ASHRAE Terminology

the temperature at which water (liquid or solid) at temperature t, by evaporating into moist air at dry-bulb temperature t and humidity ratio W, can bring air to saturation adiabatically at the same temperature t while total pressure p is constant. Also known as thermodynamic-wet-bulb temperature.

(1) variable that cannot actually be measured directly but one which can be calculated by measuring other variables (e.g., measure wet-bulb temperature and measure dry-bulb temperature to determine enthalpy). (2) variable that is calculated from one or more inputs.

chart showing operative temperatures with dry-bulb temperatures, relative humidities, and air motion by which the effects of the various conditions on human comfort may be compared.

on a psychrometric chart, the infinite number of wet- and dry-bulb temperatures which will satisfy the requirements of an air supply for a given room temperature.

the outdoor dry-bulb temperature equal to the temperature that is exceeded by 1% of the number of hours during a typical weather year.

the primary air dry-bulb temperature reduction divided by the primary air entering dry-bulb temperature less the entering secondary wet-bulb temperature.

dry-bulb temperature (DBT)

difference between dry-bulb temperature and dew-point temperature. See wet-bulb temperature.

temperature of air indicated by an ordinary thermometer shielded from solar and long wave radiation

(1) temperature of air indicated by an ordinary thermometer shielded from solar and long wave radiation. (2) in general, any thermometer that indicates the temperature of air (or other fluids), distinguished from a wet-bulb thermometer.

the temperature that a thermometer would measure for air entering the evaporator coil. (E.g., for a draw-through fan configuration with no heat gains or losses in the ductwork, EDB equals the indoor dry-bulb temperature).

the outdoor wet-bulb temperature used in conjunction with the mean coincident dry-bulb temperature, often used for the sizing of evaporative systems such as cooling towers.

a cooler that cools indoor air by moisture evaporation, thereby lowering its dry-bulb temperature and raising its wet-bulb temperature, all at a constant energy (adiabatic) level. See also evaporative cooling.

cools air by moisture evaporation, thereby lowering its dry-bulb temperature and raising its wet-bulb temperature, all at a constant energy level.

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.

(1) a plan for gathering of relevant measurement data over time to evaluate equipment or system performance. The plan defines specific M&V methods to be used, including baseline determination, performance period measurements, savings verification calculations, and acceptance criteria. The M&V methods chosen are consistent with the current facility requirements (CFR). During the implementation phase, a list is developed of specific instrumentation and data-gathering equipment that must be maintained at the site. During the hand-off phase, the type, frequency, and distribution of M&V reports to be submitted for approval is confirmed. (2) equipment to measure and record the parameters of the HVAC&R systems (i.e., temperature, humidity, pressure, electric current, kW, and volts). (3) gathering of relevant measurement data over time to evaluate equipment or system performance (e.g., chiller electric demand, inlet evaporator temperature and flow, outlet evaporator temperature, condenser inlet temperature, and ambient dry-bulb temperature and relative humidity or wet-bulb temperature, for use in developing a chiller performance map (e.g., kW/ton versus cooling load and versus condenser inlet temperature).

see outdoor dry-bulb temperature.

see dry-bulb temperature (DBT).

graphical representation of the properties of moist air, usually including wet- and dry-bulb temperatures, specific and relative humidities, enthalpy, and density.

(1) ratio of the mole fraction of water vapor to the mole fraction of water vapor saturated at the same temperature and barometric pressure. (2) ratio of the partial pressure or density of water vapor to the saturation pressure or density, respectively, at the same dry-bulb temperature and barometric pressure of the ambient air.

the dry-bulb temperature reduction achieved by the ECU divided by the entering wet-bulb depression.

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.

see dry-bulb temperature.

HVAC system that controls the dry-bulb temperature within a space by varying the volumetric flow of heated or cooled supply air to the space.