Either. I am talking about heat pumps. The efficiency formula is exactly the same. The difference is that ground water stays at a consistent 12-15 degrees C IIR

Either. I am talking about heat pumps. The efficiency formula is exactly the same. The difference is that ground water stays at a consistent 12-15 degrees C IIRC. That is close to what we as humans like to live in, so the efficiency is relatively high heat round. In the meantime air temperature fluctuates by quite a bit. The main drawback of using ground water as your heat source/sink is that it is expensive and costly to maintain relative to a resistive coil with electricity running through it.