and refrigerants.

(1) apparatus for cooling fluid out of contact with the atmosphere. (2) within a pressure-tight vessel, a heat exchanger consisting of an assembly of tubes containing the liquid to be cooled.

(also known as total energy system), a single fuel source provides all energy services such as electricity, heating, and cooling.

(1) ratio of net cooling capacity in Btu/h to total rate of electric input in watts under designated operating conditions. (2) ratio of the net total cooling capacity to the effective power input at any given set of rating conditions, in watts per watt.

the outdoor wet-bulb temperature used in conjunction with the mean coincident dry-bulb temperature, often used for the sizing of evaporative systems such as cooling towers.

water evaporated into the atmosphere as the condenser water is cooled, typically in a cooling tower.

condenser in which the removal of heat from the refrigerant is achieved by the evaporation of water from the exterior of the condensing surface, induced by the forced circulation of air and sensible cooling by the air.

a cooler that cools indoor air by moisture evaporation, thereby lowering its dry-bulb temperature and raising its wet-bulb temperature, all at a constant energy (adiabatic) level. See also evaporative cooling.

two methods using evaporating water to cool air: (1) direct, which is adiabatic and humidifies the air, and (2) indirect, which is not adiabatic and cools the air being treated without adding moisture.

cools air by moisture evaporation, thereby lowering its dry-bulb temperature and raising its wet-bulb temperature, all at a constant energy level.

controlling device for automatically regulating the flow of refrigerant into a cooling unit, actuated by changes in evaporator pressure. The basic response is to regulate evaporator pressure.

(1) a machine used to create flow within a fluid, typically a gas, such as air. (2) any device with two or more blades or vanes attached to a rotating shaft used to produce an airflow for the purpose of comfort, ventilation, exhaust, heating, cooling, or any other gaseous transport. The opening(s) may or may not have an element or elements for connection to ductwork. (3) fan consists of a rotating arrangement of vanes or blades that act on the air (impeller). Usually it is contained within some form of housing or case. This housing or case may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors and internal combustion engines. Fans produce airflows with high volume and low pressure, as opposed to compressors, which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan. (4) see also impeller.

factory-made assembly that provides the functions of air circulation, cooling, heating, or cooling and heating.

the sum of the nominal power demand (nameplate horsepower) of motors of all fans that are required to operate at design conditions to supply air from the heating or cooling source to the conditioned space(s) and return it to the source or exhaust it to the outdoors.

cooling tower with a type of packing over which the water spreads in a thin film.

(1) at the pump suction, the pressure below which the liquid will flash into vapor. See net positive suction head. (2) in a piping system, the pressure below which the liquid will flash into vapor. (3) in a vacuum-cooling chamber, that pressure corresponding to the vapor pressure at the product temperature and below which water vaporizing commences. (4) lowest temperature to which a product must be heated for its vapors to ignite in the presence of a flame when operating under standardized conditions. Compare to fire point.

(1) a perforated plate installed downstream of a fan in an air-handling unit designed to diffuse airflow equally across a downstream coil. Also called a diffuser plate. (2) in a multiple cooling tower installation, a pipe installed below and interconnecting the cold basin of multiple cooling towers to equalize the basin water levels and prevent the sump suction in one tower from drawing air or creating a vortex. (3) in refrigeration, a line or lines installed between compressors to equalize oil levels. (4) the bypass pipe in a primary/secondary flow system that hydronically decouples the primary from the secondary pumping system. See cross connection.

a heating and/or cooling system that uses motor-driven blowers to distribute heated, cooled, and otherwise treated air for the comfort of individuals or equipment.

type of mechanical draft tower in which one or more fans are located at the air inlet to force air into the tower.

in an ice plant, a device for cooling water before pouring into ice-making cans, precooler.

refers to a situation where mechanical heating and cooling equipment is off so that the space or zone temperature varies without constraint.

Solidification phase change of a liquid or the liquid content of a substance, usually due to cooling

frost formed on the cold surface (tubes, plates) of a cooling coil.

the absolute value of the difference between the starting and ending temperatures of a phase-change process by a refrigerant within a component of a refrigerating system, exclusive of any subcooling or superheating. This term usually describes condensation or evaporation of a zeotrope.

heating or refrigerating system in which heating or cooling fluid is circulated by the forces induced by the differences in densities of cooler and warmer fluids in the system or surrounding atmosphere.

the rate of sensible heat removal by the cooling coil for a given set of operating conditions. This value varies as a function of performance parameters such as EWB, ODB, EDB, and airflow rate. (Also see sensible heat.)

the total rate of both sensible heat and latent heat removal by the cooling coil for a given set of operating conditions. This value varies as a function of performance parameters such as EWB, ODB, EDB, and airflow rate. Also see sensible heat and latent heat.

ability of a thermostat or control system to terminate the heat or cooling input at a temperature other than its setting and in advance of the time that the temperature at the thermostat or control system sensor normally would cause a control change.

quantity of heat removed from a liquid to reduce it from its saturation temperature at saturation pressure to some lower temperature at the same pressure.

thermodynamic heating/refrigerating system to transfer heat. The condenser and evaporator may change roles to transfer heat in either direction. By receiving the flow of air or other fluid, a heat pump is used to cool or heat. Heat pumps may be the air source with heat transfer between the indoor air stream to outdoor air or water source with heat transfer between the indoor air stream and a hydronic source (ground loop, evaporative cooler, cooling tower, or domestic water).

temperature at which the installed heat pump capacity is equal to the heat requirement of the building. For a geoexchange system, the temperature at which supplemental heating or cooling is required. For an air-to-air system, the temperature at which supplemental heating is required. For a water loop system, the temperature at which heating and cooling requirements are equal.

heating and cooling a metal or alloy to obtain desired properties or conditions.

pressure-responsive device that cycles and/or stages condensers, cooling-tower fans, and pumps to control head pressure.

a water cooler that, in addition to the primary function of cooling and dispensing potable water, includes means for heating and dispensing potable water.

zone or space air temperature for a given hour when heating and cooling equipment is off or for an unconditioned space.

a space or group of spaces, within a building with heating, cooling, and ventilating requirements, that are sufficiently similar so that desired conditions (e.g., temperature) can be maintained throughout using a single sensor (e.g., thermostat or temperature sensor).

science of heating and cooling water.

cooling tower of hyperbolic shape that depends on natural draft for air movement through the tower. The air movement can be either crossflow or counterflow.

machine that collects ice on a cooling surface, then delivers it to storage or use in a process.

thermal storage system used for chilling processes or for comfort cooling that uses primarily the latent heat of phase change from ice to water. Ice is formed during periods of low refrigerating demand for delivery of cooling during periods of high refrigerating demand. Compare to cool storage and cold storage.

water-cooling tank in which ice is allowed to build up on the evaporator tubes to provide a reserve for cooling.

device for cooling water before it is frozen in an ice maker.

system in which a liquid such as brine or water, cooled by the refrigerant, is circulated to the material or space to be refrigerated or is used to cool air so circulated.

(1) a heat and mass transfer device used to sensibly cool a primary airstream without addition of moisture, by means of an evaporatively cooled secondary airstream. Since the secondary air provides wet-bulb depression, it represents a heat sink to the primary air. (2) an indirect evaporative cooling device consisting of an indirect evaporative-cooling heat exchanger, a means of delivering and distributing water to the wet passages of the heat exchanger, a basin for collecting water, a recirculating water pump, and the piping that connects the basin and the water distribution system.

an indirect evaporative cooling device with integrated primary (dry) and secondary (wet) air passages in a single sensible and evaporative heat exchanger.

a packaged, semi-packaged, or component indirect evaporative cooling unit. The term cooling unit is also used interchangeably for evaporative cooling unit or evaporative cooler.

type of mechanical draft tower in which one or more fans are located in the air outlet to induce airflow through the air inlets.

apparatus for cooling compressed gas or vapor between two compression stages.

quick chilling process using air at very high speed forced around the products, usually while those products are continuously moving on a conveyor belt. Compare to air-blast cooling.

the rate, expressed in Btu/h (W), at which the equipment removes latent heat (reduces the moisture content) of the air passing through it under specified conditions of operation.

that portion of the cooling effect that results in water vapor condensation in the air circulating through the equipment.

(also known as moisture tons or wet tons), cooling load required to remove latent heat.

use of a phase change of a medium for storing heating or cooling capacity. See also ice storage.

a method of internally cooling the compressor mechanism or lubricant or the reduction of discharge temperature by introducing saturated or subcooled discharge-side liquid refrigerant into the compressor or condensing unit. Liquid-refrigerant injection mass flow rate is not taken into account when calculating compressor or condensing unit efficiency, capacity, or volumetric efficiency.

ratio of actual mean load to a maximum load or maximum production capacity in a given period. See electric power load factor, cooling load factor, heating load factor.

cryocooling by adiabatic demagnetization of certain paramagnetic substances.

a modulating damper or set of dampers used to control the outdoor airflow to the system in excess of minimum ventilation outdoor air for free cooling (airside economizer). Also called economizer outdoor air damper. May also serve to provide the minimum outside airflow control.

the maximum fluid supply temperature at which the cooling load can be met without adversely affecting latent space conditions.

the maximum fluid temperature at which usable cooling can be obtained from the thermal storage device.

tower through which air movement is effected by one or more fans. There are two main types: forced draft with fans located at the air inlet and induced draft with fans located at the air exhaust. See also cooling tower.

on-site assembly of prefabricated components, each with a functional role in an air-conditioning (air-circulation, air-filtration, cooling, heating, humidification, etc.) system.

(1) a step-modulating control that is capable of controlling flow rate between the maximum and the minimum adjustable input rate in response to varying heating or cooling load. (2) method of control in which the output of the controller may vary infinitely over its range.

(1) a plan for gathering of relevant measurement data over time to evaluate equipment or system performance. The plan defines specific M&V methods to be used, including baseline determination, performance period measurements, savings verification calculations, and acceptance criteria. The M&V methods chosen are consistent with the current facility requirements (CFR). During the implementation phase, a list is developed of specific instrumentation and data-gathering equipment that must be maintained at the site. During the hand-off phase, the type, frequency, and distribution of M&V reports to be submitted for approval is confirmed. (2) equipment to measure and record the parameters of the HVAC&R systems (i.e., temperature, humidity, pressure, electric current, kW, and volts). (3) gathering of relevant measurement data over time to evaluate equipment or system performance (e.g., chiller electric demand, inlet evaporator temperature and flow, outlet evaporator temperature, condenser inlet temperature, and ambient dry-bulb temperature and relative humidity or wet-bulb temperature, for use in developing a chiller performance map (e.g., kW/ton versus cooling load and versus condenser inlet temperature).

(1) cooling a fluid by natural convection over the cooling surface. (2) cooling a space by means of air cooled by natural convection.

one in which air movement is dependent upon the difference in density between the entering air and internal air. As the heat of the water is transferred to the air passing through the tower, the warmed air tends to rise and draw in fresh air at the base of the tower. See hyperbolic tower.

rate of heat removal from a fluid flowing through a cooler (air, water, brine, etc.) at stated conditions, the difference in specific enthalpies of the cooling fluid entering and leaving the cooler. In case frosting occurs within the cooler, the latent heat of fusion and the subcooling heat of the ice (frost) must be added in determining the net cooler refrigerating capacity.

the total useful capacity of the air conditioner for removing water vapor from the space to be conditioned.

(1) (brine cooler) product of the mass rate of water or brine flow and the difference in enthalpy of the entering and leaving water or brine, expressed in heat units per unit of time. It is expressed also by the total refrigeration effect less the heat leakage losses. (2) (condensing unit capacity) rate at which heat is removed from outer media by a refrigerant in the low-pressure side or by the difference in total enthalpy between refrigerant liquid leaving the unit and the total enthalpy of the refrigerant vapor entering it. (3) (packaged air conditioners) rate at which heat is removed from the airstream, as measured entering the cooling coil and leaving the unit. (4) rate at which heat is removed by the primary refrigerant from the cooling medium (secondary coolant) that is used to transmit the refrigerating effect.

that portion of the total refrigeration capacity of a liquid cooler that produces useful cooling. This is the product of the mass flow rate of liquid, specific heat of the liquid, and the difference between entering and leaving liquid temperatures expressed in energy units per unit of time. It is represented also by the total refrigeration capacity less the heat leakage rate

total cooling capacity with fan power adjustment

the refrigeration capacity available for space and product cooling. It is equal to the gross total cooling effect less the heat equivalent of energy required to operate the cooler.

the rate of heat flow out of an object by both natural convection and radiation is proportional to the temperature difference between the object and its environment and to the surface area of the object.

refrigerating or cooling system with control that normally avoids use of power during peak-load periods and usually requires means for storage of energy.

transfer of heat from oil in a pipe or tubing to a refrigerant or brine.

piping system in which a single pipe loop provides the cooling or heating distribution to multiple devices or through secondary or tertiary loops.

extended surface cooling towers with interconnecting piping placed in supply and exhaust airstreams. A circulated heat and mass transfer fluid is alternately brought in direct contact with each airstream.

heating, air-conditioning, or radiant system in which the heating or cooling emission is overhead.

(also known as self-contained unit), complete air-conditioning unit, including refrigeration compressor, cooling coils, fans, filters, automatic controls, etc., assembled into one casing.

an indirect evaporative cooler with integrated or nonintegrated primary and secondary air passages and provided with both primary and secondary air moving devices. This device also includes the entire water distribution, collection, and recirculation system with pump and piping. This type may have provisions for installation of other heat and mass transfer devices, such as a direct evaporative cooler and auxiliary heating and cooling coils.

a factory selected wall sleeve and separate unencased combination of heating and cooling components, assemblies, or sections. It may include heating capability by hot water, steam, or electricity and is intended for mounting through the wall to serve a single room or zone.

(1) cooling tower packing. See stuffing box. (2) stuffing around a shaft or valve stem to prevent fluid leakage.

the ratio of the net refrigeration effect to the adjusted net total capacity for the cooling coil. (Also see net refrigerating effect and adjusted net total capacity.)

the maximum rate at which heat is added to storage (cooling discharged from storage).

heat exchanger made of thin plates so formed that liquid to be cooled flows through the passage between the plates and the cooling fluid flows through the alternate passages.

the relative position on the cooling unit characteristic curve corresponding to a particular airflow rate. It is controlled during a test by adjusting the position of the throttling device, by changing flow nozzles or auxiliary fan characteristics, or by any combination of these.

(1) a device for transferring heat from the incoming potable water to the spill. (2) cooler for removing sensible heat before shipping, storing, or processing. (3) device for cooling a fluid before it enters a system.

heating coil installed upstream of cooling coil or at the front of an air-handling system to preheat air.

a thermostat with the ability to preset different temperature/time settings for heating and cooling equipment.

the unmet cooling load that accumulates during a period when cooling is not provided to the load and that must be met upon system start-up. Maximum pull-down load generally occurs on a Monday morning.

the sum of the nominal power demand (nameplate horsepower) of motors of all pumps that are required to operate at design conditions to supply fluid from the heating or cooling source to all heat transfer devices (e.g., coils, heat exchanger) and return it to the source.

system of radial feeders extending outward from a centrally located district energy plant (heating or cooling). Each feeder normally is composed of one supply pipe and one return pipe.

a heating or cooling surface that delivers 50% or more of its heat transfer by radiation, which may be either an integral part of the building (e.g., floor or ceiling heating) or detached from the building elements (e.g., suspended ceiling panel).

a sensible cooling system that provides more than 50% of the total heat flux by thermal radiation.

spot-cooling effect produced in a tube into which gas is introduced tangentially, producing vortex flow.

a remote unit with cooling that is provided at the dispensing valve and accomplished by circulating cold water or cold carbonated water through one of the lines and returning the same to a refrigeration unit.

(1) a condition pertaining to air-cooled condensers in which a portion of the discharge air enters along with the fresh air, the amount of recirculation is determined by equipment design, placement in regard to adjoining objects, and atmospheric conditions. The effect is generally evaluated on the basis of the decrease in unit capacity. (2) condition pertaining to cooling towers and evaporative condensers in which a portion of the discharge air enters along with the fresh air, the amount of recirculation is determined by equipment design, placement in regard to adjoining objects, and atmospheric conditions. The effect is generally evaluated on the basis of the increase in entering wet-bulb temperature compared to the ambient.

(1) cooling of air that has been previously heated. (2) lowering the temperature of air that has been previously heated by a mechanical heating system.

heat exchanger, after the condenser, for subcooling the condensed refrigerant.

process of cooling refrigerant below condensing temperature for a given pressure, also, cooling a liquid below its freezing point where it can exist only in a state of unstable equilibrium. See supercooling.

a refrigerated vehicle where the space given to the ice or cooling element is in the end of the truck or rail car.

(1) Cooling of a space, substance or system to lower and/or maintain its temperature below the ambient one (removed heat is rejected at a higher temperature) (2) Artificial cooling

process of using heat that must be rejected or absorbed in one part of the cycle to perform a useful function in another part of the cycle.

heating coil installed downstream of cooling coil.

energy obtained from sunlight, wind, earth, geothermal sources, or bodies of water to provide heating, cooling, lighting, or water-heating services to buildings. See nondepletable energy.

air removed from a space to be recirculated or exhausted. Air extracted from a space and totally or partially returned to an air conditioner, furnace, or other heating, cooling, or ventilating system.

system of air conditioning in which packed beds of crushed stone or gravel are used for both evaporative cooling and heat energy storage.

system that reduces heat gain through a roof by cooling the outside surface with a water spray, suited for only temporary treatment because high humidity may be introduced by air intakes on the roof.

a test facility consisting of a room-side compartment and an outdoor-side compartment, each of which is equipped with instrumented reconditioning equipment. The output of this equipment is measured and controlled to counterbalance the room-side net total cooling effect of the air conditioner under test.

substance added to water used in condensers, boilers, piping, and cooling towers to prevent or minimize the formation of insoluble deposits.

the total cooling output of an air conditioner during its normal annual usage period for cooling divided by the total electric energy input during the same period in consistent units (analogous to the SEER but in I-P or other consistent units).

for the cooling season, the ratio of the total heat removed from the conditioned space to the total electrical energy input required to remove that heat, evaluated over all appliance operating modes. The quantity is expressed in units of Btu/Wh.

for the cooling season, the ratio of the total heat removed from the conditioned space to the total electrical energy input if the combined appliance operated exclusively in a space-cooling-only (COOL) mode. The quantity is expressed in units of Btu/Wh.

a factory-made assembly in one structure that includes a complete mechanical refrigerating system and that has the primary function of cooling potable water and also provides for dispensing such water, by either integral or remote means or both.

selection of heating or cooling operation by means of a combination of manual and automatic switches, which usually are located at the room thermostat.

the rate, expressed in W (Btu/h), at which the equipment lowers the dry-bulb temperature (removes sensible heat) of the air passing through it under specified conditions of operation.

(1) amount of sensible heat removed from air during cooling. (2) difference between total cooling effect and dehumidifying effect.

a panel designed for sensible cooling of an indoor space through heat transfer to the thermally effective panel surfaces from the occupants and/or indoor space by thermal radiation and natural convection.

reduction of heating (by reducing the setpoint) or cooling (by increasing the setpoint) during hours when a building is unoccupied or during periods when lesser demand is acceptable.

condenser in which the cooling medium circulates in a coil located in a shell containing the condensing refrigerant.

an operating mode that occurs during space cooling when either the refrigerant-to-water heat exchanger water pump has automatically cycled off or the rate of heat transfer to the domestic water has become negligible. With respect to seasonal performance calculations, this mode occurs when the water-heating load is satisfied but a space cooling load remains.

cooling the air of a limited portion of an enclosed space without the use of walls or partitions.

cooling by spraying a low-temperature liquid on the object to be cooled.

system for lowering the temperature of water by conductive and evaporative cooling of the water in contact with outside air. Water to be cooled is sprayed by nozzles into the air above a pond of water and allowed to fall into the pond.

liquid cooling tank whose walls are sprayed with chilled water.

an air cooler, with or without cooling surface, fitted to spray liquid continuously into the airstream.

ratio calculated from the capacity and power input values obtained at standard rating conditions.

normally open, digital, contact device in which contact closure indicates a change of status, e.g., on-off, heating-cooling, day-night, etc.

the amount of usable cooling energy remaining in a thermal storage device at any given time.

an air-distribution system that, during the cooling operation, limits the amount of mixing in the space and instead relies on thermal plumes to produce a stratified environment with cooler and fresher air near the floor and warmer and less fresh air near the ceiling. Examples are underfloor air-distribution system (UFAD) and DV systems.

a heat exchanger for cooling liquid refrigerant below its condensing temperature at a given pressure.

at a defined pressure, the difference between a given liquid temperature and the bubble point temperature.

total refrigerant heat rejection effect less the condensing heat rejection effect.

additional refrigeration effect made available by subcooling the refrigerant liquid in the condenser.

(submerged condenser), condenser in which the piping is submerged in a vessel containing cooling water.

cooling a substance below the normal freezing point without solidification.

(1) (pneumatic) the air supply piping to all controllers or other devices requiring a main air supply. (2) pipes through which the heating or cooling medium of a system flows from the source of heat or refrigeration to the runouts and risers leading to the heating or cooling units. (3) source of electric power to a system.

method of cooling air or other gas by passing it over cold surfaces.

(1) air-conditioning unit designed primarily for cooling and dehumidifying air by passing the air over cooling coils that are below the dew point of the air. (2) dehumidifier with a surface at a temperature below the dew point.

interior surfaces whose temperature is controlled or monitored for heating and cooling purposes.

any sensible heating or cooling panel that is used in testing for performance and/or rating purposes.

device that relies on the cooling effect of the airflow to change the temperature of a heated body in proportion to the air speed. Types include hot-wire anemometer, heated-bulb thermometer, heated-thermocouple anemometer, and heated-thermistor anemometer.

heating or cooling effect delivered to a product or space.

heating or cooling effect put out by a source or removed from a storage device.

the fraction of distribution system losses (gains for cooling) that are returned to the conditioned space.

(1) accumulation of energy in a body or system in the form of sensible heat (temperature rise) or latent heat (change of phase). (2) full storage: thermal storage system having capacity to meet all on-peak cooling or heating requirements by being charged off peak, and without energy added on peak. (3) fully charged condition: the state of a thermal storage device at which, according to the design, no more heat is to be removed from the thermal storage device. This state is generally reached when the control system stops the charge cycle as part of its normal control sequence. (4) fully discharged condition: the state of a thermal storage device at which no more usable cooling energy can be recovered from the storage device. (5) normally interchangeable term with cool storage or ice storage when addressing air-conditioning thermal storage systems. (6) technology or systems of accumulating cooling or heating capacity for subsequent use. (7) temporary storage of high or low-temperature energy for later use.

to supply cooling or heating to storage.

substance in which cooling or heating energy is stored.

method for cooling by the Peltier effect.

time rate of cooling equal to 12,000 Btu/h (approximately 3517 W). It is a quantity approximately equal to the latent heat of fusion or melting of 1 ton (2000 lb) of ice, from and at 32°F (0°C).

(1) amount of sensible and latent heat removed from the conditioned space. (2) difference between the total enthalpy of the dry air and the water-vapor mixture entering and leaving the cooler.

total heat load expressed in tons of cooling, the sum of the sensible tons (dry tons) and the latent tons (wet tons).

cooling produced by evaporation of fluid lost by a body or material.

chilled, elongated space for cooling foodstuffs on a movable transport system by rapid circulation of cold air.

piping system in which the fluid withdrawn from the supply passes through a heating or cooling unit to a separate return main.

an air-distribution system that uses an underfloor plenum (open space between the structural concrete slab and the underside of a raised-floor system) to deliver conditioned air into the space, typically through floor diffusers. Air is returned at a level above the occupied zone (typically at the ceiling level). Under cooling operation, UFAD systems produce a stratified environment, similar in principle to that of displacement systems. The primary difference between these systems is that UFAD outlets deliver air at higher velocity, producing greater mixing in the area near the outlet discharge.

(1) an assembly of cooling coils with drain pan, fan, and enclosure. (2) direct cooling, factory made encased assembly including an air-cooling coil, refrigerating compressor and condenser, fan and motor (usually), and directional outlet, including the necessary automatic controls.

one or more factory-made assemblies that normally include an evaporator or cooling coil and a compressor and condenser combination.

an hour in which one or more zones is outside of the thermostat set point plus or minus one half of the temperature control throttling range. Any hour with one or more zones with an unmet cooling load or unmet heating load is defined as an unmet load hour.

piping arrangement for a heating, air-conditioning, or refrigerating system in which heat transfer fluid is circulated through supply mains that are below the levels of heating or cooling units they serve.

total amount of cooling discharged from a thermal storage device, at or below the maximum usable discharge temperature, for a particular storage cycle.

cooling by vaporization under vacuum of part of the water contained in the material to be cooled.

throttling control of water during a cooling or heating process.

heating and cooling equipment that operates in stages of different capacity depending on building load, e.g., electric furnaces with several separate heater elements.

see cooling tower.

a system by which the supply air of a cooling system is cooled indirectly with water that is itself cooled by heat or mass transfer to the environment without the use of mechanical cooling.

an automatic valve that controls the flow of cooling water through a condenser to maintain a set condensing pressure.

a heat exchanger that uses the condenser water side of the system for cooling without requiring the operation of the chiller. Also a coil on the air entering side of a heat pump or HVAC unit that uses condenser water flow to precondition the entering air when conditions are favorable. See also cooling.

economizer process that uses cooling tower-water directly or indirectly in the cooling coils, permitting the chiller to be shut down when the outside wet-bulb temperature is sufficiently low.

in petroleum oils, a material, usually a solid hydrocarbon, that may separate on cooling of an oil refrigerant mixture.

latent heating or cooling load. See ton of refrigeration.

the dead band between control setpoints, such as between heating and cooling, where the lowest amount of mechanical energy is being utilized. Contrast dead band.

(1) a separately controlled heated or cooled space. (2) one occupied space or several occupied spaces with similar occupancy category, occupant density, zone air distribution effectiveness, and zone primary airflow per unit area. (3) space or group of spaces within a building for which the heating, cooling, or lighting requirements are sufficiently similar that desired conditions can be maintained throughout by a single controlling device.

space or group of spaces within a building with heating or cooling requirements sufficiently similar that comfort conditions can be maintained by a single controlling device.