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Following on the bold innovation of Ball State University to install a district-wide ground source heat exchange system for its campus in Indiana, Stanford installed and tested a similar closed loop geothermal well on its campus to determine the feasibility of adding GSHE (ground source heat exchange) to SESI. The test well proved successful, however engineers determined that an open-source GSHE system would be a better fit for SESI, given the pattern of thermal loads remaining to be served after the primary heat recovery process. The university had such a system designed, and planned to consider its installation in 2017 after SESI was successfully installed and operational for at least one year, in order to confirm system design and operational characteristics.
STANDFORD UNIVERSITY LAKE WATER IRRIGATION SYSTEM
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Furthermore, to reduce evapotranspiration loss and to keep the recreation fields and landscape open for use during the day, most of the irrigation flow currently occurs overnight, which is also the best time to perform heat rejection from the district energy system in order to minimize grid electricity peak demand and electricity costs. Campus irrigation also occurs primarily in summer when the university has excess waste heat to reject, making the potential of using the campus irrigation system for heat rejection very promising. If successful, this would reduce existing evaporative cooling tower use under SESI by 25% to 40%with corresponding water savings and system heat rejection capacity increase. To determine if this is possible, it is necessary to understand the effects to campus landscape vegetation, if any, of increasing irrigation water temperatures from the 60°F range to the 80°F range. Anecdotally, it is believed that this would not be a problem as many landscape irrigation systems deliver water at or above 80°F across the world without negative impacts. However, initial research into the effects of water temperature on landscape irrigation reveal surprisingly little knowledge about this subject. Therefore, the university is developing plans to construct a landscape test plot next to its Central Energy Facility to test these impacts under scientific control. If results are acceptable, work will continue to plan and implement a system for rejecting waste heat from the district energy system to the campus irrigation system.
However, as GSHEwas considered in 2016, andwith their thinking about energy supply now trained via the heat recovery project to first consider the use of existing resources and processes where possible, Stanford engineers decided to investigate the use of the existing campus water and wastewater systems for thermal exchange before installing a new GSHE system. University academia are investigating thermal exchange with the campus wastewater system via Stanford’s Codiga Resource Recovery Center, and campus utilities engineers are investigating thermal exchange with the separate campus domestic (drinking) water and non-potable landscape irrigation water systems. HEAT REJECTION TO THE IRRIGATION SYSTEM The advantages of using the campus irrigation system for heat rejection include greatly reduced water use; switching the water used for heat rejection from high quality drinking supplies to non-potable irrigation sources; and gaining free ‘cooling tower’ capacity. Initial data indicates that the campus' non-potable irrigation system (known as the LakeWater system) averages flows of about 1,500 gallons per minute in summer and that the temperature of the water in the system ranges between 60°F and 70°F. Rejecting 20°F into the irrigation water flow would provide 1,500 to 3,000 tons of cooling capacity, depending on the rate of irrigation flow and heat rejection used.
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