Methodology and figures of merit for designing a hybrid thermal energy storage unit

A thermal response model for designing a hybrid thermal energy storage (TES) unit is developed. The storage time and maximum operating (hot side) temperature-to-transition temperature difference are used to characterize the performance of the unit. The thermal properties of the PCM employed in the design are investigated. Integration of a design optimization algorithm into a thermal performance model of the TES-hybrid unit results in determination of a best design subject to geometric and heat loading constraints. A prototype based on this best design is build and used to benchmark the performance model. The performance measured is consistent with the simulation model predictions of performance.; Two figures of merit for hybrid TES units are developed: the volumetric figure of merit, V˜, and the temperature control figure of merit, ΔT˜. A dimensional analysis shows that these quantities are related to the performance specification of the storage unit and its physical design. The benchmarked semi-empirical finite volume model is used to study the characteristics of various plate-type TES-unit designs. A parametric study is used to create a database of optimal designs, which is then used to form simple correlations of V˜ and ΔT˜ in terms of design requirements and attributes. A preliminary design procedure utilizing these figures of merit is suggested. Sample calculations show that these correlations can be used to quickly determine the design attributes of a plate-type TES-unit, given design requirements.