Moisture permeability measurements under varying barometric pressure

Experimental methodology is developed for measuring moisture permeability of vapour and liquid. The development of theories to describe combined heat and moisture transport through porous media has been the subject of a large volume of research over recent years. These theories are important for many areas of study including the investigation of the hygrothermal performance of building envelopes. This paper highlights the difficulties of obtaining separate values for the material vapour and liquid transfer coefficients, a knowledge of which is essential if combined heat and mass transport models are to be accurately solved. The determination of these individual coefficients is not possible using existing measurement methods which enable only a total moisture permeability to be measured with the liquid and vapour flux components combined. The possibility of carrying out measurements under varying barometric pressures to obtain this data is investigated and experimental results using particle board as a test material are reported and compared with results from a previously developed analytical approach.