title: Enhancing Thermal Energy Storage in blended cementitious Composites through Sensible and Latent Heat Integration
Creators: name: Nazari Sam, Mona
Publisher: name: UNSPECIFIED
Year: 2024

description: The increasing energy consumption for heating and cooling of the continuously growing building stock is a significant cause of the global rise in anthropogenic CO2 emissions. Efficient management of thermal energy flows throughout, across and around the building envelope can lead to a significant reduction in annual energy consumption for buildings. This, in turn, enhances overall construction energy efficiency by effectively stabilizing temperature fluctuations through the day and across seasons. A highly promising approach to achieve this involves utilizing Phase Change Materials (PCMs) within blended cementitious composites, characterized by a responsive and adaptable porous microstructure that has the potential to store/release solar and/or environmental heat/cooling energy. Unlike common insulation materials, the proposed highly porous thermal energy storage (TES) composite is non-flammable, recyclable, and offers both insulation and effective heat storage/release functionality.
The correlation between microstructural parameters of porous cementitious composites and related thermophysical properties have been the object of extensive study for many decades due to its wide relevance in engineering problems and applications. Research efforts on characterizing thermal properties have predominantly focused on numerically and experimentally assessing the homogenized thermal conductivity of porous cementitious composites. However, these efforts have often disregarded the integration of sensible/latent thermal energy storage, as well as the consideration of the geometrical categorization of the pore structure. The significance of the latter becomes pronounced as the pore volume fraction increases, leading to the predominantly interconnected pores. This issue requires the thorough thermo-physical characterization of individual constituents, including their interconnections and their effects on homogeneous thermal parameters. In this context, a significant contribution of this PhD study is to investigate the optimal balance between thermal insulation and heat storage capacity, utilizing compatible materials and components.
Additionally, a simplified methodology is developed, proposing an analytical predictive model based on the findings from this research and other relevant sources. The proposed analytical model concerns the stochastic characteristic of the pore structure and allows the prediction of homogenized thermal conductivity of porous blended cementitious systems (also known as concrete foam) with/without integrated latent heat thermal energy storage (LHTES). The introduction of two fundamental parameters played a major role in this approach. Particularly, the microstructural fitting parameters A and Φm, associated with air inclusion fraction and void geometry, are defined concerning the model proposed by Nielsen (1974). The model parameters were calibrated using a wide variety of experimental data, effectively capturing microstructure's impact on thermal conductivity and TES parameters. The proposed approach aligns well with experimental findings, making it suitable for designing two-phase blended cementitious foams. This methodology is then extended to solve energy transport equations within complex mineral foam structures, including those with LHTES components. Importantly, it eliminates the need for costly experimental setups and complex computer analyses to determine effective thermal conductivity, i.e., keff.

 
The suggested novel functional material combines advanced insulation properties with significant energy storage capacity, exceeding improvements by more than 59% for thermal performance (by considering porosities higher than 74%). The determined calibration parameters and established classification of the porous composite given in this work contribute to norms and standards for the thermal characterization of porous mineral composites in application scenarios. The methodology proposed for designing this innovative functional material has the potential to extend its applicability to other porous blended composites.