Framework
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The economic panorama and the EU's main legislation concerning the reduction of the energy consumption of buildings have been challenging the buildings industry and academic community to innovate and to develop new products and technologies for improving the energy efficiency of buildings and to make use of renewable energy sources. Hence, the development of new systems to take advantage of solar thermal energy for reducing cooling and heating demand is crucial considering the challenging energy performance requirements for new buildings and retrofitting.
PCMs are materials that undergo melting/solidification at a nearly constant temperature. Therefore, they are very suitable for thermal management and TES applications. In comparison with the traditional sensible materials used in construction, PCMs provide a large heat capacity over a limited temperature range (due to the latent heat involved in the solid-liquid phase change processes) and they could act like an almost isothermal reservoir of heat. Some PCMs were identified in the literature for integration in different TES systems and several ways of containment (in order to avoid liquid leakage) have been studied and optimized.
It is known by now that commercial paraffin waxes to be used as PCMs in TES applications have typically low thermal conductivity which can be problematic regarding the efficiency of these elements. The incorporation of fins of high-conductivity material within rectangular macrocapsules containing PCMs has been one of the techniques used for containment and to improve the heat transfer through the PCM-bulk. These capsules can then be integrated in different TES systems such as PCM-enhanced concrete walls, PCM-bricks, PCM-shutters, PCM-window blinds, PCM-enhanced photovoltaic panels, PCM-enhanced solar panels, etc.. For these reasons, solid-liquid phase change in rectangular cavities is of great interest from the theoretical point of view and for the development of new TES systems.