m2·°C/W per inch versus R-value or RSI values?
It appears that the latest insulation performance values are being related in (area) x (temperature) divided by watts (energy/time). In the recent article “Understanding Energy Units” you clarified and defined types of energy units, including watts. I read it in hopes of understanding what m2·°C/W ultimately means when selecting or comparing different insulation materials but after reading it I am still left in the dark.
I also know what a metre is: it’s 3 feet 3-3/8″ inches! I have to covert it if I want to understand it. I realize that R value is a primitive way of looking at thermal performance, but is there any way of converting m2·°C/W into an R value or RSI scale for the sake of simple comprehension?
David Stewart
Saskatchewan, Canada
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Replies
David,
When discussing R-values and U-factors -- especially when you need to convert metric units to imperial (English) units -- it makes the most sense to stick to a discussion of U-factors. Leave R-values out of the discussion for the time being. For people in the U.S., it's easy to figure out your R-value later, since R=1/U and U=1/R.
In the imperial (English) system, U-factor is the number of BTU of energy passing through a square foot of material in an hour for every Fahrenheit degree difference in temperature across the material (Btu / ft2 * h * F°). In metric, the units are watts per square meter per degree Celsius (W / m2 * C°).
To convert U metric (W / m2 * C°) to U imperial (Btu / ft2 * h * F°), divide by 5.678
To convert U imperial (Btu / ft2 * h * F°) to U metric (W / m2 * C°), multiply by 5.678