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Using electric generator exhaust to heat water?

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Posted by stu on November 26, 2005, 1:29 am
 


Here in South Florida we've had 3 hurricanes in a year.

I'm setting up a 3,500 watt generator on a shelf in my garage with the
exhaust tube through the wall to vent all the gasses outside.

I am looking to add a heat exchanger to capture some exhaust heat and
use it to warm water in my HW tank.

Suggestions of home-brew or off the shelf heat exchangers please.


Posted by Pop on November 26, 2005, 1:48 am
 



: Here in South Florida we've had 3 hurricanes in a year.
:
: I'm setting up a 3,500 watt generator on a shelf in my garage
with the
: exhaust tube through the wall to vent all the gasses outside.
:
: I am looking to add a heat exchanger to capture some exhaust
heat and
: use it to warm water in my HW tank.
:
: Suggestions of home-brew or off the shelf heat exchangers
please.
:
I believe it's highly unlikely you will be able to get enough
heat, regardless of the heat exchanger, to heat any amount of
water that would be usable, especially with a genset that small.
   Besides that, it's highlt likely that the added back-pressure
from any sort of workable heat exchanger would upset the engine
tuning and you might end up wiht a pretty gunked up engine, not
sure.

No expert so I'll be interested in what others have to say, but I
doubt it would be worth the effort -

Pop



Posted by Harry Chickpea on November 26, 2005, 3:29 am
 



I have metal five gallon pails that I've stuck in the path of the
exhaust of my 5KW generator.  The water got fairly hot, but had that
distinct eau' de fumes that made it unusable.  Then I found that the
lower element of my water heater was 4.5K watts.  Two hours of direct
connection to the generator (with no other loads) made a nice 40
gallons of hot water.  That is closer than I like to run to rating,
but seemed to work OK.  You could get a small capacity electric water
heater with smaller elements and do something similar.

The more sane way to heat water down here is solar.  With FPL's rate
increase, and tax breaks, the payoff period is beginning to make sense
again.  If you must use gasoline to heat water, get a Coleman gasoline
camp stove.  You won't wear out the generator and the efficiency is
better.

There is no way I'd run a generator in my garage.  Getting all the
exhaust fumes out is one problem, getting out the gasoline smell is
another, dealing with the possibility of a fire is another, and doing
the regular oil changes that these generators need is yet another.
Even if all those problems are resolved, there is the throbbing noise
that I wouldn't put up with.


Posted by Ecnerwal on November 26, 2005, 2:26 am
 

 stu@aaronj.com wrote:


Simple off the shelf solution, ranges from free to expensive - either a
hot water boiler (aka furnace) of the oil or gas fired variety, or a gas
or oil fired hot water heater. Might be a bit difficult to find boilers
in Florida (at least free used ones). Very low restriction, so little if
any added backpressure. Tons of heat exchange surface in a boiler,
somewhat less in a hot water heater.

I have a cast-iron boiler waiting for me to get the rest of the "real"
system in place which will be applied in this manner to the exhaust of a
diesel genset. Intact, working, replaced by newer and more efficient
boiler, cost was hauling it away. 8 inch stove pipe on that, so I don't
think backpressure will be any trouble at all with a 1-1/2 to 3 inch
pipe exhaust in place of the oil gun. Heat output will obviously be much
less than with direct flame, but there's plenty of heat there being
wasted, so I expect it will be a worthwhile operation to extract it.

With any such exhaust plumbing work, considerable detail should be
applied to both reducing the odds of a leak, and detecting any such leak
before it can kill you. One way to help with that is to place the entire
generator setup in a separate shed away from the house, rather than in
an attached garage.

When I run my present gasoline generator "with the exhaust tube through
the wall to vent all the gasses outside", my level-indicating carbon
monoxide detector _always_ indicates some indoor pollution (5-15 ppm),
so all the gasses are not leaving, in fact. Several times, something not
obvious to a casual inspection has gone wrong with the system and levels
inside have become dangerous (50 to as much as 500 ppm) - I never run it
without the detector, and I have decided that the permanent setup will
be located in a separate shed, with a chimney. Screwing around with this
stuff can kill you, so I'm not screwing around with it.

--
Cats, coffee, chocolate...vices to live by

Posted by nicksanspam on November 26, 2005, 6:33 am
 



A gas water heater sounds like a nice off the shelf solution, with
the insulated pressurized tank and plumbing :-) Maybe Grainger's 1PZ64
Vanguard/Rheem 50 gal 140 pound $09 heater, listed at a 36K Btu/h input
with a 36.4 minute 90 F recovery time, R6.7 R-value, 0.58 "energy factor,"
and a 6-year tank warranty.

How efficient would that be with a $00 1500 W 90 lb Honda generator
that also makes 21K Btu/h of heat? Could we just plumb the generator
exhaust into the gas line?

Nick


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