Performance Evaluation of an Economised Indirect Multi-Temperature Transport Refrigeration System

Direct expansion (DX) refrigeration technology is almost exclusively used in multi-temperature transport refrigeration systems. Multi-temperature systems use up to three evaporators, requiring large refrigerant charges and system pressure control to operate over a wide range of set-point conditions. Despite incremental design improvements over the past decade, environmental and control issues continue to arise with DX systems. Deployment of indirect refrigeration systems (IDX) offers an alternative approach to address these issues. Indirect systems can however suffer from performance penalties, where reduced cooling capacity and COP occur under certain operating conditions. One strategy, aimed at offsetting the disadvantage of reduced refrigeration capacity, is to incorporate an economiser circuit into the primary cycle of the IDX system. Economiser cycles can enhance the refrigeration effect of the primary refrigerant in the primary to secondary heat exchanger of the indirect system. In this paper, for a multi-temperature transport refrigeration system, the performance of an optimised economised indirect system is compared with a non-economised indirect system and a contemporary direct expansion system. All tests for the economised IDX system were carried out using optimised refrigerant mass flowrate injection ratios, which were established for different operating boundary conditions. Tests were carried out to ATP standard for a Class C multi-compartment vehicle for a range of set point temperatures from -20oC to +10oC.