Conclusion

It has been mathematically and experimentaly proved that the combination outside insulation plus geothermic heating allows :

to divid the heating bill by 3×3.74 = about 11
to obtain an excellent thermal comfort and to live in tee-shirt in the house with -7ÝC outside
to emit no CO₂ which is a greenhouse effect gas
and even to be completely ecological
and energetically autonomous because due to the small powerd of 1 kW needed by the compressor, this one can be provided thanks to a windmill (for 25000€, you can get a 5 kW one) or a solar sensor of 1 kW, about 6 m²(6000€). Notice that the windmill kW and the solar kW are about the same price.
to keep freshness in summer,
or even to function in reversible mode, that is to say in refreshing mode.

Note that there is no maintenance needed, or maybe a review every decade.
(Mine has been running for twelve years, I opened the lid only to show the system to visitors)