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By Joseph Stagner, Executive Director- Sustainability & Energy Management, Stanford University
In March 2015, Stanford’s new combined heating & cooling (CHC) district energy system known as the Stanford Energy System Innovations (SESI) began operation. Over its first two years, SESI has exceeded expectations, operating slightly more efficiently, ten percent cheaper, and with greater greenhouse gas reductions and water savings than planned. Stanford is also investigating several enhancements that could make SESI even better, inching ever closer to a fully sustainable district energy system.
SESI ENHANCEMENTS NOW UNDER INVESTIGATION Even though SESI is fully operational, exceeding expectations, and has allowed Stanford to exceed state, national, and international goals for greenhouse gas reduction by several decades, the university is not stopping there. Stanford has made significant progress, investigating several potential enhancements to the system that hold great promise for further improving efficiency and sustainability while reducing cost. THERMAL EXCHANGE WITH CAMPUS WATER SYSTEMS The centerpiece of SESI is the electrification of building heating and cooling though district-wide heat recovery from its own cooling system, coupled with a renewable electricity supply. However, since this combined heating & cooling process only covers about 75% of its thermal loads, Stanford investigated ground source heat exchange to meet the balance of its heating and cooling loads and advance the system to full sustainability.
BACKGROUND In 2007, Stanford University began a journey to improve the sustainability of campus operations, including the district energy system that supports it. An in-depth analysis of how the university was using energy led to the transformation of its district energy system from one based on natural gas-fired CHP with steam distribution, to one featuring heat recovery and hot water distribution, both hot and cold thermal energy storage, and advanced control of system operation. After the discovery and planning phases that occurred between 2008 and 2011, the physical transformation took only two and a half years with construction occurring between October 2012 and March 2015. The new system, SESI, has reduced greenhouse gas emissions by 68%, reduced water use by 18%, and trimmed cost by 20% while opening a path to full sustainability. SESI has received numerous awards including being named the Best of the Best engineering project in the United States for 2015 and Best Global Green Project for 2016 by Engineering News Record.
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