Natural refrigerants and working fluids

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In Denmark, natural refrigerants are the preferred choice, leaving hydrocarbons and steam as the most promising candidates for the selected applications in this project.

Water as working fluid

Water is a promising working fluid for temperatures above 100 °C with several advantages, while sophisticated compression equipment is required to compress the large volume flow rates while being able to handle the large superheating. Centrifugal turbocompressors are able to compress large volumes with pressure ratios of up to three corresponding to temperature lifts in condensation temperatures of up to 30 K. These compressors are typically installed in series for reaching higher temperature lifts, requiring interstage liquid injection and advanced control systems.

The spindle compressor technology is characterized by very high pressure ratios and the possibility for liquid injection, which enable temperature lifts exceeding 150 °C. These compressors are very promising developments, which are expected to reach market entry within the next three to four years. 

Hydrocarbons as refrigerant

Hydrocarbons are another promising approach for the development of high-temperature heat pumps. Hydrocarbons are conventional refrigerants which benefit from the development process of high-temperature systems. The main challenges comprise the compressor optimization, the development of a lubrication system, and the cycle design as well as the optimization considering the specific boundary conditions and component constraints. 

Novel approaches

In addition to the systems using hydrocarbons and steam, there are some further developments based on novel approaches, e.g., technologies using a mixture of steam and ammonia. The advantage of this technology is the high temperatures, and limited efficiencies between 60 % and 70 % and a relatively high investment can be mentioned as barriers.

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