generator hut and reducing noise

[terracore]

This is sort of a continuation of this thread but wasn't directly correlated to most of the posts to warrant taking that thread off life support: http://punaweb.org/Forum/topic.asp?TOPIC_ID=21011&whichpage=3

Now that I have the hooking-the-generator-to-the-entire-house problem solved, with hurricane season around the corner I want to address the other problem: generator noise.

I was planning on making a small concrete slab for the generator to sit on when it's hooked up to the house. Besides keeping the chickens from kicking gravel under it and restricting air flow (has actually been a problem) I can embed steel eyelets into the concrete to give me anchor points to lock it down and take more effort and time to steal.

After Iselle I used cinder blocks (we have many from a failed agriculture experiment) to try and wall off the generator to reduce the noise but I was afraid to enclose it too much for fear of making it too hot. Now that I'm considering a permanent slab my mind is wandering to ideas of a permanent generator hut next to the house and what it might look like and how it would function. Then I thought, I'm probably not reinventing the wheel here.... what ideas or implementations have you seen?

[alaskyn66]

Plenty of videos on YouTube of people that have done the same thing... basically a insulated box with 'breath holes.. I did that when I was in edenroc.. because their were no other options at the time..

..What would King Kamehameha do..

[Tink]

I have seen generator enclosures that have masonry unit walls 6 foot high with steel doors for access, open aired to top. Inside had channel framework that held replaceable sound absorbing insulation board. Exhaust was lengthened to get a deeper tone closer to match engine decibel, muffled by better automotive type. Space around genny unit was about 3 feet for easy maintenence.

Community begins with Aloha

[MarkP]

I have pondered this at great length. Many U-tube videos show some version of a garden shed or doghouse with some small air holes cut in the side and perhaps a fan. I have sat in my car on a warm day with all the windows open and been darn hot while upon stepping outside I have been considerably cooler. I'm sure it would be the same for the generator. Anything that substantially encloses a volume of air is going to reduce the amount of natural ventilation that the engineers assumed would be there. Anything that depends on a fan would leave you in a bad way if the fan quit. You need to decide what you are protecting the generator from. Apart from theft, I think the major concern would be rain. Focusing only on the weather I think a low gazebo not much larger than the generator but with generous roof overhangs and essentially no walls would be the goal. I think that having said structure tall enough to walk inside would be essential for any permanent installation.

So far this leaves out theft security and sound reduction. A simple chain link fence and locking gate would provide some marginal security but not much. It would also leave the generator very visible should anybody come on your property for any reason, either to fix the water heater or specifically to steal stuff. Any type of fencing would also let sound through freely. For these reasons I think that solid walls for the generator hut are a necessary evil. You must simply work hard to ensure that the necessary ventilation is assured and in my opinion that ventilation should not rely on fans since they can fail. Long story short I envision as small a structure as possible to house just the generator and its ancillary systems. I picture very solid and dense walls lined inside with something that absorbs sound. It should be pretty tall with air entering at ground level and leaving at roof level. The height will create a natural draft as the warm air rises. For the types of small generators we are dealing with it is not worth treating the exhaust separately. The generator I have now mixes the engine exhaust with the engine cooling air whether I like it or not. One reason for keeping the hut small is because of expense. You will be using special materials because of the noise and there is no reason spend that kind of money to store your badminton equipment. Another reason is that the room will be full of exhaust and all temptations to loiter there should be eliminated. Storing gas and oil there makes sense though.

As for actual sound control, it seems like black magic to me. Here's what I think I know:

1. Hard dense materials reflect sound. They can also transmit it. They don't absorb sound.

2. Soft materials can absorb sound but you need a very great thickness to absorb all the sound in one pass.

3. Lead is a special case. Lead is very good at stopping sound. Obviously it is dense. It is also soft. They don't make bells or tuning forks out of lead. I once squandered the opportunity to get several lead lined wood veneer doors intended for hospital X-ray rooms. I still kick myself.

4. Every time there is a change in density some sound is reflected.

5. Every time sound is reflected some is also absorbed.

6. Fiberglass batt insulation is much better thermal insulation than it is sound insulation.

7. Acoustical ceiling tile is very mediocre thermal insulation. Its main job is to absorb sound. Anybody who has handled it can attest that it is soft and inelastic. No bells or tuning forks made of ceiling tile either. It is not dense so while it absorbs sound better than a lot of other materials it does not stop sound.

All this leads me to favor a tall outhouse shaped structure made of concrete and lined on the inside with acoustical ceiling tile. Imagine driving a golf ball inside a concrete silo. The ball would bounce back and forth like crazy but would not get through the wall. Given enough bounces it would go out a window though and so would the sound. Adding the soft absorbent stuff on the walls would absorb some of the energy with each hit, making the ball less energetic when it finally does find the window. Making the path out the window something other than a straight shot would require that many more bounces before ball or sound got out so having some kind of baffles made with acoustical tile at the cold air inlet and warm air outlet would help contain the sound. I picture the whole floor being part of the baffle system or maybe sections of wall at the bottom. As with golfing in a silo, I wouldn't want to be inside.

[MarkP]

If putting the hut next to the house incorporate a chimney up to ridge height to get heat, noise, and most importantly CO safely past the living zone.

[MarkP]

The best answer is to get one of the super-quiet generators, the Honda EU series being the standard. I run one in one end of my container while I relax in the other end and frankly the water pump is louder. I can feel the vibrations but have to remember to shut it off before I fall asleep to reduce the chances of killing myself with CO. I do have a CO detector but you can't be too careful.

Rejecting the CO and heat up high is still a good idea and reducing the sound to the absolute minimum also serves as a security measure so I would still consider the design above. I know that my neighbor has one of the quiet Hondas and while the sound is barely audible and basically doesn't register with me I can still hear it if I were listening for it, as a thief would be in the aftermath of a hurricane.

[terracore]

I did look into the Honda quiet generators but the EU7000iS is almost four thousand dollars more expensive than the equivalent wattage Costco-available generator I'm going to wall off with $40 worth of concrete. Since its only an emergency-use generator, I'm okay with semi-temporary solutions.

ETA: is

[ElysianWort]

When I grew up, the generators weren't as quiet and my dad tried a couple different things to dampen the noise, both of which were quite effective;

People around here who drive Harley Davidsons like to take the muffler off and make them as loud as possible. My dad got ahold of on of those discarded mufflers and clamped it on.

Also, with flexible metal tubing clamped onto the end of the muffler, he redirected the exhast into a 5 gallon bucket of water. Blub, blub blub. Whisper quiet.