We might make 7 kerfs 8.26" apart in a 35"x66" piece of 1" foil-faced
foamboard, as below, and slip a 1x2 into the 0.78" gap between the drum
wall and the middle of each side of the foamboard to maintain the gap,
which adds some R-value...
30 RO".5/2'inner drum radius (inches)
40 N=8'insulation board number of sides
50 T=.5'insulation board thickness (inches)
60 THETA=2*PI/N'angle per side (radians)
70 RIMAX=RO-T*COS(THETA/2)'outer board radius (inches)
80 K=2*RIMAX*COS(PI/2-THETA/2)'distance between kerfs (inches)
90 L=N*K'foamboard length (inches)
100 LC=2.54*L'foamboard length (cm)
130 PRINT N,L,LC,DIMIN,BOARDGAP
140 D=2.54*L/N'kerf spacing (cm)
150 FOR K= 0 TO N-1
160 PRINT K,K*D
170 NEXT K
# sides foamboard length foamboard id drum-board gap
8 66.05458 (in) 167.7786 (cm) 19.93374 (in) .7831316 (in)
kerf # distance from end
0 0 (cm)
Exactly. So they would block water from spiraling down the outside of the
tubes. The water would have to travel radially in towards the center and
then it is no longer in contact with the tubing. Moving inward would be
counter to the 'pancake' of warm water in the middle. But perhaps it can
just move inward enough to 'fall' off the spiral down until it reaches water
of its own temperature.
Same thing. The 'cold' water is underneath the warm water. But most of the
water is in the center of the circle around which the tubing is arranged.
(looking down from above, most of the water is inside the circle formed by
the tube spirals).
Interesting. But this *still* puts most of the warm water in a thin
'pancake' and only the outer rim of the 'pancake' is in contact with the
tubing. Once that rim of the pancake cools, it must somehow 'get out of the
way' so the rest of the 'pancake' can spread outward and thinner to come in
contact with the tubing.
If a large part of the 'core' is excluded/displaced, then you get a sort of
doughnut shape around the central 'plug'. This warm doughnut would be
thicker and contact more tubing. And that's a good thing.
This 'plug' doesn't have to be a tight fit with the tubing. In fact it
would probably help if there was a gap for the doughnut to form. But a
'thicker doughnut' would warm more of the tubing in a shorter time.
I didn't intend that you vent 'inboard' to the basement ;-) Just that it
needs to be 'vented'. Out the basement window, back to the sewer stack
would be fine.
Exactly. That is *why* you want a vent between shower and drum.
Yes, I think you have the idea. Just some 'alternate' path for the air in
the pipe between the two traps (the shower's and the drum).
You're right of course. Missed a density factor there...
Nick is hoping for >85%. But the particular GFX I have (S4-60) is more like
a two-pass shell. It has two parallel coils of freshwater to reduce the
freshwater pressure drop. The two coils are arranged in series on the waste
stack. This is not ideal as far as heat-exchanger theory though. The warm
waste water is cooled by one coil then falls to the inlet of the second
coil. So the second coil "see's" less delta T. Then the freshwater from
each coil is mixed together. But my particular situation I couldn't
tolerate the pressure drop of running the coils in series, it would be too
For the G3-60, with flow around 1.5 gpm, the effectiveness is supposed to be
about 65%. I'm only able to measure between 45 and 55% depending on the
exact day, inlet temperature and what not. So no, I'm not getting full
effect. But it is saving me money and has almost paid back already. So I
think it was worth it.
Well, you may not use as much hotwater as my family. I have a family of
five and as I've mentioned before, my adult son is a bit of a 'water
buffalo' and takes long showers. Since the heat exchanger represents a
'capital investment', and the dollar savings depends on the amount of hot
water one uses, it may not be right for everyone. But it does seem to be a
largely ignored part of home energy use.
The GFX actually gets better performance than a traditional shell and tube
or tube-within-a-tube type. This is due to the fact that waste water
spreads out in a very thin film (thinner than the boundary layer found in
traditional flooded shell). Much thinner means high film coefficient for
rapid heat transfer. Even though the water is only in the unit for 2-3
seconds as it falls through.
But it has the draw back that when you shut off the water, the water
currently in the tubing just stops and losses heat to ambient. And 'batch'
processes like filling a tub with warm water, then emptying it out 15
minutes later doesn't do *anything* in the GFX. If there isn't any
freshwater flow when the warm water goes down the drain, you just heat up a
'slug' of water in the tubing but don't get to use it. Unless you fill and
drain the tub several times, and only use one 'slug' worth of water at a
time to fill the tub.
Nick's been trying to come up with a design that would overcome this
limitation. By having a heat exchanger that can hold up a typical 'batch'
of hot water, he hopes to recover the energy in it at a later time when
freshwater flows. But with improvements in 'batch' mode, it may lose some
effectiveness in continuous-flow mode.
Yeah, my brother has told me that. But I've had a beard for 27 years now
and don't see that changing :-)
The problem here is 20 minute showers, the greywater recovery is like
trying to put a bandaid on an amputation.
1) low flow shower head
2) Install shutoff at the shower head so you can wet down, then turn it off
while you lather up, without having to re-adjust the temp.
3) By lathering you are actually giving the soap a chance to work (bind to
debris) rather than most of it rushing down the drain unused
4) turn the shower back on. If you are doing hair separately, you might
take several on and off cycles
You can easily cut each shower running-time down to under10 minutes, and
save yourselves time and money.
Plus think of all the water pumping you'll save!
No shower for you!!! -shower nazi
What you're saying is true. In the navy, where freshwater has to be
distilled from seawater, such showers were expected. Anyone caught taking a
'hollywood shower' (languising under a flowing nozzle for long periods)
would be treated to a bucket of ice water by his shipmates.
But even such frugal showering sends all the energy used to heat the water
down the drain. And heating the water takes a lot more energy per gallon
(at least in climates where the ground temperature is < 50) than pumping it.
Of course, if we all just opted out of showering all together, we could save
the nation an awful lot of energy. And the population growth would probably
shift to a negative number ;-)
And getting people to change the way they shower is a lot harder than
installing a heat exchanger to reclaim much of the energy that currently
goes down the drain.
Daestrom a couple more questions about this please?
- When you look down the greaywater tube, what do you see? I cannot figure
out if there is something to force the water to the edge of the pipe or it
is fully open for the whole diameter.
- Is there a cheaper place to buy these units? You have me enthused and I
have a perfect place to install easily that handles 60% of the house that we
use 95% of the time..morning shower and sink. Kids have all moved out (water
was too cold...LOL)
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