MAE 406 HVAC Equipment HW

MAE 406 HVAC Equipment HW - which? 5. Compute the...

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MAE 406 Homework #9 1. Why is a water-cooled refrigeration unit generally more efficient than an air-cooled unit? Hint: analyze the cycles with temperatures given in class using your Thermo book for R-22 or R-134a. 2. Why do manufacturers install the expansion valve very close to the evaporators for split systems? 3. Why do large systems use chilled water instead of piping R-22/134a around the building to air handling units? 4. Why is the evaporator (almost) always located on the bottom of a chiller and the condenser on top? What are other methods, apart from feeling the surfaces for cold and hot, to tell which heat exchanger is
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Unformatted text preview: which? 5. Compute the efficiency of a 2 ton heat pump in heating mode for following conditions. Refrigerant-R-134A Indoor temperature-70 F Outdoor temperatures-40, 20, 0 F Compressor isentropic efficiency-70% Sketch the cycle on a P-h diagram for each outdoor temperature condition on the same plot. Graph the efficiencies (kW/ton or COP) for all three outdoor temperature cases to see how efficiencies vary. 6. For the conditions in problem 5, compute the threshold price for gas ($/therm) in which the heat pump is equivalent in cost to gas heat. You may assume efficiency of the gas furnace to be 80%. Any conclusions?...
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This note was uploaded on 08/01/2008 for the course MAE 406 taught by Professor Eckerlin,terry during the Fall '07 term at N.C. State.

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