The optimisation of a thermal dual probe instrument for the measurement of the moisture content of building envelopes

Abstract

A thermal dual-probe offers significant potential benefits over existing methods for making moisture measurements in building envelopes. Previous numerical modelling work by the authors has proven the basic validity of this approach. This paper deals with the further development of the dual-probe design and the associated experimental work. Firstly, the results of design optimisation, using two and 3D Finite Element models, are detailed. Secondly, the extensive experimental work undertaken to complement the modelling work is described. The measured data obtained from the thermal dual-probes was compared with the results of the series of gravimetric analyses. Close agreement between the two methods was obtained. This work clearly indicates that the thermal dual-probe is capable of accurate, in situ moisture measurements in building envelopes. Practical application: There is a pressing need for the development of a suitable instrument capable of reliable in situ moisture measurements in building envelopes. Techniques are available to the building industry for such moisture measurements but all exhibit deficiencies in at least one critical area — for example, electrical resistance based techniques are potentially susceptible to errors related to the presence of salts within the material to be measured. A `thermal dual-probe' based technique offers significant potential benefits over existing methods. It would appear to be especially well suited, for example, to monitoring the drying out of buildings post-flood.