Super concrete achievement as I like them!
How did you make the exchanger?
If I guess correctly you have passed a garden hose ("cold cold") under the grating and that if feeds the mixer with "hot cold"? It is a good idea because all the systems which existed previously (exchanger on the evacuation pipe with plate exchanger, spiral or cylindrical ...) posed serious problems of clogging and their price was prohibitive! The subject of the recovery of calories in the sewer has already been mentioned many times on this forum but no solution was satisfactory to me. Yours seems to be a game-changer!
Also I really like your temperature measurement process! We can see the rise in T ° of cold water which is preheated by a good 10 ° C (so roughly half of what it takes)
Have you been able to estimate the kWh saved with each on / off system shower? A (quick) shower is around 2 kWh, a comfort shower is 5 to 6 kWh (and certainly more if you take it at 2!
) ... So if you can save 50% of kWh (linear at temperature rise) that would be very good!
If you want to see the calculations, they are here:
plumbing-and-health / price-reel-to-a-bath-or-of-a-shower-in-the-water-and-heat-t12727.html