Golf Cart Storage Ventilation and Electrical Classification 2

[joerob]

I am currently reviewing a new golf clubhouse which includes a golf cart storage area in the basement. These golf carts are battery powered, and thus undergo re-charging. I know that during the re-charging process, hydrogen gas if given off. The storage area is equipped with a hydrogen gas monitoring system which turns on and exhaust system when the hydrogen level is detected as 20% of the lower explosion limit (lel), and shuts off power to all of the battery chargers and alarms if 40% lel is reached.

In addition to the above, I am considering incorporating the following measures. I feel that the cart storage area should be electrically classified as a Class I, Zone II hazardous location, since failure of the ventilation system could lead to the presence of dangerous level of hydrogen in the area. Additionally, I am considering de-energing all devices in the area if 40% lel is reached, not just the chargers. And finally, all equipment that is to remain operational in the event that 40% lel is reached should be installed in accordance with Class I Zone II requirements, such as the hydrogen detection system, emergency lighting, fire alarm, etc. The remainder of the equipment does not need to be classified for non hazardous areas as it would be de-energized.

Does anyone have any experience with golf cart storage area ventialation and classifications? Do the above measures of using Class I Zone II components seem like overkill since by shutting the battery chargers off, the release of additional hydrogen should be limited, or should all equipment in the area be of Class I Zone II type?

Comments are appreciated.

 

[ChasBean1]

joerob -

I'll take a stab since nobody's come back yet. I have not designed such a system, but have an opinion:

Having the hydrogen monitoring system start and stop the ventilation fan adds a means of potential failure to a system that I believe should operate continuously when batteries are charging. I would much rather see the fan interlock with the charging station such that it runs when any one charger is plugged in.

Using the gas monitor to start a ventilating fan (to me) is like not letting your car engine have any coolant until the temperature is sensed to be too high. Another comparison might be starting an air handler to serve a building because people are starting to pass out from heat exhaustion. Does this make any sense? The operation you mention tempts fate. A safe condition is separated from potential catastrophe by potential calibration error, sensor drift, interference (you know these Nextel's mess up everything) etc., etc.

My opinion: Run a ventilation fan interlocked with the charging station. Fan size should significantly overcome the maximum anticipated production rate of hydrogen. Any one charger plugged in should start the fan. Have a standby fan that will start automatically upon failure of the operating fan. Keep the H2 sensor and provide an alarm; keep the interlock with the shutdown of the charging station.

Don't mess with starting and stopping these fans based on H2 concentration unless you have redundant indication and you know they will be on a strict calibration program.

(Just an opinion). Good luck & happy charging!, -CB

 

[walkes]

joerob

You could also have a two-stage system where a reasonable level of ventilation is provided to prevent build-up of hydrogen on the first stage (run continuously), if for some reason the sensor detects higher levels the fan system could go to a purge mode to evacuate the space.

Probably provide spark resistant components for anything in contact with the airstream.

 

[stevenw]

We have done several club houses with cart storage/charging.
NEC has all of the rules for this area.
We went with a constant fan and a second fan on the hydrogen monitor.
The storage was under the club house so we had the heat the space in the winter.

 

[ChasBean1]

Steven, couldn't find this in 2002 NEC. Section 511.8 - "Battery Charging Equipment." 2002 version goes from 511.7 to 511.9 - may have been eliminated, or is it in another section? Tx, -CB

 

[stevenw]

1999 NEC
625-29 Electric Vehicle supply equipment locatiions

 

[ChasBean1]

Stevenw - thanks for the reply; I'll check it out. Walkes, I've seen similar two-speed systems and like that idea also. I just don't like the idea of zero ventilation in an enclosed charging space pending a rise in percent LEL. That's flirting with disaster... Cheers to all, -CB

 

[joerob]

Thanks for all the responses.

This is how I have decided to proceed. Rather than have the monitoring system turn on the exhaust fan, the exhaust fan must be proven running (with the use of TWO differential pressure switches across fan) in order for the chargers to operate. I will continue to use the monitoring system as a backup. If hydrogen levels in excess of 20 % lel are detected, which should never occur when the exhaust fan is operating properly, the chargers will be disabled. Note: the room will be exhausted at a rate of approximately 5 air changes per hour.

Also, based on the redundancy used above, I am no longer classifying the area as hazardous, since any equipment failure will result in the stoppage of hydrogen production.

I have one comment regarding the two stage fan system. If the first stage is designed to adequately ventilate the area, then the only time the hydrogen levels should cause the second stage to come on if there is a problem with the ventilation system, in which case causing the system to "purge" may not be adequate. Perhaps this would work better with a second fan, rather than a two stage fan.

Any further comments welecome. Thanks for everyone's input.

 

[ChasBean1]

joerob - I like that solution much better than what you originally proposed.

Using the charger interlock you mention, either a second speed of a single fan or a second fan should be adequate. If you use one fan with two speeds, Speed 1 should remove the design volume of H2. Speed 2 can be available for design flexibility if the sensor shows that for some reason Speed 1 is not performing adequately. Likewise can be accomplished by starting a second ventilating fan (which I prefer) that can perform a standby function (based on Fan 1 failure) or a lag function (based on increase in LEL).

As a side note, just be careful of the fan flow proving differential pressure switches. If these are wall-mounted propellor fans, there will likely be little differential pressure across the fans. If they are centrifugal inline fans (or some sort of fan type mounted within duct work), higher DP will exist. You as the engineer should be privy to what DP you expect across the fan(s) you specify, and let the installer know what range DP sensor they should buy.