Battery Room Ventilation Plans

[Bill NC]

All, please let me know if you see any inherent flaws in this battery room design. The entire mechanical room for the PV solar system will be the battery room.

The mechanical room for the PV system gear and batteries is 4' x 11' x 9' tall with only exterior door. I have experience with building energy star houses that have to pass blower tests and realize the mechanical room has to be very airtight, especially at the ceiling level.

Passive ventilation consisting of a 4" PVC exhaust vent with the inlet in the ceiling centered over the batteries. The inlet is also a 4" PVC pipe that enters the room through the ceiling then extends downward ending about 6" above the floor.

There will also be a powered ventilation system that will consist of a 4" duct with the intake over the batteries at the ceiling with a 25 cfm inline exhaust fan. Looking at the Vents-US models: TT100, TT125 etc. These can be installed in series. I will still need to check the actual cfm allowing for the length of duct and elbows. I think that the Outback 8048A inverter will turn on a 120 volt circuit when battery charge reaches 80% or above. These fans are not rated for explosive atmosphere use, but from what I've read, since this system is designed to keep levels below the LEL, the fan does not have to be.

I came up with the 25 cfm by using the calculators at the links below for the largest battery system that I'm considering as an option, and came up with 25 cfm both times using the dimensions of the entire battery room.

http://www.sbsbattery.com/products-services/white-papers/material-handling/risks-of-unmonitored-hydrogen-in-battery-installations/battery-room-ventilation-calculator.html

http://na.bhs1.com/battery-room/ventilation/

The room will have an H2 detector, most likely a Macurco GD 12 or an RKI PS2, with the sensor located on the ceiling over the batteries. The RKI PS2 has a remote sensor. I'm not sure if the Macurco does or not. The H2 detector will be set to turn on the first exhaust fan at 10% LEL and the second fan at 20% LEL. This system will have a backdraft damper. I would think it should be located at the intake end of the ductwork over the batteries. What I like about the Macurco is that it has a digital read out of the LEL %.

One string of batteries will sit on the floor in a 5" deep polypropylene containment pan. The second string will be on a shelf approx. 4' higher. This shelf does not run wall to wall, but has an opening at each end to allow the free movement of H2 up to the ceiling. I will fabricate a polypropylene cover for the plywood with a drip on the front and rear that extends downward to 1/2" below the 2x4 supports. I have run the numbers on the span of the 2x4s and the max load being carried. Not shown on the drawings is a 4" I beam mounted to the ceiling that will allow batteries to be lifted onto the upper shelf with a chain fall and trolley.

There will be plywood covers that can be installed over the near row of 4 batteries when working on the far row, such that one can lean their elbows on it. There will also be a walk board that can be installed at the appropriate height to stand on when service the upper level of batteries.

When the powered exhaust fan is operating, I would expect it to draw air from both the passive ceiling vent and also from the floor level passive vent.

Options being considered:

Installing a PVC drain in the containment pan that would drain the exterior with an inline valve. In the event of a spill, the electrolyte could be collected in a bucket outside. Any dirt that collected in the tray could likewise be rinsed out into a bucket outside.

What else?

I have attached pdf drawings of the mechanical room below. I've not posted attachments before so I hope I did this correctly.

Thanks,

Bill NC


Mech Room Plan View 2014 12 29.pdfMech Room Sections 2014 12 29.pdf

[Mike90250]

I abhor the idea of batteries sharing living envelope space. Put up cement board or something that your code will allow to treat the battery room as a separate building, and provide vermin proof passive vents high and low. H2 rises, so don't create a pocket up high when placing a duct over the batteries.

And I think the H2 sensor may have a finite lifetime, and need periodic replacement. I know that O2 sensors and Co sensors have limited life times (6 mo & 5 years)

I also dislike the idea of powered ventilation, relying on fans that can fail, or wires that can spark, over the plan of a passive Hydrogen and acid fume venting system.

You may need power venting for heat control in the summer, to dissipate heat from the inverter and charger.

Perhaps Sunking will chime in with his experiences with the large battery enclosures he's done.

[russ]

In industry H2 analyzers (sensors) are the most unreliable of all - more nuisance than they are worth - just vent the room at the highest point and forget about it.

[Bill NC]

I abhor the idea of batteries sharing living envelope space. Put up cement board or something that your code will allow to treat the battery room as a separate building, and provide vermin proof passive vents high and low. H2 rises, so don't create a pocket up high when placing a duct over the batteries.

And I think the H2 sensor may have a finite lifetime, and need periodic replacement. I know that O2 sensors and Co sensors have limited life times (6 mo & 5 years)

I also dislike the idea of powered ventilation, relying on fans that can fail, or wires that can spark, over the plan of a passive Hydrogen and acid fume venting system.

You may need power venting for heat control in the summer, to dissipate heat from the inverter and charger.

Perhaps Sunking will chime in with his experiences with the large battery enclosures he's done.

The codes that I reviewed at http://www.acran.com/codes_and_compl...industry_codes all seemed to indicate firewall separations for battery systems that were over 50 gallons of electrolyte, with the NFPA code calling for a 1 hr separation which can typically be obtained with two layers of 5/8" fire rated GWB with steel studs. Cement board, while not flammable is not typically efficient at reaching a 1 hr rating since it transfers heat so readily.

No pockets, just one continuous smooth ceiling.

Hz sensors do have a limited lifetime.

I'm not necessarily relying on fans. This is a redundant system. It's my intent to monitor the system closely through the first year to see if the passive system works both summer and winter. If the H2 level never gets to 10% LEL, then the powered fan is just overkill.

I agree about heat control in the summer. I've been kicking around the idea of drawing cooler air from either the crawlspace, or from a buried PVC pipe for the makeup air for cooling. I would likely need to introduce this air into the room low, near the batteries. Maybe this could replace the higher passive makeup air vent shown on the drawings, but I'll have to give this more thought to make sure that H2 could not be forced into the crawlspace.

Thanks much for the critique.

Bill NC

[Bill NC]

In industry H2 analyzers (sensors) are the most unreliable of all - more nuisance than they are worth - just vent the room at the highest point and forget about it.

Russ, thanks. It is vented at the highest point. Do you see any flaws with the passive venting strategy illustrated in the drawings?

Bill NC

[russ]

Russ, thanks. It is vented at the highest point. Do you see any flaws with the passive venting strategy illustrated in the drawings?

Bill NC

The passive vent in and passive vent out look fine - that is what I have done and would do again.

[Bill NC]

Russ, many thanks.

Bill NC

[northerner]

Reliable fan(s) for venting hydrogen from the batteries are available. This is what I have done, and I have my batteries in boxes and pipe out to the outside using a Power Vent Fan. They may not be needed for your application as Russ has mentioned.