ASHRAE Terminology

(1) The temperature (usually of air, but could be water or earth as well) surrounding a given object, measured at a location undisturbed or unaffected by the temperature of the object. (2) For an air-conditioning or refrigeration system, temperature of the medium to which heat is dissipated (or absorbed in the case of a heat pump system).

digital controller dedicated to a specific application, such as a VAV box or water-source heat pump.

energy calculation method, usually used in prediction, in which the annual (or monthly) energy use of a building is calculated as the sum of the energy used for all of the outdoor temperature bins. The bin method allows heat pump (or other heater or cooler) performance, which is different for each bin, to be accounted for.

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.

an assembly consisting of a heat pump or air conditioner, a desuperheater, a water heater, and if required, a potable water pump, the assembly provides space conditioning and domestic hot water.

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

see heat pump, cooling, and heating.

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).

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).

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.

heat pump using a brine solution circulating through a subsurface piping loop functioning as a heat source/heat sink.

water-to-water heat pump using water pumped from a well, lake, or stream functioning as a heat source/heat sink. Note: the temperature of the water is related to the climatic conditions and may vary from 40°F to 75°F (5°C to 25°C) for deep wells.

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.

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.

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.

a PTAC capable of using the refrigerating system in a reverse cycle or heat pump mode to provide heat.

(1) output pressure of a reversing relay that changes in opposition to the input signal (i.e., as the input pressure increases, the output pressure decreases). (2) pressure differential existing in a heat pump reversing valve to affect a reversal of flow through the valve.

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).

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.

water-to-air heat pump using liquid circulating in a common piping loop functioning as a heat source/heat sink.

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.