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What sort of ventilation do you need to run a generator in enclosed space?

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  1. #1
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    Default What sort of ventilation do you need to run a generator in enclosed space?

    we have a big switchboard enclosed in a room about 1 metre deep and 2 metres wide, full enclosed walls all sides except the double door side, I want to put a smallish 2.5kw petrol generator in that room when power goes out to power some of my stuff when theres a cyclone on its way or already here, what sort of ventilation would I need to do this successfully?
    could I just prop the double doors open a third of the way or something enough so water doesn't get in too much or would a vent in each door suffice or what would I need?

  2. #2
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    I'd put vents in the doors and maybe one in the roof and then I'd still worry like crazy about petrol vapors and possibly unburnt gasses from the exhaust building up in the same small room as a big electrical switchboard...it would not fill me with confidence.
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    I would be more worried about the exhaust. If you pipe the exhaust to the outside you wont create a gas chamber.
    You can calculate the required air in by the swept volume of the motor (in litres) x the RPM to give you litres a minute, divide by 2 for a four stroke motor.
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    The short answer is "more than is practical".

    Consider if you were to do something like cook a BBQ in there or, politically incorrect these days, smoke a cigarette. A couple of vents in the door isn't going to get rid of the smoke quickly enough to avoid it reaching a high concentration inside.

    The practical solution, and the one that's actually used in such situations, is to directly route the exhaust to outside via metal pipe. Quite literally an extension of the exhaust through the roof or wall, and sealed at the point of penetration.

    That plus you also want a carbon monoxide alarm in there "just in case".

    Personally, I'd go for diesel in such a situation. It stores a lot better than petrol, and is MUCH safer in the event that it's accidentally spilled.

    Spilled diesel = needs a decent effort to get it to burn. It won't catch fire by accident. Added bonus is that the exhaust stinks - you'll immediately know if fumes are leaking into the room due to a problem with the exhaust. In contrast, CO from a petrol engine can reach deadly levels without any real smell being noticeable.

    Spilled petrol = one spark and it's BOOM in a big way in an enclosed area like that. Think Hollywood movie style "explosions" and you being blown straight through the door kind of boom.

    Alternatively, at that scale LPG is a serious option too. Quite safe if everything is done properly and you're using a legit "off the shelf" LPG generator and not trying to modify a petrol one by dodgy means. Will still need an exhaust to the outside though. You won't find them at Bunnings etc, but such generators are readily available to order. Cost = generally more expensive to buy than petrol, cheaper than diesel.

    Alternative to all of this - is there anywhere undercover outdoors that the generator can be used and just run a lead from it? That gets around all these issues.

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    Quote Originally Posted by Smurf View Post

    Alternative to all of this - is there anywhere undercover outdoors that the generator can be used and just run a lead from it? That gets around all these issues.
    Having been in places where back-up power is needed the exterior small shed with lots of holes and the exhaust pipe run up high and turned down so rain can't get in is what I have seen most often and most fixed generators are diesel. If using a small camping style genny then all of the warnings about petrol fumes are valid and I'd be using it outside but covered. When I was in the CMF we used cheap flexible hose as exhaust extenders with the small gennies used to recharge the static batteries
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    Quote Originally Posted by Moondog55 View Post
    Having been in places where back-up power is needed the exterior small shed with lots of holes and the exhaust pipe run up high and turned down so rain can't get in is what I have seen most often and most fixed generators are diesel.
    Petrol - seen one once in a backup application but it was driving a hydraulic pump (as backup to electric drive of the hydraulics) rather than generating electricity as such. It has since been replaced with diesel generating electricity (as backup to mains), and duplicate electric motors to drive the hydraulics. This was a government site, and there was a lot of concern about the safety and reliability of using petrol in an actual emergency situation, hence the switch to diesel.

    LPG - Coles supermarkets commonly have (or at least had) LPG generators as backup power. Gas bottles on the ground, generator somewhere convenient often on the roof. The ease of getting the fuel to the unit (no need for pumps etc) was presumably a factor in going for gas. Also no hassles with fuel spills etc.

    Diesel - Every other backup power installation I've seen has been diesel. Radio / TV stations, the auxiliary "black start" supply to real power stations, all sorts of things. Always diesel where an engine-driven generator is used.

    All that said, the most exciting small generator I've ever used is the one that cost $69.95 brand new, still in the box. It's pretty much made of tin foil and plastic.... Rating is 650W continuous, 850W peak. Sure, a bolt falls out every now and then (just have to work out where it came from and put it back), the fuel tank split (fixed), starting it is an adventure, black goo oozes out and ends up everywhere, the feet have fallen off, it rattles loudly (it's the "red rattling machine" as I call it, makes more rattles than power and always sounds like it's going to give up the ghost at any moment) and it makes more smoke than you'd think was possible. But it does actually generate power and for less than $70 I'd say it was good value and quite entertaining in a strange sort of way. It's had fairly heavy use, hundreds of hours mostly at full load, so it does work. Sure wouldn't want to rely on it in an actual emergency though!

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