Aclassroom 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 360kj/h. there are 10 light-bulbs 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 15000 kj/h. if the room air is to be maintained at a constant temperature of 21℃, determine the number of window air-conditioning units required.