September 01, 2007
Appeared in Distributed Energy
The 2000 Avenue of the Stars (2000 AOS) project, the latest chapter in the colorful story of Century City, has created an energy-efficient 21st-century office, dining, cultural, and retail center—with one of the few exclusive central plants in this business district—in the heart of the west side of Los Angeles. The project, a redevelopment of the 30-year old former ABC Entertainment Center and famed Shubert Theater in Century City, consists of a 720,000-square-foot, 12-story, class-A office tower, along with 45,000 square feet of destination dining, a retail/café promenade, a 10,000-square-foot cultural center, a 3.75-acre landscaped park, and a rooftop central plant.
Syska Hennessy Group’s engineering solutions for mechanical-electrical-plumbing (MEP) systems optimize energy consumption with flexibility to accommodate future demand. A life cycle analysis was completed to determine the payback of engineering a central plant on the roof of the building versus purchasing hot and chilled water from a third-party central plant facility, as do most other business residents of Century City. Syska was also engaged to provide MEP design services for such tenants as Creative Artists Agency, the Annenberg Foundation, and Imperial Capital. Trammell Crow Co., one of the largest diversified commercial real estate companies in the nation, is the developer of this project. The project architect was Gensler Associates.
Building on Energy Efficiency
Energy efficiency is the foundation of this project. The proposed project was to replace the existing 600,000-square-foot entertainment center. As a result, the community was extremely sensitive to the environmental impact of this project. It was essential to demonstrate the building’s energy efficiency despite its large scale. Syska Hennessy’s team performed an energy consumption analysis in coordination with the developer and the environmental agencies to evaluate potential environmental impact. The studies compared the projected utility usage for the new building against the history of utility consumption of the old buildings, demonstrating savings of 15% to 20%.
The 2000 AOS building envelope is, without a doubt, the most energy-efficient design in the Century City area due to double-glazed, low-E glass with a shading coefficient of 0.34. Moreover, the building’s mechanical system has an airside capacity of 1.3 cubic feet per minute per square foot and 310 square feet per ton of chiller capacity. The building is also equipped with a 100% outside air economizer to maximize energy savings and to provide a high-performance building system. In addition, supply-air velocities and chilled water temperatures were conservatively selected in order to minimize energy consumption while providing for the flexibility to increase capacity, if necessary.
Most residents of the Century City business park purchase domestic hot and chilled water from a third-party central plant. The 2000 AOS building is adjacent to Century Plaza Towers on the same large site. Initially there was consideration given to designing a larger central plant that could accommodate the Century Plaza twin towers as well as the new 2000 AOS. However, achieving that objective would have required use of a large portion of the Central Plaza, which the developer and City of Los Angeles had agreed would be retained as part of a cultural component for the community (as part of the project, the existing concrete plaza was replaced with landscaped green space). Therefore, it was decided to investigate the feasibility of building a smaller central plant exclusively to serve 2000 AOS.
Based on a projected system life cycle of approximately 25 to 30 years, MEP engineers calculated that the central plant offered a three- to four-year payback compared with the cost of purchasing hot and chilled water from the third-party supplier. Moreover, the owner is not subject to rate fluctuation based on demand.
In the Central Plant
The 2,500-ton central plant comprises two 1,000-ton chillers, one 500-ton pony chiller, associated cooling towers, and pumps. Two custom field fabricated air-handling units, one for the south side of the complex and one for the north side, are located in the rooftop mechanical rooms. The air-handling units are controlled by energy-efficient variable-frequency drives, which constantly monitor the load and adjust the speed of the fans according to the demand. This feature allows for significant reduction of electrical consumption as well as extending the life of the equipment. In addition, for off-hour usage, each floor of the building is controlled by dampers that open and close depending on the HVAC load requirements.
One critical challenge for MEP engineers was that of designing efficient rooftop equipment layouts to occupy no more than one-third of the roof area. It was essential to meet this requirement in order to make the rooftop central plant a viable option. The City of Los Angeles Department of Building and Safety requirements allow only one-third of the roof area to be enclosed for equipment installation in order to be considered as a mechanical penthouse floor. Mechanical penthouses are allowed to have limited structural support—otherwise, the roof is considered to be an additional floor, which requires beefing up the structural steel at a substantial additional cost. Because the building was already at the maximum height limit set by the city, this additional floor was not feasible.
Another challenge was the cost of the rooftop chiller room. In order to limit this cost, Syska utilized the open space beneath the helipad. So doing, it was only necessary to enclose the open sides under the helipad to create the chiller room, which was accomplished at a fraction of the cost of constructing a completely enclosed rooftop mechanical chiller room.
The central plant was camouflaged from view as much as possible to maintain the aesthetic standards desired by the community, the adjacent tenants in the Century Plaza Towers, and the developer.
The Atrium Challenge
In addition to the challenges associated with the central plant, major design changes were required to suit the requirements of Creative Artists Agency, which signed a lease agreement when the construction drawings were about 50% complete. The new design included a six-level atrium, a full bank of private elevators dedicated to the tenant, the expansion of the smoke control system, and the doubling in size of the safety system’s diesel generator set and associated system of emergency power distribution.
Schirmer Engineering, the fire consultant, developed a rational analysis and negotiated its safety parameters with the city. Syska engineers applied the rational analysis to make the system work, replacing the exhaust fans, supply fans, and smoke control system.
The biggest assets for 2000 AOS are the flexibility and efficiency of all of the building systems. For example, the electrical distribution system is designed to allow for a step-down transformer on each floor, which is located centrally—close to the load—to ensure reliability and allow for flexibility to accommodate various tenants. This system provides quality power by limiting electrical interference and other electrical system byproducts, particularly harmonics, which interfere with such electronic equipment as computers and servers.
Another feature is the automated electrical usage–monitoring system, which monitors and records each tenant’s electrical usage and reports the data to a central location for retrieval, analysis, and forecasts. It is remarkable that it was not necessary to increase the size of the Department of Water and Power vaults for electrical service (although some of the equipment was replaced), thanks to the energy efficiency of the building.
With completion of 2000 AOS in January 2007, Trammell Crow has achieved its goals: an energy-efficient, intelligent premier office, dining, cultural, and retail complex powered by a central plant that will pay for itself in as few as three of its expected 25–30 years.
Ali Hadian is senior vice president of the Syska Hennessy Group, Los Angeles.