Air Exhaust from the UPS Battery Building

The required number of air changes per hour (A) is given by the following formula:

0.045 x N x I = A
V

Where:
N = Number of cells in the battery
V = Volume of room in cubic metres
I = Charge rate in Amperes

This formula will give the number of air changes per hour required during boost charge conditions. On float charge (systems are on float charge for most of their service life), the amount of gas emitted is approximately 1.5% of that liberated whilst on boost charge and under most circumstances this will be dissipated by natural ventilation, and will not present a hazard. However, we recommend that the boost charge condition is allowed for at the design stage to ensure the appropriate decision on ventilation requirements is made.

Although Valve Regulated Lead-Acid Batteries require little ventilation under normal operating conditions, it is good practice to apply the formula to calculate the number of air changes required to achieve minimum risk under battery fault or failure conditions

This is no definitive answer to the number of air exchange. I have seen it varying from a low number (2) to a high number (30). Here is some of the related standard reference:

(1) DNV-OS-D201, Article 304: For VRLA batteries over the UPS capacity 40 KVAh (yours is 60 x 2 = 120 KVAh), the minimum 30 changes per hour. However this requirement is during the deep charge of batteries.

(2) NFPA-1: Fire Code, Article 52.3.6: the air exchange rate not less than 1 ft3/min/floor area in square foot.

(3) EN 50272-2 has a formula (Q = 0,05 x n x Igas x Crt . 10-3 [m3/h]) in the article 8.2: Ventilation Requirement.

There is another recommendation from NFPA for vented batteries – 2 air change per hour.

I worked in an offshore project where the requirement for battery room was 10 air changes per hour; while in another similar project, the requirement was the complete room air change within two minutes (equivalent 30 air changes per hour).

The formula that TonyS suggested also can be followed.

The LEL (Lower Explosion Limit) of hydrogen is 4%. So, it is recommended that the limit shall be kept lower than 1% for better safety. So, you can find the maximum hydrogen evolution from the batteries during deep charge from the vendor, and calculate the requirement of the air change rate to limit the level to below 1%.

There are other important things about the battery room ventilation and they are:

(1) The equal amount of fresh air to be intake into the room, so that no significant negative pressure occurs in the room.

(2) The standby fan should be in place so that if one fails, the other one starts

(3) The air flow can be controlled; the air flow rate requires increase for case of hydrogen detection in the room

Here is some links that also may help you (you might have already seen them):

http://www.apcmedia.com/salestools/SADE-5TNQZQ_R2_EN.pdf

http://140.194.76.129/publications/armytm/tm5-691/c-7.pdf

http://www.cholarisk.com/Files/Risk%20Note%20on%20Explosion%20Risks%20in%20Battery%20Rooms.pdf

- MS