FIXING CONCRETE: THE “PASSICHANICAL” WALL SYSTEM

Passive first, then active. That’s my design philosophy. Passive design requires an understanding of the science of how specific climatic variables interact with building materials and assemblies. In buildings, passive happens in the zone of the envelope and so I’ve come to see envelope design as paramount. Recently, I’ve been working with Thomas Gentry and Brett Tempest to develop a high performance wall system that blurs the line between building envelope and mechanical system. I’m calling it “passichanical” somewhat tongue and cheek, but maybe that will stick. Here’s a brief slighty technical synopsis of the design:

Building envelopes save energy by reducing the work required by mechanical systems to maintain interior comfort. They can accomplish this in at least three basic ways: 1) resisting the flow of heat with insulation; 2) storing heat with mass; and 3) regulating solar heat inputs to maximize or minimize gains through glazing and shading strategies. The current state of the art in the US focuses primarily on #1 for residential construction and on #3 for commercial construction, therefore considerably reducing the potential efficiency of standard building envelopes. When mass is incorporated in envelopes it is usually not configured to take advantage of thermal characteristics. In addition, as we’ve said, the ubiquitous mass material in use, portland cement concrete, requires huge primary energy usage to produce and consequently is responsible for approximately 7% of worldwide carbon emissions.

To address these deficiencies in current building envelope design, a wall system has been developed and is currently being studied at UNC Charlotte that consists of an optimized, engineered combination of innovative technologies creating a dynamic building envelope : 1) a geopolymer cement concrete (GCC) that drastically reduces the primary energy required to produce concrete; 2) a thermo-active building system (TABS) that utilizes hydronics, increased mass surface area, and roof mounted heat exchangers to deliver low-energy heat transfer in and out of the wall; 3) a carbon fiber epoxy composite that creates a structural connection between interior and exterior concrete wythes without thermal bridging or compromising hydronic thermal exchange; 4) an approach to macro-encapsulated phase change material (PCM) application that eliminates the partial phase change phenomenon common with PCMs; and 5) a unique approach to concrete mix design that optimizes for thermal performance through calculated attenuation of paste to aggregate ratios based on desired thermal response . These innovations in combination with existing continuously insulated, thermal bridge free precast concrete technology produce a revolutionary wall system that maximizes performance in all three categories for envelope energy savings: 1) insulation levels are not limited by cavity depths as in framed construction; 2) mass is configured inside insulation to take full advantage of thermal storage with volume and mix design easily adjustable to meet climate and site specific high performance requirements; and 3) the interior concrete wythe becomes a multi-layer passively augmented component of the mechanical system allowing for nuanced control (input or removal based on season) of solar and other heat sources.

WHY?
I grew up in the intense heat of Central Texas where everything living is in a constant search for shade. Whether a cow under a tree or a dog under a porch, the rationale was consistent and obvious. This logic was carried through by us humans in the older neighborhoods where houses with large front and screened back sleeping porches were nestled under the spreading canopies of oak trees clearly older than the houses themselves. This changed. Maybe it was the arrival of air conditioning and the money to be made by replacing trees with more houses. Whatever the reason, newer neighborhoods were treeless and porchless and HOT. The contrast was stark and unequivocal. The newer neighborhoods (tellingly relabeled “developments”) locked in a dependence on fuel driven, breakable mechanical systems and set a hefty baseline energy usage. They also defined two completely distinct environments, with the inside becoming a sort of prison of comfort discouraging inhabitants from venturing outside as part of their daily home life.  The older neighborhoods, on the other hand, used passive strategies (trees, overhangs) to adjust the microclimate around the buildings toward the human comfort zone, lowering cooling loads and therefore baseline energy demand while creating a “third environment” around the house that encouraged a lifestyle that included being outside.. I didn’t realize it then, but this was my first lesson in passive design and it set the tone for my future work in sustainable design. Though I see mitigating climate change as a central macro-rationale for my work, I believe that the sensible path to efficiency leads to a better, healthier lifestyle. Over the years I’ve gotten deeper into science of building envelopes and increased the scale and scope of the projects and materials that interest me, however the throughline in my research has remained constant and can be described by the motto: passive first, then active.
WHAT?
I conduct research into materials, assemblies, and systems in the context of building envelopes. I am particularly interested in high performance assemblies and how to configure them so that they interact with site conditions to minimize heating and cooling loading while maximizing durability. My associated research life has comprised essentially three phases: (1) site harvested and waste materials modeled on traditional hygroscopic systems; (2) mass produced materials and assemblies that increase functionality within the existing construction industry while maintaining certain benefits of traditional systems; and (3) concrete technologies, specifically with the goal of improving concrete’s carbon footprint and maximizing its thermal performance potential in building envelopes.
HOW?
I generally try to connect all research I do to a design project and connected publication. Sometimes this cycle has been very personal. For example when I lived in a two room mountain log cabin for three years and took a self-directed course in homesteading. Most often it has been tied to residential design and publication projects. As my interests have moved toward the larger scale and industrial, I have moved into a traditional academic lab research and journal/conference publication paradigm.