A low cost, accurate instrument to measure the moisture content of building envelopes in situ: a modelling study

This paper argues that there is a pressing need for a suitable instrument capable of insitu moisture measurements in building envelopes. Techniques do exist for such moisture measurement but all exhibit deficiencies in at least one critical area. A thermal dual-probe is investigated as a candidate for an appropriate instrument. As part of an ongoing study, two modelling approaches to investigate this issue are described. Firstly, the use of a one-dimensional heat and moisture transfer model to investigate the impact of the instrument on any moisture movement within a sample is described. Secondly, the development and testing of two and three-dimensional finite element (FE) models is detailed and initial evidence provided that there are no major barriers to the design of a successful dual-probe instrument for use in a range of building fabrics. It appears that the dual probe approach is indeed applicable to moisture measurements in typical building fabrics. A proven FE model is now available and this model will be used to optimize the design of the probe. Future papers will report on the optimization, building and testing of the instrument.