Prep Genrl Why does no one build a generator shed with non-parallel or baffled walls?

[Toosh]

My 30 year old genny died and I've replaced her with a new portable, natural gas unit. It's a larger unit which means I have to re-work the genny shed. I'm in a suburban neighborhood. Doing all that I can to make the thing quiet (and a bit clandestine) is important.

As I recall elementary school physics, sound travels in waves, thus the two best ways to soundproof is to reflect the wave and/or absorb it. Absorbing sound is easy with enough product. But no one seems to be using reflection. When I look at YouTubes to see what everyone is building for a modern genny shed they are still using a basic box. Why is no one building a pyramid (or other shape) to reflect waves back to the ground or adding baffling to the walls? What am I missing? Anyone got anything other than a basic box? How's it working for ya?

(And, yes: I know about mufflers, fans, ventilation and the other aspects of a genny shed.)

 

[knowzone]

A guess here.

Lumbar/construction materials are sold straight line, linear. A 2x4x8, or a 4x8 sheet of.

The trades/skillsets have developed around this consistency of form evaluated down to carpenters and construction workers performing consistently and repeatedly.

In other words, if you want to go full on custom Buckminster Fuller with your design, it'll cost you more than off the shelf.

kz

 

[Czechsix]

I could swear that I've seen some baffled genny sheds in the past. Can't recall where though. I'm sure they're out there, especially with all the HOA activity, etc.

 

[tech]

Why is no one building a pyramid (or other shape)

A couple of reasons jump to mind...what shape is your generator? Pyramidal? Didn't think so - lol.

A pyramid is also going to have a larger footprint to accommodate that rectangular generator...and subsequently cost more.

 

[1911user]

From an overall system aspect, there are 3 required components for sound.

First there must be an energy source.
Second is the transmission method for the energy.
Third is the resonator or what receives the energy and makes sound via resonance.
Controlling each of the 3 aspects contributes to overall levels of generated sound and how it is perceived (frequency).

If this will be non-portable, I'd get a car muffler (or 2) connected to it somehow. You want quiet, it doesn't have to be neat or attractive. If it could be mounted to a thick, rubber platform, that would help absorb engine vibration which will produce sound given a chance.

The sound energy will be generated when it is running. So to reduce the sound outside the building, it must be absorbed. Have mats of fiberglass insulation covering the walls. Free-hanging tarps close to the walls would provide another absorbing layer (or 2). You could have free-hanging pieces of heavy carpet close to the muffler exhaust outlet to break up and absorb the exiting air pulses. Don't block the exhaust though. Edit: Also make sure the exhaust heat won't set it on fire.

Sound dampening and cooling for generators is always a trade-off. All of the measures to make air movement hard will make cooling less effective. Also, consider where the engine will get clean inlet air without it being a path for sound to get out.

Another option would be to strategically stack firewood and other things around the outside of the genny shed. It would be more mass to absorb sound from the shed.

 

[Raggedyman]

could also have LOTS to do with proper airflow combustion and exhaust

 

[knowzone]

Submitted for your approval:

Construct a shed to spec utilizing your design. Augment design to highest construction standards, abiding by local zoning laws. Finish interior of shed applying spray urethane foam, (part A + part B), to walls, ceiling.

Generator is centered and mounted upon wood deck that has 4 support posts sunk into ground. On top of the deck, under the generator, is a rubber mount, (tire?) acting as a shock absorb-er.

The exhaust is routed via galvanized pipe out of the structure to an adjacent 50 gallon drum filled with water. Exhaust pipe is routed into water filled drum, down to 12-18" off the bottom.

Airflow for cooling and combustion must be accommodated as determined by your location, but easily incorporated in your construction with vent grilles or even square wire cloth to keep the critters out.

kz

 

[tech]

The exhaust is routed via galvanized pipe out of the structure to an adjacent 50 gallon drum filled with water. Exhaust pipe is routed into water filled drum, down to 12-18" off the bottom.

That will give about .75 psi of back pressure in the exhaust, effectively derating the generator set and adding wear and tear. If the drum freezes, you won't be able to use the genset until you disconnect the drum.

 

[knowzone]

That will give about .75 psi of back pressure in the exhaust, effectively derating the generator set and adding wear and tear. If the drum freezes, you won't be able to use the genset until you disconnect the drum.

Yes on drum freeze, depending upon location. Not sure about back pressure. Removal of existing muffler decreases, adding pipe reapplies. How about a larger pipe diameter? Also, the amount of wear/tear/decrease of life, relative to back pressure change? How negligible? Would you run out of fuel long before wearing out the system?

kz

 

[West]

A guess here.

Lumbar/construction materials are sold straight line, linear. A 2x4x8, or a 4x8 sheet of.

The trades/skillsets have developed around this consistency of form evaluated down to carpenters and construction workers performing consistently and repeatedly.

In other words, if you want to go full on custom Buckminster Fuller with your design, it'll cost you more than off the shelf.

kz

Yes, but if you build a pyramid over it you get the extra pyramid power.

PS, ment to quote Tech.

 

[Millwright]

Genset manufacturers make sound attenuated enclosures.

MQ Whisperwatts are some of the quietest out there. You can carry on a normal conversation with your feet on the fender of a 45KW diesel unit.

Smart money is spent on emulating proven technology.

Check the sound ratings on whatever you are thinking about buying, Spend the extra money up front and make use of a gob of engineering that has already been done. It will probably be cheeper, easier, faster in the long run. Might even save you from doing something detrimental to the unit.

The first thing to address is the muffler, exhaust noise is half the battle. There are already good parts out there, why try to do some hillbilly crap? Look for a part described as "hospital grade" or some such designation.

The enclosures are heavily insulated, knocks down the resonation from the sheet metal.

Air inlets are baffled and the radiator has louvers on the outflow side. The cooling fan is also noisy. They use a larger radiator on these to increase cooling with lower airflow, cuts down on fan noise.


All of that is great, but...

The engine itself is a large part of the decibels you are trying to contain.

Typically, air cooled, 3600 RPM screamers are just freakin' loud. A lot of mechanical noise, even without the exhaust being considered. Watch a video on engine dynos, exhaust is ported out and no fan...still incredibly loud.

Half of that battle can be won by getting an 1800 RPM unit.

I deal with some Kohler 35KW units that use a GM 4cyl at 3600RPM, miserable bastards to work on when running.

They also have some 45KWs with a GM 3.8, V-6 running at 1800 RPM, they don't rattle the fillings out of your teeth when you have the doors open.


As with most things, do your homework before jumping on the latest/greatest, cheepest out there.

 

[Kathy in FL]

No amount of noise control is going to make it silent if you are the only one that has such a set up in the neighborhood.

Consider the suburb ... and let's make it mine LOL. All of the houses in the neighborhood sit on a minimum of 2 acres, our is a tad under five. This is Florida so sound is naturally dampened by the amount of humidity in the air. Our next door neighbor has one of those "whole house" gennies that in reality only powers one side of the home despite it being a big unit. It is propane powered. We always know without having to guess when the power is off in the entire neighborhood because that thing kicks on automatically. It is worse than a giant window shaker and they went to the expense of having it on a special pad and set back for noise control purposes. There is also someone around the "L" of the street in one of the big lots (10+ acres) that has one. It also kicks on automatically and the sound carries despite the distance and location of the unit ... the sound travels through canal channels and across the retention "ponds" put in by the county for flood control.

They also both travel through the swamp behind us into an expensive subdivision where no one has one of those whole house gennies but there is a privacy wall around the community.

About the only thing that takes away from the sound of the two gennies when they run is a commercial jet liner flying low.

I've been through a couple of hurricanes that have knocked out the power for days at a time around here so I'm not just basing my experience on a single occurence.

You know what has happened multiple times? People from around the area (not just in the neighborhood or on the street) look for people with operating gennies and ask for some help with water, assuming the gennies are also operating their well.

Witnessing this is why hubby and I have put a whole how gennie closer to the bottom of our want list. For our BOL we are looking into solar power to at a minimum run the well since it is too deep for a hand pump. Here at our primary we are looking into solar gennie but not sure if it is powerful enough for our current set up needs. We are considering drilling a shallow "ag well" to see if it will work. YMMV

 

[Millwright]

About the only thing that takes away from the sound of the two gennies when they run is a commercial jet liner flying low.

Because the right equipment wasn't purchased initially, if sound discipline was a major factor in the decision.

You get what you pay for.

I worked this last storm/major outage in Tulsa, there were a few newer portables in the response.

Some of the newer units were impressive.

At half load, I had to look at the gauges to verify that they were running...with foam earplugs in. Could not hear them through 100yds of woods.

There are some really quiet units out there that you have not worked with or been exposed to.

67 dB is about as loud as a dishwasher.

After several years of disaster response, I really like the MQs. Quiet and they just sip fuel.

Generator​

Prime Rating — 20 kW (25 kVA)

Standby Rating — 22 kW (27.5 kVA)

Single/Three-Phase, 60 Hz, 0.8 PF

Enclosure​

65 dB(A) at 23 ft.

41.7 gal. (158 L) Fuel Tank Capacity

TRLR25US Trailer Available

• Standby Range (kW/kVA) 24-30/24-37.5
• Prime Range (kW/kVA) 22-28/22-35
• Continuous Range (kW/VA) 22-28/22-35
• Fuel Type Diesel
• Frequency 60 Hz
• Speed 1800 RPM
• Alternator Type Brushless, Wound Field
• Engine Manufacturer Kohler
• Emissions Tier 4 Final EPA-Certified for Nonroad Applications
• Sound Levels 67 dB(A) log average @ 7 m (23 ft.) full load at prime rating
• Fuel Capacity/Run Time 77 gal.

 

[Kathy in FL]

Those are huge units Millwright. I'm not sure of the size of the two currently in use around here. They aren't recent additions so that could be a factor; older units. I do know that both units are propane-fueled because during the storm that was in September a couple of years ago when we were without electric so long, both units ran through all of the propane in their dedicated tanks.

 

[knowzone]

These gennys are indeed a wild lot. The need to go slow is tantamount to success. Never assume anything and always assess cautiously before capitulation to the next level.

Here is a fine example from a renown engineer:

1:36
Scotty - The Screens Stay Up! Star Trek TOS Badass Moment
​

The traits of calmness, restraint, dogmatic, resolute come to mind.
In keeping with the main theme of the example given here, I suggest mono-diversity. "You will be assimilated. Your technology will become borg. Blah, blah, blah". Only this diversity is added to the Federation. The good guys!
Ahhh, but I digress.

Anyway, as I said. mono-diversity. Electricity/storage, is the Federation. Your genny, solar, wind, water(pelton wheel) are the civilizations.

Long story short, gennys are my least fav. Noisy, stinky, hungry and a month's worth of fuel will put you in the poorhouse while..........? (gallon of gas = 26 sticks of dynamite). * (( Just researched the dynamite assertion. Quotes seen, range from 10 sticks to 83 sticks.....in 4 searches!) Anyway, lots of boom power with gasoline.

This is just the power creation side. Storage of created electricity is the trick. Controller, batteries, distribution. Today's modern inverters make life easier. Built in transfer switch, charger, merging 12v DC with 120v AC. Then it goes deeper regarding the quality of electricity, or how clean it is being rendered.

Keep going and the thought occurs: "what do I need this electricity for?" Can the end goal of intended usage be accomplished from another direction? "Do I really need my electric toothbrush when this old standard one works fine."

In conclusion, the "Juice suckers", are my least fav, but I acknowledge their robust, spontaneous ability to produce a lot of electricity quickly under the right conditions. The flaw (internal combustion engine for mechanical motion), will be eradicated by future technologies.

The goal: Unlimited, instant, quiet, safe, free energy.

and then what?

kz

​

 

[Millwright]

Those are huge units Millwright. I'm not sure of the size of the two currently in use around here. They aren't recent additions so that could be a factor; older units. I do know that both units are propane-fueled because during the storm that was in September a couple of years ago when we were without electric so long, both units ran through all of the propane in their dedicated tanks.

Huge in size? That's relative. The large appearance is due to the sound/weather enclosure...what the OP was discussing.
Realistically, they are much smaller than a building that she was proposing. They are actually about 3' wide, 5-6' long, maybe 4' high....give or take. Plus, all the airflow, cooling and sound issues are worked out.

Huge in capacity? Residential units are typically 18-22KW. The two I showed were 24KW.

More expensive...Yes. But you don't have to build a building for sound attenuation. They will also live a lot longer than the air cooled screamers.

Upside, you can go get your own diesel instead of being married to the propane guy.

IMO, definitely a "Buy once-Cry once" situation.


I've seen it time and time again, human nature, people will go cheep and spend as much money in the long run to attain a given result. In the end, they still don't have what they originally desired.

This applies to many things.


ETA: there are LP/NG units out there that are equally as quiet. I worked on one at the local hospital's "Sleep Study" building, If that's any indication. It was a regular generac light commercial unit.

 

[ChetekTech]

Here are a couple of pics of my portable genny shed I put together.

Plumbed with LP. A power interconnect is mounted on the vinyl siding and runs to the manual transfer switch on the inside of the building. and a 12' power extension connects the genny to the outside wall.

The setup works and exhausts well. It helps a bit with the noise but I do leave the door open a little to allow air in for it to breathe.

 

[summerthyme]

Here are a couple of pics of my portable genny shed I put together.

Plumbed with LP. A power interconnect is mounted on the vinyl siding and runs to the manual transfer switch on the inside of the building. and a 12' power extension connects the genny to the outside wall.

The setup works and exhausts well. It helps a bit with the noise but I do leave the door open a little to allow air in for it to breathe.


View attachment 427807View attachment 427808

I'll bet if you put foam board panels in between those studs, you'd knock the noise down a lot. Or Google acoustic panels...

We have a PTO run generator. Runs off either big tractor. The Zetor is noisier, but sips fuel... the bigger Massey can be throttled down to just enough to maintain 540 rpm, and is very quiet. Not for residential neighborhoods, but great out here where we can barely see our neighbors.

Summerthyme

 

[ChetekTech]

I'll bet if you put foam board panels in between those studs, you'd knock the noise down a lot. Or Google acoustic panels...

Summerthyme

Since I leave the door (or top when not raining) open a tad while running, I didn't chase that thought. I like the idea of 2" foam and may need to add. It wouldn't add that much overall cost.

Thanks!

 

[buttie]

RPM does make a huge difference. Here is a 1.5 min video of our gen shed and a start and run of our 650 rpm Lister CS diesel. We are off grid and this generator is used for both backup power and heating the house via hydronic loops in the house and basement floors.

View: https://www.youtube.com/watch?v=dQ61ZfvIzy4

 

[Millwright]

Yes on the foam. Might even look at some egg crate over the foam.

You would need some intake louvers for airflow.

If you really want to geek out on this, put a baffle box over the inlet and outlet with an open bottom and foam them too.

This would direct a lot of the sound downward and help dissipate it.