HVAC · Systems-and-Components · Problem 3PDFSolution in PDF ↓
HVAC · Systems-and-Components · Problem 3
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Student questions asked in live office hours about this problem
OH 20: HVAC: Systems and Components-3
Q: For Systems and Components 3, I'm struggling to visualize the system — can you explain how to use the sensible heat equation to find Q at the evaporator, since I think ΔT should come from the refrigeration cycle states?
A: For a refrigeration cycle evaporator, use the refrigerant-side enthalpy change (h1 − h4) rather than a temperature difference — that's the heat absorbed from the conditioned space. Draw the refrigeration cycle schematically with the four state points, then identify which enthalpy difference corresponds to the evaporator.
OH 89: HVAC: Systems and Components-3
Q: In Systems and Components 3, the compressor draws 40 kW — isn't that the electrical input, and don't I need the compressor efficiency to find the actual work input?
A: You're technically correct that electrical input and shaft work differ by motor efficiency, but since no efficiency was given in this problem, we have to assume the conservative case and treat all 40 kW as compressor work. If an efficiency had been given, you'd absolutely apply it.