Moisture buffering "active" devices for indoor humidity control: preliminary experimental evaluations

Abstract In recent building practice, obligations of legislation relating to Nearly Zero Energy Buildings (NZEB) (European Directives 2002/91/EC and 2010/31/EU) are carried out mainly by high thermal resistance and total air tightness of the envelope, in order to minimize heat dispersions by conduction and infiltration as much as possible. These measures cause new ways of heat and moisture exchange in the building envelope and are likely to create high internal moisture load with consequences for durability of materials and inhabitants’ comfort and health. Improvement in the thermal performance of the envelope can then lead to the paradoxical need for high energy consumption in order to handle the vapor peaks indoors by using mechanical ventilation equipments. Even if with HVAC devices it is possible to provide an acceptable indoor climate, there is still a need to develop more passive and less energy intensive methods to moderate the indoor environment in NZEB. In recent decades many authors have focused on a promising strategy related to the use of “moisture buffering” materials which dampen indoor humidity variations without additional energy costs. Nevertheless, many internal finishing materials commonly used at present are still not highly performant or lead to problems of hysteresis. In the present study, we propose an alternative solution, which is the design of a moisture buffering “active” device, to be integrated in a part of the building envelope, which is able to measure the relative humidity indoors and control its loads by a low-energy-consumption fan system. The humidity control performance of the device has been dynamically tested in a climate chamber and has been compared with traditional “passive” material samples in order to measure the Moisture Buffering Value (MBV) according to the DTU test method. Experimental results showed that “passive” samples have high moisture buffering values [MBV = 6.12 g/(m 2 % RH)] and do not lead to hysteresis phenomena. The MBV measured in the “active” devices increased up to 29%, which predicts promising future applications for low-energy-consumption indoor humidity control.