Cool roofs in China: Policy review, building simulations, and proof-of-concept experiments

Abstract

While 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, CO2, NOx, and SO2 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°C, 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°C, lowered room air temperature by 1-3°C, and reduced daily roof heatflux 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.