Approach: If you think you know how to proceed and if you get stuck then hopefully you can just find the spot in the video where we're wo...
Calc: The outdoor design temperature is 50 degrees in the indoor design temperature is 70 degrees, a zoom, 15 mile an hour wind.
Calc: Outside we have an ambient temperature, design temperature of 50 degrees.
Result: That's the value we're looking for and U is the 0.076 BTO per hour foot squared F times delta T which is just 20 degrees 70 minus 50 and that gives...
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Student questions asked in live office hours about this problem
OH 19: HVAC 19
Q: For HVAC-19 (radiation through an air gap), where can I find the effective emittance equation — it's not listed explicitly in the reference handbook?
A: Search for 'parallel planes' in the reference handbook — it's given as a resistance (denominator form), not the effective emittance directly. Once you find it, you can rearrange from the resistance to the emittance form.
OH 30: HVAC 19
Q: I can't find the stack effect formula in the PE reference handbook — should I memorize it, and how do I use the table for 1-, 2-, and 3-story buildings?
A: The stack effect formula isn't in the current reference handbook — it was in older materials, which is how it ended up in this program. So yes, you'll need to know it from memory or understand it conceptually well enough to reconstruct it.
OH 40: HVAC: HVAC-19
Q: For HVAC-19, how did you find the emissivity values of 0.9 for pine and acoustic tile — I can't find them in the handbook?
A: Those values weren't in the handbook, so I provided them directly in the problem statement to make the problem solvable. If a value can't be found in the reference handbook, it should always be given to you in the problem — that's a principle to lean on when you're stuck.
OH 77: HVAC: HVAC-19
Q: For HVAC-19, shouldn't the mean temperature for the air gap be (70+50)/2 = 60°F rather than the 50°F used in the solution?
A: You're right — the mean temperature should be 60°F, and I chose 50°F in my solution. My reasoning was that 60°F isn't directly in the thermal resistance table, so I defaulted to 50°F — but technically 60°F is correct.
OH 97: HVAC: HVAC-19
Q: For HVAC-19, is R = L/k the correct relationship here, since the values given don't look like thermal conductivity?
A: Those values are R-values (thermal resistance per unit thickness), not k (conductivity) — but R = L/k is correct regardless, and they're inverses of each other. The fact that you trusted the units to guide you rather than the terminology is exactly the right approach.