Moisture buffering

Interior wooden surfaces have the capacity to buffer the maxima and minima of relative humidity (RH) indoors. Especially in high performance buildings, where high airtightness levels as well as high indoor air quality (IAQ) are required, there is great potential for energy savings by reducing the mechanical ventilation demand. The last decade, the moisture buffer phenomena has been widely researched. Relevant findings showed that the moisture buffering effect is reduced when the ventilation rates increase.

In this paper, experiments and simulations for moisture buffering of the gypsum boards is described.The small chamber (4.62 m3) installed the gypsum board on the interior surface was used for theexperiments. This chamber was located in a climate chamber. The ambient condition of the smallchamber was controlled at constant temperature and humidity. In the experiment for the relationshipbetween moisture buffering and ventilation rate, three cases of ventilation rate, i.e. no ventilation, 1.01/h and 5.0 1/h, were investigated.

Succeeding to the experimental investigations in the two test rooms at FhG the results provide for acommon exercise in context of the IEA-Annex 41 project to validate several simulation tools. Theintention of this common exercise is to simulate two real test rooms which are located at the outdoortesting site of the Fraunhofer-Institute of building physics in Holzkirchen. During the winter time testswere carried out with the aim to compare the measurements with the models developed within theIEA-Annex 41 project. As moisture buffering material served gypsum boards.

Field measurements of the indoor climate have been carried out in 128 lightweight timber-framedetached houses in Finland and in Estonia during the years 2002-2005. The temperature and relativehumidity were continuously measured in bedrooms, living rooms and outdoors for each house at 1-hourintervals over a 1-year period.

In this paper, the experiment for moisture buffering and effect of ventilation rate and volume rate of thehygrothermal materials is described. The objective of the experiment is to make clear the relationshipsbetween the moisture buffering effect and, the ventilation and volume rates of the hygrothermalmaterials. In the experiment, a layer of gypsum board as hygrothermal materials is placed on theinterior surface of the test chamber (4.60 m3). This chamber is located in the climate room which cancontrol constant temperature and humidity level (20oC and 50%rh).