The author does not mention if their system is air-sourced or ground-sourced (aka geothermal) - ground sourced systems typically use 25-50% less energy and are

The author does not mention if their system is air-sourced or ground-sourced (aka geothermal) - ground sourced systems typically use 25-50% less energy and are especially well-suited to places with colder temp extremes where an air-sourced system becomes quite inefficient. Downside is more expensive to install (need to bury a bunch of tubes in your yard) [1] http://large.stanford.edu/courses/2016/ph240/holmvik1/docs/doe-ee-0385.pdf http://large.stanford.edu/courses/2016/ph240/holmvik1/docs/d...