identify the impact of weather factors on thermal performance of green roofs. Finally, hourly
energy flows of both roofs are plotted based on energy balance model. The following conclusions can
be drawn:
(1) Cooling effect of green roof in summer is more significant on sunny days than that on cloudy and
rainy days, the maximal difference of heat fluxes through both roofs is up to 15 W/m2. Indoor air
temperature at night is about 2.5 ◦C higher for green roof than common roof.
(2) Green roof can reduce the amplitude of outer surface tem- perature fluctuation by 32.5 ◦C, and
roof local air temperature difference between green roof and common roof increases as solar
radiation rise, the maximal value can reach 5 ◦C.
(3) Under free floating condition Green roof acts as a heat sink in the daytime and as a heat source
at night, while common roof is the opposite. Under air-conditioned condition, temperature
profile pattern of green roof is similar to that of common roof.
(4) Correlation analysis shows that solar radiation is the factor most
correlated with heat flux through both roofs under free floating condition. However, under
air-conditioned condition, the cor- relation between solar radiation and heat flux through green
roof becomes insignificant, and correlations of meteorological factors with heat flux are opposite to
that under free floating condition. In addition, outdoor temperature has the highest cor- relations
with temperature parameters of green roof under both conditions while solar radiation has the
lowest ones. In terms of relative cooling effect of green roof, solar radiation is the most
correlated factor while outdoor temperature is the least one.
(5) Net solar radiation is the major heat gain for both roofs. The main heat dissipation ways for
green roof are evapotranspira- tion and net long wave radiation (accounting for more than 80%
of total heat gain), while the main dissipation ways for common roof are heat convection and net long wave radiation. The
intensity of evapotranspiration depends on soil water content of green roof greatly, and keeping a
high level of water content is benefit for the thermal performance of green roof.