Energy comparison between CO2 cascade systems and state of the art R404A systems

The focus on the global warming and the political determination to phase out the use of the HFC was clearly stated by minister for the environment Svend Auken at the IIR meeting in Aarhus September 1996 when he said: ¿It is therefore my sincere hope that in ten years time, not a single fridge, freezer or cooling plant is being built in Denmark that requires HFC¿s or other greenhouse effect gases.1¿ Taxes linked to the GWP value and phase out plans have lead to intense investigations in alternative solutions. Amongst these systems are also cascade systems for supermarkets with CO2 as working fluid for both medium and low temperature applications. In 2002 two of these cascade systems with CO2 and R404A were installed. The displays cabinets and cooling/freezing rooms are cooled directly by CO2 in the low temperature part of the cascade plant, while the high temperature part of the cascade plant is using R404A. Initial monitoring of the absorbed power and the observed employed compressors lead to the belief that there was an energy reduction, but it was difficult to quantify. The problem is that two supermarkets are not are identical. Even if they were identical in lay-out they would not use the same amount of energy due to the influence of the turnover. The Danish EPA has sponsored a research project with the purpose to find a method to make the data collected comparable and to put numbers on the energy reductions observed. This presentation describes the methods used to compare state of the art R404A technology systems and two CO2/R404A cascade systems.