Primary Innovation: Heat Recovery
Stanford’s many varied pursuits, from cutting-edge research to olympic-level athletic facilities, result in the campus having a 70% real-time overlap of heating and cooling demands. This presents the opportunity for heat recovery—using waste heat collected by the chilled-water system to meet the university’s concurrent heating need. The new heat recovery system collects waste heat from buildings via a chilled-water loop and captures it at the Central Energy Facility (CEF) for reuse, eliminating the use of cooling towers to discharge the heat. Instead, heat recovery chillers move waste heat collected from the chilled-water loop to a new hot-water loop that replaced that distributes heat to the buildings. The heat recovery system meets 93% of the heating load on campus with waste heat and reduces total campus water consumption by 15%.
The CEF's heat recovery chillers (HRC) are the first of their kind of this size—ten times the size of any unit the manufacturer, York, has ever made before. Each HRC has a 2,500-ton cooling capacity for chilled water and can simultaneously produce 40 million BTUs of heat per hour, enough to cool and heat approximately 500 houses simultaneously. The HRCs send out chilled water to campus at 42°F, which returns at 56-60°F. The heat removed from the chilled water to cool it back down to 42°F is used by the HRC to reheat spent hot water from 130°F back up to 170°F to supply for buildings that need heat. The CEF actively operates two HRCs, houses an additional HRC for back-up, and has the space to install another in case needed in the future.
Each HRC uses about 10% of the total electricity used by Stanford, so the university must be adept at how and when they are used to minimize electrical impact on the grid and the corresponding ‘demand’ charges paid for use of the grid. Stanford collaborated with Johnson Controls to transform a new patented plant optimization model into industrial-grade software, known as Enterprise Optimization Solution (EOS), and hardwire it into the new campus energy sysetm. EOS is an energy modeling and dispatch system using over 1220 variables including building occupancy, ambient conditions, time of year, projected energy prices, weather forecast, current system conditions, etc. to develop 15-minute dispatches that show the optimal way to run the plant—essentially an “autopilot" for the plant. The system predicts the university’s background electrical profile (electricity used by the buildings) for the next seven days and schedules HRC operation in hours each day so as to minimize the overall electrical footprint of the university on the grid. EOS will perform this forward-looking analysis and recalibrate the HRC operating schedules as needed every 15 minutes on a continual basis. It can be used be used in either advisory or fully automated modes, and the control room will be staffed 24/7 to monitor operations.