• Subterra Renewables

Staying On-Time and On-Budget with Geothermal

Drilling geothermal boreholes can delay construction when drilling from the bottom of the hole, after excavation. Instead, drilling from grade allows the drillers to be first on site, drill before excavation, and drill without affecting the construction critical path.

One of the key concerns that we’ve heard from developers about adopting a geothermal system that’s designed to sit underneath a newly constructed building is the impact it’s installation might have on the development timeline. Traditionally, drillers have waited until a site has been completely excavated, at which point drill rigs are lowered to the bottom of the site where they compete for space with other construction processes and generally delay the scheduled timeline.

Figure 1: Conceptual section drawing of the drill-from-grade method, where initial drill depth is 700 feet and the top 50 feet are removed, leaving only the required heat exchanger depth (650 ft.) buried ahead of excavation.

Stan Reitsma, President of GeoSource Energy (“GeoSource”) and PhD in Civil Engineering, has developed a novel geothermal drilling method to mitigate these delays. Rather than waiting, GeoSource drills prior to site excavation and returns to connect the heat exchanger loops into the building following foundation work, about the time drainage work begins.

“The developers we work with always prefer to have us drill ahead of excavation when possible. This strategy has set our company apart from our competitors,” said Reitsma.

With this method, boreholes are drilled to the depth required for the heat exchanger, plus the depth of any below-grade spaces, like basement levels or parking garages. After drilling, the plastic piping is cut at the depth of the below-grade spaces and the excess is removed so that excavation can proceed as it normally would. The plastic pipe is plugged before it is cut to prevent any soil from contaminating the piping during construction.

As an example, if the ground source heat exchanger requires 650 feet of vertical drilling and the parking garage is expected to be 50 feet below surface level, initial drilling will be to a depth of 700 feet from grade and the pipe cut to 50 feet below grade (Figure 1).

GeoSource Energy, who have drilled over 1 million linear feet of geothermal boreholes since 2004, developed and patented this method of drilling after recognizing the conflict for space that can arise between geothermal drillers, excavators, and other contractors when drilling from the bottom of the hole. Removing geothermal drills from the bottom of the hole eliminates the fight for space to avoid critical path delays and the resulting financial drag of a longer timeline.

In order to drill prior to excavation, GeoSource requires a clear site and flat ground, but does not require drilling platforms. Furthermore, no building permit is required to begin drilling, although a demolition or foundation permit is occasionally requested for peace of mind. This means that drilling can begin as construction drawings and tender packages are still being finalized.

Subterra Renewables is proud to work with GeoSource Energy on our ground source heat pump projects in Southern Ontario. We strongly recommend drilling from surface grade to mitigate impacts to construction critical path and to avoid costly delays.

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