It doesn't really compare since ground-source/geothermal systems are designed to work with a smaller temperature difference (since the earth stays about 50F mos

It doesn't really compare since ground-source/geothermal systems are designed to work with a smaller temperature difference (since the earth stays about 50F most of the year a few feet down). Business wise, if this really works at 2COP at 5F, this might take over most of the market served by ground source heat pumps though.