Integrated R744 ejector supported parallel compression racks for supermarkets. Concept and steady state simulations of configurations.

An increasing number of supermarket chains are opting for the utilization of centralised carbon dioxide refrigeration systems. However, the need to improve their efficiency in order to make them economically and environmentally sustainable worldwide becomes more and more important. One of the most common approaches is to integrate all the energy demands (cooling, air conditioning, heating, domestic hot water) in the same unit. In addition, the operation at high ambient temperatures can be made more energy-efficient with the use of parallel compression and ejectors enabling expansion work recovery. An integrated vapour compression unit where a parallel compression refrigeration system is supported by multiple ejectors has been modelled numerically. The model closely reflects the facility newly constructed in NTNU/SINTEF laboratory. The results prove the decrease of the overall power consumption of the system when using ejectors in the analysed conditions, but it is crucial to optimise the control strategy in order to further reduce the power consumption. In addition, the simulations allowed comparing three separate modes proposed for low-ambient-temperature conditions (temperatures close to or lower than 0 °C), which can be challenging for the carbon dioxide refrigeration systems nowadays.