Revisiting greywater in a drum

[daestrom]

Interesting stuff. Thanx for the information, especially the heat exchange
method. I have never heard of this technique before (never looked
either...LOL)

Some points noted:
-Your heat exchanger measurements does not live up the theory (call in
ineffieciencies maybe due to size etc.)

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.

- Your NG bill must be much higher than mine I would have to do some
research but I doubt my hot water bill was much over $135 Canuck for the
year including the rates etc. The rental was more though...LOL Then again
I
cannot separate my heating from the HW very well as I have a gas stove
etc.
I may be basing ideas on old prices. Must rethink that one.

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.

- Last thing I heard , he was talking a barrel at the end of the greywater
drain as a heat exhanger. I had suggested the "in-pipe" method and thought
he forgot it due to mechanical logistics. (maybe I haven't followed that
closely) He was also feeding it into his hot water heater as a preheater.
This method seems much more logical in the physics dept.

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.

- I like the "water has to prewarm the pipes" idea. I stated erlier that I
wait about 1.5-2 minutes for my hot shower each morning.
- I take a 10-12 minute shower each day, washing my hair and shaving too.
If
you use a blade, get a mirror in the shower and you will never shave in
the
sink again. Does a much cleaner/nicer job on your face.

Yeah, my brother has told me that. But I've had a beard for 27 years now
and don't see that changing

daestrom

 

[daestrom]

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!

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

 

[Gìmmìe Bob]

Well then I won't ask you your age....LOL

Me thinks the whole efficiency thing goes from your figures to my proposed
figures once you introduce the barrel exchanger. There seems to be a fine
line when dealing with differences.

 

[Gìmmìe Bob]

My oldest years ago would stand in the shower until the tank went cold.

I sterted going down to the basement and slowly reducing the valve opening
on the hot water over a period of about 3 minutes so he thought the water
went cold and got out....LOL

Yeah I have three sons and they burned it off pretty well like the time my
freezebug oldest came home with a 1500W microfurnace and tried to heat the
whole house. I was looking back at our elect. records the other day and
discovered I went up to 57 kWh / day for that two month period before I
figured it out. I peak max about 37 per day when the A/C is on full for a
hot summer.

Teenagers! They are definitely an art and yet a predictable science too. At
university they train them in the art of pissing off the parents
successfully too....LOL

 

[Gìmmìe Bob]

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)

 

[[email protected]]

So they would block water from spiraling down the outside of the tubes.

That seems OK, as long as they allow some water to move in the space
between the drum and the outside of the outer pipe layer.

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.

And slide under and inwards to displace warmer water above it that rises up
and out from the middle of the pancake in toroidal convective patterns like
several stacked donuts?

If we drill 4 d" holes through every vertical inch of a 1.5" x 34" dip
tube with 1.77 in^2 of flow area, 4x33Pi(d/2)^2 = 1.77 makes d = 0.23"...

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.

Altho that reduces the stored greywater volme and tends to interfere with
stratification, which is desirable if the greywater temp varies. If a slug
of 60 F water arrives, I'd like to see it slide down the holey tube and out
the bottom and immediately up and out the other dip tube without disturbing
the warmer greywater above it.

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.

The plug (stacked blocks or bricks in a foamboard box?) might make grey
and freshwater volumes equal. Perhaps we can simulate this on paper.

Nick

 

[daestrom]

That seems OK, as long as they allow some water to move in the space
between the drum and the outside of the outer pipe layer.


And slide under and inwards to displace warmer water above it that rises
up
and out from the middle of the pancake in toroidal convective patterns
like
several stacked donuts?


If we drill 4 d" holes through every vertical inch of a 1.5" x 34" dip
tube with 1.77 in^2 of flow area, 4x33Pi(d/2)^2 = 1.77 makes d = 0.23"...


Altho that reduces the stored greywater volme and tends to interfere with
stratification, which is desirable if the greywater temp varies. If a slug
of 60 F water arrives, I'd like to see it slide down the holey tube and
out
the bottom and immediately up and out the other dip tube without
disturbing
the warmer greywater above it.


The plug (stacked blocks or bricks in a foamboard box?) might make grey
and freshwater volumes equal. Perhaps we can simulate this on paper.

And perhaps two drilled dip tubes, one on each side 180 degrees apart around
the 'plug. So the drain water sinks in the tube to the elevation with the
correct temperature, and exits on each side to form the 'doughnut' of water.
A 'slug' of 60F water will just sink to the bottom of your inlet tubes and
immediately exit as you suggest. Anything warmer than water already
surrounding the tubes/plug, will automatically exit the inlet tubes at the
right level and force the coldes water near the bottom out the outlet dip
tube.

The fit of the central 'plug' doesn't need to be exact or anything, just a
general 'displacer' so the water forms a thicker doughnut vs. a thin
pancake.

daestrom

 

[daestrom]

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.

Not a thing. The inside 'barrel' looks like a smooth, 4" pipe. You can
roll a baseball right down it. This is very desirable when installed in the
home's main waste line. Any black water, (ahem, 'solids') that flow through
it from toilets just fall right through just like the aforementioned
baseball (or golfball, or grapefruit or whatever your analogy).

When water from a shower or sink drains, it comes along from some horizontal
pipe and then turns down as it reaches the vertical waste pipe. Most of
such water does *not* fall free through the middle of the pipe. It splashes
to one side or the other and spreads out into a thin film. Partly because
of the horizontal velocity it has where it enters the vertical section and
partly because of the air in the pipe tends to flow upward and push the
downfalling water to the sides. It isn't perfect, but it works.

- 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)

Well, obviously the cost is related to the particular size unit. I looked
on their web site for an 'authorized dealer' and found one in NY. When I
called them directly, they quoted me a different price (much lower). I
think the guy was giving me only a slight markup on his cost. So, you might
try that and see. My unit was shipped UPS ground.

If you have a smaller section that just covers shower or some greywater, but
still has a vertical section of pipe that will fit one, I'd go with the
smaller unit. As I said before the S3-60 that I have is a two-pass type
which is not as effective.

*REMEMBER* It *MUST* be installed vertically. If you don't have a vertical
section to install it, *don't*. A horizontal, or diagonal installation will
be very poor performance.

And of course the $ savings you get depends on how much hot water your
family currently uses and whether you use NG or electric for water heating.
But one of the things we like about ours is that we *never* run out of hot
water for the shower. Except the time the HW heater pilot went out, but
we didn't notice that until after the first kid finished ;-)

daestrom

 

[daestrom]

*REMEMBER* It *MUST* be installed vertically. If you don't have a
vertical section to install it, *don't*. A horizontal, or diagonal
installation will be very poor performance.

And by 'vertical', they mean as plumb as you can get it. Not just 'kinda'
vertical ;-)

daestrom

 

[Gìmmìe Bob]

ahhh. Thanx for that. I wondered about a slight slppe to make sure the
graywater adhered to the side(s).

If this is only a 3-4 inch copper drain pipe it csounds like it could be
built from scratch with 1/2" flex copper. I have never worked with soft
copper but it comes coiled fairly tight. Perhaps with a bending hickey and
some solder???