A room that normally contains 40 people is to be air-conditioned with window air

Question

A room that normally contains 40 people is to be air-conditioned with window air- conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h. There are 10 light bulbs in the room, each with a rating of 100 W. The rate of heat transfer to the room through the walls and the windows is estimated 15,000 kJ/h. a) If the room air is to be maintained at a constant temperature of 21?C, determine the number of window air-conditioning units required. b) Let us assume that a person dissipates 5 times more energy when dancing. For the same number of air-conditioning units and the same desired temperature, how many people should be invited to the room for a party featuring a few hours of dancing?

Explanation / Answer

people: 40*360 KJ/hr * 1 hr/(3600 sec) = 4kW Lights: 10 * 100 W = 1kW heat infiltration = -15000 kJ/hr * 1hr/3600 sec = 4.167 kW + -------------------------------- 9.167 kW of heat must be rejected Therefore, 2 AC units should be used.

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