The potential of water as a refrigerant for Heat Pumps - past, present and future approaches [7]

The paper starts with an overview of past projects and refrigeration machines where water (R718) was used as a refrigerant. Furthermore, the paper introduces various applications focusing also on ad- and absorption technologies but mainly on compression systems of refrigeration systems including heat pumps.
In the second part of the paper a low capacity centrifugal compressor system based on using water as refrigerant is introduced. The working principle of the machine with a number of various energy efficient operational modes gets explained and the machines performance under these conditions is discussed.
Finally, favorable heat pumping applications get specified resulting. These findings are confirmed by field test data, as machines are in operation since many years.
Finally, an outlook is given, where water as a refrigerant of heat pumps can expect a promising future contributing to reduce the global warming impact of the refrigeration industry.