©2018 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 60, no. 9, September 2018.
By Brian Coffield, P.E., Associate Member ASHRAE; Cindy Cogil, P.E., Member ASHRAE
About the Authors
Brian Coffield, P.E., is an associate and mechanical engineer at PAE in Portland, Ore. He was a principal and mechanical engineering discipline leader in SmithGroup’s Washington, D.C., office when he received the Technology Award. Cindy Cogil, P.E., is a principal and director of engineering in SmithGroup’s Chicago office.
American University’s Washington College of Law is one of the nation’s leading law schools, and offers a diverse collection of internationally renowned programs. The College’s purpose is focused on the concept of breaking down barriers through a strong interconnected community and an emphasis on learning as a process of discovery. The building design provides the College with cutting-edge instructional facilities while retaining the site’s historic attributes.
The College of Law project consisted of 65,000 ft2 (6039 m2) of renovations to historic Capital Hall and Chapel structures, as well as 255,000 ft2 (23 690 m2) of new construction comprising two wings (named Nebraska and Yuma after the streets they front) and a connecting atrium space that allows occupants to easily move from one building to another.
A new four-story parking garage was built below the Nebraska and Yuma wings to provide students and faculty parking on campus. The entire site was designated as a National Historic Landmark during the early stages of design, and the approvals process included intensive interaction with the DC Historic Preservation Office and the Zoning Commission. New and renovated buildings form a connected complex of teaching spaces, conference facilities, legal clinic resources, teaching courtrooms, law library, dining hall, alumni center, faculty and staff offices and multiple student study/meeting spaces.
The building program, site constraints and historic architectural design elements resulted in a spread out, low profile building design. Additionally, American University has committed to meeting the American College & University Presidents Climate Commitment and pushed the design team to pursue LEED Gold certification. To meet the project goals, the design team evaluated several different system alternatives.
The installed systems include a single central chilled water plant and single heating hot water plant to generate chilled and heating hot water for the entire law school. Yuma and Nebraska wings are fit out with a dedicated outside air system (DOAS) and radiant ceiling panels (RCPs) to provide ventilation, cooling and heating to all occupied spaces. The atrium space is conditioned with a displacement ventilation system coupled with radiant slab heating to work effectively with the interior design elements. Historic Capital Hall is fit out with an overhead VAV system due to the existing façade constraints and the Chapel is equipped with a displacement ventilation system that integrates with the existing historic interior finishes.
Energy Efficiency
A 720 ton (2532 kW) central chilled water plant includes two magnetic bearing centrifugal chillers coupled with two cross flow induced draft cooling towers. The magnetic bearing chillers are equipped with variable frequency drives and selected with an NPLV of 0.348 kW/ton (0.099 kW/kW). Variable speed cooling tower fans reduce fan power energy dramatically during part load conditions. The chilled water distribution strategy was important since the radiant panels operate using a higher temperature chilled water to avoid condensation on the panel surface. Ultimately, primary low temperature chilled water is distributed using a variable primary pumping arrangement from the chillers to all airside chilled water coils. A secondary distribution loop was designed for the RCPs that connects to the primary loop via an injection circuit and a set of secondary pumps equipped with variable speed drives deliver the warmer chilled water throughout the building.
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