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

Integrated Publishing, Inc. |