One answer to the increased demand for renewable energy lives right here in the piling industry.
A Danish manufacturer of precast concrete foundation piles is using “energy piles” that use geothermal energy to help heat and cool the buildings they hold up. Jonas Henriksen, sales engineer for Centrum Pæle A/S, says that the technology has been around for decades, but a new dimensioning tool and the call for more sustainable building practices has inspired the company to relaunch the product in earnest.
“Geothermal energy is the second most abundant source of heat on earth, after solar energy. Energy piles are the perfect opportunity to combine mechanical stability with energy supply. As we see it, this is a great way of harvesting energy and storing it efficiently,” said Henriksen.
What are energy piles and how do they work?
Energy piles are precast concrete piles with PE tubes cast inside them. The PE tubes serve as ground source heat exchangers by circulating fluid through them when connected to a heat pump. Their efficacy is twofold: they’re able to transfer the load from construction into the bearing layer and exchange heat with the soil.
They’re usually installed using soil displacement techniques or soil excavation systems. With increasing energy costs and the introduction of greater renewable energy requirements for new buildings, energy piles are becoming more and more in demand.
Typical energy piles come in dimensions from 30 centimetres by 30 cm up to 45 cm by 45 cm, in lengths from seven to 18 metres. To allow connection with tubes outside of the precast piles, the energy piles have an inlet and outlet section in the top of the pile. Inside the pile, the PE tubes run down in a “single-u” configuration, allowing liquid to flow from the inlet section down into the pile and up to and out of the outlet section.
The PE tubes are pressure tested with arc welding, which fuses two pieces of a workpiece together by using electrodes. The same welding method is used when connecting the energy pile to tubes outside of the pile.
Installation is similar to standard piles, although Henriksen points out that it’s important to be extra careful on the building site to avoid damaging the piles or the in-outlet tubes once the piles are installed. “After ramming the energy piles into the ground, it is necessary to connect the piles to a heat pump through a series of tubes,” he said.
Although energy piles require a significant capital cost investment, the low operational costs can result in a positive return on investment over time. “It is possible to achieve pay-back periods downwards of five to seven years in ideal thermal soil conditions and with the right system setup,” said Henriksen.
What are the advantages of energy piles?
Energy piles make use of shallow geothermal energy. This is the energy provided to the ground by the sun, reaching a depth of 0.5 to 20 metres. This is not to be confused with more traditional geothermal energy which comes from the core of the earth further down.
In the seven to 18 metres that energy piles are placed, the temperature of the ground is constant all year at temperatures ranging between 8°C to 10°C. There is limited fluctuation in the available energy source to supply a building’s energy demands compared with the upper layers of the ground that are subject to the changing seasons.
The advantage of using energy piles is their efficiency in establishing a ground source heat exchange system by combining heat exchangers with the foundation of the building in a two-in-one solution. This is especially advantageous for buildings where space for drilling and laying traditional geothermal heat exchangers is limited.
Another advantage is their cost-efficiency. Energy piles usually deliver heating to the building at a co-efficient of performance (COP) of between 3.2 and five. Also, energy piles are even more effective at cooling than heating. They provide a natural cooling effect during the summer, when the cool fluid from the energy piles (8°C to 10°C) is circulated throughout the building. The fluid draws out the excess heat in the building, lowering the temperature and providing efficient comfort cooling at an energy efficiency of 20 to 30 kilowatt hours of cooling per one kilowatt hour of electricity provided. This excess heat is transferred to the ground below the building, creating a heat storage by providing energy to the ground, which can be extracted when heat is needed.
A further benefit to using energy piles is their environmental sustainability. “Since the energy provided for heating and cooling comes from the ground, all it takes to operate the system is the added electricity, which – at least in Denmark – often comes from wind energy. Thus, the energy piles provide 100 per cent renewable energy on days where electricity is provided through wind, sun or hydro technology,” said Henriksen.
In collaboration with Centrum Pæle A/S, researcher Maria Alberdi-Pagola studied the design and performance of energy piles. Her subsequent 2018 thesis simulated the long-term effects and feasibility of the technology.
“[Alberdi-Pagola] developed a tool that can accurately determine how many energy piles are needed to satisfy the energy demand and also if the ground beneath is able to supply the necessary energy. The tool also suggests a foundation plan that outlines how to place the energy piles to avoid them cannibalizing on each other’s energy,” said Henriksen.
Energy piles in Canada: Realistic?
The way Henriksen sees it, energy piles can be used in most parts of the world.
“You need to start working with them from the earliest stages of a project as it does take quite a bit of planning between the heat pump manufacturer, plumbing installer and the producer of the piles themselves to make the right dimensioning of the system,” he said.
He says the perfect stage to start thinking about energy piles is when the geographical location of the building is decided, the building drawings are available and the energy demand profile for the building is known.
“These factors allow us to use our dimensioning tool to determine whether or not energy piles will be feasible for the given project. This investigation uncovers whether they can provide the necessary energy stated in the energy demand profile for the building without depleting the ground of heat, resulting in permafrost which renders the system useless.”
Centrum Pæle A/S was founded in Vejle, Denmark in 1965, and has expanded to include five factories across Europe. Together, they produce four million metres of precast concrete piles every year. For more information on energy piles, check out a two-minute video at youtu.be/7ZsnIxbi1z8. 
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