R717 (Ammonia) is the most suitable refrigerant for usage in a heat pump in industrial environments. Ammonia has a high efficiency and can easily be applied below temperatures of 80 °C. Expectations are that this range will soon be widened up to temperatures of 90 °C. Furthermore, Ammonia is a natural refrigerant that does not contribute to the greenhouse effect. Ammonia has been frequently used as a refrigerant in refrigeration systems. The experience and knowledge that has been built up due to this, can be used when installing heat pumps with Ammonia as a refrigerant. It is inflammable and toxic but due to its strong odor, leakages can be detected fast. An Ammonia installation should meet the requirements of PGS-13.
R744 (CO2) is another natural refrigerant. It is used in refrigeration installations, often in combination with Ammonia compressors in order to decrease the amount of Ammonia in the system. For low temperature freezer applications a system can be built up of CO2 compressors combined with Ammonia. For CO2 the transcritical temperature is 31 °C. Above this temperature condensation does not take place at a constant temperature, instead it occurs over a temperature range (temperature glide). Therefore the heat pump can only be applied in situations where a potential user allows for heating at non-constant temperature. Water is a suitable user. Some heat pumps do function above the supercritical temperature: CO2 supercritical heat pumps.
R718 (Water) can also be used as a refrigerant. Water has the advantages that it is easily obtained and does no damage to the environment. It can only be applied at high temperatures (> 100 °C). At these temperatures pressures in other refrigerants can become too high. A disadvantage of the use of water is its low density in the gaseous state. A relatively high compressor capacity is necessary because to this.
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