Venting [RE-wrenches]

Allan Sindelar, Positive Energy, Inc. allan at positiveenergysolar.com
Mon May 21 22:03:00 PDT 2001


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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