C031 -- Building Enclosure and HVAC System Interaction - How to Minimize Risk and Design for Success

The pace of advancement in building enclosure and mechanical system technologies in the United States (and beyond) has been significant over the past few decades, with vast improvements in durability, reliability, and control over interior environmental conditions. Unfortunately, that development has largely occurred in parallel, rather than in conjunction, with designers from each discipline rarely “crossing over” to better understand the other. In the construction of modern buildings as well as in the renovation of existing ones, this lack of understanding can lead to significant problems, especially where high-performance façade systems are utilized. Due to the multiple contributing factors, when not addressed early in the design process, these problems can be difficult to solve, often requiring creative but economically inefficient solutions.

Even as little as 50 years ago, the design of both building enclosures and mechanical systems was relatively simple. There were few governing codes and standards and expectations from building occupants were less stringent. As the industry has progressed, modern energy codes and the drive towards advanced building enclosures have led to buildings that are more airtight and better insulated than their predecessors but simultaneously less robust and more sensitive to moisture and construction defects. This is especially true for buildings constructed to stringent standards such as Passive House. Mechanical systems have evolved as well, both in terms of energy efficiency and the ability to provide better control over interior environments.

Without well-defined codes and standards, it is left up to the designers to understand how these systems impact each other. This paper will review both typical and atypical interactions between building enclosure and mechanical systems, including issues of condensation, air pressure imbalances, and occupant thermal comfort. The authors will present a framework for initial discussions among building design teams that can help to identify potential problems and work together to develop solutions.