This research addresses concerns related to Sick Building Syndrome (SBS) and evolving strategies for managing hazardous biological agents in indoor environments, such as toxic fungi. This pilot scale-model study investigates the impact of a photobioreactor (PBR) algae façade on the microclimate and on the growth of Aspergillus niger and A. fumigatus. Glass simulation chambers were built without a PBR (control), with a PBR on one side (partial PBR) or with a U-shaped PBR surrounding the test space (PBR; 40 × 40 × 40 cm), with two chambers per treatment. Temperature and humidity were recorded every minute, and 15 plates of each fungus (five per treatment) were exposed for 8 days. The PBR did not change the mean temperature but reduced the daily maximum temperature by 5.4 °C (39.2 vs. 44.6 °C) and kept humidity ≥ 80% RH for 23.9 h day−1, compared with 17.4 h day⁻¹ in the control chamber; the partial PBR gave intermediate values as expected. A. niger grew larger with increasing PBR coverage (control 6.0, partial PBR 9.0 and PBR 11.4 cm²; p for trend = 0.002), and A. fumigatus showed a similar but non-significant trend (6.8, 8.4 and 9.4 cm²; p for trend = 0.146). These results indicate that the algae façade can improve thermal comfort but may also favor mold growth, a crucial effect on building health that requires further study.