The Stanford University Energy System Innovations project includes high-efficiency standards for new buildings, continued efficiency improvements for existing buildings and a cutting-edge energy supply system.

With a replacement Central Energy Facility (CEF), Stanford University was able to cut campus energy use by 50% and dropped its greenhouse gas emissions by 68% in just 2.5 years. The 125,000 SF CEF includes a net positive energy administrative building, a heat recovery chiller plant, a cooling and heating plant, a service yard and a new campus-wide main electrical substation. The three heat recovery chillers are the largest in the United States, and they 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.

Each heat recovery chiller provides a 2,500-ton cooling capacity for chiller water and simultaneously can produce 40 million British thermal units of heat per hour. The heat recovery chillers send out chilled water to the campus at 42 degrees and returns between 56 and 60 degrees. The heat is removed from the chilled water as it is cooled back down to 42 degrees and reheats spent hot water (which returns to the CEF from campus at 130 degrees) back to 160 to 170 degrees to supply heating.

The CEF’s thermal storage system contains two five 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 is 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.