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Q: Thermal Resistance of a building material ( Answered ,   0 Comments )
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 Subject: Thermal Resistance of a building material Category: Science > Physics Asked by: markthearch-ga List Price: \$20.00 Posted: 08 Aug 2004 04:40 PDT Expires: 07 Sep 2004 04:40 PDT Question ID: 384966
 ```I need to convert the following physical properties information for an insulation material in the US, to an Australian 'R' value equivalent. density is 7.37 kg/cubic metre, thermal resistance (90 days at 23 deg celcius) is 0.671m2. deg celcius/W. The assumed thickness of the material is 90mm. Please note that to convert USA 'R' values to Australian 'R' values, you must multiply by 0.176. Thanks``` Request for Question Clarification by smudgy-ga on 08 Aug 2004 06:26 PDT ```Hi markthearch, For what thickness of material is the given thermal resistance? Is this where we are to assume 90mm thickness? Thanks, smudgy.``` Clarification of Question by markthearch-ga on 08 Aug 2004 15:38 PDT ```Hi Smudgy, Below is information from the manufacturer....does this tell you....is it the BTU.in? Therefore suggesting inch? ASTM D1622 - Density (core) 7.37 Kg/m3 (0.46 lb/ft3) ASTM C518 - Thermal Resistance 90 days @ 230C 0.671m2.0C/W (3.8 ft2.h.0F/BTU.in) Cheers, markthearch```
 ```Hi markthearch, I hope you find the following answer satisfactory; if you have any questions, please request a clarification before rating and I will do my best to resolve any outstanding issues. I looked up some information on ASTM C518, which is a thermal resistance testing standard, and it seems that the numbers you provided are probably indicating the thermal resistance of an inch thickness of material. This is supported by the Imperial units given for thermal resistance, which seem to be a "per-inch" unit as you indicated. Also see note at the end of this answer. It turns out that the numbers you have given for thermal resitance are exactly the R-values of the material in both Imperial and SI units. According to several web sources I have found, R-values in metric are given in units of m^2*C/W, and in English units of (ft^2*h*F)/(BTU). So that means that the English/US R-value is about 3.8 per inch of material, and the metric R-value is about .671 per inch of material. This also coincides with the known conversion factor between US and metric R-values: when we convert .671 metric R to Imperial R, we get 3.8125. Now an inch is approximately 25 mm; if we have 90mm of insulation we have about 3.6 inches, so the R-value of a 90mm thickness is 3.6 times the R of a single inch. So a 90mm thickness of the material has a metric R of approximately 2.416. I hope you find this answer satisfactory; if not, please feel free to request a clarification, and I will do my best to answer any questions you have. Good luck, smudgy. Here is some information on the units of R-value in both English and metric units: Metric and Imperial R-value: http://www.efunda.com/units/convert_units.cfm?From=903 http://www.efunda.com/units/convert_units.cfm?From=464 General information on Imperial R-value and calculating total R-value http://www.roofhelp.com/Rvalue.htm This website gives the units of R-value as (°F?hr?ft2)/Btu: http://www.insulation.org/metalbuilding/pages/resources/resources.html#9 Having inches in the denominator of the listed thermal resistance on your product seems to indicate that each inch of the insulation provides an (Imperial) R-value of 3.8. Google searches performed: <"r value" insulation equation>```
 markthearch-ga rated this answer: ```Very prompt response, great to also show methodology in determining answer. Thank you!```