Thermal performance and energy savings of white and sedum-tray garden roof: A case study in a Chongqing office building

Gao, Yafeng; Shi, Dongdong; Levinson, Ronnen; Guo, Rui; Lin, Changqing; Ge, J.

doi:10.1016/j.enbuild.2017.09.091

Cited by 55 publications

(19 citation statements)

References 32 publications

(48 reference statements)

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“…The total roof surface in the urban world is estimated to be around 380 billion m 2 , while the roof surface accounts for over 20% of the global urban area [4]. For low or mid-rise buildings, the heat gains from roofs account for 5-10% of the annual cooling energy consumption of a building and more than 40% of the cooling energy consumption of top-floor rooms [5].…”

Section: Introductionmentioning

confidence: 99%

Optimization of cool roof and night ventilation in office buildings: A case study in Xiamen, China

et al. 2020

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Increasing roof albedo (using a "cool" roof) and night ventilation are passive cooling technologies that can reduce the cooling loads in buildings, but the research has not comprehensively explored the potential benefit of integrating these two technologies. This study combines an experiment in the summer and transition seasons with an annual simulation so as to evaluate the thermal performance, energy savings and thermal comfort improvement that could be obtained by coupling a cool roof with night ventilation. A holistic approach integrating sensitivity analysis and multi-objective optimization is developed to explore key design parameters (roof albedo, night ventilation air change rate, roof insulation level and internal thermal mass level) and optimal design options for the combined application of the cool roof and night ventilation. The proposed approach was validated and demonstrated through studies on a six-story office building in Xiamen, a cooling-dominated city in southeast China. Simulations show that combining a cool roof with night ventilation can significantly decrease annual cooling energy consumption by 27% compared to using a black roof without night ventilation and by 13% compared to using a cool roof without night ventilation. Roof albedo is the most influential parameter for both building energy performance and indoor thermal comfort. Optimal use of the cool roof and night ventilation can reduce the annual cooling energy use by 28% during occupied hours when airconditioners are on and reduce the uncomfortable time slightly during occupied hours when air-conditioners are off. *Revised Manuscript-Clear Click here to download Revised Manuscript-Clear: Revised manuscript_NL_clear.docx Click here to view linked References

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Section: Introductionmentioning

confidence: 99%

Optimization of cool roof and night ventilation in office buildings: A case study in Xiamen, China

et al. 2020

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“…In China, the energy consumption caused by roof heat transfer accounts for 35% of the total consumption for top floor areas [2]. High-reflectance building roof surfaces with high albedo (solar reflectance), known as "cool roofs", have been used to prevent overheating of buildings by solar radiation control, reduce the cooling energy need and peak loads of buildings, mitigate heat island effect, and reduce carbon emissions [3][4] [5]. Cool roofs have been credited or prescribed in building energy efficiency standards for China [6], especially in hot summer climate areas (hot summer/cold winter and hot summer/warm winter zones).…”

Section: Introductionmentioning

confidence: 99%

“…This retention (deposition minus removal) depends on local air quality and local weather (e.g., rain), and is therefore tied to the city. For instance, Aoyama [17] considered black carbon particles as the main component of soil disposition in Japan, while Gao et al [3] affirmed fog and haze (i.e., PM2.5 and O3) soiled the cool roof surface and caused its albedo loss in Chongqing, China. The natural aging of cool roofs is mainly due to the retention of deposited soiling, such as soot, dust, salt, and biological growth when exposed to the outdoor environment.…”

Section: Introductionmentioning

confidence: 99%

Effects of natural soiling and weathering on cool roof energy savings for dormitory buildings in Chinese cities with hot summers

Shi

Zhuang

Lin

et al. 2019

Solar Energy Materials and Solar Cells

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Roofs with high-reflectance (solar reflectance) coating, commonly known as cool roofs, can stay cool in the sun, thereby reducing building energy consumption and mitigating the urban heat island. However, chemical-physical degradation and biological growth can decrease their solar reflectance and the ability to save energy. In this study, the solar spectral reflectance of 12 different roofing products with an initial albedo of 0.56-0.90 was measured before exposure and once every three months over 32 months. Specimens were exposed on the roofs of dormitory buildings in Xiamen and Chengdu, each major urban areas with hot summers. The albedos of high and medium-lightness coatings stabilized in the ranges 0.45-0.62 and 0.36-0.59 in both cities, respectively. This study yielded albedo loss exceeded those reported in the latest Chinese standard by 0.08-0.15. Finally, DesignBuilder (EnergyPlus) simulations estimate that a new cool roof with albedo 0.78 on a six-story dormitory building will yield annual site energy savings (heating and cooling) for the top floor, which are 8.01 kWh/m 2 (24.2%) and 9.12 kWh/m 2 (26.3%) per unit floor area in Xiamen and Chengdu, respectively; while an aged cool roof with albedo 0.45 and 0.56 will yield the annual savings by 5.12 kWh/m 2 (15.4%) and 2.47 kWh/m 2 (10.5%) in these two cities.

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“…Conventional impervious grey roofs in China (with an albedo of about 0.10 to 0.20) absorb roughly 80% of solar infrared radiation portion of which is dissipated to heats the roofs and atmosphere, increasing the cooling costs of air conditioning systems, and heightening the effects of global warming and UHI [7]. High albedo (solar reflectance) white roof (WR) or sedum-lineare garden roof (STGR) are commonly considered to mitigate the detrimental effects associated with grey roofs [5] [8].…”

Section: Introductionmentioning

confidence: 99%

“…Garden roof can provide evaporative cooling as well as effective thermal insulation, thereby providing year-round energy savings [8]. Garden roofs offer little, if any, global cooling potential because the albedo typically ranges 0.16-0.26 [14], and the cool moist air above the garden surface eventually condenses as rain, releasing heat [15].…”

Section: Introductionmentioning

confidence: 99%

Life cycle assessment of white roof and sedum-tray garden roof for office buildings in China

Shi

Gao

Guo

et al. 2019

Sustainable Cities and Society

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White roof (WR) and Sedum lineare tray garden roof (STGR) have been convinced to improve the energy-efficiency and provide various benefits for conventional impervious grey roofs. Some national and local standards have standardized and recommended these technologies in existing building retrofits, however, they do not include assessment and choice of a particular roof 8 retrofit in different climates. This paper presents a 40-year life-cycle cost analysis (LCCA) of an 9 office building roof retrofitted by adding either WR or STGR over an existing grey roof in five cities, 10 located in four Chinese climate zones. The LCCA find that the WR retrofits exhibit positive life-11 cycle net savings (NS) in warm winter zones, ranging 5.7-35.1 CNY/m 2 , and STGR retrofits have negative NS of -81.3--16.7 CNY/m 2 in all climate zones. The NS of both WR and STGR generally tend to improve as one moves from the coldest cities to the warmest cities.LCCA results suggest that adding new building codes concerning crediting or prescribing WR and STGR retrofits into office buildings with grey roofs in hot summer climate zones and warm winter zone in China, respectively. And featured by more specific requirements, the localized Technical Norms help promote the implementation of new building codes.

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Thermal performance and energy savings of white and sedum-tray garden roof: A case study in a Chongqing office building

Cited by 55 publications

References 32 publications

Optimization of cool roof and night ventilation in office buildings: A case study in Xiamen, China

Optimization of cool roof and night ventilation in office buildings: A case study in Xiamen, China

Effects of natural soiling and weathering on cool roof energy savings for dormitory buildings in Chinese cities with hot summers

Life cycle assessment of white roof and sedum-tray garden roof for office buildings in China

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