wooden enclosure for MEP 003

[DoubleM]

I would like to build a wooden enclosure that protects the generator from the elements and reduces noise. How close can the walls be to the generator given that there will be a opening for both cooling air and exhaust? Worried about fire hazard if I build the wall too close but do not have room for a monster shed.

 

[Ray70]

I wouldn't think you need a whole lot of clearance, provided you allow adequate intake/cooling air as well as exhaust clearance. You'll also need an enclosure that opens up or disassembles easily for fueling and oil changes as well as accessing the gages and controls, plus general maintenance. Otherwise I would think 6"-12" of clearance would be fine. Think about an ASK enclosure, its metal, but the insulation material might still be somewhat flammable if it has any coloring or coating on it. You could build your enclosure and cover the inside with a fire resistant material like hardi-board, cement board or even fire rated drywall if its going to 100% weather tight, for an added layer of safety. I'd go as big and easy to disassemble as possible to make the machine easier to work on in the event of a failure.

 

[tim292stro]

My dad did something like this for his Honda generator, the key for sound control is vibration isolation and right angles for sound to travel around. He made his with a hinged top and one end that would fold down so he could pull out the generator to service.

Sound waves are a difference in pressure in a medium at a given frequency. To control that, you need to make an enclosure that will resist (diffuse) or consume (absorb) the pressure difference at the required frequency. Higher frequencies are easier to absorb and don't travel well (think intake exhaust valves opening and closing) - unlike lower frequencies which travel well and require more design effort and mass to control (think vibration here).

If you have enough air moving through an enclosure to keep the generator cool, you should also have enough air flow to keep the enclosure material cool. For absorbing high frequencies and heat protection, I'd recommend mineral fiber lining the enclosure around the generator.

...Think about an ASK enclosure, its metal, but the insulation material might still be somewhat flammable if it has any coloring or coating on it. You could build your enclosure and cover the inside with a fire resistant material like hardi-board, cement board or even fire rated drywall...

Mineral fiber is a Class-A fire retardant material that is used for suppressing noise in things like elevator shafts - it's usually rated north of 1000C, so if it starts burning, your battery and fuel tank will have gone long before then (i.e. you'd have bigger problems to worry about). Air movement is a very powerful cooling method, using a blower that is powered from the generator head - something like this direct-drive blower, which moves about 500-1000CFM and draws less than a 500Watt halogen flood light should do it. Keep in mind the direction of the air flow in the enclosure - your generator head has a blower in it that has an airflow preference, don't blow backwards or the generator will overheat. If you mount the blower in the same enclosure space as the generator and have it suck air from outside into the generator space, then blow out the hot air it should keep your wiring short and most of the sound contained.

Sound likes to find leaks, so make the intake or exhaust air side one of your doors so that you have less to seal. Also air speed is a generator of sound - over 1-meter/second and you start getting wind noise. Everything is interconnected

 

[DoubleM]

Thanks for the feedback. I may try to insulate with something like a hood liner or dynamat. Would like to find something less expensive but heat resistent.

 

[DoubleM]

Thanks for the blower idea along with the mineral fiber. Just need to get some cost estimates.
Trying to get everything ready before Hurricane season cranks up down here

 

[tim292stro]

Check your local Home Depot or Lowe's. Figure around $6/sq-ft for 4" mineral fiber, $3/sq-ft for 2" mineral fiber. Other trade names are Rock Wool, Stone Wool, and Acoustic Batting. The blower I suggested is common for replacement in a central heat application, so you should be able to improvise with local parts.

If you can use steel studs rather than wood, it shouldn't rot - even better use cinder blocks and concrete, you can make a shed that will better withstand winds and falling/flying stuff.

For heavy rain and storms, you may have to think a bit harder about your genset placement - some questions to ask yourself: Are you within range of a good sized storm surge? Is your air intake going to be anywhere that water could puddle and clog your air intake? Is your exhaust going to fill up with water if the genset isn't running for a while? In the off-season, will critters nest or "move in" to your enclosure and ruin your wiring etc.? How will you re-fuel the genset if it's pouring rain (will you get water in the fuel?)?

Also, to make it easier to pull the generator out of the enclosure and isolate vibration transmission from the generator to the enclosure, you might want to add some air-filled wheels to the generator skids.

 

[DoubleM]

Whats the best way to attached the mineral fiber to the plywood? I have a slab poured for the generator and its located close to a deck area that is roofed. I was planning on placing the auxilary tank under this area so as not to have to be in the rain for refueling. Good shape on storm surge so far have survived Fredrick,Danny,Ivan,Katrina, and Isac not to mention a few small ones. Lost a bunch of trees and power but no storm surge ( did lose my fishing camp to Katrina). I am worried about critters but plan on putting some traps and rat posion inside the shed. Will need to make sure the blower does not hose down the generator in a hard rain.
Thanks again for the sugesstions

 

[tim292stro]

Construction adhesive on the cold side (face away from the genset, the plywood side) will work fine. Normally this insulation is wedged between studs or nailed in to place, but glue is acceptable practice.

This is a VERY crude drawing of what I'd suggest:



The black lines are your structure, the blue and red is your cold and hot air respectively, and the yellow or cream colored (depending on your monitor's settings) stuff along the structure is the mineral fiber. I drew in a secondary muffler for more sound deadening - this can be a "spare" muffler from an engine with at least 2x the displacement of the genset (a CUCV muffler would do great).

To keep critters out, use screen netting or wire mesh - everything else should be air-tight to ensure sound is only traveling in the sound treated pathways.

 

[tim292stro]

Good luck this season, it may be a wild one - out here on the left coast we just have to worry about burning down.

 

[DoubleM]

Thanks Tim love the drawings and think Ill take hurricanes over fire any day!
Good luck to you as well.

 

[tim292stro]

One last thing, even if you don't plan to paint the inside of the wood enclosure, you should back-prime the wood (inside) before you glue in the sound insulation, this will prevent the wood from getting water damage from moisture.

 

[DoubleM]

Thanks again for something I did not think about!