Measurement of thermal conductivity of samples
Prior to developing the experimental procedure for measuring
the thermal conductivity of the samples at different operating temperatures,
an experimental apparatus based on the transient plate
source was designed (Fig. 1). The apparatus was subsequently calibrated
using the known thermal conductivity values at 10 C of
three polystyrene insulation samples characterized by high,
ultra-high, and super-high density (HD, UHD, and SHD, respectively)
provided by another company [19].
A known voltage and current were supplied to the heater, and
its surface temperature (inner surface of the specimen) was measured.
Similarly, the increase in the outer surface temperature
was also measured until the steady state was achieved. This
allowed calculating the temperature difference required for
calculations.
Since thermal conductivity changes with the ambient (surrounding)
temperature, all necessary precautions have to be taken
to ensure that it will remain as constant as possible throughout
testing. For this purpose, a special temperature control chamber
was fabricated to maintain and adjust the temperature to the level
required for testing. This control chamber was made of wood and
was insulated with high-temperature heatproof material to prevent
heat loss from the box.
Nomenclature
te effective or operating outdoor temperature
Rx portion of thermal resistance measured from inward
Rtot total thermal resistance of the envelope assembly
to outdoor air temperature
ti indoor air temperature
a surface solar absorbance
It total solar radiation
ho outdoor surface conductance
eDR/ho correction factor (zero for vertical surface)
Hb direct horizontal radiation
Hd diffuse horizontal radiation
H global horizontal radiation
qgr ground albedo
h incident angle
b slope (90 for vertical wall and 0 for horizontal roof)
Fig. 1.