Effect on Rooftop Temperatures and Heat Fluxes of a Bamboo Charcoal Sublayer in Rooftop Greening Soil at a Factory Office

Kaneyuki NAKANE; Motomu KAWAMURA; Ling PI
The effect of using a thin layer of greening material on temperatures and heat fluxes recorded on the roof of a single-story factory office in Higashi-Hiroshima, Japan, was investigated from May to November, 2006. In the study, the roof was divided into two sections. One area was a non-greening control area. The other area was a greening area, which consisted of a thin layer of soil with a bamboo charcoal sublayer spread over a plastic board. The temperature of the non-greening area was the higher of the two areas during the day in all seasons, especially in August when it was mostly around 60˚C, while the temperature of the greening area was maintained at below 35˚C, which helped control the temperature of the garret. Likewise, the heat fluxes from the non-greening rooftop area to the building during the day, and from the rooftop to the external environment at night were higher than that for the greening rooftop, which were reduced to less than 10%, even during summer. The monthly total heat fluxes suggest that the heat balance for the greening area during the day was negative (rooftop to external environment), and at night in August it was positive (rooftop to garret), which was contrary to the fluxes for the non-greening rooftop. Our novel greening system using bamboo charcoal and a plastic board effectively controlled the temperatures and reduced heat fluxes on the rooftop, and showed the potential to contribute greatly to regulating room temperatures.
Bamboo charcoal; Heat island phenomena; Heat flux; Shallow-soil rooftop greening; Temperature
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