Abstract
Currently, strategies to mitigate urban heat island (UHI) effects and reduce building energy consumption are implemented worldwide. In Japan, as an effective means of mitigating UHI effects and saving energy of buildings, highly reflective (HR) roofs have increasingly been used. In this study, in order to evaluate the effect of HR roofs on building energy conservation, we investigated the solar reflectivity of a subject school roof in Osaka, Japan, in which HR roofing sheets were installed on the roof from 2010. Additionally, monthly and annual thermal loads, including the cooling load and heating load of the top floor of the school, were calculated using the thermal load calculation software New HASP/ACLD-β. Comparing the calculated thermal loads of the school after HR roofing sheet installation to before, the annual thermal load decreased about 25 MJ/m2/year, and the cooling load decreased about 112 MJ/m2/year. However, the heating load increased about 87 MJ/m2/year in winter. To minimize the annual thermal load, thermal insulation of the roof was also considered to be used together with HR roofing sheets. Thermal load calculations showed that the combination of HR roofing sheets and thermal insulation can be effective in further reducing the annual thermal load.
Highlights
The urban heat island (UHI) effect is a well-documented climatic change phenomenon [1]
Thermal load calculations showed that the combination of highly reflective (HR) roofing sheets and thermal insulation can be effective in further reducing the annual thermal load
This paper presented a countermeasure of a cool building roof to oppose the UHI phenomenon and save on the energy consumption of buildings in Osaka
Summary
The urban heat island (UHI) effect is a well-documented climatic change phenomenon [1]. Akbari et al [6] summarized the existing UHI mitigation strategies in detail, such as the development of highly reflective (HR) materials, the development of cool and green roof technologies, the development of cool pavement technologies, urban trees, etc. It showed that these UHI mitigation strategies can decrease ambient and surface temperatures in cities. The mitigation of UHIs leads to energy and energy expenditure savings, improves urban air quality and ambient conditions, and helps to counter global warming (GW). Santamouris et al [7,8,9] reviewed many articles aiming to present the actual state of the art on the development and the assessment of cool materials for buildings and structures and showed that the mitigation strategies, such as HR and emissive light colored materials, cool colored materials, phase change materials (PCMs), and dynamic cool materials, used for building roofs or facades, increasing urban albedo, green roofs, etc. can significantly contribute to UHI mitigation and the improvement of urban environmental quality
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