coefficient of heat transmission for wall assembly logic?
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"then there is brick which is provided with a value of 0.11/inch which you multiple by the brick thickness to get the whole R value of the unit (3.625”x0.11R/“=0.4)."
1. Yes, the 1/k value for Face brick is 0.11 (see table 7.38 thermal resistance of building materials of Graphic standards).
2. Problem 1: ONLY AFTER READING THE FOOTNOTE ON THE TABLE: "1/k=R per inch of thickness" is that one could realize more clearly that the whole table is showing R values. Even though the name of the table is Thermal Resistance of Building Materials" it does not say on the title that the values on the table are all R-values. Seems obvious but when reading through tunnel vision, I don't consider that clear.
So, after realizing that we then proceed to multiply the R value of 0.11 times 3.625" (the thickness of the material), that gives 0.4. so the R value of that much thickness of face brick is 0.4.
Again, for readers, 0.11 is already the R-value for one inch of "Face brick" according to tab. 7.38.
3. For the next material, described as GWB, I assume this is what the tab. 7.38 lists as "Gypsum board 1/2" ", which has 0.45 as the R value for that material. Since the footnote on tab. 7.38 says that for 1/C: 1/C=R for the thickness indicated, this reads as: every 1/2" of Gypsum board provides 0.45 of R-value.
4. "the text says “The R and C values for the various components are given in the table. however they must be converted to /conductances/ (my emphasis) for the thicknesses used." and i don’t see any conductance (k) used."
I don't know which table was provided with the problem but if I assume it was tab. 7.38 then all values (both k and C) in the table are already R-values, therefore if the question says R and C values are given in the table and then need to be converted to conductances for thicknesses used" I believe that is wrong in two or more different ways.
The first reason why this statement is not true is that R-values are already "conductance", because R-values are a measurement of "Thermal conductivity resistance", or "thermal insulance", or "resistance"(to contuctance). So there is no need to convert values given in the table again.
The second reason the statement is not true is that they C values are not given in the table, if that was tab. 7.38, all values given are R-values!. So using tab. 7.38, R-value for Gypsum board 1/2" is indeed 0.45.
If the questions uses a different table that shows C values, not R values, then yes you would need to express that as an R value by using 1/C=R (1/2.22=0.45, so the R-value of GWB=0.45).
In any case, even if you were given a C value of 2.22, this is still refering to conductivity. "In construction, C-value, or C-factor, is a measurement of thermal conductance that indicates how much heat passes though a specific thickness of insulation (or any other) material." so again, no need to "convert to conductances..."
So I believe this is a case of badly worded question.
5. "i don’t see any conductance (k) used. it seems to me i just used the R values and converted a C to R. then - well them it seems like i was given a k value for the brick (?) of 0.11/inch and converted the conductance to a R by multiplying by the thickness per inches."
To assume that k values are THE ONLY conductance values, is wrong. Like we have seen already, R, C, and k values are all ways of expressing conductance (R is just per unit area). The one that is different is U-value, which is a measure of transmittance.
I think you are correct when you say no k was used. I believe you were given an R value (0.11) and a C value (2.22).
In the future I would at least describe k as "thermal conductivity" and R as "thermal insulance".
regarding:
"it seems like i was given a k value for the brick (?) of 0.11/inch and converted the conductance to a R by multiplying by the thickness per inches.""
0.11 is R-value already, and you did not convert it to conductance, because it was already an R value it is already refering to conductance.
I would describe this as "I was given the R value of 0.11 and with that I calculated how much R value is provided by the 3.625" of Face brick by multipliying 0.11 by 3.625... which is almost 0.40 (it is more 0.39875)."
6. "you would never convert an R value to k would you? thanks"
I don't know in which scenario you would want to find out the k value from an R value but for the sake of these types of questions I'm sure it is the wrong direction.
Cheers!
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