AIR FILTRATION SELECTION GUIDELINE

GENERATION RATES

GENERATION RATE FORMULA

WHAT DETERMINES HOW MANY PARTICLES ARE IN A PARTICULAR SPACE?

G

C = ----------

Q X E

A: Size Of The Room

B: Activity In The Space

G = Generation Rate In Particles Per Minute

C: Air Distribution

Q = Air Volume In Cfm Or Cmh

D: Air Volume

E = Filter Efficiency

E: Filtration Efficiency

C = Particles Per Cubic Foot

F: Number Of People

G: Room Lay Out

CHANGING AIR FLOW

CHANGING FILTER EFFICIENCY

100000

C = ------------=

2400 x 0.25

100000

C = ------------=

2000 x 0.12

167 Particles Per Cubic Foot

417 Particles Per Cubic Foot

(Pleated Filter)

(Furnace Filters)

 

 

 

 

100000

C = ------------=

2000 x 0.25

100000

C = ------------=

2000 x 0.25

200 Particles Per Cubic Foot

200 Particles Per Cubic Foot

(Pleated Filters)

 

 

 

 

100000

C = ------------=

1500 x 0.25

100000

C = ------------=

2000 x 0.80

267 Particles Per Cubic Foot

62.5 Particles Per Cubic Foot

(80% Box / Bag* Filters)

 

 

 

 

100000

C = ------------=

1000 x 0.25

100000

C = ------------=

2000 x .90

400 Particles Per Cubic Foot

55.5 Particles Per Cubic Foot

(90% Box / Bag* Filters)

 

* DIRT VIBRATION THROUGH NON-SUPPORTED BAG FILTER IS MUCH HIGHER THAN RIGID, BOX FILTERS (NOT FACTORED IN ABOVE CALCULATION).

GENERATION RATE FORMULA

G

C = ----------

Q X E

G = Generation Rate of Particles Per Minute

Q = Air Volume In CFM

E = Efficiency of Air Filter(ASHRAE Dust Spot)

C = Particles Per Cubic Foot (0.5 Micron and Larger)

COMPARISON OF THE BEST VS. THE WORST

100000

C = ------------=

2000 x 0.9

BEST:

55.6 Particles Per Cubic Foot

(@ 2000 CFM / 90% Filter)

100000

C = ------------=

1000 x 0.12

WORST:

833 Particles Per Cubic Foot

(@ 1000 CFM / 15% Filter)

CONCLUSION: THE BEST INDOOR AIR QUALITY ON PARTICULATE CAN BE OBTAINED USING THE HIGHEST AIR VOLUME WITH THE MOST EFFICIENT FILTERS POSSIBLE.

EXAMPLE:

TYPICAL ORIGINAL DESIGN STANDARD PER ASHRAE:

G = 100,000

Q = 2,000

E = 80%

C = 64

BECAUSE OF VAV, DECREASE THE CFM TO 1500 AND RECALCULATE:

G = 100,000

Q = 1,500

E = 80%

C = 84

BECAUSE OF ENERGY AND FILTER COSTS DECREASE THE PRESSURE DROP BY DECREASING THE FILTER EFFICIENCY:

G = 100,000

Q = 1,500

E = 25%

C = 266

ENVIRONMENTAL HEALTH PEOPLE SAY YOU SHOULD HAVE 60 PARTICLES PER CUBIC FOOT. NOW LET US DETERMINE THE FILTER EFFICIENCY:

G = 100,000

Q = 1,500

C = 60

SOLVE FOR FILTER EFFICIENCY ? ?

G

E = ----------- = 111% CONCLUSION, THIS FILTER DOES NOT EXIST ! ! !

Q X C (NEED MORE AIR FLOW)