Posted: 8/13/2012 6:48:30 AM EDT
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I just go my replacement generator last week for my burnt out (ok, I fucked it up) unit.
I got this: Rigid 6800 watt I build a 4x4 enclosure that is approx 3' high on back and 4' high in front. For now it's 3 sided just to protect it from the elements (open side towards house for storage). I want to make it more permanent and place on end of my walk out concrete patio. I want to add a door and would like to run it with doors closed for quietness. My problem is sizing of the fan. How many CFM do I need to keep it cool? With the above dims its about 58 CF inside. How many air exchanges do I need? Do I have to vent the exhaust directly or can I blow it through the fan? The fan and exhaust will be on the door side facing away from the house to minimize sound. 
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The amount of airflow you need will depend on how hard you work the generator - It'll run a lot hotter under full load.
Since a lot of that heat comes from the exhaust, it's best to route the exhaust pipe outside. Ideally, the air inlets on the enclosure should be pretty close to the air inlets on the generator - i.e., near the pull cord on the front of the engine, and near the back side of the alternator (which is typically the air inlet side of the alternator). This helps ensure that both the engine and alternator receive cool air where they can best use it. Since heat rises, locating the air exhaust outlet neat the top of the enclosure usually works well. Roof-mounted attic vent fans work well... 
as do their gable-mounted counterparts... 
Installing some sort of sound-deadening material on the inside of the enclosure usually helps further reduce noise - shag carpeting works pretty well, and can often be found for free in small amounts. |
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Mine is here:
http://www.ar15.com/forums/t_10_18/626894__ARCHIVED_THREAD____Bought_a_Generator_Shed___Already_decided_to_rebuild_it.html&page=2 I use ine as a fuel shed all the time, when we loose power I pull the fuel out and then put the generator in there and plug it in... Then I bring the fuel inside... One of the better projects I have done as it is great having that fuel outside of the house in case of a fire PLUS it is ready to go as the generator shed too. |
Here's a couple of pictures of an enclosure I made for a 4KW Generac, permanently installed in a pickup truck bed - maybe it'll give you a few ideas:
It's made of 1" plywood, lined on the outside with epoxy-coated fiberglass cloth, painted with spray-on truck bed liner. The inside is lined with dense foam rubber, commonly used for rubber floor mats on stairways. A shallow in-the-bed pickup toolbox serves as the enclosure's top cover. The 240VAC fan draws cool air into the enclosure through two large holes cut in the bottom of the truck bed (below the generator) and exhausts it through the fan outlet. The engine's exhaust pipe is plumbed to a muffler mounted under the truck bed. 
Although not shown in the pictures, metal slats were later added to the outside of the air outlet, with dense foam rubber glued to their undersides for a little extra noise attenuation. |
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Quoted:
Here's a couple of pictures of an enclosure I made for a 4KW Generac, permanently installed in a pickup truck bed - maybe it'll give you a few ideas: http://i46.tinypic.com/nfskle.jpg http://i48.tinypic.com/14ky4p1.jpg It's made of 1" plywood, lined on the outside with epoxy-coated fiberglass cloth, painted with spray-on truck bed liner. The inside is lined with dense foam rubber, commonly used for rubber floor mats on stairways. A shallow in-the-bed pickup toolbox serves as the enclosure's top cover. The 240VAC fan draws cool air into the enclosure through two large holes cut in the bottom of the truck bed (below the generator) and exhausts it through the fan outlet. The engine's exhaust pipe is plumbed to a muffler mounted under the truck bed. http://img367.imageshack.us/img367/9038/56427745ub8.jpg Although not shown in the pictures, metal slats were later added to the outside of the air outlet, with dense foam rubber glued to their undersides for a little extra noise attenuation. That is awesome. How loud? |
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I just bought on of the Home Depot generators on $200 sale yesterday, and was considering a permanent building for it. I want to make the roof/sides open-able for maintenance/repairs, and BOLT it to a cement slab. Theft is not a worry up here, but I can see someone hearing it running one night and come a take it if they feel they "need" it more than I do.
I was thinking: This unit has an 8amp 12VDC outlet. Would an electric radiator fan from a car work? They move quite a few CFMs, would not use up a 120VAC outlet, and we have some lying around. That combined with a simple roof vent, should work?? |
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Here's a couple of pictures of an enclosure I made for a 4KW Generac, permanently installed in a pickup truck bed - maybe it'll give you a few ideas: http://i46.tinypic.com/nfskle.jpg http://i48.tinypic.com/14ky4p1.jpg It's made of 1" plywood, lined on the outside with epoxy-coated fiberglass cloth, painted with spray-on truck bed liner. The inside is lined with dense foam rubber, commonly used for rubber floor mats on stairways. A shallow in-the-bed pickup toolbox serves as the enclosure's top cover. The 240VAC fan draws cool air into the enclosure through two large holes cut in the bottom of the truck bed (below the generator) and exhausts it through the fan outlet. The engine's exhaust pipe is plumbed to a muffler mounted under the truck bed. http://img367.imageshack.us/img367/9038/56427745ub8.jpg Although not shown in the pictures, metal slats were later added to the outside of the air outlet, with dense foam rubber glued to their undersides for a little extra noise attenuation. Is that running a bed-mounted window A/C unit? |
| I forgot to say that I do have 1" extruded foam on the inside and there is a 1" gap along all three sides on the bottom. I looked at the gable fans but 1200 cfm is a buttload of air. I think its overkill. I'm afraid the roof mount fan would act as a horn and be a source of sound leakage on the top that points towards my bedroom windows, only about 20' away. |
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Here's a couple of pictures of an enclosure I made for a 4KW Generac, permanently installed in a pickup truck bed - maybe it'll give you a few ideas: http://i46.tinypic.com/nfskle.jpg http://i48.tinypic.com/14ky4p1.jpg It's made of 1" plywood, lined on the outside with epoxy-coated fiberglass cloth, painted with spray-on truck bed liner. The inside is lined with dense foam rubber, commonly used for rubber floor mats on stairways. A shallow in-the-bed pickup toolbox serves as the enclosure's top cover. The 240VAC fan draws cool air into the enclosure through two large holes cut in the bottom of the truck bed (below the generator) and exhausts it through the fan outlet. The engine's exhaust pipe is plumbed to a muffler mounted under the truck bed. http://img367.imageshack.us/img367/9038/56427745ub8.jpg Although not shown in the pictures, metal slats were later added to the outside of the air outlet, with dense foam rubber glued to their undersides for a little extra noise attenuation. Is that running a bed-mounted window A/C unit? Yep! Without exterior enclosures: 
View from inside the cab: 
More pictures here. |
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Here's a couple of pictures of an enclosure I made for a 4KW Generac, permanently installed in a pickup truck bed - maybe it'll give you a few ideas: http://i46.tinypic.com/nfskle.jpg http://i48.tinypic.com/14ky4p1.jpg It's made of 1" plywood, lined on the outside with epoxy-coated fiberglass cloth, painted with spray-on truck bed liner. The inside is lined with dense foam rubber, commonly used for rubber floor mats on stairways. A shallow in-the-bed pickup toolbox serves as the enclosure's top cover. The 240VAC fan draws cool air into the enclosure through two large holes cut in the bottom of the truck bed (below the generator) and exhausts it through the fan outlet. The engine's exhaust pipe is plumbed to a muffler mounted under the truck bed. http://img367.imageshack.us/img367/9038/56427745ub8.jpg Although not shown in the pictures, metal slats were later added to the outside of the air outlet, with dense foam rubber glued to their undersides for a little extra noise attenuation. Is that running a bed-mounted window A/C unit? Yep! Without exterior enclousures: http://img296.imageshack.us/img296/2673/58784255qe6.jpg Vide from inside the cab: http://img100.imageshack.us/img100/6446/40212095pq5.jpg More pictures here. If you don't mind me asking, why go with a generator/window AC unit instead of installing an AC system from a junk yard or donor truck? |
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If you don't mind me asking, why go with a generator/window AC unit instead of installing an AC system from a junk yard or donor truck? The truck originally had a factory AC system, which had proven itself to leakage-prone. Window units are NOT leakage prone - and no factory AC system is also capable of producing 4KW of 120/240VAC power. |
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Thanks, Surf & Expy.
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I just bought on of the Home Depot generators on $200 sale yesterday, and was considering a permanent building for it. .. This unit has an 8amp 12VDC outlet. Would an electric radiator fan from a car work? They move quite a few CFMs, would not use up a 120VAC outlet, and we have some lying around. That combined with a simple roof vent, should work?? Most of the 12 volt radiator fans draw quite a bit more than 8 amps DC - Typically, it's more like 15-20 amps. Also, if the generator's DC output fails, you probably won't know that the fan has stopped working. Conversely, if the AC output fails, you would probably notice it immediately, when your other AC loads suddenly stopped working. |
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Skibane,
What a cool idea! MacGyver would be impressed. Looking at the pictures over on your link, I had a couple of questions. What did you use for a boot between the passenger cab and the truck bed. Also, it looks like you had some sort of louver already centered in the truck bed for something but then replaced it when you installed the AC. Did that end up being some sort of plenum offset to center the AC output inside the cab? Again awesome. gk |
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There's no boot between the cab and bed - The openings in the bed and cab were cut about half an inch larger than the a/c, and were sealed with RTV silicone.
The louver in the center was unrelated to this project - It was for a subwoofer that had been previously mounted to the truck bed. The magnet side of the sub was actually inside the cab, with a foam rubber gasket in between the bed and cab to seal it. The idea was to use the entire inside of the cab as a "sealed enclosure" for the sub. Mounting the sub to the truck bed minimized the magnet's intrusion into the cab area. The sub was removed several years ago, but the louver was left in place. MtBiker, my apologies for wandering off-topic! 
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So the real question is....Is 1100-1300 CFM Gable vent too much flow inside the box? I think it might give the engine problems. I don't think there is any chance of too much airflow affecting the engine. The worry is the temerature getting too hot inside the enclosure but I am not even sure what I would say is "too hot". |
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So the real question is....Is 1100-1300 CFM Gable vent too much flow inside the box? I think it might give the engine problems. I don't think there is any chance of too much airflow affecting the engine. The worry is the temerature getting too hot inside the enclosure but I am not even sure what I would say is "too hot". +1. There's not much chance of it overcooling the generator, even in very cold weather. If you wan to get a little fancier, you can use the roof or gable fan with a fan speed control (Lutron FS-5F or similar), and dial in any speed you want. |