User's Manual

P/N 81-CO2MAN-001 A-3 September 2013
= CO
2
concentration fraction
= Density of CO
2
vapor in lbs./ft.
3
= Area of opening in ft.
2
(flow coefficient included)
= Gravitational constant, 32.2 ft./sec.
2
= Density of atmosphere in lbs./ft.
3
= Density of surrounding air in lbs./ft.
3
= Static head between opening and top of enclosure in ft.
A-5 DISCHARGE RATES FOR DEEP SEATED FIRES
The discharge rate required to satisfy the two minute constraint in the preceding paragraph
can be obtained. From Equation A.2, the quantity of carbon dioxide per cubic foot required to
create a 30 percent concentration is:
Equation A.5
Example
Determine the loss rate through a 1 foot by 1 foot opening in an enclosure. The midpoint of the opening
is 5 feet below the ceiling, and the system is designed to achieve a 34 percent concentration.
A number of factors must be calculated prior to applying Equation A.4
The density of air at 70°F is 0.075 lb./ft.
3
The density of carbon dioxide vapor at 70°F can be calculated from its molecular weight (44) and the
molecular weight of air (29)
0.075 lb./ft.
3
X (44/29) = 0.114 lb./ft.
3
The density of a carbon dioxide/air mixture containing 34 percent by volume of carbon dioxide is:
0.114 lb./ft.
3
X 0.34 + 0.075 lb./ft.
3
X 0.66 = 0.089 lb./ft.
3
The effective area of the opening can be reduced by a factor of 2 since there are no known openings
above this opening. The opening area for calculation purposes is thus:
1ft. X 1ft./2 = 0.5 ft.
2
The carbon dioxide loss rate through the opening is:
lb./min.
C
p
A
g
p
1
p
2
h
R 600.340.1140.5
·

232.20.089 0.075–5""
0.089
----------------------------------------------------------------------------
1.167.11==
R 8.2=
W
V
-----
1
9
---
1
1 0.3–
----------------ln 0.0396 lb./ft.
3
==