Greywater work in progress

[[email protected]]

Gary Reysa and I are now exploring a greywater heat exchanger with 3 100'
PE pipes (cut from a $60 300' piece) inside a $30 100'x4" corrugated black
plastic drainpipe vertical helix wound around a 2' square x 6' tall bolted
2x4 frame with a 4" horizontal thinwall PVC T at each end:

Warm greywater would enter the upper vertical side arm of the upper T and
cool greywater would leave via the upper vertical side arm of the lower T
and flow up into a vertical 6'x4" pipe and out the top into a septic system.
Cool fresh water would flow from a garden hose in through a cap at the end
of the lower T and up through the 3 1" pipes, and warm fresh water would
flow out from a cap at the end of the upper T into another garden hose and
into the drain tap of a conventional tank water heater.

The PVC Ts would meet the Hancor corrugated pipe with a $16 Fernco 1070-44
fitting. This 4" rubber sleeve has 2 hose clamps and a molded O-ring on
one end which fits into a pipe corrugation. It says "Overtightening of
clamp on this end of the coupling can collapse pipe wall," but it looks
like sliding a $1.28 3" thickwall PVC pipe coupling inside the corrugated
pipe will allow a waterproof 3 psi joint. As a cheaper alternative, this
might also work with a $5 Fernco straight 4" coupler.

So far, the hardest part is dividing the fresh water into 3 pipes with
an inexpensive manifold at each end that will slide into a 4" PVC pipe.
(Ferguson sells 6" Ts and 6"-4" reducers for $19 each!) Here's a Lowes
parts list for an equilateral version that clears a 4" pipe by about 1/4":

Qty Part # cost description

1 PP25052 2.04 3/4" MHT-3/4" FIP brass hose adapter
1 436 007 0.27 3/4" PVC male adapter
2 401 010 0.76 3/4" PVC Ts
2 409 007 1.48 3/4" PVC street elbows
3 437 131 1.41 1"x3/4" PVC bushings
3 436 010 1.32 1" PVC male adapters
3 435 010 4.86 FPT-1" grey PVC barb adapters
1 49303 0.32 2 1"-3/4" reducing galvanized conduit washers
3 105 733 4.29 6 3/4"-1.5" SS hose clamps
-----
$16.75 total, per end

The hose adapter and 3/4" male adapter would screw together through a hole
in a flat 4" PVC endcap, clamping the conduit washers and a rubber washer
to make a low-pressure bulkhead fitting. Trimming the Ts and elbows might
increase the 4" pipe clearance to 3/4". The lower T would have a male hose
thread and inline valve protruding to backflush the greywater path, perhaps
once per year.

This lacks the desirable thermal stratification of a drum heat exchanger
with different greywater inlet temps (altho our tests didn't show much of
that), but it's simpler to build. The 1" pipe holds 12.5 gallons of water,
so this might be close to 97% efficient (saving ~$300/year) with smaller
hot water bursts or a slow greywater flow, as in a chemical-free hot tub
with continuous water exchange. Something like this would also help:
http://sunfrost.com/efficient_shower.html.

Nick

 

[[email protected]]

There is no way you will get 97% efficiency or even anything over 25%...

Nonsense Where's YOUR NTU calc?

... You do not have true counter flow which limits your theoretical maximum
to 50%

What's "untrue" about this counterflow?

plus you are relying on plastic rather than highly thermally conductive
copper...

Just as good in the presence of crud, and a lot cheaper.

Also you do not have (from what I can tell) double walled heat exchange
which is key to preserve potability.

Each to his own walls.

... the last main reason why your design is flawed is the maintenance issues
dealing with standing grey water.

We will see...

Nick

 

[[email protected]]

... One very fundamental question. My own experience is that I can barely
fill half my bathtub when I take a shower. How much heat can you recover
from that mass of water to make your project worthwhile?

.... 15gallons x 8.33lb/gal x (110-60) = 6.2K Btu, about 2 kWh, worth about
20 cents at 10 cents/kWh? That's about $70 per year, which points out the
need for cheap parts. Then again, some people have 4 teenagers at home.

The heat exchanger we are exploring stores 12.5 gallons of fresh water and
54 gallons of greywater, so it should be very efficient with hot water use
in bursts of up to 12.5 gallons. A 10-minute shower with my 1.25 gpm head
uses 12.5 gallons.

I live alone and collect that greywater for use to flush my toilet.
The heat contained in collected bathtub water is dissipated into
the bathroom as it cools to room temperature.

That's good heat recovery, altho it might increase if your bathroom were
as cold as your cold water, and letting tub water cool may leave your feet
slightly less clean and require more frequent tub cleaning than real-time
tub draining.

It doesn't contribute anything significant to the washroom temp other
than fog up the mirror.

You might reduce the shower temp and the difference between the shower
and drain temps with a low-thermal-mass fully-enclosed shower like this:
http://sunfrost.com/efficient_shower.html.

For all that plumbing you will be better off to build a heat pump system
to draw heat from the ground in winter and to cool the house (dump
heat) in summer.

Sounds a lot more expensive, with less savings, since this heat exchanger
uses no electrical energy, but a typical heat pump needs about 1 kWh of
electrical energy to move about 3 kWh of heat.

Then again, Florida ACs with desuperheaters used to heat water, and
Powertech Ltd sell ACs that heat water in Cyprus, and PE Drew Gillett
often imagines that a kitchen fridge could heat water, and I often
think about pumping cold water through a $60 SEER 10 window AC and
back into a hot water tap.

Nick

 

[daestrom]

There is no way you will get 97% efficiency or even anything over 25% -
if you are lucky. You do not have true counter flow which limits your
theoretical maximum to 50% plus you are relying on plastic rather than
highly thermally conductive copper such as is used in commercially
available greywater / drainwater heat exchangers such as the
Power-Pipe.

The standard counter-flow or parallel flow calculations do not carry over to
'standing water' type systems. With proper stratification it is possible to
attain higher than 50%. Although I'm dubious about the 97% of Nick's
calculations (he does assume some things), it's not impossible to beat 50%
with 'batch flow' type process and good thermal stratification.

Because the water is left standing after a 'batch' of water is allowed to
flow, the thermal conductivity of the pipe wall is less important. Besides,
even with standard, flowing heat exchangers, the majority of the resistance
to heat transfer is not within the piping wall, but rather in the two film
layers formed on each side of the piping wall.

Nick and I have been around with this a few times. His ideas have some
merit in this. But texts that introduce the NTU method of calculation
stress that it is only valid for extrapolating from other heat exchangers of
similar design. That is, if you know the performance of HX-'A', you can
extrapolate how it will perform with somewhat different
flows/temperatures/area using NTU. But you can't use HX-'A' performance and
NTU methodology to extrapolate performance of a completely different design
(say, counter flow versus four-pass shell/tube). And the NTU formulae and
data Nick uses is for 'conventional' operation, not 'batch'.

Also you do not have (from what I can tell) double walled heat exchange
which is key to preserve potability. Again that is how the Power-Pipe
is able to receive UL approval as a Potable water heat exchanger.

But even as a "hobbyist" if you are willing to tolerate the above 2
problems the last main reason why your design is flawed is the
maintenance issues dealing with standing grey water. Additionally, the
Power-Pipe can be installed directly into your BLACKWATER drainstack.

So the Commercially available Power-Pipe has your design on those 3
points plus IT IS UL approved and IS commercially available. Check it
out www.power-pipe.us or www.power-pipe.ca .

$945!!! for a 4x60 'whole house' version??

What a rip-off!!! This is an obvious sub-license (or outright infringement)
on GFX-Technologies *patented* design. I say 'rip-off' because I bought a
GFX-Technologies 4" x 60" heat-exchanger for less than 1/3 the price listed
by Power-Pipe. If you really want to buy one of these, call a GFX
distributor and buy one of theirs. For me, at ~$275 (distributor discounted
from $601 list of S4-60) it was worth the investment. But at Power-Pipe's
$945, it may never pay for itself unless you house a small army.

http://gfxtechnology.com/contents.html#selection

daestrom
P.S. Overall, I'm quite pleased with my GFX product. Although I did see
some degradation in performance after the first year, I find I can 'boost'
it back up somewhat by a dose of that 'foaming' drain cleaner down the drain
nearest it. But it only lasts 3 months or so, so I don't habitually do it
(don't like using the toxic chemicals if I can avoid it).

 

[[email protected]]

The standard counter-flow or parallel flow calculations do not carry over to
'standing water' type systems. With proper stratification it is possible to
attain higher than 50%. Although I'm dubious about the 97%...

Rethinking this, 50K Btu/day = (110F-60F)C makes C = 1000 Btulb/day, ie Cmin
Cmax = 42 lb/h of water on a continuous basis (eg for small hot water bursts
or continuous hot tub water changing.) With A = Pix1/12x300 = 79 ft^2 of
U = 10 Btu/h-F surface, NTU = AU/Cmin = 18.7 and E = NTU/(NTU+1) = 0.95, no?

It seems to me that this latest version will have bidirectional plug flow
with "proper stratification," but it won't work as well as we hoped the drum
version would, with differing inlet greywater temps finding their own thermal
levels via the holey inlet tube. We hoped that a new slug of 60 F greywater
that entered a drum full of 80 f water would leave the inlet tube near the
drum bottom and exit via the outlet dip tube, without mixing with the 80 F
water above it, and that a slug of 100 F water would end up near the top of
the drum, with 80 F drum water flowing out from the bottom.

Because the water is left standing after a 'batch' of water is allowed to
flow, the thermal conductivity of the pipe wall is less important. Besides,
even with standard, flowing heat exchangers, the majority of the resistance
to heat transfer is not within the piping wall, but rather in the two film
layers formed on each side of the piping wall.

I measured U = 30 Btu/h-F-ft^2 for 2 clean still water films...

... texts that introduce the NTU method of calculation stress that it is only
valid for extrapolating from other heat exchangers of similar design.

My interpretation of chapter 3 of the ASHRAE HOF is that this NTU formula
applies to all types of "counterflow heat exchangers" with rate ratio Z
= Cmin/Cmax = 1. Different ratios, parallel flows, crossflows, and four-
pass shell/tubes would require different formulae.

... the NTU formulae and data Nick uses is for 'conventional' operation,
not 'batch'.

It also applies to small batches, IMO, up to 12.5 gallons.

IIRC, Carmen Visile's main patent claim applied to a plumbing technique
that raised the cold supply rate and GFX efficiency by making Z = 1,
compared to merely running the cold water shower supply through the heat
exchanger. (Setting the water heater temp to the shower temp will also
accomplish this.) Dr. Visile was surprised and disappointed that most
plumbing codes require double walls, on the face of it. DIY people (vs
manufacturers) have the right to make their own decisions about this.

$945!!! for a 4x60 'whole house' version?? What a rip-off!!! This is an
obvious sub-license (or outright infringement) on GFX-Technologies
*patented* design...

IIRC, Dr. Visile was also disappointed about this infringement...

Nick

 

[[email protected]]

One problem is such a leak would run down the drain and would not be
detected - until greywater shows up in your faucet.

That might happen, if you pumped the septic line back into your faucet

Unless you live well below your water source, you cannot guarantee that the
potable water line will always be pressurized. Most homes are above their
water supplies, and under certain common conditions (pump failure, water
line break, valve close, etc) can experience a sudden pressure drop and
draw a vacuum. That would suck in wastewater that could be contaminated by
e-coli, hepatitis, typhoid, cholera, botulin, etc. It would then end up in
your taps when the pressure was restored.

Followed by instant horrible death, but that's unlikely. Where would this
deadly water come from? How far would it have to travel? You might notice
a large enough freshwater leak while the system is pressurized. You might
notice it automatically. A smaller leak might be harmless. Heat exchange
expert Jane Davidson says single wall systems can be fine, with careful
design and testing.

Now, if you live rural, with your own water well and want to risk the
health of you and your family, you are merely a candidate for a Darwin
award.

Life is full of risks and rewards, but we pee in the woods, use waterless
urinals, fly, walk across streets, drive cars, and so on...

If, on the other hand, you are connected to a city water supply you are
risking your entire neighborhood. And when the city finds out about your
non-code compliant installation, not only will you be in legal trouble
(serious legal trouble if anyone gets sick from your stupidity), your water
will be disconnected until you bring your plumbing into compliance with code.

Worst-case, everyone in Los Angeles dies, except you, but later on, you get
the electric chair for mass murder. Then again, we have check valves, zone
pressure reduction valves, and every once in a while, pipes don't leak.

Dr. Visile says corrupt plumbing code dinosaurs frequently mention this
worst-case scenario: firemen pull a vacuum on the whole city water system
by pumping from hydrants. Everyone dies a few hours later. Maybe we need
to outlaw firemen.

Waste heat recovery can be worthwhile if done safely. Since safe code
compliant methods are availabe, why risk health and legal trouble on a jury
rigged unsafe non-compliant method?

Efficiency, economics, and a desire to take control of your own life.

Nick

 

[Mary Fisher]

That might happen, if you pumped the septic line back into your faucet


Followed by instant horrible death, but that's unlikely. Where would this
deadly water come from? How far would it have to travel? You might notice
a large enough freshwater leak while the system is pressurized. You might
notice it automatically. A smaller leak might be harmless. Heat exchange
expert Jane Davidson says single wall systems can be fine, with careful
design and testing.


Life is full of risks and rewards, but we pee in the woods, use waterless
urinals, fly, walk across streets, drive cars, and so on...


Worst-case, everyone in Los Angeles dies, except you, but later on, you
get
the electric chair for mass murder. Then again, we have check valves, zone
pressure reduction valves, and every once in a while, pipes don't leak.

Dr. Visile says corrupt plumbing code dinosaurs frequently mention this
worst-case scenario: firemen pull a vacuum on the whole city water system
by pumping from hydrants. Everyone dies a few hours later. Maybe we need
to outlaw firemen.


Efficiency, economics, and a desire to take control of your own life.

Hurrah!

And where would 'e-coli, hepatitis, typhoid, cholera, botulin, etc.'come
from anyway?

Mary

 

[daestrom]

I measured U = 30 Btu/h-F-ft^2 for 2 clean still water films...

So you've repeated many times ;-) What I said didn't disagree with that.
In fact I just pointed out that the difference in performance between PEX or
PVC and Cu is probably much smaller than what DVD thought.

My interpretation of chapter 3 of the ASHRAE HOF is that this NTU formula
applies to all types of "counterflow heat exchangers" with rate ratio Z
= Cmin/Cmax = 1. Different ratios, parallel flows, crossflows, and four-
pass shell/tubes would require different formulae.


It also applies to small batches, IMO, up to 12.5 gallons.

Well, you're certainly entitled to your *opinion*, but the truth will be in
the actual performance ;-)

IIRC, Carmen Visile's main patent claim applied to a plumbing technique
that raised the cold supply rate and GFX efficiency by making Z = 1,
compared to merely running the cold water shower supply through the heat
exchanger. (Setting the water heater temp to the shower temp will also
accomplish this.) Dr. Visile was surprised and disappointed that most
plumbing codes require double walls, on the face of it. DIY people (vs
manufacturers) have the right to make their own decisions about this.

Does seem like 'much ado about nothing'. I know that city water mains are
often sitting in ground water and/or run next to sewer lines. And most of
the time the pressure prevents any contamination. But +100 year old water
mains often have a few leaks. Our city has been pursuing finding them to
save the cost of the water (not the health concerns, as there aren't any).

And when the city loses pressure, the city puts out the word via
radio/tv/newspapers that a 'boil water order' is in effect, telling folks
the restored water is not yet safe for drinking (because a loss of pressure
allows in-leakage in these +100 year old water mains).

But technically the code does exist.

IIRC, Dr. Visile was also disappointed about this infringement...

What is Dr. Visile's relation with GFX-Technologies?

daestrom

 

[[email protected]]

$945!!! for a 4x60 'whole house' version??

I liked the "never run out of hot water" on the web site.
If I had 7 foot vertical drop for my greywater, wouldn't it have to be
either a well insulated drain pipe, or close to the water heater inlet for
this to work?

Maybe I misjudge the thermal losses once I've warmed up the ABS pipe.

 

[[email protected]]

... What I said didn't disagree with that.

U = 10 in the previous calc was a measured value for a clean water plastic
pipe immersed in still warm liquid manure with 6% solids, so it's probably
conservative for greywater.

What is Dr. Visile's relation with GFX-Technologies?

He's the inventor.

Nick

 

[[email protected]]

CM wrote:

really this depends how your grey drainage is set up. In areas where
its all open, a leak would be spotted within 24 hours. Districts with
sealed drainage would be different.

A household leak detector would help. Something that sounds an alarm if
more than (say) 1 gallon per month of water flows at a rate of less than
0.0001 gpm (about 10 drops per minute.) Combined with a broken pipe/flood
detector (already commercially available) which shuts off the water supply
if more than (say) 100 gallons of water flows in less than 10 minutes.

Nick

 

[[email protected]]

The closer this is to the hot water heater, the better.

With a few numbers, you may find this matters little.
Then again, it's nice to heat water near the point of use.

A 10C (about 18F) or more rise in inlet water temp will greatly reduce
the energy input burden on the hot water heater.

Or more, if 105 F shower water becomes 100 F in the drain, then heats 55 F
well water to 95 F. With a fully-enclosed shower, 90 F water might heat
well water to 85.

... having the hot water heater and the main sewer drain within
6 feet of each other may require PLANNING in house design.

That isn't required, IMO. The GWHX might be near the water heater, and
cooled greywater might flow a long distance to the drain without
affecting the heat recovery.

In my case due to soil conditions, a basement is impossible, so the
solution is similar to homes/business that do have bathrooms located
below city sewer mains. Prepare a pair of holes in the slab where the
sewer line runs out from under the slab and install a sewage ejector to
pump the waste water up to the top of the GFX pipe, and run the effluent
from the bottom of the GFX pipe back down thru the slab to connect to
the sewer line or septic tank.

Or dig a larger hole and use a flattish greywater helix with no pump.

Nick

 

[Dave Pyles]

SolarFest, The New England Renewable Energy Festival will offer an
in-depth, hands-on photovoltaics workshop during the week of July 10
through 14 2006 in Tinmouth Vermont.

Introduction into Photovoltaics

Monday through Friday, July 10th - 14th

Instructors: Richard Gottlieb, owner, Sunnyside Solar, Inc. & John
Blittersdorf, owner, Central Vermont Solar and Wind, Inc.)
A five-day program that will cover a comprehensive introduction into the
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The mornings will include presentations on solar energy (the resource),
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The afternoons of each day will be hands-on activity based, and will
include site evaluations, tour of the SolarFest site and instruction and
experience installing of all the PV powered systems for SolarFest, an
off-grid festival, which will be held Saturday and Sunday, July 15 & 16.

Workshop Fee $600:
Included in the workshop fee are lunches during the five workshop days,
free on-site camping for the week and weekend (RV camping on the weekend
[during the festival] will be $20) and tickets for both days of
SolarFest. Also included are the Solar Energy International
"Photovoltaics, Design and Installation Manual" and the workshop packet
of materials.

Registration will be limited to 20 participants.

Instructor: Richard Gottlieb established Sunnyside Solar, in
Brattleboro, Vt., in 1979 and has been teaching about photovoltaics
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Instructor: John Blittersdorf is the owner of Central Vermont Solar and
Wind in Rutland, Vt. which sells, services, and installs wind turbines
and solar systems.

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603-847-9049

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Mail in Registration, download, print and mail the form at
http://www.solarfest.org/forms/printable_prefestworkshop.html

SolarFest web site: http://www.solarfest.org

 

[[email protected]]

sewer line runs out from under the slab and install a sewage ejector to
pump the waste water up to the top of the GFX pipe, and run the effluent
from the bottom of the GFX pipe back down thru the slab to connect to
the sewer line or septic tank.

And the energy saved because of the heat is greater than the energy used to
pump all of your hot and cold waste water?

 

[[email protected]]

this makes NO sense at ALL.

Think harder

Nick

 

[daestrom]

Dr C F Vasile responded to me when I wrote to GFXtechnology with
commenting on use of the GFX product in areas with HEAVY clay soils, areas
with no basements and no empty swimming pools. I was talking about
separating greywater from black water in my new house, and he suggested a
sewage ejector as he had lived in similar areas. There is a photo of an
installed GFX in a house in Phoenix with a sewage ejector. Ok these are
often used in basements where the city sewer is higher than the basement
floor. No reason I can see not to have all the waste water route to a
area near the corner of the slab, leaving a hole large enough to put a
standard sewage ejector in place (maybe even dual pumps), pump it up thru
the GFX, then back down thru the slab to goto city sewer/septic tank.
More expensive, yes, but can cut hot water costs dramatically when used
with a tankless water heater. Figure tankless to run $6-$8/mo with 70
something degree inlet water. High 80s inlet water then drops gas usage
to $4-$6/mo or even less.

A word of warning about that. The central principle behind the GFX style
heat exchanger is that the mounting is vertical to all the falling water to
form a thin film around the surface of the drain pipe. This greatly
improves the heat transfer because all of the drain water is within just
millimeters of the pipe wall.

What you're proposing (using GFX on the 'uphill' side') would flood the heat
exchanger completely. Because the drain water side is short (longest are
only about 60"), much of the drain water would pass through without coming
near the pipe wall. Much lower performance.

If the GFX can be on the 'downhill' side, to the eductor, you would probably
get better performance.

daestrom

 

[daestrom]

I liked the "never run out of hot water" on the web site.
If I had 7 foot vertical drop for my greywater, wouldn't it have to be
either a well insulated drain pipe, or close to the water heater inlet for
this to work?

Maybe I misjudge the thermal losses once I've warmed up the ABS pipe.

Well, how much insulation do you have *from* the HW heater to the shower?
That water is hotter still.

I have mine in the basement about 15 feet from the HW heater. And I
insulated the piping from the GFX to the HW heater with your standard
pre-formed foam pipe insulation. Of course *all* my HW piping is insulated
with this stuff already.

The harder thing to insulate was the heat exchanger itself. Took some
'craft-faced' fiberglass batting and wrapped it around as best I could and
tied it off.

daestrom

 

[[email protected]]

Well, how much insulation do you have *from* the HW heater to the shower?
That water is hotter still.

The hot water plumbing is all covered with slip-on black foam chunks.

I have mine in the basement about 15 feet from the HW heater. And I

Basement? Whatzat? I have a crawl space that varies from 18" to 4'.
But the 4' end, where I thought I had a vertical drop, is where the drain
is already two feet below the floor, due to the slope of the pipe.

I am liking the idea of a separate arrangement for the water from the
shower and laundry. If a pump and GFX is truly an energy gain, I might go
for that.

 

[[email protected]]

Suppose we take a shower and collect 100 F greywater in the upper part of
a $30 100'x4" black plastic corrugated drainpipe coil containing 3 $20
100'x1" pieces of black plastic polyethylene pipe, with bidirectional
plug flow, like this, viewed in a fixed font like Courier:

shower
in
| --------->--------------------------------> hot water to shower
| | Tl |
--------- sewer ---------
| | Tg | out | 120F |
| | | | |
| | | ^ | |
| | | | | |
| |1" |4" | | tank |
| | | | | water |
| | | | | heater |
| | | | | |
| | | | | |
| | | | | |
| | |---- | |
| | | | 55F |
--------- P ---------
| ---- Tc |
-----------------| <- |-------------------< cold water supply
----

Now disable the water heater and run a slow, low-power pump P (eg
Grainger's $120 4PC86 (Taco 003-BC4-2) 1/40 HP 120V 0.43A pump) if
Tg - Tl < 5 F and Tg - Tc > 5 F, and enable the water heater again
when Tg - Tc < 5 F. For more efficient heat exchange and protection
from Legionella, we might disable the lower heating element and set
the upper thermostat to 120 F, with a small copper T heat exchanger
to lower the water heater output temp to 105 F when 1.25 gpm flows.

As an alternative, we might use a $69 Shurflo pump.

20 DIM TF(50),TG(50)I=4*ATN(1)
30 VG=1.25*8.33/62.33'volume of 1.25 gallons (ft^3)
40 V4=PI*(2/12)^2'volume of 1' of 4" pipe (ft^3)
50 NP=3'number of 1" pipes
60 V1=NP*PI/(12^2)'volume of 1' of 1" pipes (ft^3)
70 LS=VG/(V4-V1)'simulation segment length (feet)
80 NS=INT(100/LS+.5)'number of simulation segments
100 UPIPE=10*LS*PI/12'U-value of L' section of 1" pipe (Btu/h-F)
110 CFRESH=LS*V1*62.33'thermal capacitance of L' of 1" pipe (Btu/F)
120 CGREY=VG*62.33'capacitance of L' of greywater (Btu/F)
130 CSERIES=CFRESH*CGREY/(CFRESH+CGREY)'caps in series (Btu/F)
140 RC=CSERIES/UPIPE'combined time constant (hours)
150 EXPF=EXP(-1/60/RC)'exponential factor
160 FOR SHOWER = 1 TO 100'simulate showers
170 FOR M=0 TO 119'simulate 10 min shower every 120 minutes
180 IF M>9 GOTO 250'rest vs shower
190 IF SHOWER <100 GOTO 210
200 PRINT 600+M;"'";M,TG(NS-1)
210 FOR S=NS-1 TO 1 STEP -1'pipe section (ns-1<->fw in and gw out)
220 TG(S)=TG(S-1)'move greywater down
230 NEXT S
240 TG(0)=100'move greywater in
250 IF (TG(0)-TF(0))>5 OR TG(0)<60 GOTO 310'no pumping
260 IF SHOWER>49 THEN HEAT=HEAT+CFRESH*(TF(0)-55)UMP=PUMP+1
270 FOR S=0 TO NS-2'shift fresh water up
280 TF(S)=TF(S+1)
290 NEXT S
300 TF(NS-1)=55'move cold water in at the bottom
310 FOR S=0 TO NS-1'rest
320 TFINAL=(TF(S)*CFRESH+TG(S)*CGREY)/(CFRESH+CGREY)
330 TF(S)=TFINAL+(TF(S)-TFINAL)*EXPF'new fresh temp (F)
340 TG(S)=TFINAL+(TG(S)-TFINAL)*EXPF'new grey temp (F)
350 NEXT S
360 NEXT M
370 NEXT SHOWER
380 SHOWERGY=50*10*CGREY*(100-55)'50 showers with no GWHX (Btu)
390 PRINT 500+NP;"'";HEAT,SHOWERGY,HEAT/SHOWERGY,PUMP

Fewer 1" pipes also be reasonably efficient...

# 1" recovered total heat recovery pumping
pipes heat (Btu) heat (Btu) fraction events

1 199439.2 234281.3 .8512811 1570
2 206464.7 234281.3 .8812684 612
3 227208.4 234281.3 .9698102 714

0 55.27685 greywater output during each minute of last shower
1 55.36416
2 55.47161
3 56.77998
4 57.1273
5 57.5333
6 57.95969
7 58.38787
8 58.86457
9 59.37563

.... and a fully enclosed shower can help, eg
http://www.sunfrost.com/efficient_shower.html

Nick

 

[daestrom]

Now disable the water heater and run a slow, low-power pump P (eg
Grainger's $120 4PC86 (Taco 003-BC4-2) 1/40 HP 120V 0.43A pump) if
Tg - Tl < 5 F and Tg - Tc > 5 F, and enable the water heater again
when Tg - Tc < 5 F. For more efficient heat exchange and protection
from Legionella, we might disable the lower heating element and set
the upper thermostat to 120 F, with a small copper T heat exchanger
to lower the water heater output temp to 105 F when 1.25 gpm flows.

As an alternative, we might use a $69 Shurflo pump.

20 DIM TF(50),TG(50)I=4*ATN(1)
30 VG=1.25*8.33/62.33'volume of 1.25 gallons (ft^3)
40 V4=PI*(2/12)^2'volume of 1' of 4" pipe (ft^3)
50 NP=3'number of 1" pipes
60 V1=NP*PI/(12^2)'volume of 1' of 1" pipes (ft^3)

Shouldn't the volume of 1' of "NP" number of 1" pipes be....

V1=NP*PI/(12^2) / 4

Don't think it will change things much, but thought I'd point it out.

70 LS=VG/(V4-V1)'simulation segment length (feet)
80 NS=INT(100/LS+.5)'number of simulation segments
100 UPIPE=10*LS*PI/12'U-value of L' section of 1" pipe (Btu/h-F)
110 CFRESH=LS*V1*62.33'thermal capacitance of L' of 1" pipe (Btu/F)
120 CGREY=VG*62.33'capacitance of L' of greywater (Btu/F)
130 CSERIES=CFRESH*CGREY/(CFRESH+CGREY)'caps in series (Btu/F)
140 RC=CSERIES/UPIPE'combined time constant (hours)
150 EXPF=EXP(-1/60/RC)'exponential factor
160 FOR SHOWER = 1 TO 100'simulate showers
170 FOR M=0 TO 119'simulate 10 min shower every 120 minutes
180 IF M>9 GOTO 250'rest vs shower
190 IF SHOWER <100 GOTO 210
200 PRINT 600+M;"'";M,TG(NS-1)
210 FOR S=NS-1 TO 1 STEP -1'pipe section (ns-1<->fw in and gw out)
220 TG(S)=TG(S-1)'move greywater down
230 NEXT S
240 TG(0)=100'move greywater in
250 IF (TG(0)-TF(0))>5 OR TG(0)<60 GOTO 310'no pumping
260 IF SHOWER>49 THEN HEAT=HEAT+CFRESH*(TF(0)-55)UMP=PUMP+1
270 FOR S=0 TO NS-2'shift fresh water up
280 TF(S)=TF(S+1)
290 NEXT S
300 TF(NS-1)=55'move cold water in at the bottom

This value for TF(NS-1) doesn't agree with your pumping arrangement. The
ASCII art seems to show that the heat-exchanger inlet on the fresh-water
side is a mixture of cold water (55F) and water drawn from the tank bottom.
Cold water flow is 1.25 gpm, tank bottom out flow is <pumpFlow> - 1.25 gpm,
so the mixed temperature at pump discharge is TF(NS-1) = (1.25*55+(<pump
flow> - 1.25)*<tank-bottom-temp>) / <pump flow>

The only way the tank-bottom-temp would be 55F is if the fresh-water hx
outlet returning to the tank were running 55F. Or flow through the
heat-exchanger were less than 1.25 gpm so some cold water entered the tank
bottom. And either would be a bad thing.

310 FOR S=0 TO NS-1'rest
320 TFINAL=(TF(S)*CFRESH+TG(S)*CGREY)/(CFRESH+CGREY)
330 TF(S)=TFINAL+(TF(S)-TFINAL)*EXPF'new fresh temp (F)
340 TG(S)=TFINAL+(TG(S)-TFINAL)*EXPF'new grey temp (F)
350 NEXT S
360 NEXT M
370 NEXT SHOWER
380 SHOWERGY=50*10*CGREY*(100-55)'50 showers with no GWHX (Btu)
390 PRINT 500+NP;"'";HEAT,SHOWERGY,HEAT/SHOWERGY,PUMP

GIGO. Run it again after these changes.

See my other message to "Robert Gammon" about using a GFX-Star (pumped GFX
setup) with a single storage tank. Higher effiency in the heat-exchanger
due to higher flow, but *less* energy recovered because of warmer
fresh-water inlet temperature.

daestrom