− | Since stream warming is influenced by the runoff temperature and volume of runoff draining to streams, impacts are best assessed through an evaluation of thermal loads both in the stream and in runoff discharged to streams. The thermal load is a function of the flow rate, water temperature, water density and heat capacity of water (or the energy required to increase a kg of water by 1 degree Celsius). | + | Since stream warming is influenced by the runoff temperature and volume of runoff draining to streams, impacts are best assessed through an evaluation of thermal loads both in the stream and in runoff discharged to streams. The thermal load is a function of the flow rate, water temperature, water density and heat capacity of water or the energy required to increase a kg of water by 1 degree Celsius (°C). |
| 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>Janssen, E., Van Seters, T. 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 name="example1" />) | | 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>Janssen, E., Van Seters, T. 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 name="example1" />) |
| [[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]])]] |