Can geothermal be used during a harsh Winter?

Although many parts of the country experience seasonal temperature extremes — from scorching
heat in the summer to sub-zero cold in the winter—a few feet below the earth’s surface the ground
remains at a relatively constant 55 degrees. So when the outside temperature is below freezing, a
geothermal heat pump should have no trouble extracting enough heat to keep your home 72 degrees or
more. Even when the ground freezes, the frost usually only extends three or four feet below the surface
which is not deep enough to effect the geothermal loop pipes which should be buried at least 7 feet
below the surface.