Impact of air infiltration rates on moisture buffering effect of wooden surfaces

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. The air infiltration is usually taken into consideration simply as an additional fraction of air exchange. However, infiltration has a rather complex nature and can result into more localized effects compared to ventilation (mechanical) that mostly applies globally to a room. In this paper, the moisture buffering phenomena linked to the variation of air infiltration rates are studied in a cross laminated timber (CLT) test house. Both CO2 and moisture are released in the room. The infiltration rates are calculated using tracer gas techniques (CO2 decay method), while the air exchanges are calculated based on the decay of RH as well and the results are compared. In addition, the indoor relative humidity (RH) and moisture content in the construction elements are measured in different monitoring positions. The impact of airtightness and infiltration rates on the overall (‘global’) moisture buffer capacity is studied. Furthermore, the influence of the leakage location on the ‘local’ moisture buffer capacity of each monitoring position / element is also tested. Finally, the potential of using moisture is as ‘tracer gas’ for estimating the air exchanges in a room is researched.