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===Design Considerations=== Line 151:
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===Expected Performance===
→Geothermal Cooling
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==Geothermal Cooling==
===Geothermal Cooling===
This innovative approach uses one or more deep (180 m) geothermal boreholes connected in a closed loop with a pond heat exchanger to cool outflows from stormwater ponds. A metal or polyethylene heat exchanger is installed in an enclosure at the outlet of the pond. A heat transfer fluid is pumped through the closed loop to maximize transfer of heat energy from the warm water to the much colder ground. Warm outflows from the pond enter the enclosure and pass over the pond heat exchanger, which transfers energy from the water to the closed loop and into the ground. The approach was piloted by TRCA/STEP, in partnership with the City of Brampton, on a small pond in Brampton (Janssen and Van Seters, 2021<ref>Erik Janssen and Tim Van Seters. 2021. Geothermal-based Thermal Mitigation of Stormwater Retention Pond Outflows: Report Addendum. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2022/03/Geo_Cooling_Report_2021.pdf</ref> and 2022<ref>Janssen, E. and Van Seters, T., 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling.https://www.chijournal.org/C483</ref>)
This innovative approach uses one or more deep (180 m) geothermal boreholes connected in a closed loop with a pond heat exchanger to cool outflows from stormwater ponds. A metal or polyethylene heat exchanger is installed in an enclosure at the outlet of the pond. A heat transfer fluid is pumped through the closed loop to maximize transfer of heat energy from the warm water to the much colder ground. Warm outflows from the pond enter the enclosure and pass over the pond heat exchanger, which transfers energy from the water to the closed loop and into the ground. The approach was piloted by TRCA/STEP, in partnership with the City of Brampton, on a small pond in Brampton (Janssen and Van Seters, 2021<ref>Erik Janssen and Tim Van Seters. 2021. Geothermal-based Thermal Mitigation of Stormwater Retention Pond Outflows: Report Addendum. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2022/03/Geo_Cooling_Report_2021.pdf</ref> and 2022<ref>Janssen, E. and Van Seters, T., 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling.https://www.chijournal.org/C483</ref>)
[[File:Borehole drilling.jpg|thumb|500px|Borehole drilling for the City of Brampton thermal mitigation pilot project. (Photo: [[Acknowledgements|TRCA, 2020]])]]
[[File:Borehole drilling.jpg|thumb|500px|Borehole drilling for the City of Brampton thermal mitigation pilot project. (Photo: [[Acknowledgements|TRCA, 2020]])]]
'''Design Considerations'''
*Heat exchangers come in different sizes and are made of different materials. Metal heat exchangers (typically stainless steel) are more efficient than polyethylene and take up much less space.
*Heat exchangers come in different sizes and are made of different materials. Metal heat exchangers (typically stainless steel) are more efficient than polyethylene and take up much less space.
*Antifreeze solutions are needed in the hydronic circuit because a portion of the closed loop is above ground and would freeze over the winter. Non-toxic heat transfer fluids include propylene glycol/water and ethanol. The latter has better heat transfer properties and takes less energy to pump.
*Antifreeze solutions are needed in the hydronic circuit because a portion of the closed loop is above ground and would freeze over the winter. Non-toxic heat transfer fluids include propylene glycol/water and ethanol. The latter has better heat transfer properties and takes less energy to pump.
*Initial investigations suggest that systems can be sized based on the average pond outflow rate over a given year to achieve defined temperature thresholds most of the time.
*Initial investigations suggest that systems can be sized based on the average pond outflow rate over a given year to achieve defined temperature thresholds most of the time.
'''Expected Performance'''
Geothermal Cooling works best with subsurface draw outlets (1.2 m or deeper) that provide cooling of the higher flows and would be less expensive than installing additional boreholes (at least in new builds). When sized appropriately, geothermal systems can shave a few degrees off of the average pond outflow temperature.
Geothermal Cooling works best with subsurface draw outlets (1.2 m or deeper) that provide cooling of the higher flows and would be less expensive than installing additional boreholes (at least in new builds). When sized appropriately, geothermal systems can shave a few degrees off of the average pond outflow temperature.