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[[Category:Home Energy Conservation and Heat-Tranfer Control]] | |||
- Definition - the "resistance" of a substance to heat transfer by conduction (according to Energy, Its Use and the Environment) | |||
The following information is obtained from Energy, Its Use and the Environment: | The following information is obtained from Energy, Its Use and the Environment: | ||
"A measure of the resistance of the material to heat flow is the thermal resistance R, often called its "R-Value" given by R=delta over k. The higher the R-value is, the bettwer are the insulating properties of the material. Using this notation, the rate of heat flow is given by | "A measure of the [[resistance]] of the material to heat flow is the [[thermal resistance]] R, often called its [["R-Value"]] given by R=delta over k. The higher the R-value is, the bettwer are the insulating properties of the material. Using this notation, the rate of heat flow is given by | ||
Qc/t = 1/R x A x change in T | Qc/t = 1/R x A x change in T | ||
R is a funciton of both the type of material and its thickness. | R is a funciton of both the type of material and its thickness. | ||
L/k = R vlaue of insulation | |||
R-value according to Physics by Cutnell and Johnson | |||
R value | |||
- it expresses in a single number the combined effects of thermal conductivity and thickness. | |||
- Larger R values reduce the heat perunit time flowing through the material and therefore mean better insulation. It also convenient to use R values to describe layered slabs formed by sandwiching toget a number of materials with differen tthermal conductivities and idferenet thicknesses. The R values for the indicidual layeers can be added to give a single R value for the entire slabe. It should be noted, however, that R values are expressed using units of feet, hours, F and BTU for thickness, time, temperature, and heat, respectively. | |||
Revision as of 17:37, 5 October 2007
R value - Definition - the "resistance" of a substance to heat transfer by conduction (according to Energy, Its Use and the Environment)
The following information is obtained from Energy, Its Use and the Environment:
"A measure of the resistance of the material to heat flow is the thermal resistance R, often called its "R-Value" given by R=delta over k. The higher the R-value is, the bettwer are the insulating properties of the material. Using this notation, the rate of heat flow is given by Qc/t = 1/R x A x change in T R is a funciton of both the type of material and its thickness.
L/k = R vlaue of insulation
R-value according to Physics by Cutnell and Johnson
R value - it expresses in a single number the combined effects of thermal conductivity and thickness. - Larger R values reduce the heat perunit time flowing through the material and therefore mean better insulation. It also convenient to use R values to describe layered slabs formed by sandwiching toget a number of materials with differen tthermal conductivities and idferenet thicknesses. The R values for the indicidual layeers can be added to give a single R value for the entire slabe. It should be noted, however, that R values are expressed using units of feet, hours, F and BTU for thickness, time, temperature, and heat, respectively.