GFX vs home brew

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I keep wondering about the efficacy of a home brew system that is
1. Not patented 2. Not sponsored by the DOE 3. is not reliant on the RAPID fall of water thru a vertical METAL tube.
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That's because you are ignorant :-) Ignorance can be cured...
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

So a student is smarter, wiser than a PHD with a patent???
Sometimes yes, as the creative mind is at its peak in the early 20s.
However, physics clearly tells us that
1. Metal conducts heat FAR more efficiently than plastics 2. Water falls in a thin vertical film FAR faster than water that is flowing horizontally in a pipe.
OK, GFX doesn't help with heat recovery for a bath, but great for hot showers, dishwashing, clothes washing.
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Robert Gammon wrote:

Nick-
Your heat exchanger concept may or may not be better than the GFX but pissing folks off in a relevant ng is no way to "market" your device.
The GFX has some installation (retrofit) issues but after 30 years as an ME when I think of heat exchangers I rarely think of "plastic".
cheers Bob
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But plastic is FAR cheaper, and metal doesn't help much with a layer of crud and slow-moving water on both sides.

The GFX does well with its small surface...

...60% is not "great," IMO.
Here's what physics tells us on page 3.4 of the 1993 ASHRAE HOF:
1. E = (Thi-Tho)/(Thi-Tci) when Ch = Cmin and = (Tco-Tci)/(Thi-Tci) when Ch = Cmin, where
Ch = hot fluid capacity rate, Btu/h-F Cc = cold fluid capacity rate, Btu/h-F Cmin = smaller of the two rates Th = terminal temp of hot fluid (F). Subscript i indicates entering condition; o indicates leaving condition. Tc = terminal temp of cold fluid (F)...
2. Number of Exchanger Heat Transfer Units NTU = AUavg/Cmin.
3. Capacity rate ratio Z = Cmin/Cmax.
Generally, the heat transfer effectiveness can be expressed for a given exchanger as a function of NTU and Z: E = f(NTU,Z,flow arrangement). The effectiveness is independent of the temps in the exchanger.
For any exchanger with Z = 0 (where one fluid undergoes a phase change, eg in a condenser or evaporator), E = 1-e^(-NTU).
For parallel flow exchangers, E = [1-e^(-NTU(1+Z))]/(1+Z).
For counterflow exchangers, E = [1-e^(-NTU(1-Z))]/[(1-Z(e^(-NTU(1-Z))], = NTU/(NTU+1), when Z = 1.
For instance, if we use 50 gallons per day of hot water in short bursts and Cmin = Cmax = 50x8.33/24h = 17.4 Btu/h-F and A = 78.5 ft^2 (a $60 300' piece of 1" polyethylene pipe with a 50 year guarantee) and U = 10 Btu/h-F-ft^2 (with slow-moving greywater and crud outside and slow-moving fresh water inside), NTU = 78.5x10/17.4 = 45.2, and E = 0.98.

Think harder :-)
Cheers,
Nick
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BAAMMMMM! Kick it up a notch.
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AstickfortheMULE wrote:

Nick uses a LONG, SLOW moving body of water to extract heat. So in many ways, it resembles a air conditioning condenser coil. Both exchange heat relatively slowly and rely on a LONG path to effect the heat exchange. Ok, Nick's will work, 300 ft of tubing surrounding a large tube holding the greywater will transfer significant heat from greywater to the potable water.
Nick's heat exchanger can be installed in almost any orientation, but horizontal seems to be his desire. His heat exchanger will need to be cleaned out periodically of gunk, especially if toilets drain thru the same heat exchanger. He argues that his will extract more heat than the GFX, and that may be true, but he will have a much larger unit (300 feet of 1 inch tubing is more than 6 feet in length when stacked as a single layer around a larger pipe that holds the greywater)
The beauty of the GFX, is that it is metal, it can be stacked or daisy chained with pumps to extract even more heat in a smaller space. The illustrations on the web site show various parallel installations, but I wonder about the option of taking two of the 48" units, placing them side by side, and pumping effluent from the first to the top of the second before the wastewater flows on to the city sewer/septic tank.
Think I'll write the GFX team about this idea.
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It also resembles a chair, if you wrap enough cotton gauze around both :-)

Not a good idea. It wouldn't make a good wheelchair either.

Physics clearly tells me so. She seems to lie to you. How fickle.

You seem confused. In this condition, many people read more carefully. Some even stop talking and listen :-)
The 1" pipe would be in 3 100' pieces inside a 100' x 4" black plastic corrugated drainpipe which can be in 1) a 2' diameter x 6' tall coil or 2) a 7' OD x 2' ID x 4" tall flat spiral under a basement ceiling, which uses less floorspace. Nick
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wrote:

Actually, mis-applied formulae from a text book seems to be what is talking to you again Nick ;-)
If you run your same calculations with a simple flow rate of 2 gpm (a typical shower flow), what do your 'physics' tell you?
The fact that the answer is much different than when you run your 50 gpd flow rate numbers should prompt you to pause and 'thick harder'.
While I agree that 'batch' flows that do not fully purge your apparatus will give you some improvements, we haven't seenn any of your 'numbers' for that. Quoting ASHRAE formulae that are intended for continuous flow when you *know* you won't have that sort of flow rate is a waste of everybody's time.
daestrom
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Here are some numbers for that. If 100' of 3 1" pipes (polyethylene, with a 0.07" wall thickness) has 78.5 ft^2 of surface with U = 10 Btu/h-F-ft^2, 10' has 78.5 Btu/h-F...
20 UPIPEx.5'U-value of 10' section of pipe (Btu/h-F) 30 CFRESH=1.25*8.33'thermal capacitance of 10' of fresh water (Btu/F) 40 VGREY*3.14159*(2/12)^2'volume of 10' of greywater (ft^3) 50 CGREY=VGREY*62.33-CFRESH'thermal capacitance of 10' of greywater (Btu/F) 60 FOR SHOWER = 1 TO 1000'simulate showers 70 FOR M=0 TO 359'simulate 10 min shower + 350 min rest 80 IF M>10 GOTO 170'rest vs shower 90 TF(0)=TF(1)'move fresh water up from below 100 TG(0)=(100*CFRESH+TG(0)*CGREY)/(CFRESH+CGREY)'move greywater in at the top 110 FOR S=1 TO 8'pipe section (9<->fresh water in and greywater out) 120 TF(S)=TF(S+1)'move fresh water up 130 TG(S)=(TG(S-1)*CFRESH+TG(S)*CGREY)/(CFRESH+CGREY)'move greywater down 140 NEXT S 150 TF(9)U'move cold water in at the bottom 160 TG(9)=(TG(8)*CFRESH+TG(9)*CGREY)/(CFRESH+CGREY)'move greywater down 170 FOR S=0 TO 9'rest 180 HEATFLOW=(TG(S)-TF(S))*UPIPE/60'heatflow into fresh water (Btu) 190 TF(S)=TF(S)+HEATFLOW/CFRESH'new fresh temp (F) 200 TG(S)=TG(S)-HEATFLOW/CGREY'new grey temp (F) 210 NEXT S 220 NEXT M 230 NEXT SHOWER 240 FOR S=0 TO 9'results 250 PRINT S,TF(S),TG(S) 260 NEXT S 270 E=(TF(0)-55)/(100-55)'effectiveness 280 PRINT E
pipe fresh water greywater section temp (F) temp (F)
0 93.32178 93.3218 1 90.556 90.55602 2 87.60851 87.60853 3 84.60492 84.60494 4 81.62819 81.62821 5 78.71178 78.71181 6 75.86447 75.8645 7 73.08838 73.0884 8 70.3852 70.38522 9 67.75679 67.75681
effectiveness
.8515951
The fresh and greywater temps are very close, about 6 hours after a shower, since the pipe time constant is much shorter (less than 8 minutes.) These results wouldn't change much with only a half-hour between showers. The effectiveness would be higher for shorter bursts.
Maybe it's worth adding 2 more $20 100' pieces of 1" pipe (altho that would be a tight squeeze), or a handheld showerhead that only runs when a button is pushed. Who sells them?
Nick
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Oops. Fixing lines 100, 130, and 160 improves the effectiveness to 88%.
20 UPIPEx.5'U-value of 10' section of pipe (Btu/h-F) 30 CFRESH=1.25*8.33'thermal capacitance of 10' of fresh water (Btu/F) 40 VGREY*3.14159*(2/12)^2'volume of 10' of greywater (ft^3) 50 CGREY=VGREY*62.33-CFRESH'thermal capacitance of 10' of greywater (Btu/F) 60 FOR SHOWER = 1 TO 1000'simulate showers 70 FOR M=0 TO 359'simulate 10 min shower + 350 min rest 80 IF M>10 GOTO 170'rest vs shower 90 TF(0)=TF(1)'move fresh water up 100 TG(0)=(100*CFRESH+TG(0)*(CGREY-CFRESH))/CGREY'move greywater in at the top 110 FOR S=1 TO 8'pipe section (9<->fresh water in and greywater out) 120 TF(S)=TF(S+1)'move fresh water up 130 TG(S)=(TG(S-1)*CFRESH+TG(S)*(CGREY-CFRESH))/CGREY'move greywater down 140 NEXT S 150 TF(9)U'move cold water in at the bottom 160 TG(9)=(TG(8)*CFRESH+TG(9)*(CGREY-CFRESH))/CGREY'move greywater down 170 FOR S=0 TO 9'rest 180 HEATFLOW=(TG(S)-TF(S))*UPIPE/60'heatflow into fresh water (Btu) 190 TF(S)=TF(S)+HEATFLOW/CFRESH'new fresh temp (F) 200 TG(S)=TG(S)-HEATFLOW/CGREY'new grey temp (F) 210 NEXT S 220 NEXT M 230 NEXT SHOWER 240 FOR S=3 TO 9'results 250 PRINT 300+S;"'";S;TF(S),TG(S) 260 NEXT S 270 E=(TF(0)-55)/(100-55) 280 PRINT 410;"'";E
pipe fresh water greywater section temp (F) temp (F)
0 94.53323 94.53326 1 92.54844 92.54847 2 90.32916 90.32919 3 87.93309 87.93311 4 85.42671 85.42674 5 82.85161 82.85163 6 80.22588 80.2259 7 77.55527 77.55529 8 74.8424 74.84241 9 72.08957 72.0896
effectiveness
.8785163
Nick
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wrote:

Not bad, apparantly you've chosen a flow rate and section length so the time step corresponds to exactly one section length.
Because the greywater drain cross-section is so much larger than the freshwater, your Cmin/Cmax ratio ends up being about 0.24 (IIRC a 4-inch pipe with three 1-inch pipes inside). So a high efficiency of 87% doesn't really tell us how much energy we're saving. While your efficiency is 87%, it looks like you're still putting (72-55)*1.25*8.337 BTU/minute down the drain. Out of a total of 468.6 BTU/minute needed to heat 1.25 gpm from 55 to 100, that's nearly 38% of the heating.. Print out the data *during* the last shower, not 350 minutes later. I'd like to see what the greywater outlet temperature is while it's flowing. I think it's going to be a lot cooler than 72, but not sure. Better yet, print out the freshwater and greywater outlet temperatures *during* the ten time steps of the last shower.
After all, it is the temperatures out *during* flow that matter. The temperatures at the end of the stagnation period only tell us the initial startup point for the next shower. How quickly they change *during* the shower, and in what direction would be more telling.
After all, if the freshwater outlet during the shower really is at 94F, and the greywater really leaves at 72F, then you don't have conservation of energy (freshwater side picks up (94-55)*1.25*8.33 = 406 btu/min, while the greywater side gives off (100-72)*1.25*8.33)1 btu/min). That's a clue that something is wrong with these results.
daestrom
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How about the fresh water outlet temp? Line 100 below accumulates the heat energy that needs to be added during the last shower...
20 UPIPEx.5'U-value of 10' section of pipe (Btu/h-F) 30 CFRESH=1.25*8.33'thermal capacitance of 10' of fresh water (Btu/F) 40 VGREY*3.14159*(2/12)^2'volume of 10' of greywater (ft^3) 50 CGREY=VGREY*62.33-CFRESH'thermal capacitance of 10' of greywater (Btu/F) 60 FOR SHOWER = 1 TO 1000'simulate showers 70 FOR M=0 TO 359'simulate 10 min shower + 350 min rest 80 IF M>9 GOTO 200'rest vs shower 90 IF SHOWER <1000 GOTO 120 100 RHEAT=RHEAT+1.25*8.33*(100-TF(0))'reheat energy required 110 PRINT 300+M;"'";M,TF(0),RHEAT 120 TF(0)=TF(1)'move fresh water up 130 TG(0)=(100*CFRESH+TG(0)*(CGREY-CFRESH))/CGREY'move greywater in at the top 140 FOR S=1 TO 8'pipe section (9<->fresh water in and greywater out) 150 TF(S)=TF(S+1)'move fresh water up 160 TG(S)=(TG(S-1)*CFRESH+TG(S)*(CGREY-CFRESH))/CGREY'move greywater down 170 NEXT S 180 TF(9)U'move cold water in at the bottom 190 TG(9)=(TG(8)*CFRESH+TG(9)*(CGREY-CFRESH))/CGREY'move greywater down 200 FOR S=0 TO 9'rest 210 HEATFLOW=(TG(S)-TF(S))*UPIPE/60'heatflow into fresh water (Btu) 220 TF(S)=TF(S)+HEATFLOW/CFRESH'new fresh temp (F) 230 TG(S)=TG(S)-HEATFLOW/CGREY'new grey temp (F) 240 NEXT S 250 NEXT M 260 NEXT SHOWER 280 SHOWERGY=1.25*10*8.33*(100-55)'total heat energy with no gwhx 290 PRINT RHEAT,SHOWERGY,1-RHEAT/SHOWERGY
time fresh cum reheat (min) temp (F) (Btu)
0 94.56091 56.6345 1 92.93514 130.1973 2 91.38136 219.9389 3 89.96538 324.4244 4 88.72086 441.8685 5 87.6472 570.492 6 86.72784 708.6885 7 85.94302 855.0568 8 85.27464 1008.385 9 84.70704 1167.623
cum reheat shower effectiveness (Btu) heat (Btu) (fraction)
1167.623 4685.625 .7508075
Nick
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wrote:

More like I expect. Your system's outlet temperature drops from the high of 94F the longer you run the shower. The fact that it's a 'batch' process allows you to get better performance than the steady-state parameters would allow.
But show the greywater too. As I said before, if the greywater is giving off less energy than the freshwater is picking up, then something's broke. I notice you chose to show the more optimistic of the two numbers. I'll bet the greywater shows more energy going down the drain than physics would allow if these numbers were accurate.
So then it's just a matter of adjusting gwhx versus shower time to keep performance high. Too long a shower, or too short a gwhx and performance drops.
How would two showers spaced fairly close together look? Looks like this would support four, 10-minute showers a day, spaced 6 hours apart right now.
daestrom
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wrote: <snip>

Oh, I see you had done this in another branch. I'll go there and see "what's up"
daestrom
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snipped-for-privacy@ece.villanova.edu wrote:

[snip]
Question, How large a space does your heat exchanger occupy?
3 PE pipes inside a larger PE pipe is NOT very flexible. Bend radius for this configuration is measured in feet.
It not very thick, to be sure, but to collapse this into a practical shape, (100 linear feet of tubing in the rafters of a basement will NOT fit in most houses), you'll need to bend this into a coil of say about 5 or 6 feet in diameter, several feet high. You quoted some figures for the dimensions of the assembled unit, but now those dimensions as I recall them don't make sense.
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Either 1) 2' diam x 6' tall, or 2) 7' OD x 2' ID x 4" tall.

About 1'.

Nobody said it would, nitwit :-)

Wrong again. The drainpipe is about 4.25" OD.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

[snip]
Question, How large a space does your heat exchanger occupy?
3 PE pipes inside a larger PE pipe is NOT very flexible. Bend radius for this configuration is measured in feet.
It not very thick, to be sure, but to collapse this into a practical shape, (100 linear feet of tubing in the rafters of a basement will NOT fit in most houses), you'll need to bend this into a coil of say about 5 or 6 feet in diameter, several feet high. You quoted some figures for the dimensions of the assembled unit, but now those dimensions as I recall them don't make sense.
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snipped-for-privacy@ece.villanova.edu wrote:

No kidding. Somebody seems to need a definition of "greywater".
--
derek

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Derek Broughton wrote:

greywater == all water going down a drain EXCEPT water from Toilets
blackwater == all water from toilets
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