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Heat Exchanger for Gas Clothes Dryer - Page 2

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Posted by Paul on September 28, 2005, 2:06 am

  Most excellent example. I had not thought of that downside.

Posted by Brian Graham on September 28, 2005, 4:50 pm
Is the ducting insulated? Insulated ducts are readily available. Or you could
always wrap Fibreglass Pink (or whatever) around it..

A problem I have with my clothes dryer is that the exhaust runs through my
attic to an outside wall.  In the winter, the exhaust pipe (4" thin-wall
duct) is cooled by the cold air in the attic.  The moisture from the
clothing condenses and wets the inside walls.  Then the lint sticks to it
like glue.

Have to go up there and 'ram-rod' the piping each spring to clear out the
lint.  This year I layered some extra fiberglass over this (un-faced) to see
if that might help the situation.

Point is, removing heat from the exhaust will cause some condensation.  And
wet lint is troublesome to keep cleared away.


Posted by daestrom on September 28, 2005, 9:23 pm

No insulation, that was my point.  The only insulated ducts I could find are
of that 'spiral' wire & plastic crap.  And I figured the spirals would be a
lot harder to clean than a smooth bore metal duct.  As I said, I put some
fibreglass batting over/along/around it this year, so next spring I guess
we'll see how that worked out.


Posted by Paul on September 29, 2005, 3:23 am

  The spirals are hard to clean. I have done it.
The orignial post was to use a heat exchanger to tap heat
from the dryer outlet. Taking heat brings it closer to condensation.
I suppose after you take out some heat with an exchanger you would
want to insulate as much as possible.

Posted by daestrom on September 29, 2005, 10:32 pm

But since the exhaust is very nearly at 100% RH, any heat removal via a heat
exchanger would undoubtedly lead to some condensation on the heat exchanger

Now, on the one hand, recovering the latent heat of vaporization from the
water vapor driven out of the clothing would be a great energy source.
(~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60
degreesF).  So there *is* a lot of energy there to be reclaimed.

But the issue I was wondering is just *how* to keep the lint from collecting
all over the heat exchanger's wet surface and requiring tedious/frequent
cleaning?  My own experience with straight metal ducting in my attic
suggests that the lint will very quickly build up to 1/4 inch thick layer on
the leading surfaces of the heat exchanger.

Disconnecting, disassembling and cleaning the lint from something with a lot
of fins on it every month or two sounds like a royal pain in the arse.

Yet, a lot of energy to be recovered......


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