generator: supply air, exhaust and fire extinguisher
Hello. Thank you for all the answers you’ve given in the past for my generator installation.
The generator is portable 5000 watt Honda, gas engine.
The original plan was to run it outside, but now it will operate in an enclosed room. The room is a storage shack, wood construction, concrete floor. It is 7′ L x 40″ W x 8′ H. It has a wood door on top sliders.
Ceiling and walls will be covered with sheetrock. I plan to use self activated fire extinguisher. Flame Defender, it is called, although I am worried that this extinguisher is triggered at 155 farenheit.
The main question is: I am planning for about two square feet of opening for fresh air and two 70 cfm bathroom fans for exhaust. Is this enough to give the engine the air it needs?
Replies
Why wouldn't you pipe the exhaust directly out?
Assuming that someone is going to be around to start the generator, flip the transfer switch, etc. Couldn't you just leave the door open and run a fan to circulate air?
That would be ideal, but open door, I think, will be inviting theft. I have 1/2" thick chain and lock, rear windows boarded, and door has key latch. Of course, this is to deter a casual theft. A determined thief probably will come with tools, lol. My parents lived there for almost 30 years without problems, but, I've heard that there are many thefts of generators during power outs.
>>>That would be ideal, but
>>>That would be ideal, but open door, I think, will be inviting theft.
But isn't this thing only going to run during the occaisional power outage? Are thieves in your area ballsy enough to steal a running generator, knowing that you're in the house relying on the power that said generator is producing?
Automotive shops have to pull our the exaust when they run the cars inside the work areas. All you need is some flexible exaust pipe to clamp onto the existing exaust port. Then just treat it like a furnace stack with double wall pipe. 6" seems big.
Well, you have several issues to address with your design. Let's look at them one at a time:
Shed construction: Personally, I am biased in favor of raising the shed off the ground a bit with 'pier blocks.' This method gives you a pretty good air space under the shed, which eliminates any rot / moisture issues and really cuts down on critter problems. Heck, I cut a 6" hole in the floor of mine ... and the local feral cats nest in there, keeping mice away too!
When will you use the shed? Usually when the weather is crappy. I suggest a substantial overhang above the door. Indeed, you can arrange things so you can reach it all from the door, and need not enter the shed at all.
Generators have a few other needs, apart from storage. The need air. They need fuel. They need a way to deliver the power where needed. And, they're noisy. Let's look at these concerns.
Fuel: Gasoline is quite hazardous to store, and it quickly 'goes bad' with age. Therefore, the amount you store should be quite limited, even with a 'fuel stabilizer.' Gasoline should be stored apart from the generator itself; I'm imagining a 'cupboard' built into the outside wall of the shed, and completely lined with cement board. Your key words are 'non absorbent' and 'non flammable.'I might even make the floor here of metal grating. This cabinet needs two air vents- one to let clean air in and another to let stinky air out. Size this cabinet no larger than two jerrycans.
This means that you'll be transporting gasoline in time of need. Make provisions for transferring this fuel.
Oddly enough, the space above the 'gasoline locker' might be a good place for an additional locker, where you can keep the tools and parts associated with the generator.
You'll need access to the generator to fuel it. This area needs to be designed to handle whatever little spills and drips there might be.
The generator compartment needs plenty of ventilation. Alas, 'good ventilation' solutions and noise suppression solutions tend to contradict each other.
That's why I suggest that the exhaust be piped directly out of the compartment where you have the generator, as a first step. I'll return to this part in a moment.
The generator compartment - apart from the fill area - should be made of something soft and sound absorbent, over a hard, reflective face. This is one instance where acoustical ceiling tiles - the heavy ones, made of gypsum - and the plywood T-111 outer skin of the shed can work together. Where you have your air vents, box them in as you would an exhaust fan, and line them with your sound absorbing material.
For the exhaust gasses, I suggest extending the exhaust pipe directly out of the generator enclosure, into a separate compartment. This other compartment will be lined with sound absorbant materials (like unfaced fiberglass) and will be constructed so as to make the gasses change direction several times before exiting. The exit should be quite large, large enough that you do not feel a strong flow , and screened to keep out the critters.
So ... how do you get power to the house?
Well, first off, your hut should have a ground rod. Then, you should have the generator wired to an appropriate receptacle on the outside of the shed. When you want to use the generator, you can connect it to your house using the appropriate extension cord, to a 'pigtail' off the transfer switch. The transfer switch will keep the pigtail from becoming 'hot' when the house is using utility power. Your cord should have FOUR wires in it.
As for fire protection .... you're on the right track. Talk to the guys who service your local McDonald's kitchen hoods; they can probably set up a dry chemical "Ansul" system at an affordable price. We're talking maybe three heads and a powder canister: pretty straightforward.
Thieves? The usual advice applies: Keep it as secret as you can, make them work to get to it, have an alarm to tell you they've arrived, and prepare an active response. Another reason to keep the genny quiet, to bolt it down and lock it up, keep it in sight, and limit access to it.
That's another nice thing about raised sheds; the dog likes to lay under them.
External exhaust
We plumb our exhaust with about 12-inches of flexible stainless exhaust hose, to connect from the stock exhaust to a custom bent exhaust system. Any muffler shop can bend up exhaust pipe for you. if your pipe configuration is long enough or has a lot of bends, they can lay it out with pre-expanded ends so you can hook it up with clamps after you have it onsite.
The exhaust is run up through the center of a 6-inch double wall chimney pipe and centered/secured with muffler hangers which you can buy either from the guys who bend your tubing. At the top of the chimney we leave the exhaust two exhaust pipe diameters below the top of the chimney pipe, and then the standard chimney cap goes on to keep birds and weather out of your exhaust pipe.
The air inlet is sized based on the air filter. take an old pleated filet apart, measure the area, and multiply by 4. That is all the screend inlet area you really need. The screen allows way more air flow than engine can pull through the filter.
You still might want to put in larger screened inlets and the exhaust fans on thermostatic switch, so they come on at about ten degrees above your normal summer high temps to prevent the fire extinguisher from triggering. It is cool enough here that I wouldn't worry about a generator your size, and area cooling. But our generators are larger than yours, (50-kW), and we have the radiators mounted on the end wall of the building with electric fans to push the air out through them.
The dry wall should be at least 5/8 fire rated.
Noise can't be suppressed? Look at this one:
http://www.yamaha-motor.com/outdoor/products/modelspecs/622/0/specs.aspx
60db .... you could set it next to you in the living room, and still not have to crank the volume on the TV.
Wait ... you got one of those cheap imports for 1/10th the price? Gee, I wonder how thay can make them so cheap. I wonder about the quality of the "AC" they deliver - you wouldn't find ME plugging anything electronic into them!
Sometimes you do get what you pay for.