An interesting story popped up in my Web feed a while back. It concerned UK contractor Balfour Beatty working on a drilled pile system that integrated geothermal loops. I thought it was an interesting approach, and posted it to a few LinkedIn groups I participate in, including the Deep Foundations Institute group and the International Ground Source Heat Pump Association group. The folks in the IGSHPA group had input I wanted to share with my foundation drilling readers.
How the Drilled Piles Work
First, a bit about the system. The concrete and steel prefab piles integrate closed-loop systems that work with a ground-source pump to heat and cool buildings. One thing I like in reading about this, is that Balfour Beatty didn't just use willing clients as test subjects; the company designed and built the system into its Glasgow-area piling facility. The system, according to the New Civil Engineer article, has saved Balfour Beatty thousands of dollars per year in electricity to heat and cool the facility (and to run fans for drying rooms).
Companies can win customers by putting faith in the technologies they sell. But the professionals—including some who’ve worked on foundation failure investigations—on the IGSHPA group expressed caution.
“I had a central Ohio developer who wanted to use poured-in-place concrete piles to support geo for his homes to save on installation cost,” said Jeff Persons, president of Geo Source One and a certified GeoExchange designer. “Had to tell him I wasn’t the person for his application as I've seen too many frost heave situations and could not accept responsibility for a pile failure as a result of frost development on a geothermal loop.”
But Balfour Beatty’s design uses driven piles, which do not actually bear loads. They’re driven to the depth required by the geothermal system design.
Persons goes on: “I see from the UK projects that the loop lines may be attached to the exterior of a driven or vibrated pile such that it is less likely to cause freeze damage to the concrete. I can visualize this as an effective means to install loops in coastal sediment areas where conditions are uniform and free of abrasive rock/debris and where the loop design can be set to avoid operation at sub freezing temperatures. Because many of these support piles are relatively shallow depth it will be critical that the water table be high to maintain adequate moisture for heat transfer.”
Integrating Geothermal, Drilled Piles
Persons has fair points. And even with the loops on the outside of the piles protected by a steal sheath, I think it comes down to proper engineering, design and installation. Michael Dilling of Hoosier Energy Associates, a geothermal equipment wholesaler, agrees.
“I know there are buildings in Canada where loops are under the building. But integrating the loop with the actual structural foundation needs to be a case by case investigation,” he said “A good loop design company can model the performance and determine if that is a good possibility or to stay away from it. It's all in the science and engineering.”
Balfour's approach seems to mirror Dilling's advice. Their website says for such projects “the architect, structural engineer, geotechnical engineer, geothermal engineer and building services engineer need to be included early on to undertake an integrated feasibility study.”
I encourage foundations and geothermal contractors to read through the NCE article. (The magazine’s a great resource trades people.) It may not be a new approach, but I thought it was novel. National Driller covers several markets where drilling contractors work and its interesting to see areas where those markets overlap.
Stay safe out there, drillers.
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