A few weeks ago, the Bethesda Bungalows crew’s only concern about installing geothermal at the KellyGreen house was whether the drilling equipment would be able to navigate the small lot’s steep front slope. Turns out, it was another issue altogether—poor soil—that derailed the builder’s and homeowners’ hopes of including the super-efficient ground-source heat pump system. To prepare for the installation, the team had graded the front yard to reduce the slope and allow the drilling equipment onto the site. However, once drilling began, the soil proved unable to support the boreholes and excessive groundwater exacerbated the problem. According to project manager Brad Beeson, the drill just couldn’t make progress, as holes kept caving in with water and silt. Beeson says the drill averaged an inch per hour, a rate that would have dragged the normally two- to three-day process out by weeks—an expense that was neither feasible nor practical.
What made the situation particularly mind-boggling is that Bethesda Bungalows has installed geothermal on other projects nearby, with no similar soil problems.
So, after two days of attempts, the team decided to pull the plug on geothermal. The news came as a disappointment to the build team as well as the homeowners, but won’t affect the project’s ability to obtain LEED certification. Switching systems will impact the home’s long-term energy costs for heating and cooling, but will save about $15,000 in initial expenses.
In place of geothermal, Bethesda Bungalows plans to spec either an ultra-efficient Carrier Infinity two-zone forced-air system (which they’ve installed on other projects) or a newer technology—an alternative heat-pump system that uses an interior water cabinet heat exchanger rather than an outside fan. Aside from the two days of wasted drilling, the change will cause little else in the way of schedule adjustment, though a small portion of green space will now be lost to accommodate the two Carrier units if those are the replacement selected.
For more information on geothermal systems, see our previous coverage or resources from the NAHB Research Center, the International Ground Source Heat Pump Association, or the Geothermal Exchange Organization.
Katy Tomasulo is Deputy Editor of EcoHome.