Determining Cfm - Greenheck 240XP-CUB Manual

Determining CFM (cfm)
After the model is known, the cfm must be determined.
Consult local code requirements or the table below for
suggested air changes for proper ventilation.
The ranges specified will adequately ventilate the
corresponding areas in most cases. However, extreme
conditions may require "Minutes per Change" outside
of the specified range. To determine the actual number
needed within a range, consider the geographic
location and average duty level of the area. For hot
Area
Assembly Hall
Attic
Auditorium
Bakery
Bar
Barn
Boiler Room
Bowling Alley
Cafeteria
Church
Classroom
Club Room
Sample problem:
A building requires an exhaust fan to ventilate a general
office (see diagram below) which measures 30 ft. x 40
ft. x 8 ft. The office is often crowded.
Solution:
The total room volume is 30 ft. x 40 ft. x 8 ft. = 9600
cubic feet. From the chart, the range for general offices
is 2-8 minutes per change. Since the office has heavier
than normal usage, 4 minutes per change is
recommended. Therefore, the required exhaust is:
9600 ft
4 min.
16
Suggested Air Changes for Proper Ventilation
Room Volume
cfm =
Min./Chg.
Min./Chg. Area
3-10 Dance Hall
2-4 Dining Room
3-10 Dry Cleaner
2-3 Engine Room
2-4 Factory
12-18 Foundry
1-3 Garage
3-7 Generator Room
3-5 Gymnasium
4-10 Kitchen
4-6 Laboratory
3-7 Laundry
3
= 2400 cfm
climates and heavier than normal area usage, select a
lower number in the range to change the air more
quickly. For moderate climates with lighter usages,
select a higher number in the range.
To determine the cfm required to adequately ventilate
an area, divide the room volume by the appropriate
"Minutes per Change" value.
Room Volume = L x W x H (of room)
Min./Chg. Area
3-7 Machine Shop
4-8 Mill
2-5 Office
1-3 Packing House
2-7 Projection Room
1-5 Recreation Room
2-10 Residence
2-5 Restaurant
3-8 Rest Room
1-5 Store
2-5 Transfer Room
2-4 Warehouse
Since the air to be exhausted is relatively clean, this is
an ideal application for a model GB fan.
Note: In this example, make-up air was provided
through a set of louvers at the wall farthest from the
exhaust fan. If there were no provisions for make-up air
in this room, a supply fan would also have to be sized.
The supply cfm should equal the exhaust cfm. Supply
fan location should be as far as possible from the
exhaust fan.
Min./Chg.
3-6
3-8
2-8
2-5
1-2
2-8
2-6
5-10
5-7
3-7
1-5
3-10