I have been watching that relationship develop the last many months, xoruss. Always upbeat, you have been the happiest since she came into your life than when I knew you before. Everything tells me you guys are a great match, and will be a highly effective couple, and preppers. Congratulations.
As to the genset, I pretty much agree with WolfBrother. (Like, when do I not? The guy knows his stuff.) But I do believe there are quite a few other things that can be done to reduce not only the sound signature, but air consumption, exhaust, and cooling air signatures. Plus, I will probably add a few things to reduce the chances of discovery through other means, too.
1. Since the genset does need to be protected from the weather, and barring an adequate place in the shelter, which I am pretty sure is not available, WolfBrother's suggestion of a small building makes perfect sense. However, I do think there are a couple of alternate ways to provide that protection, and begin the task of mitigating the genset's give-aways.
An 1,100-gallon propane tank is not going to be moved around. It is possible, besides the permanent line required from the propane tank to the genset, to have the materials stored to run a propane appropriate hose from the tank to another location if the genset needs to be moved.
If the tank has a wet-leg so smaller tanks can be refilled, so much the better. Then you just keep 20-, 30- 40- or 100-pound tanks filled with a couple of them with the genset in case it needs to be moved, or just to have an alternative in case the propane tank must be turned off due to fire, or some other reason.
Now, many of the things I will be suggesting will not be able to be used if the genset is moved. But, with the mitigation that they will provide, it might not need to be, anyway. Just an FYI.
2. As an alternative to the shed WolfBrother brought up, with the air cooling/sound reduction room section, you might think about what I have planned if I am ever fortunate enough to be in a similar situation. It would be closer to a doghouse than a shed in size, all-be-it a very large one. The doghouse needs to be on skids, and it can have a floor or not. If it does have a floor, have heavy cross member across the floor joists to spread the weight of the genset over as much space as possible. Even if it is not very heavy.
You will probably want to go ahead an mount the genset on skids, too. Even if it has its own. You want higher ones, (4" x 4" treated lumber), so you can add a spring mounted platform, even if the genset is spring mounted on its frame. You want maximum vibration reduction. Plus, if the oil must be changed by draining it from the bottom of the oil pan, it will be much easier to have space under it for an automotive oil collection container that cobbling something up that probably will not work nearly as well.
Since the genset will be on springs to cut down on ground vibrations, you will need to use flex joints on fuel lines, exhaust lines, and electrical connections. And, depending oh how many of the other things I recommend you decide to do, you may need some flexible ductwork connections. Okay. Vibration handled.
3. Exhaust first. I very highly recommend you pick up a spare muffler or two. A third one if you want to make what I am about to suggest and keep the original in reserve. The original muffler type and style needs to be on the engine, since the engine has been tuned to run best with it, and the muffler has been tuned to quieten the sound a reasonable amount and let the engine run efficiently.
That does not mean, however, that you cannot do additional quieting with additional mufflers, and as WolfBrother said, exhausting the gasses into a large area that is sound deadened and opened to the sky. The works in a couple of ways. One, the more compact the exhaust stream is, the louder it will be when it is discharged into the open air. By letting the muffler exhaust into a good sized room, that sound will be reduced by the sound insulated walls. Also, since the air is moving much more slowly, and upward, to boot, the remaining sound, already at a lower volume, will be going straight up, not out horizontally, making it very much more difficult to hear from any distance except straight up.
In order to reduce the mechanical noise of the engine running, the fan blowing air, generator whine, and such, the cooling air flow around the genset needs to be handled much the same way. If the room is well insulated, just a screen between it and a separate chamber in the expansion room will work. And again, open to the sky to direct that sound up, rather than out.
If you make arrangements for adequate cooling air flow, you can make a simple shroud to go over the genset and use large HAVC ductwork to move the hot, noisy air to the second expansion room for a bit more efficiency.
All good things. Now, if you add an after market, or home built muffler between the original muffler and the exhaust expansion room, you can greatly reduce the final sound level even more. And get away with a smaller exhaust expansion room. A few tutorials from the internet or books from the library will give you the information to buy or build a second stage muffler.
While not quite a muffler, if you use a shroud around the genset and ductwork to the second expansion chamber, you can use some sound absorbing baffles inside to reduce the amount of sound traveling with the air. The ductwork will need to be a bit bigger to compensate for the flow losses, but that will not be much.
With these changes, rather than a room size insulated room open to the sky, you can make another doghouse size room at one side or the rear of the genset doghouse, or just combine it with the heat and sound insulated wall between the two rooms, as well as the outer walls. It would be a good idea to insulate the entire building the same way, to reduce the signatures from the genset itself, too. Run the dividing wall between the two expansion rooms up, too. It can run all the way up, or be stopped somewhere in the lower area of the chimney. Once the 'airs' get some distance away from the sources, it will not make much difference if they are mixed.
Even with the walls well insulated, you will still want to build an additional wall all the way around the building, a couple inches away from the outside of the inner wall, with this outside wall being what is finished to get the particular look wanted to match the house or other outbuildings. However, this wall will be as holy as the holiest monk that ever lived. It will be your screened air intake for the engine combustion air, as well as the cooling air. Use wide overhangs on the roof with soffit screens to provide additional means of air flow.
And not only can it provide a very low speed, high volume air intake system for the genset, it can be one of several supplying the shelter(s). Some sound baffled ductwork from the cavity the width of the room, with a right angle turn near the opposite wall, from both walls, of course, will lower the sounds going out the intakes. When the air is flowing not much will escape anyway, but it might be necessary to run the genset when the intakes are open.
Run 4” – 6” PVC pipe from a collection point midway up one of the cavities and lay a pipeline to the shelter air intake room. Same precautions I always suggest. A sump leading to an absorption pit, a cut off valve, blast valves if at all possible.
You can also run a second PVC pipe from the shelter to the doghouse, and up the inside of the “chimney’ as part of the air exhaust of the shelter.
Too add a bit of 'cute' camouflage to the system, and since the expansion room needs to be well more than head height anyway, you can slope the roof quite a bit, bringing it down to 12" or so inside, again well insulated, and build it several feet into the air. Add a chimney cap to it to keep rain and pests out, and you have a luxury doghouse that does not only conceal and isolate a genset, but with good aforethought, planning, and building, several other things already mentioned can be accomplished.
Another pair of alternatives. If the cooling and combustion air intake and engine exhaust and engine cooling air ducts have tees in them, with closing valves, medium diameter culvert can be run from the doghouse to a couple of rock features, water feature or two, playground equipment, patio set up, and probably some other things that would work well to camouflage the open ends of the air pipes and air ducts.
Rock cribs, in the form of decorative yard features, can be carefully, and artfully, arranged to allow air flow either in or out. Rock gabions using woven or welded wire fence, or even chain link fence, can be used as either decorations, or as actual fence posts. With the rocks stacked with air gaps, the screened intake or exhaust pipes can collect air or allow exhaust to escape.
By using PVC, ABS (for exhaust), or steel pipe as parts of various structures or elements of the place, many different possibilities present themselves to allow clandestine pulling in and blowing out air.
Not to mention, the Gabions might be used to support yard lights. Or antenna poles. Or security system poles or risers. Or intercom boxes. Or be used as fighting positions (but only if provisions are mad so they cannot be used by an aggressor to harm you.
Besides the rock features, water features, playground construction and equipment, and patio construction and features, there are many more things that can be used to camouflage air movement infrastructure. Certain kinds of fences. Some types of fence posts. Guttering (which should be on every building), the very walls and roofs themselves.
‘Decretive’ cupolas, functional attic roof wind turbines and functional gable end ventilation screens. ‘Abandoned’ power poles. Just think outside the box and push the envelope. Oh. Often times while creating air handling infrastructure, the means to locate communications antennas and run communications wire will present themselves, so go ahead and get those elements installed during the building, even if not to be used right away.
There are quite a few more ways to accomplish what the OP is asking about, so if anyone needs more, just e-mail me.
If there are any questions feel free to ask.
Just my opinion.
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