Bioreactive Skins: Evaluating Microalgae Façade Systems for Thermal and Daylighting Performance in Los Angeles

Façade-integrated photobioreactors are sustainable architectural elements due to their ecological, economic, and environmental benefits. Similar in appearance and application to curtain walls, their applications as green and bioreactive windows seem promising. However, challenges in modeling building physics parameters such as daylighting and thermal control often hinder feasibility studies to research their applicability. This paper aims to propose a methodological framework to evaluate the impact of different microalgae species on occupant comfort when integrated into building façades. The study focuses on Los Angeles climate and investigates the year-round total energy consumption, lighting and thermal comfort performance of two distinct microalgae strains, Chlorella vulgaris and Pseudanabaena sp. The method involved measuring light transmittance of algal cultures in different concentrations; then using these to calculate solar heat gain coefficients and visual transmittance levels for defining photobioreactor systems for building performance simulation using Grasshopper plugins, Honeybee and Ladybug. Three distinct façade design (FD) scenarios were optimized in terms of algae density, window-to-wall ratio, wall type and thickness, insulation thickness, and heating/cooling setpoints. Results indicate that photobioreactor façades have significant potential to enhance thermal comfort, improve daylighting performance, and reduce energy consumption throughout the year. Viable alternatives exist for both strains; however, their effects differ: Pseudanabaena sp. demonstrated 26-44% improvement in mean thermal comfort violation (TCV) across all three façade designs compared to C. vulgaris, attributed to its lower solar heat gain coefficient. FD1, consisting solely of algae-integrated windows, showed better thermal comfort while hybrid designs were sensitive to the placement of algae windows. Regarding daylighting, FD3 achieved highest mean useful daylight illuminance (UDI ~47%) for both species, though with greater spatial non-uniformity. Energy performance revealed configuration-dependent optimal species selection. Sensitivity analysis revealed hierarchical parameter influence: cooling setpoint demonstrated dominant effect on both energy and thermal comfort, while window-to-wall ratio (WWR) affected daylighting the most. Optimal solutions for Los Angeles require performance-priority-specific selections: FD1 with C. vulgaris (10-15% concentration) for thermal comfort prioritization, FD2 with Pseudanabaena sp. (40-50% concentration) for energy optimization, and FD1 for daylighting maximization. This research demonstrates a comprehensive, transferable methodology that enables comparative studies while presenting design guidelines for Los Angeles PBR façade applications.