Consulting-Specifying Engineer - May 2008 - (Page 40) Baseline cost Space heating 11.9% Space cooling 33.5% Pumps 4.9% Cooling tower 0.8% Fans – AHU 8.3% Fans – miscellaneous 1.3% Fans – parking garage 2.9% Service water heating 0.2% Office equipment 7.3% Miscellaneous equipment 5.7% Elevators and escalators 3.1% Lighting – unconditioned 7.4% Lighting – conditioned 14.9% Proposed cost Space heating 14.3% Space cooling 19.9% Pumps 10% Cooling tower 2.2% Fans – AHU 7.7% Fans – miscellaneous 1.7% Fans – parking garage 3.7% Service water heating 0.3% Office equipment 7.3% Miscellaneous equipment 6.6% Elevators and escalators 4% Lighting – unconditioned 6.4% Lighting – conditioned 16% Figures 1 and 2: The baseline energy cost budget (left) and the proposed energy cost budget (right) illustrate a drop in chiller use and an increase in pumps and cooling towers, with a 22.4% overall savings. Source: SmithGroup (Continued from page 36) Office flexibility A 10- x 16-ft pattern of chilled beams is integrated with a 10- x 8-ft pattern of light fixtures, and can accommodate open office space and up to 80% closed offices in a flexible, modular arrangement. The setup eliminates the need to relocate chilled beams for the majority of tenant needs, and light fixtures will only require occasional relocation. Temperature control zoning requires small diameter water tubing and two-way control valves. These easily can be moved if office zoning requirements change, to the extent that each chilled beam could serve as its own temperature zone without any airside modification. Infrastructure Penthouse air handling systems include dual-heat-wheel energy recovery for all interior zones, which constitute the majority of chilled beams, delivering primary air with high filtration and low dew point temperature to offset room latent loads. Normal 100% outside air constant volume operation may be reduced to suit extended occupancy schedules using variable frequency drives and building zone control dampers. Separate air-handling units serve the perimeter chilled beams, operating with a range of outside air percentage in concert with excess ventilation air from interior zones and CO2 monitoring, and enabling off-hour heating with the least fan energy possible. The chilled beam system serves the primary office area extending from the 10th floor down to the second floor. Conventional local HVAC systems serve 200,000 sq. ft of architecturally and programmatically diverse lower level functions, including entrance, parking and elevator lobbies, retail, conference, and dining. Energy benefits Energy modeling indicates that the annual energy cost budget will be 23% below that of ASHRAE Standard 90.1-2004, with a building façade that includes abundant vision glazing. Besides lower fan horsepower, the most notable energy reduction is achieved through waterside economizing. One reason this works is because the free-cooling season for generating 60 F chilled water is much longer than that of a VAV system, or even than that of an underfloor air distribution system, as air-side economizers are constrained by high outdoor relative humidity during “shoulder seasons.” Architectural context For Constitution Center’s new skin, solar energy control, daylight, infiltration resistance, blast-resistance, and views of a 1-acre private inner garden are provided by advanced curtain wall and high-performance (0.3 shading coefficient) glazing technologies, including three thicknesses of laminated glass and a unitized panel system. The views to the outside are equally inviting. In an area that was once considered the edge of the city’s center, the renovated building is now at the hub of a high-activity federal and private sector mixed-use zone with access to commuter rail, subway, and highways. It is also only a short ride from Ronald Reagan Washington National Airport. With the input of David Nassif Assocs., architects, engineers, technology consultants, program manager Kramer Consulting, and general contractor James G. Davis Construction, the Constitution Center is set to emerge as a highly secure yet visually appealing model of sustainable design, energy efficiency, flexibility, and comfort for up to 6,000 occupants. Karidis is vice president and director of mechanical engineering with SmithGroup, Detroit. 40 Consulting-Specifying Engineer • MAY 2008
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