©2013 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 55, no. 5, May 2013.
By Mark O. Koller, Member ASHRAE
About the Author
Mark O. Koller is a senior mechanical engineer at Interface Engineering in Portland, Ore. He is a member of the Oregon ASHRAE chapter.
The Portland State University (PSU) Academic and Student Recreation Center (ASRC) is located on the campus of Portland State University in the heart of downtown Portland, Ore. The 208,000 ft2 (19 323 m2) building serves as the new home for the PSU School of Social Work, the Oregon University System Chancellor’s Office, the PSU Student Recreation Center, the PSU Bike Hub, the City of Portland Archives, as well as other retail and restaurant tenants. Its central downtown urban-infill location, where an outdated single-story structure once stood, capitalizes on existing utility infrastructure and public transportation, with light rail, streetcar, and bus routes directly adjacent.
This fast-tracked design build project presented challenges to the design team, not only with regards to schedule and budget, but also challenges associated with accommodating the many different uses, tenants, and occupancy types within the building. Mechanical systems needed to be designed to address the needs of classrooms, offices, retail, a gymnasium, restaurants, natatorium, multiuse rooms, and archive spaces. Additionally, all of the complex interactions between building systems and tenants needed to be accurately modeled to estimate energy consumption. In the end, the project was delivered on time, within budget, exceeded its LEED target, and has been consuming less energy than predicted.
The following is a summary of the main building systems, energy savings strategies, and design considerations implemented at the PSU ASRC. Also included is information on the building’s predicted and actual energy use.
One of the central energy savings strategies at the ASRC was the reuse of an existing groundwater extraction well. Underneath an existing sidewalk directly adjacent to the project site was an old 170 ft (52 m) deep groundwater well, which was constructed in 1968, and served the previous building’s mechanical systems in a single-pass configuration. The groundwater was pumped from the ground by a vertical line-shaft pump, where it was then used by the previous building’s mechanical equipment, and then discharged directly to the sanitary system.
The design team saw this existing groundwater well as a valuable site resource that could be used for the new six-story ASRC facility. The existing well could produce 340 gpm of 56°F (21 L/s of 13°C) water, which was calculated to be enough to provide direct cooling for the new facility on all but the warmest periods of the year. To supplement the cooling provided by the groundwater on the warmest periods of the year, a small supplemental air-cooled chiller was designed into the new system. In addition to rehabilitating the existing well to like-new condition, a new injection well was drilled to deliver the groundwater back to the aquifer, instead of dumping it to the sanitary system as the original building did. Figure 1 provides a simplified schematic of the groundwater, chilled water, and condenser water loops in the new ASRC building.
Iron fouling bacteria, as well as other forms of contaminants can be an issue with open loop groundwater systems. As a precaution against contamination, as well as to hydraulically isolate the building systems, plate heat exchangers were used to separate the groundwater loop from the building’s water loops. Additionally, a new premium efficiency pump motor was provided and controlled with a variable speed drive. The variable speed drive allows for slowly ramping up or down of the groundwater flow to meet building demand, as well as reduce disturbed sediment from being brought up by the well.
Heating Water System
The building heating water is provided by two high-efficiency condensing natural gas boilers with 15:1 burner turn down capabilities and boiler management system. The condensing boilers are complemented by a building distribution system that is configured with variable-primary pumping that minimizes pump energy. It features variable speed pumps, two-way valves, and a minimum flow bypass. Each 3,000 MBh (879 kW) boiler is sized for approximately 50% of the total building load, allowing the boilers to modulate in unison to precisely meet the building load, as well as to maximize the efficiencies of the boilers by maintaining as low a firing rate as possible.
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