2.3. Instrumentation and measurement
A weather station was installed near the roof to record the local meteorological data, including
air temperature, relative humidity,solar radiation, wind speed and precipitation. Type-T thermocou-
ples were set at different heights along the vertical direction of green roof and common roof,
measuring temperatures of different layers. For green roof, 28 thermocouples measured temperatures
of seven positions, including indoor air, inner and outer surface of sandwich panel layer, drainage
layer, substrate layer, canopy layer and local air temperature 15 cm above vegetation. And for
common roof, 16 thermocouples measured temperatures of four positions, including indoor air, inner
and outer surface of sandwich panel, air temperature 15 cm above the panel. All the thermocouples
were connected to a data acquisitions system which scanned all sensors every one minute and stored
the data in a local computer. Four TDR (Time Domain Reflectometry) sensors were used to measure volu-
metric water content of substrate layer, and four humidity sensors were set above the roofs to
record local relative humidity. Further- more, six heat flux sensors were installed at the inner
surface of sandwich panel to measure heat flux through both roofs. And these sensors were put near
the center of the roof to avoid edge effect. The measuring periods contained three weather
patterns, namely clear day, cloudy day and rainy day. All the experimental equipment used for field
measurements and their specifications are presented in Table 1.