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).

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.)

(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.

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.

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.

ability of a wire to carry electric current safely without undue heating.

(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.

the ratio of annual output energy to annual input energy, which includes any nonheating season pilot input loss and, for gas- or oil-fired furnaces or boilers, does not include electric energy.

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

group of welding processes wherein coalescence of metal is produced by heating with an electric arc or arcs, with or without the application of pressure, and with or without filler metal.

International, diverse organization representing building system design and industrial processes professionals around the world. (Formally known as American Society of Heating, Refrigerating and Air-Conditioning Engineers.)

International, diverse organization representing building system design and industrial processes professionals around the world. (For the US Internal Revenue Service (IRS), known as the American Society of Heating, Refrigerating and Air-Conditioning Engineers.)

a source of thermal energy, other than solar, used to provide the service water heating, usually in the form of electrical resistance heat or thermal energy derived from combustion of fossil fuels.

steam, hydronic, or electric heating device located at or near the floor.

a ducted centrifugal fan used in a heating, ventilating, and air-conditioning system. See also centrifugal fan, fan.

a closed, pressure vessel that uses fuel or electricity for heating water or other fluids to supply steam or hot water for heating, humidification, or other applications.

surfaces of the boiler that are exposed to the products of combustion on one side and water on the other, expressed in area units (of the side receiving the heat).

design maximum rating of a steam or water boiler expressed as the total heat transferred by the heating surfaces in Btu/h (kW). Sometimes expressed in horsepower or pounds (torque, kilograms) of steam per hour. Compare to boiler capacity.

model based on first-principles engineering methods that provides information on the energy-using systems in a building (heating, ventilation, and air conditioning; lighting; occupancy; plug loads; building envelope). The model, along with weather data, serves as the input data for a specific computer building energy simulation program. When run, the computer simulation program will estimate the energy use and demand in the described building for a time interval specified in the building energy model. Depending on the kind of simulation program and how it is set up to run, various kinds of output may be produced.

(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.

heating or refrigerating piping system in which circulating water or brine is completely enclosed, under pressure above atmospheric, and shut off from the atmosphere, except that the expansion/compression tank could be open to the atmosphere. See also water system.

the ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump system, including the compressor and, if applicable, auxiliary heat, under designated operating conditions.

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.

a heater installed within the collector loop when testing the solar domestic-water heating system with a nonirradiated array.

a unit that is designed to provide space heating and potable water heating from a single, primary energy source.

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.

an operating mode where the heat pump is space heating and the desuperheater is heating domestic water.

(1) adjustment of the fuel rate and air/fuel mixture ratio in response to heating load and flue gas air condition over the full range of the burner capacity from some preset minimum to 100%. (2) device or series of devices that control the flow of fuel and combustion air in the desired ratio to provide efficient combustion.

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

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.

(1) portion of the total refrigerant heat-rejecting effect of a condenser, which is used for condensing the entering refrigerant vapor to a saturated liquid at the entering refrigerant pressure. (2) the portion of the total heat rejection of a condenser that is used for desuperheating and condensing the entering refrigerant vapor to a saturated liquid. This is the product of the mass rate of refrigerant flow and the difference between the enthalpy of the entering refrigerant vapor and that of the saturated refrigerant liquid at the leaving pressure.

see heat pump, cooling, and heating.

(peak nucleate boiling heat flux), heat flux for which the surface coefficient of heat transfer between a heating wall and a liquid under nucleate boiling is a maximum. Also called maximum nucleate boiling heat flux.

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.

act of controlling the refrigerating cycle or heating cycle to periodically melt the unacceptable accumulation of ice on evaporator tubes, windows, etc.

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

A heat exchanger in which superheated gas exiting a refrigeration (or air-conditioning/heat pump) system releases heat whenever the system is operating, thus enabling energy recovery to be performed (e.g., for domestic or service water heating).

heat exchanger, preceding the condenser or incorporated in it, for removing all or part of the superheat.

sensible heat rejection from gaseous refrigerant in a condenser. Occurs prior to the gas-to-liquid phase change.

process using dielectric heating with high voltage and high frequency or ultrahigh frequency electric fields.

system where the combustion heat and the products of combustion are transferred directly to the heated medium.

withdrawing cooling or heating potential from thermal storage.

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 heating demand per unit area. Customary units are kW/hectare or therms/acre.

(1) heating water for domestic or commercial purposes other than space heating and process requirements. (2) potable hot water as distinguished from hot water used for heating.

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) 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.

steam heating in which a return pipe carries both condensate and air. The return pipe is always above the waterline in the boiler in a gravity system.

heating system utilizing two fuel or energy sources, such as gas, oil, coal, or electric power, either as alternate sources or with one as a booster to the other.

method of separation and automatic return of liquid refrigerant from an accumulator in the low side to the high side of the plant.

(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.

average electrical power input to the equipment within a defined interval of time, in watts (i.e., the sum of: the power input for operation of the compressor, excluding additional electrical heating devices, the power input of all control and safety devices of the equipment, and the proportional power input of the conveying devices for the transport of the heat transfer media through the heat pump only. Also, indoor-side and outdoor-side pumps, whether internal or external, whether provided with the equipment or not).

permanently installed electric heating as the principal source of space heating throughout an entire dwelling or business establishment.

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

systems that primarily use a combination of mechanical equipment, airflow, water flow, and electrical energy to provide heating, ventilating, air conditioning, filtration, humidification, and dehumidification for the purpose of human comfort or process control of temperature and humidity.

(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.

boiling phenomenon corresponding to the development of a continuous vapor layer on the heating surface that separates this surface from the boiling liquid.

a heating terminal unit that primarily consists of one or more finned tubes and a casing cabinet.

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.

an electric, gas, or oil-burning appliance designed to supply heat through a system of ducts with air as the heating medium. Forced-air furnaces circulate the heated air by means of a fan or blower, whereas gravity furnaces depend primarily on natural convection.

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

(1) the process of determining the ability of the HVAC system to deliver heating, ventilating, and air-conditioning services in accordance with the final design intent. (2) that full range of checks and tests carried out to determine if all components, subsystems, systems, and interfaces between systems function in accordance with the contract documents. In this context, function includes all modes and sequences of control operation, all interlocks and conditional control responses, and all specified responses to emergency conditions.

(1) enclosed chamber or structure in which heat is produced, as by burning fuel or by converting electrical energy. (2) part of a warm-air heating system in which energy is converted to heat.

arc-welding process wherein coalescence is produced by heating with an arc between a continuous filler metal (consumable) electrode and the work. Note: shielding is obtained entirely from an externally supplied gas or gas mixture.

arc-welding process wherein coalescence is produced by heating with an arc between a single tungsten (nonconsumable) electrode and the work. Note: shielding is obtained from a gas or gas mixture. Pressure may or may not be added.

group of welding processes wherein coalescence is produced by heating with a gas flame or flames, with or without the application of pressure, and with or without the use of filler metal.

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.

condensate return arrangement for low-pressure steam heating systems, featuring a constant waterline in the boiler.

heating degree day.

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 heat pump capacity and the building heat requirement are equal. Heat pump heating effect. See compressor heating effect.

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.

(1) rate of heat delivery by the refrigerant assigned to the compressor in a heat pump. (2) rate of heat delivery by the refrigerant assigned to the compressor in a heat pump system equal to the product of the mass rate of refrigerant flow produced by the compressor and the difference in specific enthalpies of the refrigerant vapor at thermodynamic state leaving the compressor and saturated liquid refrigerant at the pressure of the vapor leaving the compressor.

technology or systems used to store heating capacity.

a heating system where the externally applied heat source follows (traces) the object to be heated (e.g., water piping).

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

process of adding heat energy causing a rise in temperature or a transfer of sensible heat into latent heat. See also district heating, heating system.

the rate of heat that the equipment adds to the conditioned space or heat transfer fluid in a defined interval of time, expressed in Btu/h (W).

coil that uses a heat transfer fluid, condensing refrigerant, or direct electrical resistance elements to provide heating to heat fluids (air, gas, or liquids).

the period of operation including prepurge, primary heat-producing energy flow, and postpurge.

see degree day.

[i.e., HDD65 (HDD18)]. For any one day, when the mean temperature is less than the local or country-specific common temperature base. Annual HDDs are the sum of the HDDs over a calendar year.

the outdoor dry-bulb temperature equal to the temperature that is exceeded at least 99.6% of the number of hours during a typical weather year.

heating rate required to replace heat loss from the space being controlled.

(1) ratio of the heating building load to the steady-state heating load. (2) ratio of the total heating of a complete cycle for a specified period, consisting of an on time and off time, to the steady-state heating done over the same period at constant ambient conditions.

for the space-heating season, the ratio of the total space heating delivered to the total electrical energy input if the combined appliance operated exclusively in a space heating only mode. The quantity is expressed in units of Btu/Wh. For SI use, compare coefficient of performance.

sensible heat carried away by the flue gas and the sensible and latent heat carried away by the water vapor in the flue gas.

one in which heat is transferred from a source of energy through a distribution network to spaces to be heated.

amount of heat produced by the complete combustion of a unit quantity of fuel. The gross or higher heating value is that obtained when all the products of combustion are cooled to the temperature existing before combustion, the water vapor formed during combustion is condensed, and all the necessary corrections have been made. The net or lower heating value is obtained by subtracting the latent heat of vaporization of the water vapor formed by the combustion of the hydrogen in the fuel from the gross or higher heating value.

the amount of heat produced per unit of fuel when complete combustion takes place at constant pressure, the products of combustion are cooled to the initial temperature of the fuel and air, and the vapor formed during combustion is condensed. HHV is expressed in Btu/lb (J/kg) or Btu/ft3 (W/m3) for gaseous fuel and in Btu/lb (J/kg) or Btu/gal (J/l) for liquid fuel.

heating load factor

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

(also known as hydronic heating system or wet heating system) heating system for a building in which the heat-conveying medium is hot water and the heat emitters are radiators, convectors, or panel coils.

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

heating load for a given hour.

duct and fittings used for conveying air in residential, commercial, institutional, and industrial heating, ventilating, and air-conditioning systems.

the equipment, distribution systems, and terminals that provide, either collectively or individually, the processes of heating, ventilating, or air conditioning to a building or portion of a building.

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.

one in which combustion products do not come into contact with the material to be heated, heating of the material is accomplished by radiation or conduction from the heated surface.

one in which a fluid, such as air, is circulated to the material or space to be heated or is used to heat air so circulated.

range of electromagnetic radiation wavelengths greater than those of visible light and shorter than those of microwaves, generally between 0.8 micrometer and 1 millimeter. IR originates from either incandescent or nonincandescent hot bodies or from flames. The energy is used as a means of direct heat transfer from the source to the object(s) to be heated without materially heating the intervening air.

a self-contained packaged water-heating device that is capable of providing a continuous supply of hot water at a predetermined temperature without any storage capacity. Energy sources can be fuel fired (natural gas/propane), electric, or steam fired. The term is typically utilized for domestic water-heating applications, but pool, spa, and radiant heating systems are also an application. Another term that is used on smaller heaters is point-of-use heaters. Some manufacturers allow for multiple unit installations when the need for larger capacity is required.

a seasonal efficiency number that is a combined value based on the formula listed in AHRI Standard 920 of the two COP values for the heating season of a direct expansion dedicated outdoor air system (DX-DOAS) unit water or air source heat pump, expressed in W/W.

alcohol thermometer used to measure low velocities in air circulation by heating the large bulb of the thermometer above 100°F (38°C) and noting the time it takes to cool from 100°F to 95°F (38°C to 35°C) or some other interval above ambient temperature with the time interval being a measure of the air current at that location.

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

(1) in gravity warm air heating, the duct running horizontally from the furnace to the riser or stack. (2) in plumbing, a water conductor from the roof to the storm drain.

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.

electric, gas, or oil-burning appliance designed to supply low-pressure steam or hot water for space-heating application. A low-pressure steam boiler operates at or below 15 psig [103 kPa (gage)] steam pressure, a hot-water boiler operates at or below 160 psig [1100 kPa (gage)] water pressure and 250°F (120°C) water temperature.

use of fluids less than 200°F (50°C) (in round numbers) for district-heating supply, permitting use of energy sources formerly discarded.

raising the temperature or change of phase of a solid or fluid by use of fossil-fuel burners, electric resistance heaters, heat pumps, or other systems that require energy to operate.

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) method of defrosting in which the temperature of the evaporator coils is allowed to rise naturally during an off-cycle, during which no refrigerant is supplied. (2) rapid heating of the evaporator coil during the off part of each cycle.

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

piping system in which the condensable vapor withdrawn from the supply main passes into a heating unit and returns as condensate to the same supply main.

heating or refrigerating piping system in which the circulating water or brine return main is connected to an open-vented elevated tank that serves as a reservoir to accommodate expansion and contraction of the fluid and as an inspection point for the condition of the fluid. See also down-feed system, water system.

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

a boiler that is shipped complete with heating equipment, mechanical draft equipment, and automatic controls, usually shipped in one or more sections. A packaged boiler includes factory-built boilers manufactured as a unit or system, disassembled for shipment, and reassembled at the site.

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.

terminal device that combines a true VAV box in parallel with a fan and optional heating coils. Fan operation is intermittent.

actual load for heating the system following setback.

A device that is powered by means of an electrical plug and matching socket or receptacle. This excludes devices that are accounted for as part of major building end uses such as HVAC, lighting systems, and water heating.

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

(1) heating a food product prior to a subsequent treatment. (2) in air conditioning, to heat the air ahead of other processes. (3) to heat the water prior to heating by the auxiliary thermal source.

surface having the heating medium on one side and fluid (or extended surface) on the other.

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

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.

a procedure employed for verifying the accuracy of the measuring techniques (temperature, airflow rates, duct heat calibration) employed in determination of the room heating effect. This qualification procedure is periodically employed in determining the room heating effect.

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 system that transfers heat to objects and surfaces within the heated space primarily (greater than 50%) by infrared radiation.

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

to lower the temperature of air that has been previously heated by a mechanical heating system.

(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.

comes from internal heat sources. It is used for space heating, domestic or service water heating, air reheat in air conditioning, process heating in industrial applications, or other similar purposes. Recovered heat may be stored for later use.

interconnected parts forming a closed circuit in which refrigerant is circulated and having the condenser located to transfer heat to the zone to be heated.

refuse used as a combustion fuel source to provide heat in a district-heating plant.

heat rejected in one part of a system and used to perform a useful function in another part.

heating coil installed downstream of cooling coil.

raising the temperature of air that has been previously cooled either by mechanical refrigeration or an economizer system.

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.

providing comfort heating for single-family living quarters.

the electrical conducting medium that is heated by an electric current and that also dissipates this heat into the air or a fluid.

welding with resistance heating and pressure, the work being part of the electrical circuit.

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.

the total heating output of a heat pump during its normal annual usage period for heating divided by the total electric energy input during the same period in consistent units (analogous to HSPF but in I-P or other consistent units).

a fluid of known properties (e.g., water, steam, or brine) that is used as a heating medium.

(1) a volatile refrigerant (usually a single refrigerant or an azeotropic mixture) of known properties that is used as a heating medium. (2) volatile or nonvolatile substance in an indirect refrigerating system that absorbs heat from a substance in space to be refrigerated and transfers this heat to the evaporator of the refrigerating system.

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

an enclosed space within a building that is heated by a heating system whose output capacity is greater than or equal to 3.4 Btu/h·ft2 (10 W/m2) of floor area but is not a conditioned space.

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

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

hot-water heating system in which each radiator is connected in series with the next and all flow returns to the boiler in the loop. Also known as a single pipe or one pipe system.

see domestic hot water.

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.

heater installed within the collector loop when testing the solar domestic-water-heating system with a nonirradiated array.

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.

an operating mode that occurs during space heating 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 heating load remains.

(1) movement of air into and out of buildings, chimneys, flue gas stacks, or other containers and is driven by buoyancy. Buoyancy occurs due to a difference in indoor to outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the chimney effect, and it helps drive natural ventilation and infiltration. (2) movement of air or other gas in a vertical enclosure (e.g., duct, chimney, building), induced by the density difference between the air or other gas in the enclosure and the ambient atmosphere. Note: stack effect is a significant concern in heating-system design for tall buildings in cold climates. Sometimes referred to as chimney effect. (3) pressure difference caused by the difference in density between indoor and outdoor air due to an indoor/outdoor temperature difference. (4) the vertical airflow within buildings caused by temperature differences between the building's interior and exterior.

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

a modulating control that cycles a burner between the reduced input rate and OFF if the heating load is light. If a higher heating load is encountered that cannot be met with the reduced input rate, the control goes into a modulating mode where it either gradually or incrementally increases the input rate to meet the higher heating load. If, at that point, a lower heating load is encountered, the control either gradually or incrementally decreases to the reduced input rate.

heating foods or other materials to kill microorganisms, usually to a temperature of 212°F (100°C) or higher.

arc welding process wherein coalescence is produced by heating an arc or arcs between a bare metal electrode or electrodes and the work. Note: the arc is shielded by a blanket of granular fusible material on the work. Pressure is not used, and filler metal is obtained from the electrode and sometimes from a supplementary welding rod.

(1) air delivered by mechanical or natural ventilation to a space, composed of any combination of outdoor air, recirculated air, or transfer air. (2) air entering a space from an air-conditioning, heating, or ventilating apparatus for the purpose of comfort conditioning. Supply air is generally filtered, fan forced, and either heated, cooled, humidified, or dehumidified as necessary to maintain specified conditions. Only the quantity of outdoor air within the supply airflow may be used as replacement air.

(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.

a combination of equipment and auxiliary devices (e.g., controls, accessories, interconnecting means, and termi­nal elements) by which energy is transformed so it performs a specific function such as HVAC, service water heating, or lighting.

a heat exchanger for indirect heating of water, typically for domestic use, which is designed to be used without a water storage tank. See instantaneous heater.

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.

a systematic process or service applied to heating, ventilating, and air-conditioning (HVAC) systems and other environmental systems to achieve and document air and hydronic flow rates. The adjustment of fluid flow rates through distribution systems by manually adjusting the position of dampers, valves, etc., or by using automatic control devices to control the position of dampers, actuators, valves, etc.

(1) thermal energy storage may refer to a number of technologies that stores energy in a thermal reservoir for later reuse. They can be employed to balance energy demand between day time and night time. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment. The principal application today is the production of ice, chilled water, or eutectic solution at night, which is then used to cool environments during the day. (2) thermal energy storage technologies store heat, usually from active solar collectors in an insulated repository for later use in space heating, domestic or process hot water, or to generate electricity. Most practical active solar heating systems have storage for a few hours to a day's worth of heat collected. There are also a small but growing number of seasonal thermal stores used to store summer heat for space heating during winter.

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.

(1) relay activated by change in temperature. (2) relay in which the displacement of the moving contact member is produced by heating of a part of the relay under the action of electric currents.

(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.

trap installed on the discharge side of a heating unit and designed to pass air freely on start-up and condensate at a subcooled temperature, but to prevent steam vapor passing into the return. It can have a bellows or encapsulated metallic diaphragm containing a small quantity of volatile liquid. At the bottom of the diaphragm or bellows is attached a hardened, self centering valve head operating on the pressure side of the valve seat. At ordinary temperatures and atmospheric pressure, the valve is fully open to permit free passage of air and cold condensate. The trap discharges at a fixed temperature below that of steam saturation temperature and closely follows the steam pressure/temperature curve.

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

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.

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.

climates that have more than 9000 annual heating degree-days base 65°F-day (5000 annual heating degree-days base 18°C-day).

ratio of the total to the apparent volumetric efficiency. Also called real or no-clearance volumetric efficiency.

U-factor converted into electrical terms for calculations in electric heating. The amount of heat flow, in watts per square foot per degree Fahrenheit temperature difference (W/ft2·F) between air on the inside and air on the outside of the building section (wall, floor, roof, or ceiling). For conversion, W = 0.293U.

addition to the capacity of a heating system (as calculated for heat loss) to provide quick warm up in the morning.

latent heating or cooling load. See ton of refrigeration.

number which indicates interchangeability of fuel gases, obtained by dividing the heating value of a gas by the square root of its specific gravity.

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.

the region normally occupied by people within a space. In the absence of known occupant locations, the occupied zone is to be between the floor and 1.8 m (6 ft) above the floor and more than 1.0 m (3.3 ft) from outside walls/windows or fixed heating, ventilating, or air-conditioning equipment, and 0.3 m (1 ft) from internal walls.