05-14-2016, 04:08 PM
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.
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.