See below to understand how a CO2 heat pump works
How does a CO2 heat pump work? A CO2 heat pump works like a refrigerator in reverse. The pump contains a fan that forces air through an evaporator that contains a refrigerant. The heat in the air passes through the evaporator and is absorbed by a natural refrigerant (CO2), which is ozone friendly and totally inert.
The warm gaseous refrigerant is circulated in the system via a compressor (electrically powered). As it passes through the compressor, its pressure rises, as does its temperature. This hot refrigerant then passes through a heat exchanger to heat the water, which is finally pumped to the storage tank.