In the most applications, a good CO2 heat pump is in a class of its own. The reason for this is that it can heat liquid to much higher temperatures than other refrigerants can. This increases energy efficiency, as other heat pumps need assistance from a fossil or electric heat source to heat the liquid all the way to the desired temperature. If you utilize this advantage on both the cold and hot side of the heat pump, for example, you can get free domestic hot water at a hotel in the summer when delivering cold water for comfort cooling. In such cases, you can achieve a COP (Coefficient of Performance) as high as 8-9. This means that for every kW of electricity used, you get 8-9 kW out.