by A thesis submitted to the University of Plymouth in ... - PEARL home

Brian Pilkington
In situ measurements of building materials using a thermal probe
Abstract
This work concerns the in situ measurement of thermal conductivity and thermal
diffusivity of building materials, so as to provide improved data for the
estimation and prediction of energy efficiency in buildings. Thermal data
sources and measurement methods currently used by industry to inform
building design were found to give flawed values for the thermal properties of
materials as found in situ. A transient measurement technique, carried out by
means of a thermal probe, and used in various other industries, was
investigated as an alternative, relatively non-destructive, rapid and economic
means of obtaining representative results.
An analysis of the literature associated with the technique's history, theory and
practice was carried out. Four strands of scientific research were undertaken:
traditional thermal probe solutions were assessed; computer simulations were
used to model probe behaviour while avoiding practical, experimental error;
laboratory based measurements were carried out with materials of known and
unknown thermal properties using varied parameters, including moisture
content; an apparatus was developed for fieldwork, and in situ measurements
were carried out on real buildings, using novel analysis routines.
Results for thermal diffusivity values achieved by the thermal probe method
were found to be unreliable. Representative thermal conductivity values were
achieved for structural materials with varied moisture content, both in controlled
laboratory environments and in situ under diverse environmental conditions,
which had not previously been achieved. Heat losses from the probe open end
and the material adjacent to it were shown to currently prevent reliable values
being obtained for building insulation materials.
The thermal probe technique was successfully transferred from laboratory to in
situ measurements. It was shown that various calibration factors reported in the
literature could not be relied upon to transfer successfully between material
types. A significant cause of error in the measurement of insulation materials
was identified and a guarded probe was proposed to overcome this. The
technique was shown to provide much improved thermal conductivity data for
structural building materials, whether as samples or in situ, with the potential to
expand this success to insulation materials in the future.
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