Integrated hygrothermal performance of building envelopes and systems

Many recent, moisture-originated failures in  low-rise residential and  high-rise residential/commercial buildings have put a significant pressure to change construction codes in North America and Europe. However, solutions to moisture induced problems may be difficult when several interacting mechanisms of moisture transport are present. Recently, a new approach to building envelope durability assessment has been introduced in North America. The approach employs moisture engineering, which requires system information about the wall systems as constructed or with aging characteristics coupled with advanced modeling to predict the long-term performances of building envelope systems. This permits the comparison and ranking of individual building envelope systems with respect to total hygrothermal performance. While critical information can be obtained by investigating the one to one relationships of a building envelope to interior and exterior environments, the total behavior of the actual whole building is not accounted for. This paper goes one step further, by incorporating the individual hygrothermal performances of all walls, roof, floor and mechanical systems. The direct and indirect coupling of the building envelope and indoor environment with HVAC system are included in the analysis. The full house hygrothermal performance of an aerated concrete wall system are examined for a hot and humid climate. The hour by hour drying potential of each system was then numerically analyzed using real weather conditions of Miami. The results clearly demonstrated the limited drying potential for the wall  system  in  that  climate.  Furthermore,  the selected exterior thermal insulation strategies and interior vapor control strategies in this study clearly show the critical behavior of the full house with respect to drying initial construction moisture. The results show the importance of the total hygrothermal behavior of the whole house to the coupling between the various envelope parts, interior and exterior environments and HVAC system. From these results moisture control strategies  are  identified  for  the   whole  house hygrothermal performance.