A modeling and simulation approach for thermal energy storage devices.
Résumé
The energy efficiency simulation of building systems requires an accurate modelling of their individual components as well as a reliable representation of the dynamic interaction between them. We present in this paper, a modelling approach for an energy storage device, following an object-oriented paradigm based on the MODELICA modelling language. The model predicts 3D fluid motion in a thermally isolated cylindrical tank as well as the temperature profile variation, of the fluid within, in respond to variable tank volume, inlet and outlet conditions. The model integration in multi-component systems is straightforward via the simulation environment OpenModelica and does not require co-simulation as it was the practice in multi-domain simulations. A simulation test of the model shows its ability to achieve reliable results in a compromise manner between computationally light 1D models and computationally heavy CFD models. It also shows that in charging a 300L storage tank with cold water, a temperature uniformity in water layers inside the tank could not be achieved before 3h which is equivalent to half of the charging cycle period. This shows that the horizontal isothermal layer division used in the traditional 1D models, shall no longer be suitable for the future energy efficiency simulations of larger more complex multi-components systems integrating storage devices as the charge/discharge cycles becomes shorter and more interactive. Hence, a modelling and simulation approach such as the one described in this paper will be useful for the future energy efficiency studies related to thermal storage systems. 1. Context In recent years, policies to promote improved energy efficiency have been established in response to European and International regulatory obligations. Thermal energy storage has proven to be a technology that can have positive effects on the energy efficiency of a building by contributing to an increased share of renewable energy and/or reduction in energy demand or peak loads for both heating and cooling [1]. For example, the integration of a thermal energy storage device in an air conditioning application can shift the power consumption from peak periods to off-peak periods which contributes significantly in reducing the energy consumption and increasing the overall efficiency of the chilled water plant. However, such component integration have created additional challenges to design and manage the resulting more complex system, where the storage device dynamic behavior plays a significant role between the energy supply and energy demand loops. To approach these challenges, an accurate modelling of the storage component dynamic behavior is required from one hand and from the other an easy and effective way to couple it with other components and simulate their interaction simultaneously is needed in order to evaluate the energy efficiency of the resulting multi-component system. Achieving these two requirements, simultaneously, was difficult to accomplish in traditional modelling and simulation practices. From one side, 3D-CFD (Computational Fluid Dynamics) tools are used for accurate modelling of the storage devices but the resulting models require large computational resources and computing time and are limited in terms of coupling with models from different simulation domains. From the opposite side, 1D-DAE (Differential Algebraic Equation) tools use simplified 1D models of