Hi ThMihov, welcome to ER
I envy how far you've gotten with this project
I can't wait to see the results!
I see that what you have made is a small heat buffer. I'm not sure of the heating needs that your home will have, but a 60-liter tank may not be much. A long time ago I started a thread on
heat accumulators (which by now has lost its photos), but to cut it short:
- With a slightly larger, and well insulated, tank you will have heat stratification - warmer water at the top and cooler water at the bottom
- If you keep the copper coils in the lower part of the tank, transferring heat to the cooler water will be more efficient
- Taking the warmer water from the top of the tank will make heating your space more efficient, possibly allowing you to run the HP less often
- Instead of 1 coil from 8mm tube, connect 2 or 3 coils from thinner tubes in parallel - lower pumping losses and possibly more surface area.
- Keep the tank indoors - the higher ambient temperature will reduce heat loss, and whatever heat does escape will warm the house, not the outdoors.
These would be for bumping the efficiency if you ever go to a new version. It might turn out that the tank you have already covers your needs.