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).

ratio of the apparent heat recovered to the sum of the thermodynamically limited maximum possible in a counterflow heat exchanger of infinite heat transfer area; plus, all external energy inputs including, but not limited to, fan energy, auxiliary heaters, cross leakage, and casing loss. Note: This ratio adjusts heat exchanger effectiveness for auxiliary energy inputs of the energy recovery system.

exchanger that transfers heat from an exhaust airstream to a separated supply airstream. Note: fixed plate, rotary wheels, heat pipes, runaround coil loops, and shell and tube condensers are the most common types.

(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.

in a parallel flow or counterflow heat exchanger, the arithmetic mean of the temperature differences between the two fluids at both ends of the exchanger.

a colloquial term for a heat exchanger used to refrigerate a secondary coolant.

a heat exchanger for cooling brine with an evaporating refrigerant.

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.

The thermally insulated section of a cryogenic plant that contains the components operating at low temperatures (heat exchangers, distillation columns, pipes, etc.).

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).

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.

a heat exchanger in which the primary heat transfer vapor changes its state to a liquid phase.

heat exchanger tube manufactured to special requirements such as tolerances, finish, and temper.

heat exchanger in which fluids flow in opposite directions approximately parallel to each other, inlets for the two fluids are at opposite ends of the exchanger.

heat exchanger in which fluids flow perpendicular to each other. Compare to counterflow heat exchanger.

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.

the ratio of the thermal energy transferred to or from the conditioned space to the thermal energy transferred at the equipment distribution system heat exchanger. Energy delivered to or from the conditioned space includes distribution system losses to the conditioned space.

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.

two pipes arranged concentrically, one within the other, and in which one fluid flows through the inner pipe and the other through the annulus between them.

two fluids separated by two walls with the space between open to the atmosphere so that a fracture on one wall will not transfer one fluid into the other. Used in water systems with a potable fluid and a potentially hazardous fluid.

(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.

ratio of the actual heat transfer to the thermodynamically limited maximum heat transfer possible in a counterflow exchanger of infinite transfer area.

(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.

heat exchanger assembly for transferring heat between two isolated fluid sources. The recovery system may be of air-to-air design or a closed loop hydronic system design. The system will include all necessary equipment such as fans and pumps, associated ducts or piping and all controls (operating and safety), and other custom-designed features.

heat exchanger, usually of the shell-and-tube type, over which liquid refrigerant is dripped or sprayed and evaporated.

heat exchanger installed in the hot-gas duct between the boiler and the stack to transfer a portion of the heat (that would be lost up the stack) to the feedwater.

a boiler whose heat exchanger consists of only finned tubes.

condition existing when the flame resulting from the combustion of the fuel comes into contact with any interior surface of the furnace. It has the potential of causing damage to the heat exchanger.

in a heat exchanger with a bundle of tubes, the section that is effectively traversed by the external fluid.

in a thermal storage system or a heat pump, a closed loop of piping, plastic tubing, or ducting used as a heat exchanger between the ground (acting as a low-grade heat source or heat sink) and a circulating fluid.

(1) heat exchange surface area of any heat exchanger available for transmitting heat. (2) process of heat transfer in which heat flows from one substance to another. (3) (also known as heat interchanger), device to transfer heat between two physically separated fluids. See also superheater.

outside area of a heat exchanger through which heat flows. See fin.

in a heat exchanger with a bundle of tubes, the section that is effectively traversed by the external fluid just before it passes through the tube bundle. The area measured is the lesser area of the two heat-exchanger surfaces.

(also known as tube sheet), plate located at the end(s) of a multitubular shell-and-tube heat exchanger, into which the tubes are fixed.

(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.

(also known as water heater), heat exchanger taking heat from steam or water rather than heat directly.

the heat exchanger that removes heat from or adds heat to the conditioned space.

(1) a factory-made assembly of elements in which the heat is transferred from the liquid to the refrigerant, causing the refrigerant to evaporate and the liquid to be cooled. (2) heat exchanger designed to cool liquids.

superheater or desuperheater.

apparatus in which fluids exchange heat by flowing in an assembly of separated channels.

a heat exchanger that can be cooled by air, brine, water, or refrigerant vaporization to cool oil in a lubrication system.

the heat exchanger that rejects heat to, or absorbs heat from, a source external to the conditioned space.

heat exchanger in which fluids flow approximately parallel to each other and in the same direction.

fixed plates that separate and keep the hot and cold fluids separate. See also plate liquid cooler.

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.

(also called plenum box and plenum chamber) (1) a compartment or chamber, to which one or more ducts are connected, that forms a part of the air-distribution system and that is not used for occupancy or storage. A plenum often is formed in part or in total by portions of the building. (2) an air compartment that is attached to, or is an integral part of, a forced-air furnace which is designed to either distribute the heated air after it leaves the heat exchanger in the case of a supply plenum or to collect air that enters the return inlet in the case of a return plenum. (3) component forming an interface between a ductwork and one or more air terminal devices, by virtue of its design or by the inclusion of accessories, it can also be used to equalize the pressure/velocity across the air terminal device.

the design that permits the continued operation of the combustion blower in a power vented unit, power burner unit, or forced draft unit for a period of time after the main burner is shut off for the purpose of venting of residual flue gas in the heat exchanger and the venting system.

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.

(1) device designed to intercept radiated heat. (2) in a furnace, a sheet of metal or other material supported between the heat exchanger and the casing to protect the casing from heat, not to be considered as a heat transfer surface.

(1) externally cooled heat exchanger in the high side of a refrigerating absorption system for condensing absorbent and separating it from the refrigerant before passing it to the condenser. (2) in electricity, a device for converting AC to DC current.

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

simple cycle gas turbine to which has been added a heat exchanger to warm incoming combustion air with heat from exhaust gases in order to increase thermal efficiency.

finned-tube coils (closed system) or spray chambers (open systems) in which a liquid is circulated by gravity or pump action through a heat source exchanger and then through a heat sink exchanger. Antifreeze may be used in the coil loop and a desiccant in the spray system.

exchanger having a surface on which a fluid can be solidified and the solid layer scraped off.

(1) the fluid that flows through the condenser as a coolant. (2) fluid that flows through a heat exchanger that transfers thermal energy from the primary transfer fluid to the application that uses solar energy.

nest of tubes or pipes, or a coil of tube or pipe, contained in a shell or container. The pipe(s) carries a fluid through it, while the shell is also provided with an inlet and outlet for flow of another fluid.

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.

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

(1) at a defined pressure, the difference between a given vapor temperature and the dew-point temperature. (2) the difference in temperature between the saturation temperature corresponding to the measured outlet pressure and the measured outlet temperature of the refrigerant vapor leaving the heat exchanger.

(1) group of tubes in a boiler that absorb heat from the products of combustion to raise the temperature of the vapor passing through the tubes above the temperature corresponding to its pressure or saturation temperature. (2) heat exchanger used on flooded evaporators, where hot liquid on its way to enter the evaporator is cooled by giving up heat to both dry and superheat the wet vapor leaving the evaporator.

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.

any air conditioner or heat pump that has three major assemblies separated from each other. The compressor would be in a first assembly, with one refrigerant heat exchanger in a second assembly, and the second refrigerant heat exchanger in a third assembly.

any air conditioner or heat pump that has two major assemblies separated from each other with both assemblies being indoor. The compressor and one refrigerant heat exchanger would be in one assembly, with the other refrigerant heat exchanger in a second assembly.

any air conditioner or heat pump that has two major assemblies separated from each other between indoor and outdoor. The compressor and one refrigerant heat exchanger would be in one assembly, with the other refrigerant heat exchanger in a second assembly.

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.