Optimal Scheduling for a District Cooling System with Chilled Water Storage: Comparative Assessment of Vapour Compression and Absorption Refrigeration Cycles

Abstract

District cooling (DC) systems are able to exploit locally available energy in order to supply cooling to local end-users through an integrated DC network. The present work aims at obtaining the critical decisions in the performance of a DC network at the operating level. End-users can be of different type (e.g., residential or commercial) with different demand profiles and an optimal strategy needs to be employed in order to satisfy the demand and minimise energy usage. In published literature the vast majority of the studies employ simplified mathematical models in order to describe the thermodynamic cycle used and only a handful of studies take into account the actual dynamics of the system transition from one state to the other as well as the time delay attributed to the cooling medium transfer through the network. The critical decisions involve the operating conditions and optimal allocation for the cooing of existing units in a suitable time interval, which form the basis for the satisfaction of requirements in cooling under demand variability. Although reduced order models of the process of ABR cycle are used, the time delay of the cooling medium transfer through the pipes is considered through the employment of validated first order plus time delay models. The proposed optimisation framework enables the identification of demand driven, highly performing solutions through the direct consideration of all interacting factors over a pre-defined time horizon. Optimal results include the definition of the optimal allocation of produced cooling effect in such way that cooling demand is always satisfied.