This project has been creeping along very slowly. Mostly because we don't have enough food to fill the 160 liter freezer, but we finally turned it on and moved what we had, so that the freezer part of our fridge could be defrosted (first time in 2 years).
Before the move, I insulated the back side of the chest freezer with foam (~7mm thick) then styrofoam with reflective coating on one side (~5mm thick).
Before:
After:
I also added wood spacers to move the condenser coils an extra 15mm away.
Underneath I only had enough insulation for part of the compressor compartment:
After a few days of running for the temperature to stabilize (inside temp between -15C and -17C), I checked the power consumption: 2.866 kWh over 234.1 hours, of which 38.19h was on-time. This was on the lowest temp setting on the t-stat (#1 out of 1-6). Today I put the freezer on a timer, so that it has power only during night hours between 2200h-0600h, plus 1h in the middle of the day between 1300h-1400h. I also bumped the t-stat to #2, but I will be monitoring the performance - possibly I can go back to setting #1 and/or resign from the 1300-1400 on-time. This should be easier once I source some foam insulation for the sides, bottom and top.