Moisture Control in Indoor Environments: When Hygric Inertia May Contribute to Deliver Better Comfort Conditions

The importance of moisture control in indoor environments is increasingly recognized Air humidity affects buman bealth and comfort, and it is also connected to the durability of several building components and to energy efficiency. In many cases, it is possible to control the level of humidity with passive solutions, taking advantage of the moisture buffering capacity of hygroscopic materials. Nevertheless, current standards do not give any prescriptions on this matter. In this paper we investigate how the hygric inertia of a room may contribute to improve the indoor comfort conditions. In particular, the aim is to fix a desired value of hygric inertia of a room in relation to its size, use and air change rate in order to maintain the amount of relative humidity under a given threshold. The study has been conducted through simulations, using the Effective Capacitance model with the software TRNSYS 18. The indoor conditions are typical of the winter period in a cold climate, with a constant air temperature of 20°C and a very low humidity of the inlet air (30 %RH). Two moisture production patterns have been used to simulate the conditions of a bedroom and of a living room, and the maximum value of relative humidity has been registered after 10 days of simulation. This study demonstrates the importance of the hygric inertia to mitigate the peaks of humidity, especially in the case of small rooms. A good ventilation remains the most important condition (also considering indoor air quality), but high values of bygric inertia, which can be obtained through the use of finishing materials with a good moisture buffer value, allow to avoid over-ventilation also with great benefits in terms of energy consumption.