An independent academic study on the Energy Efficiency of Carbon Dioxide (CO2) in Small Commercial Cooling Applications, comes to the conclusion that caution should be given regarding claims – especially from commercial sources – of energy improvements for CO2-technology between 18 and 37 % for example, in order to get objective results from such comparisons.
The study has compared CO2-technology with HFC-technology for light commercial cooling applications, on the base of thermodynamic considerations and on a literature review. There are very few explanations for the claimed advantages of CO2-technology compared to the so-called baseline HFC-technology. However, a number of often non disclosed information, like the choice of the compressor, or of its motor, could have influenced considerably the energy efficiency in both 2 cases.
Basically, using data from optimized CO2-technology together with those from standard non-optimized HFC-technology cannot produce objective comparison results.
Indeed, for thermodynamical reasons, the CO2 cycle is intrinsically less efficient than classical cycles with standard refrigerants like HFCs. Such cycles have reasonable thermodynamic efficiencies, despite the fact that they were firstly price-optimized, so that they could be further energy optimized.
When trying to substitute this technology by the CO2 cycle it is definitely necessary to modify it further on, in order to be able to compete with the standard HFC cycle, so that optimizing CO2-systems only can achieve the same energy consumption than existent HFC-systems. When those would be further energy-optimized they would therefore be largely more energy efficient than CO2-technology.
The only situations when CO2-systems can show a better efficiency are in heat pump applications where the high temperature from the compressor side can be utilized for certain heating tasks (like in heat pumps), but this is not the case in commercial cooling when heat is absorbed from a cold room and directly rejected to the ambient air.