EN Optimization strategy for system management of cold thermal energy storage (CTES) in conditions of dynamic changes in energy carrier value

Abstract

In world of contemporary challenges involving the continual increase in demand for energy resources and corresponding environmental pollution, the necessity has arisen to develop and implement advanced technologies to reduce energy consumption. This calls for enhancing energy utilization efficiency and optimizing energy generation systems, taking into account the utilization of alternative and renewable energy sources. Specifically, thermal energy storage becomes crucial as an effective economic option. Thermal energy storage systems enable meeting heating or cooling needs during optimal periods when it is more energy-efficient. Traditional management methods rarely prove optimal due to fluctuating electricity tariffs, cooling loads, and ambient temperature. This leads to suboptimal achievement of maximum savings in the utilization of thermal energy storage systems. In this work, the advantages of Cold Thermal Energy Storage (CTES) systems based on Ice Thermal Energy Storage (ITES) were analysed alongside existing management strategies implemented in most enterprises and buildings utilizing ITES. A simplified engineering methodology for analysing the thermodynamic efficiency of CTES was proposed. It was determined that cold losses during exergy analysis during storage are caused by both losses through surfaces and internal exergy losses (i.e., exergy consumption due to irreversibility within the reservoir). For modern systems, exergy losses encompass both external and internal components. As an example, if the heat transfer at the external surface temperature of the storage reservoir equals the ambient temperature, external exergy losses would be zero, while total exergy losses would be entirely due to internal consumption. Conversely, if heat transfer occurs at the liquid's temperature for storage, a greater portion of exergy losses will be due to external losses. In all cases, the cumulative exergy losses, comprising internal and external exergy losses, remain constant. The implementation of CTES allows for shifting the use of electrical energy from peak to off-peak hours. During off-peak hours, electrical energy is used to charge the storage to fulfil (fully or partially) the peak demand for refrigeration equipment. Ice-based ITES has the potential to reduce maximum energy consumption, peak demand, and most importantly, the average cost of energy consumed