Air Change Rates

Topics: Rooms, Building, Construction Pages: 3 (432 words) Published: December 3, 2014
Air Change Rates

Room
CFM

Volume

CFM

Air change rate per hour can be expressed as;
ACR = 60 x CFM / V

(1)

Where;
ACR = air change rate per hour
CFM = air flow through the room (Cubic Feet per Minute)
V = volume of the room (Cubic Feet)
For example;
Room = 10 x10 x 8 = 800 cubic feet
Supply Grille = 10 x 8 x 6 with 6 inch flex duct attached delivering 80 cfm @ 0.1in. static pressure ACR = 60 x 80 / 800
ACR = 4800 CFH (Cubic Feet per Hour) / 800
ACR = 6.0
Conclusion: The complete volume of air filling this room is completely changed 6 times in one hour when the ventilation equipment is delivering its air to the room for that length of time. However, to be also considered is that the comfort system delivering the air does not always run for the whole hour straight. So to factor in the change rate, one must consider the demand for ventilation requirements based on building construction, heat load requirements, and buildings environmental characteristics. Such as shade, direction of exposure, glass, radiant, convection, and conduction heat loads. The more efficient the building construction, the lower the demand to heat or cool, thus reducing the air changes per hour unless the blower is set to run all the time in the “on” position as is normal in commercial settings.

The tables on the following pages show common Air Change Rates for buildings / rooms;

Building / Room

Air Change
Rates
- ACR (1/hr)

Building / Room

Air Change
Rates
- ACR (1/hr)

All spaces in general

min 4

Court Houses

4 - 10

Attic spaces for cooling

12 - 15

Dental Centers

8 - 12

Auditoriums

8 - 15

Department Stores

6 - 10

Bakeries

20

Dining Halls

12 -15

Banks

4 - 10

Dining rooms (restaurants)

12

Barber Shops

6 - 10

Dress Shops

6 - 10

Bars

20 - 30

Drug Shops

6 - 10

Beauty Shops

6 - 10

Engine rooms

4-6

Boiler rooms

15 - 20

Factory buildings, ordinary...
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