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For comparison, phenolic foam insulation has a k-value of around 0.018 W/(m⋅K), [23] while wood varies anywhere from 0.15 to 0.75 W/(m⋅K), and steel has a k-value of approximately 50.0 W/(m⋅K). These figures vary from product to product, so the UK and EU have established a 90/90 standard which means that 90% of the product will conform to ...
The construction industry makes use of measures such as the R-value (resistance) and the U-value (transmittance or conductance). Although related to the thermal conductivity of a material used in an insulation product or assembly, R- and U-values are measured per unit area, and depend on the specified thickness of the product or assembly. [note 2]
Although the concept of U-value (or U-factor) is universal, U-values can be expressed in different units. In most countries, U-value is expressed in SI units, as watts per square metre-kelvin: W/(m 2 ⋅K) In the United States, U-value is expressed as British thermal units (Btu) per hour-square feet-degrees Fahrenheit: Btu/(h⋅ft 2 ⋅°F)
Instead the formula that would fit some of the Bonales data is k ≈ 2.0526 - 0.0176TC and not k = -0.0176 + 2.0526T as they say on page S615 and also the values they posted for Alexiades and Solomon do not fit the other formula that they posted on table 1 on page S611 and the formula that would fit over there is k = 2.18 - 0.01365TC and not k ...
Architects and engineers call the resulting values either the U-Value or the R-Value of a construction assembly like a wall. Each type of value (R or U) are related as the inverse of each other such that R-Value = 1/U-Value and both are more fully understood through the concept of an overall heat transfer coefficient described in lower section ...
The effectiveness of bulk insulation is commonly evaluated by its R-value, of which there are two – metric (SI) (with unit K⋅W −1 ⋅m 2) and US customary (with unit °F⋅ft 2 ⋅h/BTU), the former being 0.176 times the latter numerically, or the reciprocal quantity the thermal conductivity or U-value W⋅K −1 ⋅m −2.
Most experimentally determined values of the thermal contact resistance fall between 0.000005 and 0.0005 m 2 K/W (the corresponding range of thermal contact conductance is 200,000 to 2000 W/m 2 K). To know whether the thermal contact resistance is significant or not, magnitudes of the thermal resistances of the layers are compared with typical ...
Closed-cell foams are superior insulators. While open-cell foams typically have R-values of 3 to 4 per inch (RSI-0.53 to RSI-0.70 per inch), closed-cell foams can attain R-values of 5 to 8 per inch (RSI-0.88 to RSI-1.41 per inch). This is important if space is limited, because it allows a thinner layer of insulation to be used.