Multi-objective problem of optimizing heat transfer and energy production in algal bioreactive façades

Challenges imposed by the increasing energy demand in buildings had directed research towards investigating more energy efficient designs, which were usually aided by sustainability techniques. Double skin facades decrease buildings' energy demand, enhance indoor thermal comfort, limit undesired solar irradiation and restrict external air flow. Integrating microalgae photobioreactors in such systems adds up to the previous benefits algal biomass and solar thermal energy production. The aim of this study is to optimize such integration for maximizing thermal and biological energy generation. This was achieved by determining the optimal design variables of the cellular and multistory designs through a detailed framework comprising graphical optimization, shading analysis, and hourly thermal simulations. These simulations were performed by an integral analytical thermal model to investigate the thermal performance of the two double-skin bioreactive façades. Shade impact on both designs proved to be dependent significantly on both the location and the design dimensions. However, the cellular design of the façade had full solar exposure for vertical panels as the cavity width was kept below 1.1 m. Key findings showed that the optimum tilt and panels’ width were 34.1° and 2 m for the multistory design, while the optimum tilt and cavity width for the cellular design were 47.4° and 0.6 m. The multistory design, with thermal and biological energy generation of 53.9 and 6.8 W/m2, surpassed the cellular design whose energy generation was limited to 47.1 and 4.1 W/m2.