Thermal conductivity analysis establishes the principles for the
design of a hot box apparatus and the minimum requirements for
the determination of the steady state thermal performance of the
building constituents when exposed to controlled laboratory conditions.
The hot box apparatus is required to establish and maintain
a desired steady temperature difference across the test specimen
for the period of time. The elapsed time required is that necessary
to ensure constant heat flow and steady temperatures, and,
for an additional period adequate to measure these quantities to
the desired accuracy.
The hot box apparatus, constructed to measure the heattransfer
in the horizontal direction, is used for testing walls and other vertical
structures. When constructed to measure heat transfer in the
vertical direction, the hot box is used for testing roof, ceiling, floor,
and other horizontal structures. The hot box apparatus constructed
was able to measure the rate of heat flow through an element of
known area for known test conditions while limiting extraneous
heat flows.
Thermal imaging, also called thermography, is the production
of non-contact infrared or heat pictures from which temperature
measurements can be made. Portable infrared cameras scan samples,
then instantly convert the thermal images to pictures for
monitoring or quantitative temperature analysis. Test setup contained
a thermal camera provided with an FPA type detector with
a resolution of 120 × 120 pixels. An automatic calibration for the
ambient and camera temperature and for the air humidity was provided.
Thermographic images were recorded with the camera and
analyzed with software to obtain the temperature variations.
Inorder todetermine the thermal conductivity ofthe specimens,
a guarded hot box was constructed in accordance with ASTM C1363
[10]. The specimens were located on the sixth side of the box. An
electric heater with a fan was used to heat the box from inside. The
heat flow rate through the metering chamber walls is limited by
the use of highly insulated walls. Two thermocouples were placed
on the inside and outside of each face of the box. A thermal imager
was used for monitoring the temperature at the outside surface of
the test specimens. Steady state conditions were reached in about
10 h. The interior of the box was kept at 52 ◦C.