Thermosiphon: funny name for funny device.
Indeed, in the Arctic, permafrost has a constant temperature, on the first meters, of about -6 degrees. But with global warming, summer periods will increase this temperature. However, the calculation of foundations in the permafrost imposes a reference temperature. And that’s where thermosyphons come in.
These are refrigerators that allow a heat exchange between the deep ground and the surface. So they work like a refrigerator, but as they are not electrically powered, the pump is based on the principle of Archimedes.
The greater the difference between the surface and the subsoil, the better the operation will be. The thermosiphon will therefore allow to cool the soil, and keep it at a temperature below the design temperature.
It is a technique commonly used in arctic regions, particularly in northern Canada and Russia where they have existed since the 1960’s.