a b s t r a c tWhile the concept of reflective roofing is not new to China, most Chinese cool roof research has taken place within the past decade. Some national and local Chinese building energy efficiency standards credit or recommend, but do not require, cool roofs or walls. EnergyPlus simulations of standardcompliant Chinese office and residential building prototypes in seven Chinese cities (Harbin, Changchun, Beijing, Chongqing, Shanghai, Wuhan, and Guangzhou) showed that substituting an aged white roof (albedo 0.6) for an aged gray roof (albedo 0.2) yields positive annual load, energy, energy cost, CO 2 , NO x , and SO 2 savings in all hot-summer cities (Chongqing, Shanghai, Wuhan, and Guangzhou).Measurements in an office building in Chongqing in August 2012 found that a white coating lowered roof surface temperature by about 20 1C, and reduced daily air conditioning energy use by about 9%. Measurements in a naturally ventilated factory in Guangdong Province in August 2011 showed that a white coating decreased roof surface temperature by about 17 1C, lowered room air temperature by 1-3 1C, and reduced daily roof heat flux by 66%.Simulation and experimental results suggest that cool roofs should be credited or prescribed in building energy efficiency standards for both hot summer/warm winter and hot summer/cold winter climates in China.

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HIGHLIGHTS  Temperatures, heat flux and energy uses were measured in office building, Chongqing.  Comparing white and sedum-tray garden roofs to black roof for one year.  White roof reduced 1.6 times annual energy savings than sedum-tray garden roof.  Natural aging of white and sedum-tray garden roofs has been discussed.

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.