This paper describes a mathematical model for the simulation of the behaviour of an economised indirect (IDX) refrigeration cycle for use in multi-temperature cargo transport systems. The research is framed in the context of the exclusive use of direct expansion (DX) refrigeration systems, which to date has been the technology of choice for multi-temperature transport cargo systems. Recent investigations suggest that IDX systems may provide operational and environmental advantages compared to existing DX systems. A key issue with IDX systems concerns the use of a secondary working fluid which necessitates the deployment of an additional heat exchanger. As a consequence, an additional temperature difference across the heat exchanger exists which results in the reduction of system cooling capacity and COP. Previous research in this area has shown that the incorporation of an economiser cycle into the primary refrigeration circuit may for IDX systems, under certain conditions, be effective at improving system capacity and COP. However for improvements to be accrued, the economiser cycle control must be optimised. Given the wide range of operating conditions and permutations, the development of a simulation tool for comprehensive analysis of the economiser cycle is essential. For this purpose, a mathematical model of a multi-temperature economised IDX system was developed in MATLAB. The purpose of the simulation model is to act as a design and evaluation tool for economised IDX systems, thereby enabling the performance of such systems to be examined and optimised. Validation studies and sensitivity analysis of the economiser model are presented and discussed.
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