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dbarry14 (Mechanical) (OP)
16 Oct 08 15:52
I am working on a warehouse that will have a battery charging station in it, and I will need to provide exhaust.  I have found information on battery charging rooms talking about number of air changes per hour, but since this is just a small corner space of the whole warehouse, that doesn't really apply.  I also saw where ASHRAE 62 calls for 1 CFM/charging ampere.  The IMC just calls for ventilation as required.

I was thinking about installing a hood of some sort with a flow rate determined by using the 1 cfm/charging ampere.  There will be an explosion proof fan on the roof.  Any other ideas?
GMcD (Mechanical)
16 Oct 08 19:26
Use all stainless steel ductwork, and why not just use a scroll type utility fan with the motor out of the airstream?  Fan (blades and scroll) should be either heresite coated, epoxy coated, or all stainless steel.

I'd do the capture hood, as well as an auxiliary high level exhaust inlet just under the highest point of the ceiling/room to capture the hydrogen gas that can come off some batteries while they charge.  Capture hood should cover 30% more than the footprint of the battery charging area, and then use the old 125 cfm per foot of exposed hood lip as the fan/ventilation sizing guide.

Depending on the amount/frequency of battery charging, your local Authority Having Jurisdiction may also want a discharge stack from the exhaust fan above the roof to disperse and dilute the fumes/contaminants.  This application is almost like a Laboratory fume hood exhaust application.
DrRTU (Mechanical)
16 Oct 08 21:33
We have designed numerous new office/warehouse buildings near Chicago. You are correct in the applicable codes. Most code inspectors require a ventilation system but do not give guidance on the means or quantities. We have been using 400 CFM (exhaust) per charger.  Locate inlet of the duct behind the wall charger. The 400 CFM seems to meet the CFM and charging rates addressed by the codes. The codes on lead acid battery charging were drafted around the use of chargers in a confined -  not in the corner of a large volume. We use a non-spark gland on the fan and spiral duct to the square duct on the wall. Continuous fan operation.
Wareagl487 (Mechanical)
17 Oct 08 7:31
As DrRTU stated, the code was designed for charging in a small room.  For years we did distribution facilities all over the nation.  Per their prototype design documents, a exhaust fan was placed directly on the roof above the charging area with no ductwork at all without suffering repercussions from the AHJ.  Seemed funny to me that a exhaust fan 25+ feet above a charging area peeing out only 400 cfm would have any effectiveness what so ever - but it has passed inspections in all locations by many different code inspectors.

If I was doing it without direction, I would do it similar to the Dr's.

Andy W.  
chicopee (Mechanical)
19 Oct 08 22:23
You may want to interlock fan to battery charger.
gasdetector (Mechanical)
12 Nov 08 15:40
The concern in a battery cahrging application is the production of Hydrogen gas during the charging process. Hydrogen has an LEL/LFL of 4% by volume (40,000 ppm).
We typically control the exhaust fan for these areas with a Hydrogen gas sensor with a measurement range of 50% LEL and set the low alarm relay to operate "fai-safe" and trigger at 10% LEL and connected to activate the exhaust system.
This saves energy multiple ways by not having the exhaust running unnecessarily.

Ron S.

hollandhvac (Mechanical)
13 Nov 08 1:46
Have been in this descussions many times with lots of people and I do the following.

A continues flow of through the battery room needs to be garantied and therefor I use a duty/ standby exhaust fan with alarm indication on the control panel incase a fan failed to work.

The maximum hydrogen level needs to be 25% of LFL and de max LFL is 3,8 or 4.0 % percent depends on what source you take. So the airflow through the battery needs to be calculated against the hydrogen output from the battery's at float charge normal condition. Some people want it to be done at boost charge when you get a higher production of hydrogen.

Now there could also be a cooling requirement in the room when you are in the warmer area of the globe, which means that either of the two air flows for hydrogen or heat load requirement the highest need to be installed.

For the duct work: the suppy is at low level say 0,3 meter from the foor and the exhaust is at high level since hydrogen lighter than air. For this reason a falce ceiling is not allowed, since it can gather there and produce an explosive mixture. Have seen designs where there is a low level exhaust as well on the same exhaust duct so exhaust the acid fumes.

The duct work used is the normal galvanized sheet metal with epoxy coating.

The fans an other debate need to be ex proof

Ex (d) IIc T3 with non sparking fan. now this is a very high spec and basically you can tansport 100% hydrogen trough this.

For the civil works check if there are nt beams going through the room that you might get pockets of hydrogen there whiche are not ventilated. have had this once and made a dict work inside the battery room to vent each pocket.

Like to know others opinion about this. and I hope it has helped you.

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