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daestrom wrote:

I'd like to see what the greywater outlet temperature is while it's
flowing.

How about the fresh water outlet temp? Line 100 below accumulates
the heat energy that needs to be added during the last shower...

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 M9 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)=55'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


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