Ching Dictionary of Architecture: Heat Transfer

Ching Dictionary of Architecture: Heat Transfer

Convection = The transfer of heat by the circulatory motion of the heated parts of a liquid or gas owing to a variation in density and the action of gravity.

Conduction = The transfer of heat from the warmer to the cooler particles of a medium or of two bodies in direct contact, occurring without perceptible displacement of particles themselves.

Radiation = the process in which energy in the form of waves or particles is emitted by one body, passed through an intervening medium or space, and absorbed by another body.

Thermal conductivity = The time rate of heat flow through a unit area of a given material of unit thickness when the temp. difference across the thickness is one unit of temp.

Thermal conductance = the time rate of heat flow through a unit area of a given material when the temp. difference across the specified thickness of the material is one unit of temp.

Thermal resistance = the reciprocal of thermal conductance, expressed as the temp. difference require to cause heat flow through a unit area of material of given thickness at the rate of one heat unit per unit time.

R-value = A measure of thermal resistance of a given material, used esp. to specify the performance of thermal insulation. The total R-value for a building component or assembly is the sum of the R-values for each layer in the component or assembly.

Thermal transmittance = the time rate of heat flow through a unit area of a building component or assembly when the difference between the air temp's on the two sides of the component or assembly is one unit of temp. Also called the coefficient of heat transfer.

U-value = A measure of the thermal transmittance of a building component or assembly, equal to the reciprocal of the total R-value of the component or assembly.

1/R(total) = U, IE. 1/R+R+R+... = U

Thermal break = An element of low thermal conductivity placed in an assembly to reduce the flow of heat between highly conductive materials. Also called thermal barrier.

Infiltration = the flow of outside air into an interior space through cracks around windows and doors or other openings in the envelope of a building