Moisture Infiltration In Fractures And Consequences On The Hygrothermal Performance Of Building Facades

Abstract

Moisture transfer in porous construction materials car Nomenclature c Specific heat capacity [J.kg−¹.K−¹] g Moisture flow [kg.m−².s−¹] ries many causes for their degradation: mould devel opment and freeze-thaw damage are favoured by the gl,r Wind-driven rain [kg.m−².s−¹] −2 accumulation of water, and chemicals such as chloride ions and carbon dioxide may accelerate the fracturing of cementitious composites. Over time, microscopic and macroscopic cracks progressively develop under the effects of mechanical loading and sorption/desorption cycles: their influence is to be accounted for in long-term hygrothermal performance assessments of the building envelope. Current simulation codes for heat and moisture transfer modelling in building facades do not allow accounting for the presence of cracks and defects in the material layers. The present work aims at integrat I Solar irradiance [W.m ] Kl Liquid permeability [s] kf ,l Fracture liquid permeability [s] Lv Latent heat of vaporization [J.kg−¹] pc Capillary pressure [Pa] pv Vapour pressure [Pa] q Heat flow [W.m−²] RH Relative humidity Rh Horizontal rainfall [mm.m−²] T Temperature [K] U Wind speed [m.s−¹] u Crack aperture [m] −3 ing such effects of damage in simulations at the scale of building facades. Experimental measurements of crack patterns were integrated into a newly developed w Moisture content [kg.m ] Greek symbols α Heat transfer coefficient [W.m −2.K−1] numerical model predicting coupled heat and moisture transfer in multi-layered components. The consequences of fractures on the hygrothermal performance of these components were then investigated by comparing damaged and undamaged materials in a series of simulation cases. Cracks were found to accentuate the amplitude of daily sorption/desorption cycles and moisture accumulation in the walls, particularly in case of impacting rain. Their impact on the overall thermal performance is small, although not negligible in case of water infiltration towards an insulation layer.