20 September 2011
With the fast increasing of installations of geothermal heat pumps, the demand of accurate design of the system is growing. In situ thermal response test (TRT) provides a
necessary method to accurately evaluate site-specific geothermal properties in the design of heat pump systems. Results of 31 in situ thermal response tests, carried out in closed loop boreholes in the Greater Toronto Area (GTA) have been analyzed. Derived samples of geothermal conductivity yield a median of 2.07 W/(mK), with 25% and 75% percentiles of
1.84 and 2.19 (W/m/K), respectively. The lowest value, 1.61 W/(mK) was derived from the area of northern part of downtown Toronto, where a thicker overburden of clayey silt till, Halton formation, was reached to 72 meters in depth. Test borehole was drilled to 154
meters, from ground surface, and no free water was encountered. The highest value of geothermal conductivity is tested from the east part of GTA in the town of Uxbridge, where
artisan water was encountered during test borehole preparation. Advective heat transfer with groundwater flow is believed to have led to an elevated apparent conductivity. Borehole
thermal resistance exhibits, 25%-ile, median and 75%-ile magnitude, of 0.066, 0.073 and 0.084 (Km/W). Undisturbed ground temperatures, measured by TRT in GTA, varied from
8.91 to 11.41 oC, and about 55% of samples were within the range from 10.2 to 10.4 oC.