Dynamic modelisation of interaction between wall and indoor air

The current methodology used for testing the thermohygrometric behaviour of building structures is proposed by the standard UNI EN ISO 13788. This Standard evaluates the risk of hygrometric damages due to: 1) critical moisture conditions of the inner surfaces of the building; 2) interstitial condensation within the structures The proposed procedures are valid in the case of steady state and are applied on a monthly basis. However, the steady state calculation is not completely correct mainly because the vapour production is not constant neither in time nor in space. For example, residential buildings are not occupied during most of the day. Therefore, in the case of a residential building, there is an intense generation of moisture mainly during a certain period of the day. Then, for a better control of the indoor values of relative humidity (and of partial vapour pressure) inside a given room, the indoor moisture production should be not considered constant and it may be appropriate to assess the importance of the hygroscopic properties the walls and furniture, able to act as a moisture buffer. In this paper, using a simplified model taking into account the interactions between the vapour concentration of the indoor air and the interior walls and furniture, the role played by the hygroscopic capacity of the indoor walls and furniture for the evaluation of indoor relative humidity is analyzed.