Photobioreactors as a Dynamic Shading System Conceived for an Outdoor Workspace of the State Library of Queensland in Brisbane: Study of Daylighting Performances

In the field of responsive shading systems, the use of photobioreactors (PBRs) containing microalgae seems to be a promising technology. Within this framework, this paper presents a case study where a PBR was specifically conceived as a shading system for an external workspace located on an open terrace of the State Library of Queensland (SLQ) in Brisbane. The proposed shading system makes use of PBRs as translucent screening elements, capable of regulating natural light to provide adequate visual comfort for a multi-purpose workspace, despite exposure of the site to direct sunlight and fluctuating weather conditions. The microalgae (Scenedesmus Obliquus) cultivated within the shading elements contribute to improving the environment by bio-sequestrating CO2 and producing oxygen. They are also a valuable raw material containing bioactive compounds with various applications including nutraceutical products, livestock feed, and biofuel synthesis. In addition, their green pigmentation is visually engaging and allows for the filtration of solar radiation. The paper focuses on analyzing the daylight performance in the outdoor workplace under the PBR shade. The biomass density of the PBR is adjustable across a wide range of light transmittances (10%-80%) to counter the highly variable outdoor conditions. For different Tv values, illuminance values were calculated using the simulation tool DIVA-for-Rhino and then analyzed as both point-in-time illuminance in June, September and December, and through climate-based daylight metrics such as the Daylight Autonomy and the Useful Daylight Illuminance. As a further step, the daylighting performances were compared to two other climates (Turin, Italy, and Dubai, United Arab Emirates), to verify which setting of the PBR may be suitable for different boundary conditions, thus making the system more widely applicable. The results in Brisbane showed that for clear sky conditions, higher levels of biomass saturation are needed (Tv < 20%) to remain in the 300-3000 lx ‘optimal’ illuminance comfort range, with lower concentrations (Tv < 30%) to remain within the 300-6000 lx ‘acceptable’ illuminance comfort range. Differently, in overcast sky conditions, the optimal range of illuminance is easily obtained with reduced levels of biomass saturation (Tv < 80%).