| Low-Cost Thermochemical Heat Storage by Using Cement-Based Composite Materials Matteo Pavese1; Luca Lavagna1; Davide Burlon1; Roberto Nistico1; Vincenza Brancato2; Andrea Frazzica2; Eliodoro Chiavazzo1; 1POLITECNICO DI TORINO, Torino, Italy; 2CONSIGLIO NAZIONALE DELLE RICERCHE, Messina, Italy; PAPER: 265/AdvancedMaterials/Regular (Oral) SCHEDULED: 15:55/Sat. 26 Oct. 2019/Leda (99/Mezz. F) ABSTRACT: In Europe, heating is responsible for the most part of the residential energy demand [1]. To reduce energy consumption, thermochemical materials (TCMs) coupled with renewable heat production (e.g. solar thermal) seem a very promising option for seasonal heat storage. Among the TCMs, salt hydrates provide the highest energy density [2], but has poor mass and heat transport properties. On the contrary, highly porous materials like zeolites present good mass and energy transfer, but have high cost and rather low energy density [3]. The coupling of a porous material and a salt hydrate would be an optimal solution to guarantee both transfer properties and energy density, provided that the cost issue is addressed. In this work, we developed a composite TCM, based on hydrated cement for the porous matrix and on calcium chloride or magnesium sulfate as salt hydrates, that allows a significant reduction of the cost per unit energy stored. Usually, the conditions of cement hydration are chosen to obtain a low porosity material, to provide high mechanical properties. By increasing the water-to-cement (w/c) ratio in the cement paste, however, the hydrated cement becomes highly porous. Thus, the first part of the work was to characterize cement at very high w/c ratios by density measurements, N<sub>2</sub> physisorption analyses, microscopy and mechanical testing. Once the best preparation conditions for porous cement were selected, two techniques were used to prepare the composite materials: the standard impregnation method from aqueous solutions and a novel one-step technique where cement was hydrated with a concentrated solution of the chosen salt instead of distilled water. The energy density of the composites was estimated by DSC analysis and a preliminary calorimetric characterization was performed by monitoring the temperature of the samples during hydration with liquid water. The observed temperature lift was a measure of the heat generated during the hydration step. The most interesting materials were finally characterized by equilibrium water vapor adsorption isobars. A preliminary economic analysis, based on thermal energy cycles at a maximum temperature of 80°C and 140°C (common flat-plate or evacuated-tube solar collectors, respectively), was also performed. The price per stored kWh was calculated for literature-based materials and for the cement-based composites. The results showed a three-fold reduction of price per stored kWh with respect to zeolite-based systems [4]. References: [1] "Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions on an EU Strategy for Heating and Cooling", European Commission, Brussels, 16.2.2016 [2] K. Visscher, J. Veldhuis, Ninth International IBPSA Conference Proceedings, Montreal, Canada, August 15-18, 2005. [3] L. Scapino, H. Zondag, J. Van Bael, J. Diriken, C. Rindt, Applied Energy 190 (2017), 920-948. [4] S. Hongois, F. Kuznik, P. Stevens, J.J. Roux, Solar Energy Materials and Solar Cells 95 (2011) 1831-1837. |
