Basic Documentation

Table 1. Air Driven Laboratory Rooms with Fume Hoods - Supply Airflow Turndown Ratios.
VAV Fume
Hoods in
Room
4 5 6 8
Foot Widths
Total Fume
Hood Exhaust
Total
Room
Exhaust
Room
Supply
Airflow
R
O
O
M
Laboratory Room
Size:
(Length)
(Width)
(Height)
Floor Area
Room Volume
Excess
Room
Exhaust
Airflow
For
Negative
Pressure
4' 5' 6' 8' Min.
cfm.
6
Max.
cfm
7
Total
Miscellaneous
Room
Exhaust
Min.
cfm
8
Max.
cfm
9
Room
Minimum
Air
Changes
Per Hour
Min.
cfm
10
Max.
cfm
11
Room
Supply
Turndown
Ratio
1 1 150 750 350 950 9.3 100 700 7.0 : 1
2 1 200 1000 400 1200 10.7 150 950 6.3 : 1
3 1 250 1250 450 1450 12.0 200 1200 6.0 : 1
4 1 350 1750 550 1950 14.7 300 1700 5.7 : 1
5 2 300 1500 500 1700 13.3 250 1450 5.8 : 1
6 2 400 2000 600 2200 16.0 350 1950 5.6 : 1
7 2 500 2500 700 2700 18.7 450 2450 5.4 : 1
8
Length: 25 ft
Width: 10 ft
Height: 9 ft
Area: 250 ft
2
Vol.: 2250 ft
3
250
12
cfm
2 700 3500
200 cfm
(2 Bench
Snorkels)
900 3700 24.0 650 3450
5.3 : 1
9 3 450 2250 850 2650 11.3 500 2300 4.6..:..1
10 3 600 3000 1000 3400 13.3 650 3050 4.7 : 1
11 3 750 3750 1150 4150 15.3 800 3800 4.8 : 1
12 3 1050 5250 1450 5650 19.3 1100 5300 4.8 : 1
13 4 600 3000 1000 3400 13.3 650 3050 4.7 : 1
14 4 800 4000 1200 4400 16.0 850 4050 4.8 : 1
15 4 1000 5000 1400 5400 18.7 1050 5050 4.8 : 1
16
Length: 25 ft
Width: 20 ft
Height: 9 ft
Area: 500 ft
2
Vol.: 4500 ft
3
350
12
cfm
4 1400 7000
400 cfm
(4 Bench
Snorkels)
1800 7400 24.0 1450 7050
4.9 : 1
17 5 750 3750 1350 4350 12.0 900 3900 4.3 : 1
18 5 1000 5000 1600 5600 14.2 1150 5150 4.5 : 1
19 5 1250 6250 1850 6850 16.4 1400 6400 4.6 : 1
20 5 1750 8750 2350 9350 20.9 1900 8900 4.7 : 1
21 6 900 4500 1500 5100 13.3 1050 4650 4.4 : 1
22 6 1200 6000 1800 6600 16.0 1350 6150 4.6 : 1
23 6 1500 7500 2100 8100 18.7 1650 7650 4.6 : 1
24
Length: 25 ft
Width: 30 ft
Height: 9 ft
Area: 750 ft
2
Vol.: 6750 ft
3
450
12
cfm
6 2100 10500
600 cfm
(6 Bench
Snorkels)
2700 11100 24.0 2250 10650
4.7 : 1
6. NFPA 45 and Standard ANSI/AIHA Z9.5 requires that VAV fume hoods maintain a minimum exhaust airflow of 25 cfm per square feet of internal hood work surface area.
7. Maximum exhaust airflow is based upon a vertical sash fume hood with an average face velocity of 100 fpm and a 30-inch maximum sash opening height.
8. Total Room Minimum Exhaust is the sum of the Total Fume Hood Minimum Exhaust plus the Constant Volume Room Exhaust.
9. Total Room Maximum Exhaust is the sum of the Total Fume Hood Maximum Exhaust plus the Constant Volume Room Exhaust.
10. Room Minimum Supply Airflow is the Total Room Exhaust minus the Excess Room Exhaust Airflow For Negative Pressure.
11. Room Maximum Supply Airflow is the Total Room Exhaust minus the Excess Room Exhaust Airflow For Negative Pressure.
12. The amount of Excess Room Exhaust Airflow For Negative Pressure is the approximate amount needed to maintain 0.010 inches of negative pressure for the size of room.
Page 4 of 8 Siemens Industry, Inc.
Document No. 149-978