Holistic approach to achieving low-energy, high-rise residential buildings

As codes and standards evolve toward low- or net zero–energy buildings, the practicality of achieving these targets in high-rise concrete construction gets increasingly challenging. High-rise residential buildings are becoming more common as cities redevelop and add density. Current design and construction practice for high-rise multi-unit residential buildings present a number of constraints with regard to achieving high levels of energy performance. These practice issues typically include (a) the desire to maximize glass to enhance marketability, daylight, and views; (b) the desire to provide access to the outdoors via extended balconies; (c) the need for Code-mandated non-combustibility and life safety requirements; (d) a preference for building systems that minimize exterior construction access and streamlines construction sequencing; (e) the adoption of increased structural load requirements; and/or (f) the drive to minimize initial capital costs. The outcome of these combined constraints is often poor energy efficiency, with the burden of higher operating costs deferred to future owners. There has been significant industry discussion on the poor energy performance of this class of building, but there is very little guidance or long-term factual strategic information beyond broad principles of minimizing glazing areas, maximizing glazing performance, increasing airtightness, and adding more insulation to opaque areas. This article explores the prospect of energy use becoming a primary consideration in high-rise residential buildings and what that will likely mean for the typical competing constraints mentioned earlier. This article utilizes the current common construction practices for concrete-framed, high-rise residential buildings in heating dominated climates (ASHRAE Zones 4 to 7) as a baseline to evaluate the impact of the interconnected variables related to reducing overall heating energy use. The objective is to weigh the impact of individual improvements against integrated bundles of measures to develop a roadmap and a better understanding of a practical path toward low-energy, high-rise residential buildings. The article focuses on solutions related to building envelope performance but from a holistic perspective that recognizes the interaction and contribution of mechanical systems typical of this construction type. The building envelope parameters covered includes glazing performance (for both conventional and innovative technologies) and opaque wall performance (with a focus on specific details to reduce thermal bridging rather than increasing insulation levels). The analysis presented draws upon three-dimensional thermal modeling, whole building energy analysis, field testing and monitoring, and typical construction costs. The goal is to develop realistic targets for high-rise buildings and identify improvements that can be arrived at by market forces rather than those that can only be realized through more stringent and enforceable codes and standards.