Venting [RE-wrenches]

[Joel Davidson]

I knew someone in this group would help me see the light :-)
1. Gassing voltage is assumed.
2. You are correct. 4 each 2-module series strings in parallel at 5.88 amps =
23.52 amps.
3. I'm not a backdraft flap or power vent guy. I prefer a room or building that
passively vents gas (low in, high out).
4. I prefer sheetrock for standard fire protection. Some people like plywood
battery cabinets. Some like metal cabinets. Some people use the Rubber Maid
boxes and shed sold at home improvement stores.
5. Some building inspectors require active venting (a fan) - and spill
containment pans and eye wash stations. The no-brainer solution is to use sealed
batteries that cost twice as much and last half as long as golf cart batteries.
In southern California, most building inspectors cringe when they see a big,
flooded battery bank. Lately, California PVers are compiling a list of batteries
that qualify for the $750 grant (SB1345).
Thanks a lot, Allan. Your ideas are appreciated.
Best regards,
Joel Davidson

"Allan Sindelar, Positive Energy, Inc." wrote:

> Joel,
> 1. Shouldn't battery voltage be factored in? Batteries gas as the voltage
> reaches and exceeds approximately 2.35vpc.
> 2. I think the I in your example should be 23.52, not 11.76.
> 3. Backdraft should be covered. If the house has negative pressure, air can
> be blown back down a vent pipe and into a room.
> 4. Framing lumber and wallboard both rot if they contact battery acid. I
> don't think you should recommend those materials.
> 5. If a vent fan, such as the Power Vent, is hooked to a voltage-sensitive
> relay, it uses only enery otherwise spent finishing a charge or gassing the
> full batteries anyway. Just saying "A fan will consume energy." misses that
> point.
> 6. Most home systems (your target readership, I think) don't have battery
> rooms, just battery boxes. I'd focus your recommendations on the latter.
> Hope this helps.
> Allan at Pos E
> ----- Original Message -----
> From: "Joel Davidson" <joeldavidson at earthlink.net>
> Sent: Tuesday, May 15, 2001 2:05 PM
> Subject: Re: Venting [RE-wrenches]
>
> > BATTERY VENTING
> >
> > 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.
>
> > 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.
> >
>
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