| Title | District Geothermal Heating Using EGS Technology to Meet Carbon Neutrality Goals: A Case Study of Earth Source Heat for the Cornell University Campus |
|---|---|
| Authors | Jeff TESTER, Steve BEYERS, J. Olaf GUSTAFSON, Terry JORDAN, Patrick M. FULTON, Adam J. HAWKINS, Jared D. SMITH, Jood Al ASWAD, Koenraad BECKERS, Rick ALLMENDINGER, Larry BROWN, Frank HOROWITZ, Daniel MAY, Tasnuva Ming KHAN, and Matt PRITCHARD |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | direct use, district heating, co-generation, cascaded energy utilization, heat pump thermal augmentation |
| Abstract | The two main objectives of Cornell’s direct use study were (1) to characterize the geothermal resource in local region, and (2) to evaluate reservoir development and end use options in terms of their estimated levelized costs for delivering baseload heat (LCOH) for use in Cornell’s district energy system. We analyzed regional and local geologic and geophysical data and logistical site attributes to se1ect possible drilling sites on Cornell property. Data collected and evaluated included oil and gas drilling records from the Appalachian Basin in NY State, including bottom-hole temperatures and logs; regional structural geologic feature mapping; passive and active seismic imaging; and gravity and aero-magnetic surveys. . We considered several reservoir options to extract heat from subsurface rocks from depths of about 2.3 to 5 km in both sedimentary and crystalline basement rocks with temperatures ranging from 70 to 125oC. The GEOPHIRES techno-economic simulator. was used to estimate LCOHs for both fracture-dominated and porous-media flow reservoirs. Several thermal-hydraulic reservoir models were utilized to explore the sensitivity of costs to rock properties, well placement, and flow conditions. Parameters evaluated included, initial rock temperatures, porosity, permeability, well separation distances, and production mass flow rates. A critical part of our study included the integration of heat pumps to increase the thermal energy supplied to Cornells district heating system. Using heat pumps significantly improves the thermal energy extraction rate from fluids circulating through the geothermal reservoir – in many cases the quantity of energy utilized was multiplied by a factor of more than 2. Not only does heat pump augmentation result in “boosting†the resource temperature to meet basic district heating system needs, it also results in lower fluid re-injection temperatures, thus increasing the thermal energy recovered per cycle. Heat pumps integrated into Cornell’s energy system were optimized for supply and demand temperature conditions, and as a result have much higher coefficients of performance and lower electrical requirements than comparable conventional air-source or shallow ground-source heat pump systems. Designing facilities for effective use of low temperature heat greatly improves the LCOH of a deep direct use system. Both distribution and end-use temperatures are important variables in determining the value of the thermal energy extracted from a given geothermal resource along with the cost of distributing the heat to buildings on campus. Supplying lower temperatures in a district energy system to heat buildings is inherently more efficient. Cornell has adopted this approach in upgrading all campus buildings, laboratories and greenhouses to replace steam supply with hot water. This transformation allows the use of lower temperature fluids produced from the geothermal reservoir. Whereas many past studies have focused on the geothermal supply side of the system, this study suggests that building design and heat supply standards at the surface for institutions like Cornell may be just as important in achieving reasonable LCOHs as the costs and performance of the subsurface components. Such customization of site-specific needs in the design and optimization of surface infrastructure not only lowers technical and economic risks but also is likely to increase the attractiveness of geothermal district heating projects for investors and city planners as they retrofit technologies to achieve renewable energy and/or low carbon emission goals. |