Crew attaches heat exchanger tubing and instrumentation to reinforcement cage and energy foundation pile at the Denver Housing Authority (Photo: John McCartney, University of Colorado Boulder) Energy Foundations Gain Traction in North America Use of energy foundations has grown exponentially over the last decade in Europe and is increasingly receiving attention in North America. For new construction, geothermal energy foun- dations are more economical to install than the “conventional” ground source heat pump (GSHP) systems that require installing energy loops in non-structural boreholes or trenches outside of the foot- print of the building. In contrast, with this energy-foundation type of GSHP system, geothermal tubes are inserted directly into the structural piles or diaphragm walls supporting the building. No additional holes are drilled, thus the payback period for installing a dual-purpose energy foundation system is much shorter. “Energy foundations,” or “energy piles” as they are known in Europe, is a generic all-inclusive term referring to all types of foundations: deep or shallow, driven or drilled. The first energy foundations were driven precast concrete piles with embedded heat exchange loops. Now, most geothermal foundations have heat exchangers attached to reinforcement cages in drilled or augured foundations. However, geothermal pipes also reside in secant walls, diaphragm walls and raft foundations. Besides office buildings, factories and residences, energy foundations are installed in bridges, roads and tunnels. In several cases, geotextile geothermal probes that line tunnel walls provide heating and cooling to nearby buildings and residences. Origins in Austria Geothermal energy foundations are a promising alternative to fossil fuels, said Heinz Brandl, Ph.D., Vienna University of Technology. This renewable energy source, which uses the natural ground temperature for heating and cooling, traces its origins to AUTHOR: Sharon Boranyak, Independent Technical Writer, Topeka, Kansas the invention of the heat pump in 1855 by Austrian mining engineer Peter Ritter von Rittinger, he said. Having worked with geothermal foundations some 30 years, Brandl is known worldwide for combining research and development, theory and practice. He was a keynote lecturer at DFI’s Middle East Conference in Dubai in March 2012. “The idea [for dual-purpose founda- tions] came from a small, Austrian civil engineering contracting company, Nägelebau, which produced precast driven concrete piles,” Brandl said. “In the beginning, these energy piles were installed mainly for residential use. Then I recommended that they increasingly use large-diameter bored piles and perform in-situ research measure- ments. I had an early sense of a promising future for near-surface geothermal energy using foundations of all kinds.” Austria-based Enercret, a wholly owned subsidiary of Nägelebau, focuses on exploiting geothermal energy through the use of such ground-contact concrete DEEP FOUNDATIONS • SEPT/OCT 2012 • 83
