Performance of Compact, Closed Cavity, Double-skin Curtain Wall

A proposed design for a compact, closed cavity, double-skin curtain wall system in the Marine climate of the West Coast raises questions of potential for interstitial condensation. The design calls for a closed cavity enclosed with insulated glazing units on the exterior side of an aluminum frame and a single glazed light on the interior. The potential for air infiltration into the closed cavity creates the risk for condensation within the cavity during extended periods of cold weather. Condensation is considered problematic since the sealed nature of the system would not allow for access to clean the glass. In a first step a three-dimensional analysis of the proposed curtain wall design is undertaken to identify surface temperatures. This allows accurate assessment of the potential for condensation. The analysis confirms that condensation is likely assuming the curtain wall framing experiences air infiltration. Strategies for mitigating the effects of condensation were examined to better understand their benefits and shortcomings. An estimate of the volume of desiccant required to mitigate the potential for condensation is calculated. The volume of desiccant proves to be excessive and the option of pressurizing the interstitial cavity to minimize infiltration is examined. The option of using the building’s mechanical system to pressurize the cavity is analyzed. Energy modeling software is used to simulate the air exchange and evaluate the impact of pressurizing the cavity using the mechanical system. The results of this analysis confirm that a dedicated ventilation system will be required to substantially mitigate the risk of condensation.