ASHRAE Terminology

evaporating water into air without external gain or loss of heat. Sensible heat in both air and water becomes latent heat in evaporated vapor. The air is cooled and humidified.

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

measured property of a material or assembly of materials, heat flows by a combination of conduction, convection, radiation, and latent heat exchange and may depend on orientation, direction, or both. The specific test conditions (i.e., sample thickness, orientation, environment, environmental pressure, surface temperature, mean temperature, temperature difference, and moisture distribution) should be reported with the values. The symbol K is used to denote the lack of pure conduction or to indicate that all values reported are apparent. Materials with a low apparent thermal conductivity are called insulation materials.

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.

chilled ceiling systems have a very low profile (often flush with the ceiling) and work by means of convection heat transfer and induced air movement in the room in which they are placed. Chilled ceilings lack the ability to control the humidity or provide ventilation and must be paired with a ventilation system in order to maintain latent heat gains.

a self-contained cabinet without a fan whose primary functions are (1) the conversion of the sensible heat of unsaturated air passing through the cabinet to latent heat by the process of evaporating recirculating or nonrecirculating water directly exposed to this air and (2) the movement of this air through the cabinet that allows a portion of this water to evaporate.

temperature at which a vapor liquefies if the latent heat is removed at standard or stated pressure. See also dew point, saturation temperature, boiling point.

one that circulates the products of combustion and extracts available heat to a point that causes condensation to occur. Some of this latent heat of condensation is recovered as usable energy, resulting in higher operating efficiency.

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.

the sum of sensible and latent heat losses above room temperature of the flue gases leaving the furnace or boiler.

during the freezing of produce, that part of the graph of temperature against time in which the temperature remains virtually constant. The freezing plateau is induced by the time required to remove latent 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) heat energy required to cause a change of state from solid to liquid at constant temperature. For ice to water, 143.5 Btu/lb (333.8 kJ/kg). (2) latent heat involved in changing between the solid and the liquid states.

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.

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

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.

product of the mass of water evaporated times the latent heat at the evaporating temperature.

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

latent heat absorbed by ice at 32°F (0°C) in liquefying into water phase at 32°F (0°C). For precise data, 143.5 Btu/lb. (334.4 kJ/kg), for definition of ton, 144 Btu/lb (2.326 kJ/kg).

sum of all kinetic and potential energies contained in a substance due to the states of motion and separation of its several molecules, atoms, and electrons. It includes sensible heat (vibration energy) and that part of latent heat represented by the increase in energy during evaporation.

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.

the change in enthalpy associated with a change in humidity ratio, caused by the addition or removal of moisture.

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

quantity of heat released on change of unit mass of saturated vapor to saturated liquid with no change in temperature, measured in Btu/lbm (J/kg).

quantity of heat required to change a unit mass of ice to water at 32°F (0°C) temperature, measured in Btu/lbm (J/kg).

quantity of heat required to cause a change of state of a substance from a saturated liquid to a saturated vapor with no change in temperature, measured in Btu/lbm (J/kg).

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.

a self-contained unit including a fan and fan motor whose primary functions are (1) the conversion of the sensible heat of unsaturated air passing through the cabinet to latent heat by the process of evaporating recirculating or nonrecirculating water directly exposed to this air and (2) the movement of this air through the unit.

uses a pipe surrounded by a coil in order to form a radiator system. Passive chilled beams have no method for maintaining the humidity of a room and must be paired with a ventilation system in order to maintain latent heat gains.

ratio of the sensible heat to the sensible plus latent heat to be removed from a conditioned space.

[also known as sensible heat factor (SHF)], the ratio of sensible heat transfer to total (sensible + latent) heat transfer for a process. Also see sensible heat and latent heat.

(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.

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

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

latent heating or cooling load. See ton of refrigeration.