A classroom 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 dissi - pate heat at a rate of about 80 Watts. 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 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. What is the source of heat being generated for the light bulbs and for the students?

Question

Donovan Fernandez

Engineering

7 April, 21:01

A classroom 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 dissi - pate heat at a rate of about 80 Watts. 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 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. What is the source of heat being generated for the light bulbs and for the students?

+1

Answers (1)

Know the Answer?

Mara Powers · Answer 1

a) Heat energy given out by 40 people

= 40 x 80 = 3200 J in one second

Heat energy given out by 10 light bulbs

= 10 x 100 = 1000 J in one second

Heat transfer by wall = 15000 x 1000 J in one hour

= 15000 x 1000 / 60 x 60

= 4166.67 J in one second

Total energy

= 3200 + 1000 + 4166.67 J in one second

= 8366.67 J

To drive this much of heat, we need 2 air - conditioner of 5000 W each.

b) Source of heat for bulb is electrical energy of bulb

For the students, source of heat by student is the bio - chemical reactions taking place in the body of the student which is exothermic.