However, there is pressure to limit the use of HFCs. The UK Government, for example, does not regard HFCs as a sustainable technology in the long term. The absorption cycle refrigerator is a potential competitor to vapour compression systems in the short term. Very popular in Japan for air conditioning applications and for use in boats and caravans. The COP is typically less than 1, i.e. much lower than vapour compression systems, but it uses heat rather than mechanical energy as the high grade energy input.
Heat is much cheaper.
The choice of the fluids is critical. Many forms of gas cycle refrigeration are possible but the most common is the reversed Brayton working in open cycle with air as the working fluid. Less efficient than vapour compression systems but the difference reduces as the output temperature falls. However, practical devices operate only approximately as Stirling cycles and their implementation has been disappointing. The displacer remains stationary and the piston descends.