Hygroscopic behaviour of coating materials in transient conditions

Abstract

In countries with a mild climate, of which Portugal is an example, it is not common for dwellings to have continuous heating systems. Usually a discontinuous heating takes place, generating strong variations of temperature and, consequently, of relative humidity throughout the day. Under these circumstances the phenomenon of surface condensation takes on large proportions, being a problem for the users and bringing about economic and social consequences.In our opinion the hygroscopic behavior of the wall and ceiling covering materials, as well as the furniture and textiles inside the dwellings, condition the hygroscopic inertia, parameter which is essential for the control of surface condensation.We present on this paper a mathematical model to estimate the relative humidity variation of a room depending on envelope configuration, ventilation rate, water vapour production and outside climate, and considering the interference of the hygroscopic materials contribution to the balance of the humidity of indoor air.For the purpose of measuring the hygroscopic behavior of some wall and ceiling covering materials, we present an experimental study in order to determine a coefficient that will represent the mass exchange between the materials surface and an ambience of variable relative humidity.We also present some results obtained in numerical simulations produced by a computer program using the proposed model for inside relative humidity variation.