ASHRAE Terminology

the gross sensible capacity less the actual fan power. (Also see gross sensible capacity.)

useful net, available refrigerating capacity of an air conditioner for removing sensible and latent heat from the space being conditioned.

the effective coil surface temperature when there is dehumidification. This is the temperature to which all the supply air would be cooled if 100% of the supply air contacted the coil. On the psychrometric chart, this is the intersection of the condition line and the saturation curve, where the condition line is the line going through entering air conditions with slope defined by the sensible heat ratio ([gross sensible capacity]/[gross total capacity]). (Also see gross sensible capacity and gross total capacity.)

a pressure relief valve that incorporates means of minimizing the effect of back pressure on the operational characteristics of the valve (opening pressure, closing pressure, and relieving capacity).

design maximum rate of heat output.

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.

(1) measure of the maximum amount of energy or material that may be stored in a given system. See also nameplate rating, air-conditioner capacity. (2) the rate of heat removal by the refrigerant used in the compressor or condensing unit in a refrigerating system. This rate equals the product of the refrigerant mass flow rate and the difference in the specific enthalpies of the refrigerant vapor at its thermodynamic state entering the compressor or condensing unit and refrigerant liquid at the thermodynamic state entering the mass flow control device. (3) the rate that heat is removed or added to a system. (4) maximum load for which a machine, apparatus, device, or system is designed or constructed.

(of a machine, equipment, or thermal storage), ratio of the average load required, in the period of time considered, to the capacity in mass, volume, or energy terms. Reciprocal of storage factor.

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).

available capacity of an air conditioner for removing sensible and latent heat from the space to be conditioned (Btu/h).

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.

the amount of heat that can be transferred into the storage device at a specified rate for a specific set of values for the initial temperature of the storage device, the temperature rise of the exiting fluid, and the mass flow rate of fluid through the storage system.

(1) ratio of the rate of net heat output to the total energy input expressed in consistent units and under designated rating conditions. (2) ratio of the refrigerating capacity to the work absorbed by the compressor per unit time.

the friction loss through a column of pipe with a line shaft through it such that fluid flows in an annulus. Column friction loss is dependent upon both capacity and the length and diameter of column and shaft used.

(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.

apparatus for determining the refrigerant flow rate and, subsequently, the capacity of a refrigerant compressor by measuring the heat input required to balance the refrigerating effect produced in the evaporator by the compressor.

(1) design maximum rate of heat removal by the refrigerant assigned to the compressor in a refrigerating system. This is 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 its thermodynamic state entering the compressor and the refrigerant liquid at saturation temperature corresponding to the pressure of the vapor leaving the compressor. (2) device, such as a clearance pocket, movable cylinder head, or suction bypass, by which compressor capacity can be adjusted without otherwise changing the operating conditions.

space of controlled volume to give the effect of greater or less cylinder clearance, thereby changing compressor capacity.

(1) device for controlling compressor capacity by rendering one or more cylinders ineffective. (2) device on or in a compressor for equalizing the high- and low-side pressures for a brief period during starting in order to decrease the starting load on the motor.

apparatus for determining refrigerant flow rate and, subsequently, the capacity of a condensing unit by measuring the heat input required to balance the refrigerating effect produced in the evaporator by the condensing unit.

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.

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

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

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).

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

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.

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.

capacity of an environment or environmental factor to bring about destruction of a specific metal by the process of corrosion.

directional pattern of the heat transfer fluids used in energy-exchange equipment where the warmest fluid “A” indirectly contacts the warmest fluid “B” at the entering side of the equipment and the coldest fluid “A” indirectly contacts the coldest fluid “B” at the leaving side of the equipment. Most energy exchange equipment is designed to use this method of heat transfer as it creates the highest log mean temperature difference (LMTD). When an energy exchange equipment is designed for counterflow heat transfer, and it is correctly connected in the field, the results would be loss in heat transfer capacity.

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.

part of an electric bill based on kilowatt demand and the demand interval, expressed in dollars per kilowatt. Note: demand charges offset construction and maintenance of a utility’s need for large generating capacity.

output capacity of a system or piece of equipment at design conditions.

ratio of various physical properties (such as density or heat capacity) and conditions (such as flow rate or mass) of such nature that the resulting number has no defining units of mass, rate, etc. Also called a nondimensional parameter.

the amount of thermal energy that can be removed from the storage device during a period of time and for a specific set of values for the initial temperature of the storage device, the temperature of the entering fluid, and the mass flow rate of fluid through the storage system. Compare to storage capacity.

ratio, or percentage, obtained when the total output capacity of a system is divided by the total output capacity of all the terminal devices connected to the systems. Example: to express the ratio of VAV supply air fan capacity to the total capacity of the VAV terminal devices as a percentage.

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

for disposable and manually renewable devices air filters, it is the average arrestance multiplied by the amount of ASHRAE dust fed to the device measured to the nearest gram. See also MERV rating.

for devices whose renewal mechanism is designed to restore the performance characteristics of the device to starting conditions, dust -holding capacity per cycle is determined by feeding dust until a steady-state condition is achieved. The dust-holding capacity per cycle is averaged over at least four cycles. The result is expressed in g/cycle to the nearest gram.

for disposable and manually renewable devices, this is dust-holding capacity divided by net effective filtering area. For self-renewable devices, dust feed is continued until the steady-state condition is achieved in several cycles. Dust-holding capacity per unit area is then the average arrestance multiplied by the dust fed during the steady-state period divided by the area of media consumed during the same period. Dust-holding capacity per unit area is expressed in g/m2 (g/ft2).

reciprocal (opposite) of resistance. The current carrying capacity of any wire or electrical component.

The provision of capacity deployed by the balancing authority to meet NERC and regional reliability organization contingency requirements.

(1) capability for doing work. (2) capacity for producing an effect. Having several forms, which may be either stored or transient, and can be transformed from one into another. Forms include thermal (heat), mechanical (work), electrical, radiant, and chemical. (3) time rate of work being done.

(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.

that lower portion of the building envelope, including opaque area and fenestration, that has conditioned or semiheated space above and is horizontal or tilted at an angle of less than 60°F (15°C) from horizontal but excluding slab-on-grade floors. For the purposes of determining building envelope requirements, the classifications are defined as follows: (a) mass floor: a floor with a heat capacity that exceeds (1) 7 Btu/ft²·°F (39.7 watt h/m² °C) or (2) 5 Btu/ft²·°F (28.4 watt h/m²·°C) provided that the floor has a material unit mass not greater than 120 lb/ft³ (1924.6 kg/ m³), (b)  steel joist floor: a floor that (1) is not a mass floor and (2) that has steel joist members supported by structural members, (c) wood framed and other floors: all other floor types, including wood joist floors.

the manufacturer's rated capacity at the defined rating point for HVAC equipment. Equipment capacity should be adjusted for altitude and other effects.

refrigerating effect in watts, Btu/h, or tons (12,000 Btu/h) produced by the evaporation of refrigerant passed by the valve under specified conditions.

contaminant capacity divided by contaminant loading, expressed as a percent.

the continuation of heat transfer after the heat transfer system/equipment has been removed or de-energized. The effect is due to the thermal mass of the space and capacity of that mass to store/release heat. See thermal inertia.

load (uncorrected) that a machine, apparatus, device, or system is designed to deliver.

total rate of heat removal from all sources by the evaporator of a refrigerating system at stated conditions. It is numerically equal to the system refrigerating effect.

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.

(1) the amount of heat necessary to raise the temperature of a given mass one degree, numerically, the mass multiplied by the specific heat. (2) the capacity of a body to store heat.

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.

technology or systems used to store heating capacity.

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).

control of the thickness of a bank of ice for off-peak cool storage, also for use with milk coolers and other refrigerating cabinets in which refrigerating capacity is stored by means of ice.

actual productive mass output of an ice-making plant in a given time.

power capacity as measured by means of an indicator diagram.

fuel burning capacity of an appliance in British thermal units per hour (Btu/h) [kilowatts (kW)] as specified by the manufacturer. Appliance input ratings are based on sea-level operation and need not be changed for operation up to 2000 ft (600 m) altitude.

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.

electrical or gas loads that by contract can be interrupted by the supply system in the event of a capacity limit in the supplying system.

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.

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

trap with an adjustable bellows and steel valve head located downstream of the steam system. It operates on temperature rise, with the setpoint adjustable from the outside. It discharges at a fixed temperature for protection from freezing and for high-capacity venting requirements.

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.

(1) amount of heat per unit time imposed on a system by the required rate of heat addition or removal. (2) energy absorbing device. (3) material, force, torque, energy, or power applied to or removed from a system or element. See also capacity.

in a thermal storage system, the ratio of average daily load to maximum capacity. A 100 kW chiller meeting an average load of 75 kW would have a diversity of 0.75.

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.

a compounded, synthetic dust used for air cleaner capacity and efficiency testing.

a floor with a heat capacity that exceeds (a) 7 Btu/ft2·°F (143 kJ/m2·K) or (b) 5 Btu/ft2·°F (102 kJ/m2·K), provided that the floor has a material unit mass not greater than 120 lb/ft3 (1920 kg/m3).

a wall with a heat capacity exceeding (1) 7 Btu/ft2·°F (143 kJ/m2·K) or (2) 5 Btu/ft2·°F (102 kJ/m2·K), provided that the wall has a material unit weight not greater than 120 lb/ft3 (1920 kg/m3).

capacity for doing work, usually expressed in work units (foot-pounds or newton-meters), sometimes in heat units (Btu or joule). Energy may be inherent in the speed of a body (kinetic energy) or in its position relative to another body (potential energy).

the minimum capacity, expressed in percent, that the system will operate continuously and in a stable manner.

boiler designed and constructed to include increments of capacity.

the mass of water vapor removed from the process air per unit of time and expressed in kg/h (lb/h).

a ratio of the moisture removal capacity in lb of moisture/h (kg of moisture/h) to the power input values in kW at any given set of standard rating conditions expressed in lb of moisture/kWh (kg of moisture/kWh).

full-load, continuous rating of a generator, prime mover, or other equipment under specified conditions, as designated by the manufacturer and usually indicated on an attached plate. Compare to capacity.

(1) (equipment effective capacity), maximum load that a machine, apparatus, device, or system is capable of carrying under service conditions. (2) capacity (volume) of a room after deducting the loss of space due to coils, columns, air ducts, dunnage, and other dedicated space required to provide air circulation.

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

the gross sensible capacity less the default rate of fan heat assumed by the manufacturer, this rate of fan heat is not necessarily the same as for the actual installed fan.

the gross total capacity less the default rate of fan heat assumed by the manufacturer, this rate of fan heat is not necessarily the same as for the actual installed fan (see adjusted net total capacity). (Also see gross total capacity.)

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 volumetric flow rate, L/s (cfm), equivalent to the mass flow rate of dry nitrogen that would be passed for a specified inlet pressure if discharge had been to standard atmospheric pressure of 101.325 kPa (14.696 psi) absolute.

(1) the capacity recorded and reported by a given test. (2) the capacity reported by the manufacturer for a specified device.

a theoretical capacity of the thermal storage device, which in many cases is greater than the usable storage capacity. This measure should not be used to compare usable capacities of alternative storage systems.

(1) (general) current, voltage, power, or driving force delivered by a circuit or device, terminals or other places where current, voltage, power, or driving force may be delivered by a circuit of device. (2) capacity, duty, performance, net refrigeration produced by a system. (3) process of transferring data from an internal storage.

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 number of standard drinks drawn under standard test conditions without the beverage exceeding 40°F (4.4°C) at a draw rate defined by the manufacturer within a given time limit.

the ratio of capacity to power input at specified operating conditions. Using consistent units, the performance factor may be expressed in dimensionless form as a coefficient of performance (COP) or as the energy efficiency ratio (EER).

the capacity of the permanent bleed provision, expressed either as a percentage of the nominal capacity or in kW (Btu/h or tons) of refrigerating effect produced by the evaporation of that amount of refrigerant flow.

expansion valve of a type used on large capacity systems (e.g., direct-expansion chillers) where the required capacity per valve is beyond the range of direct-acting valves, this type of valve is under the control of a direct acting valve.

required on lithium bromide absorption equipment to remove noncondensables (air), which leak into the machine, or hydrogen (a product of corrosion), which is produced during equipment operation. Even in small amounts, noncondensable gases can reduce chilling capacity and even lead to solution crystallization. Purge systems for larger sizes above 100 tons (359 kW) of refrigeration typically consist of these components: vapor pickup tube(s), noncondensable separation and storage tank(s), and vacuum pump or valving system.

(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.

total useful capacity of a refrigerant condenser for removing heat from the refrigerant circulated through it.

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 fan coil under test reduces or increases the dry-bulb temperature of the air passing through it.

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.

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 quantity that which a water well can produce per unit of drawdown.

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

capacity in energy units per unit time based on tests performed under standard conditions.

the amount of thermal energy required to complete one charging cycle of a thermal storage device. The storage capacity will always be a greater value than the usable discharge capacity of the thermal storage device. Compare to discharge capacity.

discharge capacity divided by charge capacity.

(1) ratio of the volume occupied by the quantity of a particular product stored to the maximum that can be stored, taking into account the requirements of that particular product. (2) reciprocal of capacity factor.

the air that flows through the device being tested. During the test, test air should be at the temperature, humidity, pressure, and atmospheric dust concentration prevailing at the time of the test. Test air for arrestance and dust-holding capacity measurement may be indoor ambient air.

standard that sets forth methods of measuring capacity, or other aspects of operation, of a specific unit or system of a given class of equipment, together with a specification of instrumentation, procedure, and calculations. See MOT.

the sum of the products of masses and heat capacities of all components (including the transfer fluid) contained within the insulating envelope of the thermal storage device.

(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.

(also known as cycle figure of merit), ratio of the integrated discharge capacity to the hypothetical maximum available capacity for a single cycle of operation.

total useful capacity of a refrigerant condenser for removing heat from the refrigerant circulated through it.

the product of the mass flow rate of refrigerant and the difference in enthalpy between the leaving and entering refrigerant, expressed in energy units per unit of time.

(also referred to as an in-line fan) a centrifugal impeller located within a cylindrical or rectangular housing, discharging in an axial direction. Its performance is similar to that of a centrifugal blower except its capacity and pressure are lower due to the less efficient fan arrangement.

a modulating control that both cycles a controlling device between two preset conditions, could be between OPEN and CLOSED, or between ON and OFF, or between two stages or levels of capacity control.

a system intended to deliver continuous, stable power to the critical load. The majority of modern UPS systems are of two fundamental types: (a) “static,” in which incoming alternating current (AC) power is rectified to direct current (DC) and then inverted back to AC, with batteries in the DC portion that assume the load when incoming power fails or anomalies occur, and (b) “rotary,” in which incoming AC power drives a propulsion unit that turns a generating device, with a heavy flywheel storing kinetic energy that continues to turn the generating portion when incoming power fails or anomalies occur. Either type can be made up of one or more modules running in parallel to add capacity or redundancy or both. DC UPS systems, which eliminate the inverter and deliver DC power to the ITE, are also used.

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

percent capacity realized over a period of time that a system is operated.

the meter used to calculate a monthly energy and/or demand charge at a specific utility/customer connection, more than one may be installed per customer and per site due to different supply voltages, capacity requirements, physical separation distances, installation periods, or for specific customer requirements or utility programs.

an engineered direct-expansion (DX) multisplit system incorporating at least one variable capacity compressor distributing refrigerant through a piping network to multiple indoor fan-coil units, each capable of individual zone temperature control, through integral zone temperature control devices and common communications network. Variable refrigerant flow utilizes three or more steps of control on common, interconnecting piping.

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

an engineered direct expansion (DX) multisplit system incorporating at least one variable capacity compressor distributing refrigerant through a piping network to multiple indoor fan-coil units, each capable of individual zone temperature control, through integral zone temperature control devices and common communications network. Variable refrigerant flow uses three or more steps of control on common, interconnecting piping.

the change in heat stored in unit volume of material for unit change of temperature.

the change in stored moisture per unit volume of porous material and per unit moisture potential change.

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

during a drying process, the ability of a substance to retain water.