Thermal Autonomy

Metrics for quantifying thermal comfort and energy consumption focus on the role of mechanical systems, not architecture. This paper proposes a new metric, "Thermal Autonomy," that links occupant comfort to climate, building fabric, and building operation. Thermal Autonomy measures how much of the available ambient energy resources a building can harness rather than how much fuel heating and cooling systems will consume. The change in mental framework can inform a change in process. This paper illustrates how Thermal Autonomy analysis gives rich visual feedback as to the diurnal and seasonal patterns of thermal comfort that an architectural proposition is expected to deliver. Thermal Autonomy has far-reaching utility as a comparative metric for envelope design, identifying mechanical strategies, and mixed-mode operation decisions. Foremost, it is a generative metric to quantify ways that the building filters the ambient environment. The use of Thermal Autonomy is illustrated through parametric building thermal simulation and analysis. The concepts and techniques presented here were born of practical necessity as well as theoretical discourse. As a firm located in the San Francisco Bay Area, many of our projects are in California coastal climates that should not require building heating or cooling much of the year. In spite of this, most buildings are extensively conditioned even in these climates. Thermal Autonomy is a concept developed to show our clients architects, engineers, and building owners the patterns, degree, and quantity of thermal comfort for a given design. Even in our work in more extreme climates, such as New York or India, we have found that Thermal Autonomy, in concept and practice, is applicable and potent. We often liken Thermal Autonomy to sailing. While modern sailboats are equipped with motors for days without wind, design of the boat is optimized for sail-driven locomotion. So too should buildings be able to "sail" using the "free" energy of wind, air, sun, and internal heat sources to temper the indoor environment. The resultant autonomy is not just a building that is self-reliant but one that is calibrated to the climatic context, connecting occupants to the changing weather.