Modern Refrigeration and Air Conditioning Author: | Language: English | ISBN:
B001TKQO6E | Format: PDF
Modern Refrigeration and Air Conditioning Description
- Paperback
- Publisher: Goodheart-Wilcox Publisher; 18 edition (January 31, 2004)
- ASIN: B001TKQO6E
Another edit
This time the issue is that the authors do not understand the important difference between conductivity and conductance. Conductivity (k), an intensive property, is the energy transfer rate for a unit thickness of a material, and is given in tables everywhere. Conductance (C), an extensive property, is the energy transfer rate for (your) specific thickness of material. They use the wrong term in the definition, intermix the terminology, and use the same symbol (K) for both concepts. Thank goodness electrical engineers don't do the same thing with resistivity/resistance! In their defense I have come across numerous people in the HVACR industry who do not understand this basic concept, but these guys are supposed to be experts!
In addition they incorrectly worked out their three material example, which is obvious by their inability to reconcile the units in the last few steps. The correct answers are 0.29 for K and 3.46 for R. In the next example they introduce air films, and give reasonable values (6=exterior 15 mph winter wind, 1.65=horizontal interior still air) for them although they don't mention they are conductances. They improperly introduce U as resistance to heat flow (it's actually a measure of total conductance) but they finally use the correct formula.
lowered to 1 star from initial four stars, and about to pitch the book into the garbage.
end of additional edit
Edit: As I continue to go through this book I am flabbergasted at the number of math errors. On page 567 they casually claim 20 tons is 55.2 kW. The first issue is that they are comparing energy with power. The SI unit for thermal energy is the kilocalorie. The second issue is that 20 tons = 70.3 kW using the normal ton conversion.
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