UFC 3-410-04N
25 October 2004
Q
=
Minimum required ventilation airflow rate, in cubic feet per minute
(cfm).
PC
=
Percent concentration of hydrogen allowed in room (PC = 0.01 to
keep the hydrogen concentration at 1 percent).
Formula (2) assumes complete mixing of the air inside the battery maintenance
facility. In most cases, use a safety factor k to determine the actual ventilation rate.
See Figure 2.1 of the ACGIH IV Manual to select a "k" value.
QA
=
Qxk
(3)
QA
=
The actual volumetric ventilation rate, in cubic feet per minute (cfm),
which can be expressed in air change per hour (ACH) using the
following formula:
ACH =
QA x 60 /Room Volume
(4)
Example. Per manufacturer specification, one fully charged lead calcium cell, at 77
degrees F (25 degrees C), will pass 0.24 amperes of charging current for every 100
ampere-hour cell capacity, measured at the 8-hour rate, when subject to an equalizing
potential of 2.33 volts. Calculate the required rate of ventilation for a battery bank
consisting of 182 cells. Each cell has a nominal 1,360-amphere hours capacity at the 8-
hour rate and being equalized at an electrolyte temperature of 92 degrees F (30
degrees C).
At 92 degrees F (30 degrees C), FC is doubled
FC
=
0.24 amp x 2 = 0.48 amp
AH
=
1360 amp hr
0.016 ft3/amp hr cell
K
=
ft3
ft3
0.48 amp
C=
x 182 cell = 19
x 1360 amp hr x 0.016
hr
amp hr cell
100 amp hr
ft3
1 hr
19
x
3
hr 60 min = 32 ft
(5)
Q=
0.01
min
Assume a room size of 8,000 cubic feet (226.5 cubic meters) with a safety factor
of k = 2, charging 3 banks of battery.
8-3
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