The thermal conductivity of the polystyrene building insulation
is affected by the change in operating temperature. In all cases,
higher temperature results in greater thermal conductivity. The
results reported here also show that thermal conductivity
increases with the reduction in material density.
The thermal conductivity of the samples is affected by the temperature
at the mid-thickness of the insulation material and this
change is particularly significant around noon. According to our
data, the increase in thermal conductivity of the wall and roof
can reach as much as 9.4% and 20%, respectively.
The accumulated heat through the insulation layer within the
wall-roof assembly, which produces increase in its temperature,
indicates the change in insulation thermal conductivity. Indeed,
the change in heat accumulated within the wall and roof is particularly
pronounced around noon and can reach 4% and 14%, respectively,
compared to the heat based on k24. Consequently, this will
affect the cooling load calculation when operating at temperatures
exceeding 24 C.
The effect of Rroof is higher on the heat transmitted through it
compared with Rwall, due to the significant amount of solar radiation
incident on the flat surface of the roof. For the maximum value
of kwall and kroof, the peak in the cooling load for both walls and
roof, as measured on July 15th at 11:00 pm, is higher by
0.766 kW compared with the reference value of 41 kW, obtained
using k24.
The results of this study confirm the need to mandate that thermal
insulation material manufacturers provide the k-values of
their insulation materials at different operating temperatures for
different densities of the samples, as this would allow building
designers to accurately assess the energy requirements of
buildings.
The effect of the moisture content on the thermal conductivity
of the insulation should also be investigated. This will be considered
as a further step in this research.