The central HVAC unit for Kettering Labs goes down over the summer, and the clas

ID: 2997070 • Letter: T

Question

The central HVAC unit for Kettering Labs goes down over the summer, and the class in KL221

wishes to install window mounted air-conditioning units having 18,000 Btu/hr cooling capacity.

The classroom contains 43 people with an average resting heat dissipation rate of about 325 kJ/h

per person. There are 10 lights in the room, each with a rating of 100 W. The rate of heat transfer

to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air

is to be maintained at a constant temperature of 21

Heat produced due to people = 43*325 = 13975 kJ/h = 13975000 J/h = 3881.94 J/s

Heat produced due to lights = 10*100 = 1000 W = 1000 J/s

Heat coming in due to walls and windows = 15000 kJ/h = 4166.67 J/s

Thus, total heat production rate = 3881.94 + 1000 + 4166.67 = 9048.61 J/s

Heat removing capacity of of one air conditioning unit = 18000 Btu/h = 18000*0.293 = 5274 W = 5274 J/s

Thus, number of air-conditioning units required = 9048.61/5274 = 1.715

Thus, approximately we need 2 air conditioning units

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