ASHRAE Terminology

time rate of steady-state heat flow through a unit area of a homogeneous material, induced by a unit temperature gradient in a direction perpendicular to that unit area. Units are Btu in./h·ft2·°F or Btu/h·ft·°F [W/(m·K)].

alcohol thermometer used to measure low velocities in air circulation by heating the large bulb of the thermometer above 100°F (38°C) and noting the time it takes to cool from 100°F to 95°F (38°C to 35°C) or some other interval above ambient temperature with the time interval being a measure of the air current at that location.

instrument for measuring the CO₂ concentration in a cold storage atmosphere working on the principle that CO₂ has a thermal conductivity different from other gases. Concentrations of other gases can also be measured using this principle.

SI absolute temperature scale on which the triple point of water is 273.16 K and the boiling point is approximately 373.15 K (1 K = 1°C). The Kelvin is the fraction 1/273.16 of the temperature of the thermodynamic triple point of water. See triple point.

three laws describing the motions of planets in their orbits: (1) the orbits of planets are ellipses with the sun at the common focus, (2) the line joining a planet and the sun sweeps over equal areas during equal intervals of time, (3) the squares of the periods of revolution of any two planets are proportional to the cubes of their mean distances from the sun.

the product of the line current (amperes) times the nominal system voltage (kilovolts) times 1.732 for three-phase currents. For single-phase applications, kVa is the product of the line current (amperes) times the nominal system voltage (kilovolts).

ratio of absolute viscosity to density of a fluid. A measure of a fluid’s resistance to flow in units of centistokes.

energy caused by the velocity of molecules.

(1) stop valve between receiver and liquid main in a refrigeration system. (2) stop valve on boiler head.

ratio of the emissivity of a heat radiator to the absorptivity of the same radiator is the same for all bodies, depending on frequency and temperature alone, and is equal to the emissivity of a blackbody.

when ionization is complete, the conductivity of an electrolyte is equal to the sum of the conductivities of the ions into which the substance dissociates.

optical absorption bands of a solution are displaced toward the red when its refractive index increases because of changes in composition or other causes.