Why Energy Foundations (Energy Piles) are the talk of the town

By Tom Chadwick, CEO

Geothermal solutions are in the limelight in the US, as many cities move away from conventional forms of HVAC. Here we explain what they are and how they work.

What is an Energy Foundation or Energy Pile?

Imagine turning the concrete foundations of your new building into an energy source that could reduce energy consumption by 40%. This is the basis of Energy Foundations and Energy Piles. Geothermal systems have been harvesting energy from the ground for over fifty years, using buried pipe networks and ground source heat pumps (GSHP). In the past ten years technology has enabled this geothermal heat extraction to become a preferred way to deliver heating and cooling to 21st Century buildings. It is clean, cost-effective, space-efficient and quiet. GI Energy (GIE) specializes in utilizing buildings foundations to install state-of-the-art geothermal heating and cooling systems during the construction stage. We worked hand in hand with Skanska to develop this process, and together installed the first Energy Foundation – at Oxford University in 2001.

How do Energy Foundations work?

The premise is simple: deep foundations have underutilized thermal mass, which can absorb and store heat energy better than many other materials. For little additional construction cost, the energy loops of a geothermal exchange system can be buried in the concrete piles, retaining walls and other building infrastructure. These loops are then connected via heat exchangers to the internal heating and cooling distribution systems of the building. A modest amount of electricity is required to drive the pumps, but no combustion is needed, an advantage over traditional natural gas and oil heating systems. Carbon and greenhouse gas emissions as well as local pollutants are materially reduced. While most building footprints don’t have enough foundation surface area to allow the entire heating and cooling to be run by a geothermal system, you can typically offset 20%-50% of the heating and cooling loads. This means typical HVAC can be sized to meet a smaller load, reducing upfront equipment costs as well as water usage in a cooling tower. The owner is taking advantage of the pile foundations that are being built for the structure of the building, putting them to dual use. This approach has become widely adopted in the UK where GIE accounts for 90% of the installed capacity.

Why are they the talk of the town?

In New York City, for example, the 80X50 program demands an 80% reduction in carbon emissions by 2050. In January 2016 the City passed a law requiring all government buildings to investigate geothermal options, starting in 2017 (See footnote 1). The New York State Public Service Commission is considering creative options such as using the City’s water-mains for geothermal purposes. New York State Energy Research and Development Authority (NYSERDA) is backing this agenda to ensure the momentum continues. However, effective widespread geothermal deployment in New York – and across the country – is unlikely to be achieved unless Energy Foundations are properly understood. 

Where are Energy Foundations used?

Energy Foundations make sense anywhere pile foundations (or large-scale slab foundations) are being deployed. In a new construction, it is cheaper to install geothermal loops in the foundations than it is to install them in a separate borefield. In Central London, where space is at a premium, building owners using deep foundations consider an Energy Pile solution as standard – a testimony to its effectiveness. The huge new London Crossrail Stations (the largest civil engineering project currently in the UK) is putting loops in their retaining walls to provide “free energy” to the above-ground infrastructure. London’s Bulgari Hotel has ground loops embedded in the retaining walls in its basement. GIE built the first system in New York City at Trevor Day School and designed the system for the Federal Building in Seattle. We are now working to install Energy Piles at a million square foot corporate headquarters in Silicon Valley.

Client Concerns

Is the structural integrity of the foundations impaired?

No. GIE have worked with Cambridge University (2006) and Imperial College, London (2006), to undertake extensive studies on the impact of burying geothermal pipe in concrete foundations. Both studies concluded that there was no resulting structural weakness.

Won’t this slow down the construction program?

No. GIE clients will testify that there is no impact. Our teams are experienced at working with other on site contractors and our long experience installing Energy Foundations means that we have finessed the process. For example we install the pipes in the steel cages used in foundations before contractors bring them onto site. We are able to avoid issues before they arise, by designing a system that works both on paper and also in the midst of the construction site. That is our unique offering.

What happens if one of the loops starts leaking?

This has never happened on a GIE led Foundation project, and we have been installing them since 2001. However, we always build in extra system capacity, so that in the event of a leak occurring we can isolate and shut off the problematic pile.

Why is the USA behind Europe in adopting this technology?

The US lags behind the UK in terms of adoption of this technology, but not in terms of interest. A key issue in the US is the insistence of general contractors in breaking up geothermal system installation into its constituent parts (the design of the ground loop, the loop installation, the headering into a manifold, the installation of the mechanical and electrical equipment, the installation of the control package, the commissioning) often using different suppliers and generalist contractors for each component. There is some initial cost saving on paper by doing this, but what is lost is a single point of contact and a single point of accountability. The individual contractors and suppliers work to different standards and none have experience in running the whole system. We regularly encounter building owners who have had a negative experience with their geothermal system, because no single provider has taken responsibility for it.
energy pile usage chart

 How difficult are they to Install?

The installation is not a challenge. Polyethylene pipe to contain water (or a water-glycol mix) is inserted in the steel rebar cages that form the basis of modern foundations, and concrete is poured into the cage once it is in the ground. The loops are then connected to headers and tied into manifolds that take the water to the central plant. Energy Piles can also be inserted when the rebar cage is slid into wet-set concrete. The trick is not the design, but working under the pressure of a complex construction site and avoiding conflict with the other trades, whilst maintaining the integrity of the system. In the UK we have worked hand in hand with Skanska since 2005 to successfully deploy numerous foundation solutions.

energy pile illustration

geothermal loop 

 

 

 

 

 

 

Geothermal loops are generally installed to full depth of pile, maximizing geothermal energy. These pictures show the reinforcement cage at the top of the pile 

Examples of the typical installation of Energy Piles

installation energy loopenergy foundation construction

 

 

 

 

 

 

 

 

How much do they cost to install?

Energy Piles do not require additional drilling in same way a conventional geothermal borefield does. It is less expensive to install a geothermal system as the building’s foundations are being built than it is to install the loops as a separate part of the project elsewhere. There is of course site supervision and work associated deploying the pipe in the foundations. The cost of the plastic pipe is minimal compared to the cost of the foundation, and fixing the piping onto the rebar cages is a quick process. As previously discussed, clients have found that installing Energy Foundations does not impact construction program schedules. Once the piles are hardened in place they are connected to the central mechanical room heat pump, just as a conventional geothermal system would be. The building benefits from energy savings and operational savings for years to come.

Moving forward

Advances in heat pumps have been matched by stellar jumps in controls automation and seamless combination with other technologies such as solar PV, Cogeneration and energy storage. Buildings can now achieve ‘Net Zero’ status with Energy Foundations at their core. Energy Foundations are a great way to add LEED points to a building. Since GIE started putting geothermal loops into the foundation piles of new buildings back in 2001, we have been at the center of this unique energy solution.

If you have any questions on energy foundations, or to learn more about how they could help your development, please don’t hesitate to reach out to our Chief Engineer Amir Yanni, or call us on (312) 894-4646. We look forward to speaking to you.

[1] See http://council.nyc.gov/d22/documents/120715GeothermalPassing.shtml

geothermal energy piles
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