Question

3.10 What minimum ventilation air quantity will be required for the room in Question 3.9 if the office is 5,000 sq.ft.?

Given from Q3.9:

• 15 people, moderate activity
• 5 copy machines, 500 W each
• 15 suspended light fixtures, two 50-W lamps each

Answer 1

Ans) Given,

Office area = 5000 sq.ft

15 people with moderate activity

5 copy machine, 500 W each

15 suspended light fixture with two 50 W lamps each

We know,

Air quantity required per person in office room = 5 CFM (cubic foot per minute)

quantity required for 15 person (Q)= 5 x 20

Q = 75 CFM

Therefore ventilation for 5000 square feet = air rate/ft² x area

For office building, air rate /ft² = 0.06

Hence ,required quantity(Q) = 0.06 x 5000

Q = 300 CFM

Total ventilation required = 75 + 300

Q = 375 CFM  

Now , for 500W machine,amount of heat generated is 500 J/sec

1 J/s = 3.41 BTU/hr, hence 500J/s equal to,

= 500 x 3.41 BTU/hr

= 1705 BTU/hr

Total number of copying machine = 5

Hat generated by 5 machines = 5 x 1705

= 8525 BTU/hr

We know, air quantity required (Q)= heat to be removed / (1.08 x difference in indoor and outdoor temperature)

Assume indoor temperature 70F and outdoor temperature as 50F

Difference in temperature = 70 - 50

= 20F

Putting values,

Q = 8525 / (1.08x 20)

= 395 CFM

Now , total number of 50W bulbs = 15 x 2

Total 50W bulbs = 30

Heat generated by one 50W bulb = 50 x 3.41

= 170.5 BTU/hr

Heat generated by 30 bulbs = 170.5 x 30

= 5115 BTU/hr

Ventilation required(Q) = 5115 / (1.08 x 20)

Q = 237 CFM

Hence, Total ventilation required(Q_T) = 375 + 395 + 237

Q_T = 1007 CFM