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...
daestrom wrote:

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.

Here are some numbers for that...

Oops. Fixing lines 100, 130, and 160 improves the effectiveness to 88%.

20 UPIPE=78.5'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=10*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 M10 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)=55'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


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*8.33=177 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=291 btu/min). That's a clue
that something is wrong with these results.

daestrom