A Real Time Control Strategy for Optimisation of an Economised Indirect Multi-Temperature Transport Refrigeration System

This paper describes an approach for control of an economiser cycle based on the use of economiser pressure as the primary control parameter. In the study, the economiser cycle was used to optimise a multi-temperature indirect (IDX) transport refrigeration system, where hydronic secondary loops were utilised. In transport refrigeration applications, IDX systems can offer the potential to address a number of important environmental and control issues associated with direct expansion (DX) systems. IDX systems may also give rise to reduced capacity and COP through increased compressor pressure ratios associated with the hydronic secondary circuit and power requirements of the liquid secondary pumps. One approach by which this issue can be addressed is through use of an economiser cycle, which provides a mechanism for performance enhancement by augmenting the refrigeration effect of the primary refrigerant, in the primary to secondary heat exchanger of these systems. Previous work ascertained that by control of the mass-flow injection ratio, an economiser cycle can be used to optimise indirect multi-temperature systems for a wide range of diverse operating conditions. This method of control necessitates mass-flow instrumentation which is impracticable for field applications. An alternative method of control described here, is based on a more easily measured economiser pressure, thereby eliminating the requirement of mass-flow instrumentation.