Burying a generator vault into a bank

[jenkinsph]

If you want to duct cool air thru the compartment this is how I would do it.
Put in some 2x6 lumber to raise the floor with the lumber perpendicular to the front door.
Put plywood over the lumber leaving an opening across the back wall about six inches wide and a couple of cutouts directly beneath the genset.
An option to make it quieter would be to fasten 1" duct board insulation to the bottom side of this plywood floor.
Screen the front opening with hardware cloth to limit bugs and mice.

Install a piece of duct board on the ceiling with open ends for the air to flow through. Make this to allow about 8 inches short of the side walls of your compartment. I would make this baffle about 8" deep x 24" horizontal. Center the fan in the middle of trough of this baffle.

Install a vent fan in the roof with a vent thru the roof. Most have an adjustable thermostat you set from 90 to 135F. This could be a smaller residential size with lower fan noise. Extend the vent high enough for the snow in your locale.

Duct board is 1" fiberglass compressed insulation board used for hvac ducts. It is available in 4'x10' sheets for about $40-50, One sheet should be enough for this project. Any left over pieces I would use on the front wall. Available from most hvac supply stores.

A vent fan as pictured 1320 cfm with thermostat is about $60 to 75 plus a piece of single wall pipe to raise the dome above the roof for snow. Having this chimney of sorts will also help draft the air up as heat rises. Just have to clear the snow away from the lower opening at ground level.

Building the duct board plenum depends on the roof you have. If you have a ceiling inside that is flat and sealed you can form the duct board with out the top side and staple this to the ceiling. Shape it similar to the first picture. If you have open roof ceiling rafters then make the four sided plenum as in the second picture with the hole cut out for the fan in the top.

The main idea is to have padded ducts with turns to lower the noise levels. The exhaust and engine intake air should easily dissipate through these ducts. Set the thermostat to the lower setting on the thermostat and wire to the genset power outlet.

 

[Sodo]

Wow jenkins thats good work. Will read carefully. Thanks!

 

[PILOON]

A few tricks I picked up.
Once ran a 3 KW portable genset with a short extension that allowed me to have the muffler outlet in a 'hole in the ground'. The hole was about the size of a 5 gal pail. The only sound we could hear was the clacking of the valves! The earth absorbed the exhaust noise and from 10-15 ft away we could have normal conversation.
That was a Briggs powered about 5 HP with a screw in tin can muffler.

Another situation whereby I had a wood box enclosure that I stapled old carpeting on the insides and that greatly absorbed just about all the engine noises. Exhaust was piped to a 'hole in the ground'.

The carpet/box trick also works very well for a compressor. (that is how I learned the noise abatement trick)

In my house the water pump is installed in a carpet lined closet area so I never hear anything.

 

[Sodo]

Cool tricks! Interesting idea using the ground for a muffler.

The generator I have is muffled pretty well, well enough that the intake seems loud. What seems like the loudest sounds emanate from the sheetmetal. Might have to wait awhile before I cover the walls with carpet ( the pretty Cedar & all) i might have to look at it for awhile. But no qualms covering the door & ceiling. :thumbsup:

 

[dragoneggs]

Nice work Sodo... thanks for sharing. Good stuff, jenkins! I had to read it three times but solid engineering, albeit I do have a second good pour of red wine in front of me. :drink:

 

[Jim Timber]

It looks like an old mine shaft. I like it!

I'd do the raised floor as was mentioned. There's a couple options for exhaust/ventilation - you could just do a regular stack sticking straight up; or you could run one in the hill further away as long as it doesn't have too much flat run to it, you should keep convection going. 6" PVC isn't too expensive and will not cause maintenance problems in the future.

 

[PILOON]

It looks like an old mine shaft. I like it!

I'd do the raised floor as was mentioned. There's a couple options for exhaust/ventilation - you could just do a regular stack sticking straight up; or you could run one in the hill further away as long as it doesn't have too much flat run to it, you should keep convection going. 6" PVC isn't too expensive and will not cause maintenance problems in the future.

Having played with exhaust pipe extension B4 on a Briggs powered genset I advise some caution. I had added some 6 ft or so of 3/4" pipe to get the sound away and that worked for noise however it created back pressure, so much so that within 5 mins I could have seized up the engine.

I think the idea of regular exhaust into larger conduit as suggested might be best, Adding a fan or blower to vacate fumes should work.
Also being an internal combustion engine you want to provide a fresh air intake as oxygen is needed.

 

[jenkinsph]

Having played with exhaust pipe extension B4 on a Briggs powered genset I advise some caution. I had added some 6 ft or so of 3/4" pipe to get the sound away and that worked for noise however it created back pressure, so much so that within 5 mins I could have seized up the engine.

I think the idea of regular exhaust into larger conduit as suggested might be best, Adding a fan or blower to vacate fumes should work.
Also being an internal combustion engine you want to provide a fresh air intake as oxygen is needed.

The raised floor allows the cool air to enter beneath the engine so the engine is in the ventilation path. That also allows for a plentiful supply of fresh air for the combustion process. Having the air flow rising from the floor inlets to the top outlets is ideal as it improves circulation around the genset. The powered ventilator can cycle in very cold weather and help to keep the engine warmed up to operating temperature when under lower loads.

 

[Sodo]

I think the idea of regular exhaust into larger conduit as suggested might be best, Adding a fan or blower to vacate fumes should work.
Also being an internal combustion engine you want to provide a fresh air intake as oxygen is needed.

The generator has always worked fine sitting on the ground. The current plan is to K.I.S.S. I'll try a large single duct that channels generator's hot air and exhaust out (maybe 8 inch steel heating duct?). And a 120v fan running off one of the generator's 120v outlets, for the inlet air, simply pressurizing the entire vault. A thermometer inside the vault to confirm whether the fan is sufficient. The main reason for this is noise. I don't know how much of the noise will come out the 8" duct (& fan openings).

 

[Jim Timber]

I was suggesting just a stack coming off the roof of the room. Not connected to the generator in any way. Having the ability to put the generator in the back of a truck and move it in a storm is a higher priority to me.

 

[Sodo]

Vertical out the roof would be quieter I think. Right now, exiting thru (the door) is easiest, I will try that first. I'll start with a simple plywood door (just a cover) and if it seems to work I'll build a better one out of solid wood.

A raised floor would be harder to get the generator in and out. But the plan is it would be semi-permanent in the vault.

 

[PILOON]

Simply stapling an old carpet to the door will kill off a whole lot of noise.

You mention running a fan on 112 VAC outlet--that works OK but with many gensets you have choice of 110 OR 220 and not both at same time.

 

[Jim Timber]

I've got both on mine.

A little ramp to go up over the intake duct would be a piece of cake.

 

[Sodo]

Mine runs 120v and 240v same time. Got this duct-fan on Craigslist, $25, ( (this morning, 2 miles & 20 minutes after my last TBN post :thumbsup:. Perfect!) They sell new for $92 with 5 year warranty, I guess $25 is OK since it will run only when the generator's running. At 435 cfm it will exchange the vault volume (90 cu ft) every 2 minutes. Hope that's OK.

Forecast is for snow on thanksgiving. Got conduit, wire, carpet, fan, long underwear, supplies, gonna headout to my hideout!

 

[Jim Timber]

You should be fine with that either sucking fresh air in, or pulling exhaust air out. Personally, I'd use it in a stack and send the heat up and out, with some venting around the door, or just leave the door open a little when the genset is running.

The carpet suggestion was a good one too. Being in the hillside will help immensely, but you'll still get an echo box sending sound outward through the opening.

 

[jenkinsph]

That is a lot smaller fan and duct than I would use. Having the fan in the wall or door without ducting will allow a lot of noise to pass through it. Be careful to monitor the temperature closely would hate to see you overheat the genset.

 

[Sodo]

I think a thermometer will tell the story. I'll check air temp in, and air temp coming out. I'll know if its OK pretty quickly. Do you think the spread between the in/out will be about the same in the summertime? I suppose I'll find out.

 

[PILOON]

I'd wrap that ducting with felt or carpeting otherwise it will act like an echo chamber and amplify exhaust noise.
If you use that fan to evacuate exhaust if will probably cook in short order. Probably better to move cooling air IN which in turn would push hot air out.

 

[jenkinsph]

I would have an over temperature shut down on the genset to reduce the chance of over heating. The fan and ducting I suggested are several times the size of what you purchased.

I would not expect the enclosure in the hill to make much of a difference in summer/winter operating temperatures "when running". It will help if left in place for storage purposes.

 

[dragoneggs]

I think the overheat temp switch is a great idea.