Bridging The Mechanical / Enclosure Gap

In the United States, the realm of building enclosure design and commissioning is separate and distinct from the realm of mechanical design and commissioning. This paper will illustrate how and why these disciplines have been historically separated and outline the consequences of this division and describe the opportunity that a closer relationship between the two represents in terms of costs and environmental impact.
Building Enclosure Commissioning (BECx) is a mature process designed to ensure a building’s exterior and its environmental separating materials and assemblies meet an Owner’s Project Requirements (OPR) in terms of durability and air tightness. The results of BECx efforts are both predictable and measurable. How can the BECx process better dovetail with the work of mechanical design and commissioning to inform mechanical design in terms of system type and size?
Today, mechanical systems continue to be designed and evaluated largely independent from a building’s predicted or actual air leakage parameters. Given the significant carbon impact associated with the construction of new buildings, durability is a paramount value in the fight against climate change. Similarly, mechanical systems, in addition to providing the environmental conditions necessary for human comfort and health, also present an enormous energy draw and carbon contribution at the global level. While the importance of building air tightness and mechanical efficiency are symbiotically interlinked in terms of their function and importance, there is a fundamental practical and cultural divide in the practice of designing, constructing, and evaluating these systems. This divide represents a void of understanding as well as an enormous opportunity for cooperation among the design and commissioning professionals responsible for a building’s enclosure and its mechanical systems.
State-of-the-art BECx processes include testing and metrics such as whole building air tightness protocols that reveal the actual air leakage of a constructed building. These tests can be conducted to include and exclude mechanical systems, thereby providing a wealth of information for the benefit of both designers and owners.
This paper first summarizes the existing BECx process by which building air tightness and durability can be predictably achieved and measured. It goes on to discuss ways the result of these efforts can been incorporated into mechanical design and commissioning efforts. Case studies from the authors’ work together on a set of elementary schools in Massachusetts substantiate the assertion that a tight range of predicted results can be reliable in terms of design projections.
The paper will conclude with recommendations for a model with which the correlation of projected enclosure leakage rates can inform both the initial equipment as well projected energy cost of mechanical systems. When available and considered, this information can inform decision making models to dramatic effect: Because first and operational costs of mechanical equipment are variables that are dependent on equipment size, type, and efficiency, owner’s equipped with accurate predicted mechanical performance are empowered to understand the impacts of their decisions in terms of payback duration, cash flow modelling, carbon impacts, and lifecycle costs.