The San Francisco Public Utilities Commission (SFPUC) headquarters in downtown San Francisco at 525 Golden Gate—called "the greenest office building in North America"—opened in July 2012 to widespread acclaim for its sustainability and energy savings. Compared to similar 13-story office buildings, 525 Golden Gate produces 50 percent less of a carbon footprint and uses 32 percent less energy and 60 percent less water.

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The SFPUC headquarters houses more than 900 employees and includes a data center in the lower level, a childcare center and café. For ratepayers, the SFPUC estimates that building and owning its new headquarters will allow the department to save local residents around $3.7 billion ($500 million in 2012 dollars) over the expected 100-year life of the building. 

Solar and wind power, high efficiency mechanical systems, natural ventilation and daylight harvesting all contribute to the remarkable energy savings at 525 Golden Gate. The exterior of the sleek 13-story building uses roof-mounted solar arrays and wind turbines which can generate up to 7% of the building's energy needs. On the interior, additional shading devices control glare and minimize heat gain while light shelves facilitate daylight harvesting. Lighting and work station equipment shut off automatically after hours. SFPUC's goal was to be an example for building smart, efficient and sustainable buildings in response to the dwindling natural resources, said Masoud Vafaei, SFPUC's Project Engineer.

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Complexity demanded teamwork

The scope of the SFPUC building project entailed an exacting design and construction process. Nial Keeling, P.E., project engineer for heating, ventilating, and air conditioning (HVAC) with ACCO Engineering Systems in San Leandro, California, the mechanical contractor on the project, said the project's complexity demanded great teamwork and relied on building information modeling (BIM). "This was not a standard job. The sheer volume of paperwork involved in this job, including owner-directed changes and RFIs (requests for information), was huge due to the complexity of the systems. Everyone on the team worked well together."

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SJ Engineers of San Francisco, California, provided the mechanical engineering including HVAC, plumbing and fire protection at 525 Golden Gate. Any chillers selected for the building's HVAC system had to meet extreme efficiency requirements in order to meet the design goal of LEED Platinum certification. "An analysis had to be made in non-biased conditions to determine the type of efficiencies each chiller manufacturer could achieve," said Kreyne Sato, principal engineer at SJ Engineers.

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On the interior of the building, shading devices control glare and minimize heat gain while light shelves facilitate daylight harvesting.

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After factory certified testing to AHRI (Air Conditioning, Heating & Refrigeration Institute) Standard 550/590 for water cooled chillers, two Daikin Magnitude chillers were selected—one 500-ton and one 250- ton unit. With their magnetic-bearing oil-less compressors and integral variable frequency drives, these chillers are 40 percent more energy efficient than traditional centrifugal compressor chillers. In addition to their efficiency, the compact footprint, weight, and electrical service of the Daikin chillers were factors in their selection, according to Sato.

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The performance of the Magnitude chillers allows the building to satisfy every operating condition efficiently, especially at part load which occurs frequently in the mild San Francisco climate. "There's always demand for cooling in this building. You have the data center in the lower level and other areas that require cooling every day," said Ron Yaffe, senior sales engineer at Norman S. Wright Mechanical Equipment Inc., representatives for Daikin in the San Francisco area.

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Traditional mechanical system with a modern twist

The building's HVAC system design is based on a traditional four-pipe system and includes the two chillers, two rooftop cooling towers for the chilled water system, two large variable air volume (VAV) custom air handling units, heat exchangers, and an underfloor air-distribution system that conserves building space and minimizes ductwork and uses personal control of airflow. "The chillers are inherently efficient," says Alex Brown, senior engineer with SJ Engineers. "In addition, we also included other efficiency features such as a chilled water economizer that goes into the system which allows the chillers to ramp down to their minimum capacity before shut off."

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The building's underfloor air-distribution system (also known as a raised floor plenum) accommodates data lines and most of the ventilation infrastructure including air handling equipment, as well as linear and swirl diffusers in the floor supply air for cooling. The building envelope includes operable windows which occupants can control. If a window is opened, the building automation system shuts off the flow of conditioned air through the underfloor system to the corresponding zone.

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The advanced underfloor system serves to reduce heating, cooling and ventilation costs by more than fifty percent. Overhead areas accommodate return air booths. "From a service point of view, it's very practical for equipment to be accessed with fewer restrictions than overhead placement allows," Nial Keeling said.

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