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Jan. 22, 2016 — In an effort to become one of the most energy-efficient universities in the world, Stanford University in Stanford, Calif., launched the Stanford Energy System Innovations (SESI) project in 2012. At the heart of the three-year SESI initiative is heat recovery.
After researching a number of options, Stanford decided to transition from a fossil-fuel-based, combined heat and power system with steam distribution to an electrically powered, combined heat and cooling system with hot water distribution.
The idea is to capture waste heat from the district chilling system to produce hot water for the district heating system. To make the project a reality, Stanford installed more than 20 miles of hot water piping and retrofitted 155 buildings to convert the campus from a steam- to a hot water-based system.
Stanford and its design engineering team from Affiliated Engineers, Inc., worked with California-based R.F. MacDonald Co. to determine the equipment needed for the heat recovery system. Stanford considered a number of manufacturers for the boiler design and selected Cleaver-Brooks following a plant tour and meeting with its engineering team.
“Stanford’s system is one of the largest, hot water boiler systems of its type, and the CBEX Elite boilers successfully respond to varying heat loads, thus achieving one of Stanford’s main objectives,” said B.J. Sewak, project manager at Stanford. “Cleaver-Brooks’ design team demonstrated their ability to work seamlessly and very quickly with Stanford’s design engineers to come up with a solution, knowing that cost-effective pricing was paramount. Cleaver-Brooks and R.F. MacDonald really showed they were willing to walk the talk. We knew they weren’t just going to pick equipment from their catalog.”
Sewak added that Cleaver-Brooks’ emphasis on safety, its proven ability to customize products, and five-year extended warranty also factored into their decision.
The Cleaver-Brooks large-capacity CBEX Elite firetube boiler met Stanford's specifications of 125 pounds of hot water design pressure and 1,800 HP of nominal heat output at high efficiency with low NOx. Additionally, the CBEX Elite firetube boiler costs less than an industrial watertube boiler, which the university initially thought was required based on the specifications.
Cleaver-Brooks and R.F. MacDonald designed three hot water generators to heat 4,100 GPM of hot water from 160 degrees F return water temperature to 190 degrees F supply water temperature. The equipment was constructed so that each boiler has its own dedicated VSD-driven primary pump.
The boilers fire natural gas, with amber oil as a backup.
Technicians from R.F. MacDonald and Cleaver-Brooks installed the CBEX Elite boilers and auxiliary equipment, including a Cleaver-Brooks economizer, air silencer, combustion air pre-heater, and atomizing air compressor for oil firing.
R.F. MacDonald Vice President Michael MacDonald said it is uncommon to put an economizer on top of a hot water boiler to get the stack temperature down, but they did so in this instance. At high fire on natural gas fuel, the flue gas temperature leaving the boiler is 280 degrees F. The economizer drops the flue gas temperature to 219 degrees F, which results in a fuel savings of 1.5 percent.
The Hawk 4000 advanced boiler room control was included on the CBEX Elite system for even more fuel savings. The Hawk controls the economizer exit temperature control, combustion air heater temperature control, O2 trim control, operating safeties and limits, and start-up and shutdown.
Stanford’s system is one of the largest hot water boiler systems of its type, and the CBEX boilers successfully respond to varying heating loads, thus achieving one of Stanford’s main objectives. Shortly after the hot water system was brought online, it effectively handled campus heating loads, and Stanford was able to shut down its central plant as planned.
Today, about 57 percent of campus waste heat is being reused to meet 93 percent of campus heating loads, and the CBEX Elite boilers are meeting the area’s emissions requirements of 9 ppm NOx firing on natural gas and 40 ppm NOx firing on amber fuel oil.
According to Joseph Stagner, executive director of the Department of Sustainability and Energy Management at Stanford, the SESI project has cut Stanford’s Category I and II GNG emissions by 68 percent and is expected to save the university $420 million, or 31 percent, over the next 35 years compared to the previous cogeneration system.
For more information about Cleaver-Brooks, visit cleaverbrooks.com.