A Tale of Two Houses by Bowman and Tande
Part II—Acting Like an Engineer
After a little thought, you are able to narrow down your list to four important factors that influence the rate of heat transfer: wall thickness, wall surface area, thermal conductivity of the wall, and the difference in temperature between the inside and outside of the house. As an aspiring engineer, you like to think in mathematical terms and decide to give variable names to each of these factors. Pulling out your pad of paper again, you write out the following variable definitions:
- Q = rate of heat transfer
- x = wall thickness
- A = wall surface area
- ΔT = inside-outside temperature difference
- k = thermal conductivity
You know these factors are important, but aren’t completely sure what effect each of them will have or how they are interrelated.
| If… | Heat transfer will… | ||
|---|---|---|---|
| Difference between inside and outside temperatures is increased? | increase | decrease | no change |
| Wall thickness is increased? | increase | decrease | no change |
| Wall area is increased? | increase | decrease | no change |
| Thermal conductivity is increased? | increase | decrease | no change |
| 1. Q and x | Q = mx+b | Q = mx | Q = mx2 | Q = m/x |
|---|---|---|---|---|
| 2. Q and A | Q = mA+b | Q = mA | Q = mA2 | Q = m/A |
| 3. Q and ΔT | Q = mΔT+b | Q = mΔT | Q = mΔT2 | Q = m/ΔT |
| 4. Q and k | Q = mk+b | Q = mk | Q = mk2 | Q = m/k |
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