Tuesday, April 23, 2013

How to calculate ventilation requirements for a battery room ?

The following is an example of a calculation of ventilation requirements for a battery room with lead acid batteries.  Lead acid batteries release hydrogen during charging as well as on float (trickle charge after the full charge).  Hydrogen concentration above 5% is not a safe situation.  A spark can create explosion when the hydrogen concentration is high.  The following procedure explains ventilation requirements for a battery room to keep the hydrogen concentration below 1%.

This following calculation will show you the ventilation requirements during normal float conditions.

During abnormal conditions higher ventilation may be required depending upon the condition.

Amount of hydrogen release during normal float condition for a flooded battery is given as

VHy (cubic feet per hour) = 0.0148 x FC (where FC is float current in Amps)

If the battery room has N number of cells then the total volume of hydrogen released per hour

VTHy  = VHy x N (cubic feet/hour)

Let us assume the free volume of the battery room is Vr (cubic feet)

(free volume is the actual volume of the room minus the volume taken by objects in the room including batteries)

Time required to reach 1% concentration of hydrogen t = Vr/100 VTHy.

In other words complete air exchange is required in every t hours is enough ventilation to keep the hydrogen concentration below 1%.

Higher charge voltage, temperature, thermal runaway, overcharge condition will significantly affect the hydrogen generation rate of a lead acid battery.  Care should be taken to accommodate all the possible abnormal conditions.

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