Subcooling with AC and adiabatic gas cooling for energy efficiency improvement: field tests and modelling of CO2 booster systems

In the last decade several plant configurations and components have been proposed to increase the efficiency of CO2 refrigeration systems. Among these, subcooling is considered a simple but effective solution, together with the employment of adiabatic cooling systems at the gas cooler. In this work, a fully instrumented CO2 booster plant installed in a supermarket is considered, to compare parallel compression, subcooling and adiabatic cooling. Subcooling is performed taking advantage of chilled water available from the HVAC system. The experimental data are used to validate a model for the comparison on a yearly basis. Parallel compression and subcooling show to be almost equivalent in terms of yearly energy use, while the adiabatic cooling system gives the best performance. Comparisons reveal that the subcooler cooling capacity should be chosen carefully to avoid oversizing, while the influence of the EER for the chiller appears quite small. Subcooling performed at the expense of an HVAC plant shows to be an interesting solution, while a great benefit was experienced with the employment of an adiabatic gas cooler.