The heat energy required to raise the temperature of 1 pound of water degree Fahrenheit (joule). For the metric equivalent, see Joule.
Tag: temperature
Coefficient of Thermal Expansion
The coefficient of change in dimension of a material per unit of dimension per degree change in temperature.
Degree Days
A unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the “base temperature”; the base temperature is taken as 65° F (18.3° C) in the U.S.A.
Dew Point
The temperature at which air becomes saturated with water vapor. The temperature at which air has a relative humidity of 100%.
Dry Bulb Temperature
The temperature of air as measured by an ordinary thermometer.
Equiviscous Temperature (EVT)
The temperature at which a bitumen attains the proper viscosity for built-up membrane application.
Equiviscous Temperature (EVT) Application Range
The recommended bitumen application temperature range. The range is approximately 25° F (14° C) above or below the EVT, thus giving a range of approximately 50° F (28° C). The EVT range temperature is measured in the mop cart or mechanical spreader just prior to application of the bitumen to the substrate.
For Asphalt
- Mop Application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise (0.125 Pa·s).
- Mechanical Spreader Application: the temperature at which the asphalt’s apparent viscosity is 75 centipoise (0.075 Pa·s).
Note: In order to avoid the use of two kettles if there are simultaneous mop and mechanical spreader applications, the EVT for mechanical spreader application can be used for both application techniques.
For Coal Tar
- the recommended EVT for roofing coal tar (ASTM D 450, Type I or III) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise (0.025 Pa·s).
Ignition Temperature
The lowest temperature at which combustion will occur spontaneously under specific conditions.
Low Temperature Flexibility
The ability of a membrane or other material to resist cracking when flexed after it has been cooled to a low temperature.
Service Temperature Limits
The minimum or maximum temperature at which a coating, SPF or other material will perform satisfactorily.
Thermal Block
A compression-resistant insulation block installed between structural steel roof panels and their supporting members to help maintain insulation R-values and reduce condensation.
Thermal Bridge
The penetration of a material of high thermal conductivity (e.g., a metal insulation or roof membrane fastener) through a material of low thermal conductivity (e.g., thermal insulation); the result is a lowered thermal resistance for the assembly.
Thermal Conductance
The thermal transmission in unit time through unit area of a particular body or assembly having defined surfaces, when unit average temperature difference is established between the surfaces. C=Btu/h·ft2·°F (C=W/m2·K).
Thermal Conductance (C)
The time rate of heat flow through a unit area of a body induced by a unit temperature difference between bodies. In English (inch-pound) units of measurement, the number of BTUs that pass through a specified thickness of a one square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1° F. In English (inch-pound) units it is expressed as Btu/h·ft2·F. Note 1: A thermal conductance (C) value applies to a specific thickness of a specific material. Note 2: It is mathematically incorrect to multiply or divide the thermal conductance (C) value for a specific thickness of a material to determine the thermal conductance value of a different thickness of the same material. Note 3: It is mathematically incorrect to add thermal conductance (C) values to determine overall thermal performance. If it is necessary to determine the overall thermal performance of a construction, it is appropriate to convert the individual thermal conductance (C) values to thermal resistance (R) values (i.e., R= 1/c), and then add the thermal resistance values (i.e., RT=R1, + R2 + …).
Thermal Conductivity (k)
The time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient is called thermal conductivity (k or kvalue). In English (inch-pound) units of measurement, it is the number of BTUs that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1°F. In English (inch-pound) units it is expressed as Btu·inch/h·ft2·°F. Note 1: A thermal conductivity (k) value applies to 1 inch (25 mm) thickness of a specific material. Note 2: It is mathematically incorrect to add, multiply, or divide the thermal conductivity (k) value of a material to determine the thermal performance value of a different thickness of the same material. If it is necessary to determine the thermal performance of a specific thickness of a material, it is appropriate to convert the thermal conductivity (k) of the material to a thermal resistance (R) value (i.e., R = 1/k), and then perform the mathematical calculation.
Thermal Cycling
Sequence of values caused by a repetitive temperature differential due to changes in radiant energy.
Thermal Expansion
The increase in the dimension or volume of a body due to temperature variations.
Thermal Insulation
A material applied to reduce the flow of heat.
Thermal Movement
Changes in dimension of a material as a result of temperature changes.
Thermal Resistance (R)
Under steady conditions, thermal resistance is the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area. In English (inch·pound) units it is expressed as °F·ft2·h/Btu. Note 1: A thermal resistance (R) value applies to a specific thickness of a material or construction. Note 2: The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C). Note 3: Thermal resistance (R) values can be added, subtracted, multiplied, and divided by mathematically appropriate methods.
Thermal Shock
The stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant sunshine.
Thermal Stress
Stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction.
Thermal Transmittance (U or U-Factor)
Thermal transmittance (U or U-factor) is the time rate of heat flow per unit area under steady conditions from the fluid (e.g., air) on the warm side of a barrier to the fluid (e.g., air) on the cold side, per unit temperature difference between the fluids. In English (inch·pound) units expressed as Btu/h·ft2·°F. Note 1: A thermal transmittance (U) value applies to the overall thermal performance of a system (e.g., roof assembly). Note 2: Thermal transmittance (U) is sometimes called the overall coefficient of heat transfer. Note 3: Thermal transmittance (U) is reciprocal of the overall thermal resistance (RT) of a system (i.e., U = 1/RT).
Wet Bulb Temperature
The temperature of air as registered by a thermometer whose bulb is covered by a water wetted wick.