# waste heat recovery



## hoofinitnorth (Oct 18, 2006)

My husband wants to know if there is a good way to take waste heat (likely including some exhaust) from the diesel back-up generator when it runs in the winter and reuse it (maybe pump it into the house, say at least the crawl space or laundry room where the house heat doesn't reach as well (until we get the in-floor heating system in place)).

I know that heat pumps/exchangers farm BTUs for energy/heating from 45-degree soils & water, so why not reuse 90-degree air? The simplest I can figure is to filter the air somehow to ensure breathable quality and then pipe it into the house. Would also need some sound filtering, I think. The distance is minimal (less than 15 feet)... Basically the generator is in it's own shed next to the house. It only runs as needed, for up to 6 hours at a time, between solar charges. As you can imagine, this happens mostly in the winter, when we could use the extra heat. The generator currently directly exhausts out of an auto-louvered vent, but it does sometimes overheat due to insufficient venting (usually in the summer when it exercises). This means we open the door to the shed or add a fan to better push the hot air out of the shed through the vent. All that heat out to waste!

Ideas?


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## ericjeeper (Feb 25, 2006)

A tragic carbon monoxide leak. and you would be blowing it directly into the house.
Volkswagen used the heat off the engine and exhaust for years. So I suppose it will work just fine.


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## Ross (May 9, 2002)

Belarus tractors used a recovery system off their exhaust to heat a cab. Just have a CO alarm to be sure it isn't leaking!


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## Jim-mi (May 15, 2002)

Another consideration you would be adding additional 'back pressure' to the engine . . .at a certain point that would not be a good thing. . . . .unless 'large' diameter pipe was used.
. . .can you weld\braze it 'gas tite' . . ?


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## OntarioMan (Feb 11, 2007)

Perhaps run the exhaust through a water chamber, and extract as much of the exhaust heat as possible. You could then pump the water through an indoor radiator to add heat to your house.


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## wy_white_wolf (Oct 14, 2004)

VW bugs used a waste heat system off the exhaust manifolds for the defrosters and cabin heat.

I feel it would be better (safer at least) if you piped the exhaust though a chamber to heat water. Then pump the water to where you want the heat.


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## Ross (May 9, 2002)

The Belarus system was a jacket around the exhaust pipe that cycled air through the jacket and wouldn't add back pressure.


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## WisJim (Jan 14, 2004)

Look at exhaust systems made for boats with inboard motors, expecially boats using car engine conversions. There are water cooled exhaust manifolds made that might work in your situation, or you could make your own.


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## Windy in Kansas (Jun 16, 2002)

If I were running a generator for up to 6 hours at a time I would probably run the exhaust into some 33 gallon barrels welded end to end to form a tube with only the two outer most ends in place, one for inlet, one for exit.

I would surround the barrel tube with fist sized rock which are in a well insulated bin. As the generator runs it would heat the rock which would hold the heat. From the bin I would have air ducts leading to the house, one for return air, one for sending heated air to the house. 

I doubt the unit would capture anywhere near all of the exhaust heat unless you make a really long tube giving a longer time for the rock to absorb exhaust heat.

If you do go to that much trouble you might as well also make a solar collector to add heat to the rock.

If the generator could be run for less time more frequently you might consider heating water instead of rock. The heated water could be sent to a well insulated tank and then be used to feed your conventional device for heating water. With it preheated it would require less energy to finish the heating.


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## fishhead (Jul 19, 2006)

You could also put the engine radiator in the house and push air through it with a fan. A friend of mine has an engine radiator in his house attached to the water line of his outdoor wood burner. It puts out a lot of heat.


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## solidwoods (Dec 23, 2005)

Build a metal box about 18 x 18 x 36. 
Run 2" tubes through the ends of the box (like a pack of straws).
Water in the box/ exhaust in the tubes.
Make the tubes vertical to gravity off carbon.
Mixing box at the bottom.
Boom- Exhaust gas to water heat exchanger.
Hot water circulating pump to PEX tubing,, your choice from here- in floor heat/radiators/heat exchanger in the forced air system.

Make the exchanger big, insulate it (rock wool is nice), if the exchanger is too big it will just make condensation in the bottom of the exchanger (drain that)

Use Plenty of exhaust tubes and no back pressure problem.

The water in the exchanger must be vented to the atmosphere at the top, and kept full of water.
jim


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## MrPG (Oct 9, 2005)

If the diesel was watercooled it would be easy. Adding an oil cooler and pumping the warmed oil into the house and back would probably be a lot more efficient and less intrusive. Just make sure you have the pump on the oil cooler be strong enough to move the oil that distance.


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## solidwoods (Dec 23, 2005)

Engine water temps are right in the range of usefulness 170-deg. So heat exchanging eng. water heat to heating systems water is safe/easy/cheap. Cheap because this type of work gives back a $ savings.

I don't know the engine oil optimal temp. And optimal temp could be different then the normal operating temp. Because oil is so valuable to the workings of the engine, I'd make sure the oil temp is exactly where it needs to be.

If you exchange heat off the engine oil, I'd do it at the unit. You don't want to transport oil. If you have a leak , you'd rather it be water.
Also you cold be adding quite a bit more oil to fill the transportation lines.

An exhaust to water heat exchanger is nice also.

jim


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