An important side note, his "lift" (the difference between his hot and cold side) was like 17 degrees F... A higher pressure air compressor will do more, but by carefully selecting your refrigerant to have a boiling point that changes rapidly with pressure, a heat pump can easily have a lift of 70 degrees, which is needed to heat a house in the winter, while still having manageable pressure ranges.

Tangentially, to convert this open loop system he has set up from cooling to hearing you'd have to move the radiator from outside to inside. To convert a heat pump, you just need one valve at the compressor that reverses the input and output, pretty much.