On Jan 25 , at 10:52 PM, Pierre Abbat wrote:
> >> R-factor, > > You mean the unit of insulation? I don't know how that's defined, but it > should be simple to label the insulation with the metric equivalent. It is defined as the reciprocal of the rate of heat flow (in Btu/h) through a slab of insulation divided by the area of the insulation (in square feet) and divide by the temperature difference from one side of the slab to the other. Here is a great quote about units for the R-value for thermal insulation, from an authoritative source with a sense of humor. ---------------------------------------------------- "The commonly used unit for R (which, in the United States at least, is almost never stated) is the square foot-Fahrenheit degree-hour per British thermal unit (ft^2·F°·h/Btu). (Now you know why the unit is rarely stated.)" Source: "Fundamentals of Physics" by Halliday, Resnick and Walker, Fifth Edition, Part 2, pg. 470 ---------------------------------------------------- Yes, that snide parenthetical comment at the end is actually in this highly respected, serious, college level physics text book. Clearly this can be converted to m^2·C°·s/J . Furthermore, factor, s/J, is equal to 1/W so the R value can be simplified even further to m^2·C°/W. I don't think it worth my time to calculate how many ft^2·F°·h/Btu are equal to one m^2·C°/W or vice versa. (Bear in mind that the temperature units represent difference in temperature from one side of the slab to the other. Therefore, in converting units (if you're crazy enough to bother) the relation is 1 °C = 5/9 °F and not the other relation which involves the Fahrenheit scale's 32 °F shift from the zero point. The zero point is irrelevant when differences are considered.)
