Owner Stanford University
Lead Design Firm/MEP Engineer Affiliated Engineers Inc.
Structural Engineer Rutherford + Chekene
Civil Engineer BKF Engineers
Architect ZGF Architects
MEP Contractor ACCO Engineered Systems
Control System Johnson Controls Inc.
To university engineers, the Stanford Energy System Innovations (SESI) project represents nothing less than a revolution in the way campuses in the U.S. should be heated and cooled. Stanford University eagerly uses SESI to demonstrate to corporate, municipal and other school officials that they, too, can save energy, reduce water use and drastically reduce greenhouse-gas emissions.
The $485-million effort—in fact, four projects in one—replaces an aging 50-MW natural-gas-fired cogeneration plant with a new heat-recovery system to provide heating and cooling to the campus. A new 80-megavolt ampere electrical substation brings electricity from the grid and direct-sourced renewable-energy suppliers. Crews also converted 155 campus buildings from steam to hot-water distribution and installed a 22-mile-long network of new pipe. “You could take any one of those four projects and it would be a significant engineering challenge,” says Krista Murphy, principal with lead design firm Affiliated Engineers Inc. (AEI). “We were tackling all of those at the same time.”
Since completion last April, facilities managers have flocked to study SESI. “We’ve had overwhelming demand—tours are booked months in advance,” says Joseph Stagner, executive director of sustainability and energy management at Stanford. Leaders from other universities, the President’s Council of Advisors on Science and Technology and even France’s ambassador have made the pilgrimage to SESI.
Change of Heart
To learn how Stanford cut campus energy use by 50% and dropped its greenhouse-gas emissions by 68% in just two and a half years, visitors start at SESI’s heart—the 125,614-sq-ft central energy facility (CEF), located on the west side of the campus. The CEF houses what Stanford calls the star of the show: three heat-recovery chillers—the largest in the U.S.—that strip waste heat from 155 campus buildings via a closed chilled-water loop and use it to preheat a separate closed hot-water loop that distributes heat to the same buildings.
From dorms to hospitals to sports facilities, a variety of campus structures provides a huge heat-recovery potential. The system captures 57% of building waste heat, reusing it to meet 93% of campus heating needs. For most of the year, the system precludes the need for cooling towers to discharge excess heat, which reduces water consumption on campus by 15%.
Each heat-recovery chiller (HRC) provides a 2,500-ton cooling capacity for chilled water and simultaneously can produce 40 million BTUs of heat per hour. The HRCs send out chilled water to the campus at 42°F, which returns at 56°F to 60°F. The heat removed from the chilled water as it is cooled back down to 42°F reheats spent hot water (which returns to the CEF from campus at 130°F) back up to 160°F to 170°F to supply heating.
Additional efficiency results from the switch from steam heat to hot water. Line loss of up to 20% in the old steam system dropped to under 4% with hot-water piping. The switch also saves the school several million dollars a year in operations and maintenance. Further, the school’s previous cold storage existed in the form of ice. “Chillers take about 25% more energy to make ice than they do cold water,” he says. By using out-of-date systems that create steam and ice, “America has been hitting it with a sledgehammer because energy was so cheap, and that’s how things evolved.”
The CEF’s thermal storage system contains two 5-million-gallon tanks to store cold water and a 2.3-million-gallon tank for hot water. The tanks double as reservoirs for power, allowing flexibility to operate the heat-recovery chillers and other equipment during times of lower energy pricing or when outside air temperatures are optimal. For example, when it’s hot during the day, excess heat can be converted and stored as hot water, instead of being rejected out of evaporative cooling towers, and then used during the cooler nighttime hours.
A two-story administration building surrounds a small plaza, which has the hot-water thermal storage tank at its center. The tank, painted Stanford red and lit at night, evokes a beating heart at the center of a “system that pumps energy around the campus,” says architect Joseph Collins, partner with ZGF Architects.
Large expanses of glass provide transparency into the areas that house the HRCs and other mechanical equipment. Vivid colors clearly demark the complex piping in a way that provides visual clarity to students and visitors. For example, light-blue piping indicates the cold-water loop returning from campus, while dark blue pipe contains re-chilled water after the heat has been removed. Similarly, hot-water pipes are painted orange and red.
“We do many heat-recovery chillers, but I don’t think we have any that are showcased the way this is, with glass surrounds and strong colors,” Murphy says. “All of it tells a story, even at the equipment level.”
To control the complex system, Stagner spent months programming a control “brain” that models, operates and verifies performance efficiency at the facility. After patenting the system, Stanford tasked control-system subcontractor Johnson Controls to develop it into a viable commercial product. Dubbed the Central Energy Plant Optimization Model (CEPOM), the algorithm performs a 10-day look-ahead every 15 minutes, considering campus loads, weather patterns, price of electricity, available equipment and many other factors. It then computes the optimal dispatch plan, and it can even be used as an “autopilot” to run the plant. The program performs about 30% more efficiently than what a human can do, Stagner says.
Led by contractor Whiting-Turner, construction began in 2012. While one crew assembled the complex plant, another worked its way through the active campus to install 22 miles of new pipe.
Hot-water pipe can be installed more quickly and at less expense than steam pipe, which needs to be buried to a 15-ft depth—below all other utilities—to reduce the risk of heat damage from steam leaks. By contrast, the pre-insulated hot-water pipe system, sourced from Denmark, was buried 3 ft to 5 ft below the surface, without the need to construct concrete vaults or anchors. As a result, crews installed the system in two and a half years, instead of the 10 years it would have taken to replace the steam pipes. The old steam pipes remain abandoned in place.
To convert each campus building from steam to hot water, the team designed a standardized heat-exchanger skid, with only the capacities varying by building. “This allowed the long-lead equipment to be ordered directly by Whiting-Turner before the mechanical subcontractors were hired. The prefabrication allowed building shutdowns to be much shorter, with less disruption to research and building occupants,” says Damon Ellis, Whiting-Turner vice president.
Converting 155 buildings—while the CEF was still under construction and the cogen plant continued to provide steam heat—presented the team with a logistical puzzle. To solve this, AEI turned to regional heat exchangers—also skid-mounted—which converted the cogen’s steam to hot water. Then, a mini hot-water loop transported the water to each pre-converted building. “Use of the regional heat exchangers gave us the single most important ability to execute this job,” says Michael Bove, principal with AEI.
As part of the new substation, crews placed nearly 40 miles of copper wiring underground. Four miles of overlap between the wiring and piping allowed crews to work more efficiently and reduced campus disruption.
While some may balk at the $485-million price tag, the project was “completely driven by astute economics that allow this university to have such a well-crafted and well-performing endowment,” Stagner says. “It’s smart business.”
Stanford carefully studied multiple options, including replacing the natural-gas cogen plant, and found that the heat exchange system would actually cost $459 million less over a 35-year life cycle while providing environmental and efficiency benefits.
“One of the things that we’ve talked to other universities about is to not be too taken aback by the enormity of this project,” Bove says. “Any university could do bits and pieces that have happened here. Stanford just had the vision and ability, both financially and scope-wise, to do it all at once.”
And the technology continues to improve. Stanford’s real estate division retained AEI and architect ZGF to design a new, 1.5-million-sq-ft campus to house 2,300 Stanford employees in Redwood City. Due to efficiencies in the new buildings and their heat exchangers, the system can operate with water heated up to just 110°F, instead of the 160°F needed to heat the main campus. In fact, the team estimates the heat pumps at the new facility will operate at 0.7 KW per ton, instead of the 1.3 KW per ton measured at SESI.
“That’s the evolution of this,” Bove says. “As the temperature comes down, the heat-recovery equipment gets more efficient.”