The high environmental impact associated to the refrigeration sector has favoured, from the viewpoint of energy efficiency,
 the use of more efficient refrigeration methods.  Double-stage compression refrigeration systems are among these methods,
 which were developed in the XIX century, and at the moment, are mainly used in commercial refrigeration in medium- and 
low-temperature applications. Double-stage systems are an efficient solution, from the viewpoint of energy consumption, 
since they permit to produce cold with COP and cooling capacities higher than the ones resulting from single-stage 
compression systems.

This Doctoral Thesis tackles an in-depth experimental study of double-stage compression systems based on ‘compound’ 
compressors, for what an industrial-type facility has been developed. From the obtained data, the desuperheating between 
compression stages using the direct liquid injection system and the liquid subcooling using the subcooler system have been 
analysed. The analysis is based on the experimental study of the plant operating with the previous mentioned systems in 
comparison with the cycle operating without inter-stage systems. The refrigerating fluid used to carry out the tests was 
the HFC-404A in an evaporating temperature range between -36 and -20ºC and in a condensing temperature range between 30 
and 47ºC.

Furthermore, the experimental results and a comparative analysis of the plant while operating with the most usual 
refrigerants in commercial refrigeration for medium- and low-temperature applications, the HFC-404A and the HFC-507A, 
are also presented.