Ben Welter - Thursday, March 10, 2016
Stanford University's new $485 million heating and cooling system has won the Editors' Choice Award in the annual Engineering News-Record Best of the Best competition. The Stanford Energy System Innovations project, completed in April 2015, has cut campus energy use by 50 percent. Three heat-recovery chillers in the new central energy facility (CEF) strip waste heat from 155 campus buildings via a chilled-water loop and use it to preheat a separate hot-water loop that distributes heat to the same buildings.
ENR describes the system in detail:
"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. ...
"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."