scope:

INTRODUCTION

The occurrence of inwards vapor flow, leading to interstitial condensation or moisture accumulation in interior finish materials, has been identified and studied by various researchers, e.g., Wilson 1965; TenWolde and Mei 1985; Sherwood 1985; Southern 1986; Andersen 1987; Sandin 1993; Straube and Burnett 1995; 1998; Künzel 1999, 2005; Karagiozis 2002; Pressnail et al. 2003; Lawton and Brown 2003; and Wilkinson et al. 2007. Studies have investigated occurrence of this phenomenon both in hot and humid, and cold climate areas and for different compositions of wall assemblies. Various strategies have been suggested by researchers although not all studies agree on the effectiveness of each proposed method. Most of the previous work done on inwards vapor transport aimed at reporting the occurrence of inward moisture movement due to high temperature gradient, and a full set of data had not yet been produced and analyzed. The cyclic vapor flow driven by solar radiation and the influence of the wall composition on the hygrothermal performance and durability of wall systems subjected to such flow needed to be further looked upon to provide a more comprehensive understanding of the phenomena. To answer these needs, a project entitled "The nature, significance and control of solar-driven diffusion in wall systems" (ASHRAE RP-1235) was initiated and supervised by ASHRAE Technical Committee TC 4.4 "Building Materials and Building Envelope Performance." Three institutions were involved in this project, namely the Building Envelope Laboratory of Concordia University, Montreal, Canada, the Building Physics Laboratory of the Katholieke Universiteit Leuven (KULeuven) Belgium, and the Building Technology Center at Oak Ridge National Laboratory (BTC/ ORNL). Drs. Dominique Derome, now with Swiss Federal Laboratories for Materials Testing and Research (EMPA) Switzerland, Jan Carmeliet, now with Swiss Federal Institute of Technology Zürich (ETH Zürich) and EMPA Switzerland, and Achilles Karagiozis of ORNL formed the team of researchers at the heart of this project.

The overall objective of the project was to develop a better understanding of the nature and significance of solar-driven inward vapor diffusion. More specifically, the project intended to:

• to identify under which conditions (climate, wall compositions) solar driven vapor transport may lead to durability problems

• to develop appropriate design guidelines to predict and manage this phenomenon as a function of climate

• to transfer the knowledge generated from this research into the ASHRAE Handbook of Fundamentals.

This paper presents a summary of the work performed in this project. Figure 1 presents the interrelations of the different tasks of the project. The next section reports the experimental work which looked at the behavior of assemblies using smallscale samples and large-scale samples in laboratory settings, and in the field. The following section reports the parametric study performed using simulation. Finally, guidelines and major conclusions are presented.