Regarding the article 'How Geothermal Heating and Cooling Can Improve Building Efficiency' (April 2019, p. 18), I thought I'd add an advisory note.
I advise against ever laying out deep pipe lines in a grid arrangement, i.e. many risers in the space of, say, a football field. One such installation, designed by another firm here in Toronto in the 1990's, worked well until peak cooling was called for by the heat pumps located within the facility.
The ground in the core of the grid heated up to the point where return glycol temperatures exceeded 120 degrees F. The core acted as a heat sink but could not reject any energy to the substrate, save for on the perimeter of the piping grid.
The engineering firm in question had to make a choice: pay for the addition of a closed-circuit, evaporative cooler for supplementary heat rejection... or go bankrupt. They chose the latter and are now operating under a new name. (Shame on them.)
Another word to the wise: Insulate the downward riser to 1/2 of its length, thereby assuring that any heat exchange will be between the riser and the ground, as opposed to between the upward and downward flows.
Yours Very Truly,
Michael McCartney, P.E.
M.E. McCartney Engineering Ltd., 117 Brampton Road, Toronto, Ontario M9R 3K3; Phone: 416-838-1274; E-mail: firstname.lastname@example.org
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