Moisture buffering capacity of highly absorbing materials S. Cerolini a, *, M. D’Orazio a , C. Di Perna b , A. Stazi a a Department of Architecture, Construction and Structures (DACS), Faculty of Engineering, Polytechnic University of Marche, Via Brecce Bianche, 60100 Ancona, Italy b Department of Energetics, Faculty of Engineering, Polytechnic University of Marche, Via Brecce Bianche, 60100 Ancona, Italy 1. Introduction The demand for controlling energetic consumptions and gas emissions led several European states to adopt regulations requesting low values of transmittance for the building envelope. For this reason designers and building constructors introduce thick layers of insulating material in walls and roofs even in mild climates and the producers of building components are bringing out new highly performing products with regard to thermal performance and air permeability. This fact causes a general reduction of the envelope’s air permeability and the increase of indoor RH% levels in occupied buildings. The importance of indoor RH% on respiratory comfort [1], skin humidity [2] and perceived indoor air quality [3] is well known. Besides, high levels of relative humidity may cause the deterioration of building materials [4] and, in combination with a sufficient nutritive capacity of the substratum, they play a crucial role on mould growth and biological organisms proliferation [5,6]. On the other hand the introduction of HVAC systems providing an adequate mechanical ventilation in order to discharge high moisture loads seems not to be a solution, particularly in small, low-density interiors, such as houses, where it would be a source of noise for people who live into, besides causing a further rise in energetic consumptions. A promising strategy in this sense is related to the use of hygroscopic materials to dampen indoor humidity variations. By means of laboratory and field measurements and numerical models, researchers have shown that several materials used in the building construction (cellular concrete, bricks, wood and wood- based materials [7–10] and cellulose insulation [11]) or in furniture and furnishing [12,13] (textiles, wood and paper) interact dynamically with the indoor air they are exposed to [14], helping to improve indoor climate, in terms of hygienic conditions, comfort and air quality [15,16], and contributing to reduce energy consumption for heating and cooling [17]. The necessity of a standardized quantity to characterize the moisture buffering capacity of materials led [18] to define the Moisture Buffer Value (MBV) and to propose an experimental method for practical categorization of materials. The practical MBV (MBV practical (kg/(m 2 %RH))) is defined as ‘‘the amount of water that is transported in or out of a material per open surface area, during a certain period of time, when it is subjected to variations in relative humidity of the surrounding air’’. The hygroscopic materials tested by the NORDTEST Project [18] are concrete-based, wood, gypsum and brick. Starting from these results and considering the recent innova- tions introduced in material industry, this research tries to extend the dynamic characterization to highly absorbing materials coming from industrial sector. The possibility to use highly performing materials to dampen indoor RH% variations could actually improve the system’s efficiency, allowing to reduce the moisture buffering exposed area. Energy and Buildings 41 (2009) 164–168 ARTICLE INFO Article history: Received 20 May 2008 Received in revised form 1 August 2008 Accepted 14 August 2008 Keywords: Moisture buffering capacity Cellulose Effective thickness Vapour resistance Mass surface exchange coefficient ABSTRACT This research investigates the possibility to use highly absorbing materials to dampen indoor RH% variations. The practical MBV of sodium polyacrylate, cellulose-based material, perlite and gypsum is evaluated for a daily cyclic exposure that alternates high (75%) and low (33%) RH% levels for 8 h and 16 h, respectively. The adjustment velocity to RH% variations and the presence of hysteretic phenomena are also presented. The cellulose-based material proves to be the most suitable for moisture buffering applications. Starting from this material’s properties, the effect of thickness, vapour resistance factor (m) and mass surface exchange coefficient (Z v ) on sorption capacity is evaluated by the use of a numerical model. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +39 071 2204587; fax: +39 071 2204783. E-mail addresses: simona.cerolini@email.it, s.cerolini@univpm.it (S. Cerolini). Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild 0378-7788/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2008.08.006