For the last 7 years refrigerant C02 has been used for domestic air to water heat pumps for domestic hot water in Japan.
Major manufacturers like Hitachi, Daikin, Mitsubishi, Toshiba, Sanyo have been selling them by the 100,000 for years in Japan.
The Govenment in Japan provide yen incentive for purchase of this type of water heater.

As this is old technology in Japan we can expect this type of equipment to be available soon in Europe

Are there any service engineers in Japan who can provide some hands on technical experiance for us European engineers who have no Co2 heat pump experiance.