battery room ventilation

[howls88]

I found another thread that asks a similar question but I did not see an answer to the question.

I have a situation where there is a battery room that has a dedicated exhaust system with hoods over the battery cabinets. The problem is that the current design has more supply air than exhaust air and therefore the A/C system is recirulating the battery room air to the rest of the rooms served.

All the information that I have found online and experiences at other power plants have the air exhausted out with no recirculation. In this instance, we are required to keep the battery room to 74 degrees +/- 5 degrees.

All my thoughs are that recirc is not allowed, but I have not found that documentation that states that, and changing the design from recirc to 100% exhaust would be extremely costly due to building constraints.

Is this allowed, and if not, what codes or standards would support that?

 

[KiwiMace]

IMC 502.4 and IFC 608.6 give you the choice of 1 cfm/sf or maximum concentration of Hydrogen to 1.0% of room volume. Note that 1 cfm/sf usually far exceeds that required by the hydrogen sensor method and particularly so with VRLAs which emit less H2. I assume when you say cabinets, that these are VRLA batteries, not wet cells and you have more than 50 USgal of electrolyte as permit minimum.

IMC 510.2 requires a hazardous exhaust system for H2 [LEL is 4%, requirement where 25% of this (ie 1%) could be possible in normal operation]. So per IMC Section 510, you need to provide the ventilation as exhaust, use a sparkproof fan, room should be kept at negative pressure to adjacencies...

If you are stuck for exhaust flowrate, check the sensor method calculation and see if this is ok for your current fan, and that the local AHJ is down with it. Use the peak emission rate for the type of battery you have.

You don't specify your climate. The sweet spot for batteries is 77degF. Running at 69degF (the lower point of your range) will have an adverse effect on capacity. I would close up this tolerance.

 

[KiwiMace]

Oh, I meant to also say that IMC 510.4 prohibits recirc to occupied spaces; to your actual question.

 

[marcoh]

Every battery room I have designed has had a dedicated AC plant for the room plus exhaust ventilation as required.

Your options seem to be to increase the exhaust (to say 90% of the supply air into the room to maintain negative pressure, AHU must have sufficient outside air to provide the makeup air) or to provide a dedicated AC plant for the battery room.

 

[howls88]

IMC 510.4 prohibits the recirculation of hazardous air. But if the concentration is below 1%, which is less than 25% of the lower flammability limit of 4%, would the air then be considered hazardous per IMC? Please keep in mind that the battery cabinets with, VLRA batteries, are being exhausted and in theory, no hydrogen should get to the general space which is also being exhausted.

If it is not considered hazardous, the air could then be recirculated. So the main question is whether the air is considered hazardous.

Thanks again,

Geoff

 

[mauricestoker]

Plastic batteries would be an alternative. DoD has done that for decades.

 

[KiwiMace]

Talk that IMC 510 classification issue with your AHJ. Personally, i would never consider a recirc system because of the less likely hazards from accidental shorts, battery fires. Also, the setpoint at 77degF almost commands a dedicated system.

The above code is pretty clear that exhausting from the cabinets does not preclude general exhaust from the space.