3.3. Vertical temperature distributions of both roofs
In order to have a comprehensive understanding of green roof’s characteristic, temperature
distributions along the vertical direc- tion of both roofs during typical day in summer are
presented in Fig. 9. As is illustrated in Fig. 9(a), temperature distribution for green roof under
free floating condition was like a saddle sur- face. There were two phases in temperature
development. The first phase was from 7:00 am to 3:00 pm, during which vertical temperature sequence
was: indoor air > inner surface of structural layer > roof local air > middle soil layer > outer
surface of structural layer. Green roof acted as a heat sink and absorbed heat from both sides. The
second phase was from 3:00 pm to 7:00 pm, vertical temperature sequence was: indoor air > inner
surface of structural layer > outer surface of structural layer> middle soil layer> roof local air,
heat flowed out of the room and green roof performed as a layer of thermal resistance. Temperature
distribution of common roof is shown in Fig. 9(b). From 7:00 am to 6:00 pm, common roof absorbed
solar radiation and acted as a heat source, releasing heat to both sides. And during 6:00 pm to
7:00 am, common roof behaved as a heat sink, absorbing heat from both sides. Comparing Fig. 9(a)
with Fig. 9(b), it can be seen that green roof could not only resist heat penetration but also
absorb heat from indoor environment on sunny days in summer. At night, green roof absorbed less
heat from indoor space than common roof because of sky long wave radiation
and heat storage effect of soil layer.