Investigating the impact of using modified cool materials by titanium dioxide (TiO2)-based photocatalytic self-cleaning nanoparticles in urban facades on urban microclimate parameters

On the one hand, one of the most important global strategies to improve thermal comfort in urban spaces is using cool materials (high albedo materials) in urban facades. On the other hand, using cool materials in urban facades is a big challenge. Over time, the albedo of cool materials that modified by titanium dioxide (TiO2)-based photocatalytic self-cleaning materials (PSTiO2) does not decrease. In fact, its self-cleaning property prevents the loss of the initial albedo of the material. The self-cleaning performance of these materials was investigated in previous researches. However, their thermal performance in urban space has not been investigated yet. This paper studied the performance of these materials on the urban square facade. The thermal performance of PSTiO2 on the thermal comfort of the urban square was evaluated by ENVI-met(v4). The results simulated by ENVI-met software with field measurements in the urban Square were compared. Field measurements of air temperature were conducted on 22 July and 30 March. The results showed that these materials, despite their self-cleaning properties, have significant thermal impact in the urban environment. Using plaster modified by PSTiO2 (albedo 0.6) improved slightly by nearly 0.2 °C the thermal comfort of the urban square. Whereas, white paint modified by PSTiO2 (albedo 0.9) reduced the physiologically equivalent temperature (PET) by 0.5 °C, because reflection of solar radiation increased between the buildings facades. The simulation results showed that due to the space is more enclosed in the square entrance, the mean radiant temperature (Tmrt) increased. As a result, PET index rose too. This study shows that employing cool and self-cleaning materials in the urban facades of Jolfa Square, in addition to have self-cleaning property, is effective in the amount of thermal comfort of the square. In the parts of the square where the enclosure is less, an improvement in thermal comfort was observed. The performance of the cool and self-cleaning materials in the facade in terms of thermal comfort is completely dependent on the physical parameters of the urban space.