Moisture potental theory application for modelling of enclosing structure unsteady-state moisture regime

Abstract

Introduction. Known calculation methods for enclosing structure unsteady-state moisture regime proposed by K.F. Fokin, are examined. The first one describes moisture transfer in a sorption zone, and another allows calculation in oversorption zone also. “Thermodynamic moisture potential” of enclosing structure materials introduced by V.N. Bogoslovsky is described. Moisture potential F developed by V.G. Gagarin and V.V. Kozlov is shown. The moisture potential F allows describing water vapor and liquid moisture movement in material in a consistent way. The scientific novelty of the study is the development of calculation method based on moisture potential F. Practical relevance of the study is the possibility to obtain performance humidity values of enclosing structure materials by means of calculations for engineering practice. Materials and methods. A moisture transfer equation is derived on the basis of process physical interpretation, A mathematical model, consisting of heat conductivity equation, derived moisture transfer equation, spatial-time domain, boundary and initial conditions, is formulated. Moisture potential in single-layer and multilayer enclosing structures is determined using finite difference method. Results. Calculations for four types of enclosing structures are made on the basis of the proposed mathematical model: single-layer aerated concrete wall; a wall made of aerated concrete masonry base and clay brick cladding; a wall made of aerated concrete masonry base and mineral wool insulation with thin plaster layer; a wall made of aerated concrete masonry base and expanded polystyrene insulation with thin plaster layer. Conclusions. Calculated performance humidity values of enclosing structure materials were lower than values stated in regulatory documents. The presented results allow to define building heat loss definition and heating system design more accurately. Specification data on maximum wetting plane position obtained earlier were proved within the framework of the developed theory: in enclosing structures with aerated concrete base and mineral wool insulation maximum moisture content is located at the joint of plaster and insulation layers; in enclosing structures with aerated concrete base and expanded polystyrene insulation maximum moisture content is located in the insulation layer. Acknowledgements. Authors are deeply indebted to V.V. Kozlov, PhD in Technical Sciences, and V.K. Akhmetov, Doctor of Engineering Science, Professor, for discussion and useful comment in the course of study.