...reduced energy bills, put a significant dent in greenhouse gases and reduce the need to build 105 GW of electrical capacity by 2030. If not designed well, GHPs can have unintended consequences, such as astronomical costs, increased energy use and polluted groundwater. The devil, as they say, is in the details.
Fundamentally, GSHP technology benefits from ground temperatures, which are a relatively constant 50°F to 60°F, requiring less “lift” to pump heat to and from a building. WSHPs used in underwater applications rely less on constant temperatures and more on evaporative or deepwater cooling; they also can run summer to winter. Combined with high-grade insulation, windows, ducts and climate controls, GHPs make sense in many buildings.
Although geothermal heat exchange grew up in the Midwest, where seasonal changes make it easier to predict performance in small homes, it now is being implemented in all corners of North America on a wide variety of projects. Designers also are learning how to use the earth or a nearby water source as a storage device to reject heat during the cooling season and extract it later. That gives geothermal a “cool” factor, but not everyone is fully unlocking the potential.
The key, experts say, is figuring out how to balance the load to keep the pump’s compressors working as little as possible over the year. Installation is a big factor in predicting performance, as well as cost. All GSHPs are closed loops, arranged in a vertical or horizontal fashion. They generally do not cost more than conventional furnaces; laying the ground loops is the added cost. The wells require expensive, shallow trenches, more expensive boreholes or a combination of both. Installation equates to a few dollars per foot up to $25 per foot, according to U.S. government statistics.
Nonetheless, heat pumps are infinitely flexible inside a building. Users can tailor them to regional needs, and some even are designing “hybrid” systems to take advantage of local power, geology and climate. One such system, designed for Canadian airline company WestJet’s headquarters in Calgary, Alberta, incorporates heat sinks in the six-story, 314,000-sq-ft building’s foundations. By looping tubes inside 105 bored piles, “we reduced the capital cost,” says Bererton. This method is more mature in Europe, where foundations commonly double as heat exchangers.
Because geothermal systems still are relatively new to the many players on a project team, the unexpected easily can arise during installation. Completed last January at a cost of about $100 million, the WestJet corporate building lost 30% of its ground loop due to pier-construction problems, requiring workers to drill 20 additional, small-diameter boreholes at 350 ft deep.
Normally, the building’s water-to- water heat pumps would need 200 boreholes, so the owner still saved more than $700,000 and expects to save $200,000 per year in energy while emitting about 2,000 fewer tons of carbon dioxide. Part of the savings is due to the unusual addition of a conventional chiller and condensing boiler. The secret sauce, Bererton says, is a computer controller that takes into account daily costs of electricity and natural gas and accordingly cycles the systems on and off to deliver the best bang for the buck. “We are targeting that the COP is better than the price ratio of electricity and natural gas,” says Bererton. “We only run the heat pumps when it is going to save us money.”
Drilling equipment is another low-hanging fruit ripe for innovation. In Chicago, a homebuilder whose friend, and now wife, convinced him to build her a greener home is leading the charge to cut costs for vertical-well construction in...