Why use water as a refrigerant?
Water has a GWP of zero, no ozone depletion potential, and no toxicity or flammability, so it is not affected by HFC quotas, PFAS rules, or flammable refrigerant safety limits. It also has a very high latent heat of vaporization. These properties make it attractive for long-life equipment where owners want to avoid future regulatory risk. For building owners and data center operators with sustainability targets, choosing water avoids the reporting and compliance burden associated with fluorinated refrigerants.

How do water vapor compression chillers work?
In water vapor compression chillers, a small fraction of the water evaporates under deep vacuum, cooling the remaining water, and a high-speed compressor raises the vapor pressure so it can condense at a higher temperature. In the eChiller, about 1% of the water evaporates, and the temperature rises from 16 °C to 52 °C across the compressor. Because pressures are so low, the CIBSE Journal notes that EN 378 certification and F-gas leak monitoring are not required. Because the refrigerant is water, any leak simply releases water vapor, which removes environmental and safety concerns associated with other refrigerants.

Where are R-718 chillers used?
Water-based chillers suit applications that need chilled water at 16 °C or above, such as data center and IT room cooling, chilled beams, and process cooling. Siemens and BT were early adopters of the eChiller, with BT operating high-density server systems cooled by eChillers since 2017 in Hamburg. As data centers move to warmer chilled water temperatures, the application range for R-718 chillers is widening. Higher chilled water temperatures in modern data centers increase the number of hours when free cooling is possible.

What role do absorption chillers play?
Absorption chillers use water as the refrigerant and lithium bromide as the absorbent, driven by heat rather than electricity. They are widely used in district cooling, combined heat and power plants, and industrial sites with waste heat. Absorption and adsorption systems make up a significant share of R-718 use, especially in Asia and the Middle East. Large absorption chillers can deliver several megawatts of cooling and are common in Japan, China, and South Korea.

How are water vapor heat pumps used in industry?
Mechanical vapor recompression (MVR) and steam-generating heat pumps compress water vapor to produce steam or high-temperature heat for evaporation, drying, and distillation in food, dairy, chemical, and pulp and paper industries. These systems can recycle waste heat and replace fossil-fuel boilers, supporting industrial decarbonization. Research and demonstration projects in Europe are extending water vapor heat pumps to higher temperatures and capacities. MVR systems are already widely used in evaporators for dairy, sugar, and chemical processing, and newer designs aim to deliver steam directly for broader process use.

What efficiency can R-718 chillers achieve?
The eChiller achieves an EER of 3.4 at 35 °C ambient and 7.4 at 21 °C, with a seasonal EER above 11 in northern German conditions. Performance is best when chilled water temperatures are relatively high and condensing temperatures are moderate. This makes R-718 chillers well suited to temperate climates and data center applications. Seasonal efficiency is especially important for data centers, which run cooling systems all year.

What additives are used?
Water used as a refrigerant can include corrosion inhibitors to protect metal components, and binary mixtures may be used in absorption systems. Water treatment is important to prevent scaling, corrosion, and biological growth. Specialty fluid suppliers provide inhibitor packages and monitoring services.

What are the limitations of R-718?
Low vapor pressure means large vapor volumes and the need for large or very high-speed compressors. Water freezes at 0 °C, which limits use to applications above freezing unless special technology is used. Capital costs can be higher than conventional chillers, and the supplier base is small. Manufacturers are working to reduce compressor size and cost through new turbo-compressor designs.

How does regulation affect the market?
HFC phase-down rules and the EU F-gas Regulation’s 2050 HFC phase-out encourage technologies without fluorinated gases. PFAS concerns around some HFOs also increase interest in natural refrigerants. Energy efficiency requirements for data centers and buildings favor high-efficiency free-cooling chillers. Building certification schemes also reward the use of zero-GWP refrigerants.

Which R718 refrigerant market segments are growing fastest?
Industrial high-temperature heat pumps; data center cooling; water vapor compression systems with centrifugal and multi-stage compressors; district cooling and utilities; and food processing and cold chain applications are the fastest-growing segments. Industrial heat pumps for steam generation in food, dairy, and chemical plants are expected to grow fastest, as companies look for ways to replace fossil-fuel boilers with electrified process heat.