Getting ready to install my stationary CH&P;generator, any concrete experts?

[Dune]

It is about a 50HP inline four diesel, normally aspirated. I am building a bunker next to my house foundation. Planning on a monolithic slab/footings. I am thinking that I will make the slab strong enough for the task rather than making specific beds, so that I can mount another engine later on, without having to plan it all out now. I am figuring plenty of iron, 6" thick slab, and high strength mix. The slab will be 10'x12'. any input/advice? Thankyou.

 

[Dune]

Yeah, I guess I should have been clearer. I am building an underground bunker next to the foundation of my house. The floor of the bunker will be level with the floor of my basement. The roof of the bunker will be concrete. My question is how stong must the slab be constructed. I have little interest in calling a university, but thanks for the thought.

 

[Sting]

You may be better off with a piece of precast.

http://www.spancrete.com/

 

[JustWood]

My genset is 300 HP ,prolly weighs around 8000lbs. It's on 8'x16' pad 6" thick. Fiber in the crete. Nothing fancy . Been there 5-6 years with no problems. It actually isn't even bolted down and it hasn't moved at all.

 

[Dune]

You may be better off with a piece of precast.

http://www.spancrete.com/

Thanks for the tip. What I am doing is pretty traditional. The opening is spanned with corrugated metal decking, re-rods are supported as needed, then concrete is poured on top, like in a parking garage.

 

[pybyr]

My genset is 300 HP ,prolly weighs around 8000lbs. It's on 8'x16' pad 6" thick. Fiber in the crete. Nothing fancy . Been there 5-6 years with no problems. It actually isn't even bolted down and it hasn't moved at all.

That's some generator! Do you use it to power a sawmill, or what? Seems like if it's for residential or shop use, it's barely under load!

 

[pybyr]

It is about a 50HP inline four diesel, normally aspirated. I am building a bunker next to my house foundation. Planning on a monolithic slab/footings. I am thinking that I will make the slab strong enough for the task rather than making specific beds, so that I can mount another engine later on, without having to plan it all out now. I am figuring plenty of iron, 6" thick slab, and high strength mix. The slab will be 10'x12'. any input/advice? Thankyou.

One thing to consider is to try to de-couple your 'bunker' from the foundation and then de-couple the engine from the slab that it's on. People have done some interesting things in recent years using the Lister-type low RPM diesels for small-scale CH&P;-- and some have discovered the hard way that life is no fun for you (and/ or your neighbors, if they are nearby) if the engine/ genset has any vibration that happens to resonate in some way in relation to the slab, nearby structures, etc. Granted, a 4cyl will have less vibration, and higher-frequency vibration, than a single-cylinder, but it still might really resonate/ transmit in unexpected and unwelcome ways.

Somewhere I ran across a description and photos (which I cannot now re-find) of someone who poured a slab, then set two good-sized tires laying on their sidewalls, then filled the tires with styrofoam packing peanuts (packing them in to a high density), then set some large (maybe 4x6') timbers over the tires, and then attached the engine/ genset on top of the timbers. Seemed like a pretty good idea, in many ways, including the fact that it'd give you your desired ability to change engines later. You might want to have some sideways attachments with strap in case the engine wants to "walk around" sideways.

 

[dvellone]

If you're doing it yourself take your time and do some research.
Your concrete mix plant should be able to offer you some advice as well. They usually know their mixes and proper slump for what you're after.
A higher psi concrete (5000psi for instance as opposed to 3000 which is common for most basement slabs) will give you greater compressive strength but you'd want to order a lower water:cement ratio to help prevent shrinkage. Be sure to cure properly and slowly no matter what you use, but high psi concrete will cure at a faster rate causing shrinkage cracks if you're not especially careful to cure properly.
Don't place your welded wire fabric too low - 1/3-1/2 height of slab thickness is what you're after. If placed too low it won't help to prevent cracks or hold together any cracking that may occur.
And most importantly of all, make sure your subgrade is well compacted and that you have drainage in place. No matter how high the psi is, or how well you place and cure the concrete, a poorly prepared subgrade will ruin it all.

 

[JustWood]

Am I understanding that you are wanting the roof of your bunker to be the pad your gen sits on.

 

[JustWood]

My genset is 300 HP ,prolly weighs around 8000lbs. It's on 8'x16' pad 6" thick. Fiber in the crete. Nothing fancy . Been there 5-6 years with no problems. It actually isn't even bolted down and it hasn't moved at all.

300 hp @ 8000 lbs! i cant even imagine a car way that much= u sure?

Inline Detriot 6 cyl. diesel with 250KW gen head. My 6000lb loader woodn't pick it.

 

[JustWood]

My genset is 300 HP ,prolly weighs around 8000lbs. It's on 8'x16' pad 6" thick. Fiber in the crete. Nothing fancy . Been there 5-6 years with no problems. It actually isn't even bolted down and it hasn't moved at all.

That's some generator! Do you use it to power a sawmill, or what? Seems like if it's for residential or shop use, it's barely under load!

Mill,pallet equipment and processors.
Got all the goodies to hook house and shop up . Just doesn't make sense now to do it with business the way it is ,only running a few days a month.
Hooked it up this way so I woodn't be hostage to National Grid and their highway robbery demand charge.
Just bought a 34,000 volt transformer and looking into selling excess power to grid. Don't know if it will be profitable or not. In the research stages now. We will see.

 

[Dune]

Am I understanding that you are wanting the roof of your bunker to be the pad your gen sits on.

No sir. The generator will go in the bunker, safe, dry, out of sight and mostly, quieter. Eventualy I will add another generator to keep it company. The second generator will run on gassified wood, for the eventual time when I can no longer aquire sufficient quantities of waste vegatable oil.

 

[JustWood]

I think 6" of fibercrete wood suffice but for all the more rebar is and for the extra "feel good " of puttin it in, midas well throw it in, me thinx.

 

[drdoct]

Is the bunker just for the generator or are you planning to populate it while it's running? I really don't understand why the bunker or is it a northern thing? Also, what's going on top of the ceiling of concrete? anything?

 

[Dune]

Is the bunker just for the generator or are you planning to populate it while it's running? I really don't understand why the bunker or is it a northern thing? Also, what's going on top of the ceiling of concrete? anything?

The generator needs to live somewhere. It is a diesel, so above ground it would be loud. It must be seperate from living quarters since it is an engine with fumes and such. It is a combined heat and power unit, not a standby, so it will be run often and need to be in close proximity to the existing boiler piping. There needs to be a roof of some sort, concrete is durable and should help deaden the sound. Noise is potentialy a big issue. I have a busybody living right next door.

 

[pybyr]

consider the air needed to burn the diesel, room may require intake blower to provide adequate combustion air.

Why not just have a pipe, tube, etc., from outdoors to the engine's air cleaner (maybe with a preheat box next to exhaust manifold for cold weather). That way the space around the engine can be warmer than outdoors (since Dune is aiming to put the coolant heat to other uses in other locations, the space won't be heated by a radiator as would otherwise be expected). Perhaps use one of those concentric intake/exhaust systems such as are sometimes used for gas stoves (forget the proper term).

 

[Dune]

consider the air needed to burn the diesel, room may require intake blower to provide adequate combustion air.

Why not just have a pipe, tube, etc., from outdoors to the engine's air cleaner (maybe with a preheat box next to exhaust manifold for cold weather). That way the space around the engine can be warmer than outdoors (since Dune is aiming to put the coolant heat to other uses in other locations, the space won't be heated by a radiator as would otherwise be expected). Perhaps use one of those concentric intake/exhaust systems such as are sometimes used for gas stoves (forget the proper term).

Yeah I am going to run a P.V.C. pipe for air supply into my garage which is abutting the bunker. The inlet air is actualy one of the larger sources of noise on an engine (not counting the exhaust and the radiator fan, which I am eliminating), believe it or not, so I am hoping to baffle that part of the noise problem by having the inlet in the garage. Engines actualy like cold air, it is denser. As to the temp, in the engine room, no worries there, the engine will keep it plenty hot. I can't go concentric to the exhaust, as it is being piped underground for a ways, then exiting through a large cast iron lamp post that I got from a junkyard in a city. The lamp post is just large enough for the exhaust pipe and some chimney effect space around it.

 

[JustWood]

Sounds like a cool project! I'd like to see pics of your set up when done. This is a project I considered with my genset but I wood of had to change the location closer to house and shop. The extra wire I wood have needed was going to cost $4800 + a block building etc. so it's on the back burner.

 

[Dune]

Yeah, thanks. It is a big project for me, but an investment too. I should be able to completely eliminate my electric bill plus have enough surplus to charge an electric car I plan to buy as soon as they hit the market, and at the same time reduce the amount of firewood I have to gather and process.