To reduce the heat island phenomenon, we have designed an original system to secure water surfaces by continuously sprinkling stored rainwater onto the surfaces of a building coating with photoactive TiO₂ film. The solar light converts the building surface coated with TiO₂ film to a highly hydrophilic one, minimizing the amount of water needed to form thin water film on the surface. Then, the evaporation from the water film generates the effective latent heat flux and cools down the building surfaces and its surrounding atmosphere. The cooling effect also decreases the amount of air conditioning usage, which reduces energy consumption and artificial heat emission. Thus, our system achieves both increasing water surface and saving energy to reduce the heat island phenomenon without losing comfortable life.
The cooling system applied to glass curtain walls (130 m²) coated with TiO₂ films in a room of an actual building. The minimal amount of water was sprinkled by a special hose on the top of the glasses in this summer, and the room and the glass surface temperatures were measured. And also, thermal loading was evaluated when the air conditioner was set for 25 ºC. Figure shows that this system cuts the thermal loading by 14 % on average. The results suggest that the system is effective on reducing energy consumption and also the cooling down the building surface and the room within it in the actual building.