Revisiting greywater in a drum

Gary writes:

http://www.builditsolar.com/Projects/GreyWaterHE/gwinbarrel.htm

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...
20 PI=4*ATN(1) 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) 110 DIMIN=2*SQR(RIMAX^2-(K/2)^2) 120 BOARDGAP=RO-(DIMIN/2+T) 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) 1 20.97233 2 41.94466 3 62.91698 4 83.88931 5 104.8616 6 125.834 7 146.8063
Nick
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wrote:

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...
daestrom
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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 much. :-(
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 :-)
daestrom
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cold
energy
100
If
can
would
\$300
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
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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
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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)

exchange
like
waste
warm
be
again
a
greywater
thought
preheater.
'batch'
a
and
I
too.
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Oops.
20 PI=4*ATN(1) 30 RO".5/2'inner drum radius (inches) 40 N=8'insulation board number of sides 50 T=1'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) 110 DIMIN=2*SQR(RIMAX^2-(K/2)^2) 120 BOARDGAP=RO-(DIMIN/2+T) 130 PRINT N,L,DIMIN,BOARDGAP 140 D=2.54*L/N'kerf spacing (cm) 150 FOR K= 0 TO N 160 PRINT K,K*D 170 NEXT K
# sides foamboard length foamboard id drum-board gap 8 63.22615 (in) 19.08018 (in) .7099085 (in)
kerf # distance from end
0 0 (cm) 1 20.0743 2 40.1486 3 60.2229 4 80.2972 5 100.3715 6 120.4458 7 140.5201 8 160.5944
Nick
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