Cooling potential of transparent roof spray on public buildings: Evidence from hot-humid areas

Transparent roof is widely used in public buildings to meet the requirements for both building appearance and indoor daylighting environment. However, the excess input solar radiation permitted by the daylighting roof deteriorates the indoor thermal environment, raising building air-conditioning energy consumption. Water spray has been widely used in urban outdoor, building indoor environment, and opaque envelopes, and offers remarkable cooling capacity.

However, its cooling potential on transparent roof of public buildings has rarely been explored. This study investigated the surface and indoor cooling effects under different spray conditions by a field experiment in hot-humid areas. The findings indicate that the average cooling effects of continuous spray scenarios on exterior surface, interior surface, and long-wave radiation are 17.1–17.5ºC, 9.2–9.6ºC, and 64.5–66.3 W/m2, respectively. Meanwhile, the exterior surface temperature of the sprayed roof can be reduced to a lowest value within 10 mins once the spray operates in the overheating period.

The average cooling effects of intermittent spray scenarios on exterior surface, interior surface and long-wave radiation are 9.4–15.9ºC, 4.1–7.8ºC, and 24.1–47.7 W/m2, respectively. Operation conditions sorted by the magnitude of surface cooling effect are ranked as 30/10 min>20/10 min>10/10 min>10/50 min>10/20 min (spray and interval time). Particularly, the cooling effect does not monotonically decrease with the interval time while increasing monotonically with the spray time.

The indoor air temperature and mean radiant temperature under continuous spray scenarios are 4.1–4.4ºC and 5.3–5.7ºC, respectively, whereas the values of them under intermittent spray scenarios are 1.2–2.3ºC and 1.6–2.9ºC, accordingly. Technical-economy evaluation indicates that water consumption is primary cost factor in spray systems, which should be paid attention to in application.