THERMAL BEHAVIOUR OF SOLAR WALL COUPLED WITH PCM TRIPLE GLASS UNIT IN BUILDING APPLICATIONS

This study is aimed to numerically investigate the thermal behavior of a passive solar system for bio-climatic buildings. A test-case room equipped by a south-oriented solar wall is outlined for numerical simulations in several geometrical and functional configurations such as: i) single glass; ii) single glass and insulated roof; iii) triple glass unit (TGU) filled by air and insulated roof; iv) TGU filled by phase change materials (PCM) and roof layer filled by PCM. Two paraffins (Octadecane and RT21 Rubitherm®) have been tested as filling PCM in the numerical models. The applied environmental characterization for the system, in terms of incident solar radiation and external temperature, is gathered by ASHRAE method by considering south Mediterranean climate conditions in winter season. Numerical models are based on a finite element approach in order to solve the buoyancy-driven flow and thermal distribution inside the room. Navier-Stokes and energy equations are spatially discretized by using Lagrange second-order elements, computations have been carried-out in transient conditions during several days, until a periodic stabilized regime was achieved. By adopting the enthalpy formulation for the energy equation, one single equation is used to solve transient conduction and convection heat transfer in both the solid and liquid phase for filling melting/freezing materials. Results are mainly presented as air-velocity and temperature fields. Some crucial aspects for system suitability are then analysed, such as exchanged thermal energy, thermal storage capacity of the solar wall, overheating conditions inside the room, vertical thermal gradients inside the occupied zone of the room, effectively working conditions for PCM with respect to their melting temperatures, heat losses by the system during the night and solar heat gain (SHG) for the several studied configurations.