Venting [RE-wrenches]

[Joel Davidson]

I apologize for incorrect battery venting formulas in my book (but no one ever
caught them). If I ever get a spare couple months (yeah, sure), I will finish
the revised edition. Here is the revised section on battery venting. Feedback
please.

BATTERY VENTING

Battery rooms must be properly vented to prevent the build-up of potentially
explosive hydrogen gases released during charging. The correct charge controller
will limit out-gassing during normal charging. However, topping off and
equalization charging, requirements for long battery life, will produce
hydrogen.

Concentrations of 4% hydrogen are explosive. 2% is the recommended maximum
concentration for battery storage areas. Use the following formula to determine
the size of your battery room:

Q = 0.0135 x I x N

Q is the necessary quantity of air ventilation in cubic feet per minute (CFM).
I is the charge rate in Amperes.
N is the number of series connected cells.

For example, a PV system with eight 100 Watt modules (rated 17.1 V, 5.88 A) and
sixteen 6 Volt batteries is wired for 24 volts DC. The required venting is
0.0135 x 11.76 x 12 = 1.905 CFM or 114.3 cubic feet per hour. Most rooms are 8
feet in height with 4 air changes per hour. A room 8’ x 6’ x 6’ has 288 cubic
feet volume and naturally vents 1152 cubic feet per hour, almost 10 times the
required 114.3 cubic feet per hour.

Energy efficient homes have as low as one half an air change per hour. The
example system battery room in a tight home should be at least 228.6 square
feet. The occupants of tightly built home should also be concerned about carbon
dioxide, radon and other pollutants.

Provide vent openings at the bottom of battery room doors and at the highest
point in the ceiling. Ceilings should have no exposed rafters or framing that
can trap hydrogen which is lighter than air.

If you are unable to provide enough room for natural venting, build a vented
battery compartment or cabinet out framing lumber and drywall board. Install a
gas water heater or clothes dryer type vent pipe at the very top of the battery
cabinet and run the vent straight to outside air. Put a screen over vents to
prevent mice, bugs, and birds from nesting in your battery box. Use the battery
vent only for venting batteries.

If you can not vent your battery compartment straight up and out a ceiling, use
a small fan to push the air upward through a wall vent and out of the building.
A fan will consume energy. Never run the battery vent pipe horizontal or
downward as gas will collect in it.

VRLA or sealed batteries emit very little gas but also require air exchanges to
prevent hydrogen build up. Typically, 12 Volt, 100 Ampere Hour VRLA batteries
produce 20 cc per hours gas at 2.4 volts per cell. 20 batteries in a 10 feet x
10 feet x 8 feet unvented room would produce 400 cc/hr divided by 28,317
cc/cubic feet = 0.0141 cubic feet per hour. The allowable maximum 2% gas
accumulation in the 800 square feet unvented room is 16 cubic feet. 16 cubic
feet divided by 0.0141 = 1134 hours or 47 days.

Do not tempt fate. Do not enter a closed battery room or open a battery
compartment or cabinet with a cigarette in your mouth or use a lighted flame,
match or candle. Open battery compartments carefully and let them air for a few
minutes before working in them. Be overcautious.

For peace of mind, lock the battery room or compartment and put up a sign that
reads DANGER-BATTERY ROOM-KEEP OUT.





Baran Galocy wrote:

> Lyn,
>
> Call the battery manufacturer.  Ask them to "spec-out" a battery room for
> you.  Much of it has to do with the location of the battery room, itself.
> If they won't do this, it is tantamount to an admission that it need not be
> done.   Is it an "add-on"  to the outside of an existing structure or a
> "built-in" room that is part of the original structure?  Article 511-2 of
> the NEC calls out vent. specs for commercial structures.  Also 551-10 (d)
> addresses storage battery venting  for rv's.   Article 690-71 (h) deals
> directly with storage batteries, and does NOT spec out forced venting.  Do
> what I do, either conform or ask for a conference with the building
> inspector's supervisor.  It is up to YOU to establish safe and sane
> guidelines where none exist, NOT your building inspector who has only a
> fraction of your knowledge.  Don't let this one incident set the standards
> for the future of battery rooms in your county.
>
> On the other hand, is there a danger in accumulated fumes?  Suggest to the
> B.I. that you incorporate catalytic battery caps to remove the explosive
> vapors.  Find a compromise, smile all the time, be charming but brave.  Half
> of the inspection process is a dog-and-pony show, the other half is serious
> business (to your bottom line, and the safety of your client).  Ask the
> inspector why, if you need forced venting, that the issue was not addressed
> by the NEC?  Does he think he's onto something they omitted?   Learn the
> fine line of pacifying the building inspector while gaining his/her respect
> as a knowledgeable installer of renewables and you will create a great
> working environment for both of you.
>
> - - - -
> To send a message: RE-wrenches at topica.com
>
> Archive of previous messages: http://www.topica.com/lists/RE-wrenches/
>
> List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm
>
> Check out participant bios: www.mrsharkey.com/wrenches/index.html
>
> Hosted by Home Power magazine
>
> Moderator: michael.welch at homepower.com
>

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email To: RE-wrenches-unsubscribe at topica.com
This email was sent to: michael.welch at homepower.com

T O P I C A  -- Learn More. Surf Less.
Newsletters, Tips and Discussions on Topics You Choose.
http://www.topica.com/partner/tag01
==^================================================================