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

Abstract

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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“…8,98 The first way to apply PDRC is to directly apply a passive PDRC coating on a terrestrial entity that needs to be cooled, such as the cooling roof is shown in Figure 14A. 98,99,[101][102][103][104][105][106][107][108][109] Roofs in most residential buildings are exposed to substantial solar radiation during the daytime, resulting in a high roof temperature (up to 60 C). This heat is transferred to the living space, placing a higher cooling load on the air conditioner.…”

Potential benefits and optimization of cool-coated office buildings: A case study in Chongqing, China

“…Improvement of building energy efficiency is one of the key issues to achieve energy conservation and environmental sustainability, as buildings contribute over 40% of primary energy consumption and one-third of global CO2 emissions worldwide [1]. One of the effective ways to improve the building performance is to select cool surfaces with high albedo (ability to reflect sunlight, spectrum 0.3 -2.5 μm; also known as solar reflectance) and high thermal emittance (ability to radiate heat, spectrum 4 -80 μm) [2]. Utilizing cool coatings helps save energy [3] and reduce power-plant emissions of CO2, SO2, and NOx in conditioned buildings [4] and improve thermal comfort in non-conditioned buildings [5] in hot weather, while it may also increase heating demand or result in thermal discomfort in cold weather [6].…”

“…Thus, the annual maintenance costs for non-cool and cool surfaces were set the same. (2) In terms of the initial costs between the cool and non-cool coatings, a guideline released by the U.S. Department of Energy [44] shows that cool surface products are usually similar in cost or slightly more expensive than similar non-cool alternatives. For instance, the median market price of a white single-ply membrane is the same as a black single-ply membrane.…”

Analysis of the rule of window-to-wall ratio on energy demand of residential buildings in different locations in China

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