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(Commercial HVAC) Emergency exhaust fans for battery charging stations.

I’m hoping there are some commercial techs in here that can answer a nonresidential question.

I do electrical service for stores like Home Depot & Lowes. I was responding to a work order put in by one of the HVAC vendors for Home Depot. All the description said was “ Exhaust fan in receiving has no power going into it”. The only exhaust fan in receiving was the one for the lift battery chargers. The tech was correct, there wasn’t any power going to the fan but it was because the fan was on a toggle switch. The switch wasn’t labeled and it was right next to the emergency shut off for the battery chargers. The fan didn’t come on when I hit the switch but I was able to confirm power at the fan after I turned the switch on.
I always assumed these fans had H2S gas sensors that turned the fans on automatically and that they were only in place for emergencies.

My question is should these fans be on a toggle switch or not? The HVAC tech seemed to overlook the switch so I’m wondering if it’s not common practice, or if he just didn’t know.
I copied and pasted part of my work report below.

I’m not an HVAC tech but it seems strange to have a toggle switch for an exhaust fan that’s only intended to be used during an emergency and it seems even more strange for someone to install the switch right where a light switch would be. I’m assuming it’s not common practice or else the HVAC tech would have known about the switch and turned the power on before creating the work order. I don’t know if the fan is meant to be toggled (which I find strange) or if the fan is meant to come on automatically with a hydrogen gas sensor, which would make more sense to me considering that your supposed to run if you smell H2S gas, even if it means abandoning someone who has passed out, but I’m not an HVAC tech so I don’t know if this is normal or not. I left the switch on and spoke with the store manager. I gave him my phone number so the HVAC tech can call me if they decide to put in an HVAC ticket for it but I doubt they’re going to.



    EBEBRATT-Ed Member Posts: 15,835
    You would have to check with the local or state building dept. I would thing they would run 24/7
  • ratio
    ratio Member Posts: 3,696
    I've installed a few exhaust fans over charging stations. @EBEBRATT-Ed is right, that's a call you're going to have to make to the building official to get details on the sequence of operation. FWIW, the most recent one I installed, over a c. 15-20 bay forklift charging station, ran 24/7 & had an alarm (light & buzzer) that would energized if the fan stopped sucking. A few used combustible gas detectors to bring on the fan. One, in an EV development lab, actually caused an evac alarm if the levels kept rising after the fans energized.

    My personal guess is that it's not a (local) code requirement but rather a corporate requirement & the employees are supposed to turn the fan on when they charge something—but I'm just an anonymous internet kook.

  • hot_rod
    hot_rod Member Posts: 22,472
    Sometimes corporations like that have their own building design teams, architect and engineers. So it could be a corporate wide policy.

    Possibly it's covered in NFPA 91 code?

    One of my customers in Missouri was a mechanical engineer that worked for WalMart and oversaw the mechanical design of their stores in the US.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • JohnWhite6607
    JohnWhite6607 Member Posts: 16
    My new theory is that the employees are supposed to turn the fan on when there charging something like ratio said, and that one of them tried to but the fan didn’t come on, they turned the switch back off, put in the HVAC work order, HVAC troubleshot and found no power (because the switch was off), then put in an electrical work order, then I get there, hit the switch, the fan has power going to it but doesn’t come on, then i tell the store to put in another HVAC work order (which they didn’t seem to eager to do)

    I’ve been in a ton of Home Depot’s & Lowes and I’ve never once noticed one of these fans on. That could be because they’re on sensors or because the employees just don’t use them.
    I’m gonna look at the exhaust fan in the next Home Depot I’m at and see if there’s a sensor or if there’s any low voltage going it. If there’s not and it is solely controlled from the switch then I’ll call the store and suggest another HVAC work order. Thank you for the insight.