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[[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.
*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.
*The enclosure can be bottomless if the soils and groundwater table is suitable for rapid infiltration.
*Borehole field and heat exchanger sizing should be done based on the estimated (modelled) or, preferably, monitored thermal load, with a target of achieving 95% of the desired temperature threshold recognizing that it is not feasible to cool large flows. Elevated outflow temperatures occur most frequently during low flows (i.e. dry weather flows).
*The pump used to circulate the heat transfer fluid through the ground loop may be powered by an electrical connection or solar panels. Larger systems may need designated electrical connections.
*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.
==References==
==References==