Recent developments indicate that CO2 and NH3 are the most promising refrigerants for future heat pumps. Today two high pressure compressor technologies are offered with an attractive combination of high delivery temperature and high COP which is ideal for district heating purposes: CO2 (carbon dioxide/R744) transcriticalpiston compressorheat pumps and new NH3 (ammonia/R717) heat pumps using Vilter’s single screw compressor. Also the twin screw compressor technology using NH3 is under strong development and is expected to be introduced within a short term . In Denmark CO2 compressor heatpumps have been installed in Frederikshavn and Marstal in combination witha CHP plant and a high temperature NH3 single screw heat pump is under construction in Drammenin Norway (Nielsen 2011). But as the technology is still rather new, experiences about efficiencies and dependability is still to come.

The role of large scale heat pumps for short term integration of renewable energy.pdf

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