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Geo-exchange: down but not out

Although lower natural gas prices have taken some of the shine off geo-exchange systems, they can still have a place in a renewable energy setup

Geo-exchange heating and cooling systems were big a decade ago, but that was before natural gas prices plunged and the payback of using the ground as a heat source in the winter and a heat sink in the summer became less attractive.

But don’t count this technology out quite yet, said energy specialist Thomas Barr, managing partner and project director with NuEnergy Systems, an Edmonton-based special energy project company.

“The biggest thing we’ve determined is that there will never be a silver bullet,” he said. “There’s always going to be a combination of these technologies to maximize the efficiency and generation of any type of building.”

There is currently less than a dollar per gigajoule difference between a natural gas system and a geothermal structure operating at a conservative 300 per cent efficiency — something Barr calls the “spark gap.”

“The main cost delta between a geo-exchange system and a conventional system is the cost of the ground loop,” he said. “So if the cost of your ground loop is $10,000 to $100,000 you’re not going to be able to offset that amount of energy at less than a dollar per gigajoule difference.”

Over the long term, however, a geo-exchange system can make sense.

“It offsets 60 to 70 per cent of your heating and cooling demand — it’s huge,” said Barr.

Barr’s company considers geo-exchange as one potential component of a renewable energy system.

“As a design/build firm we don’t just look at a single type of energy — we look at the aggregate impact of all the technologies put together. So, for example, adding more insulation would reduce the heating/cooling demand of a geo-exchange system while a geo-exchange system would reduce the overall energy demand or requirements to put more photovoltaic panels on the roof or on the ground.”

For Barr, it’s “energy efficiency before energy generation.”

“How can I reduce the impact of overall energy required in a building, both thermally and electrically?”

NuEnergy Systems starts every project by determining the energy needs of a building.

“We look at a good, better and best situation. A good building has a requirement of roughly between 40 and 45 BTUs (British Thermal Units) per square foot. A better system for the building would be between roughly 30 and 35 BTUs per square foot. The best kind of situation would be between 15 and 20 BTUs per square foot. We determine what spot along that spectrum the building belongs to.”

If the building qualifies in the “good” category, they then determine how much it would cost to upgrade the building envelope.

“So if we included $30,000 for a building envelope upgrade, how would that affect the subsequent BTU per square foot requirements? If that lowered the BTU requirements substantially enough, we can reduce the costs of the geo-exchange — which offsets itself — then we have a win-win situation.

“Even if they come at par with energy efficiency upgrades versus energy generation, we’re still in a win-win situation because you’re building a more comfortable, more resilient building that doesn’t require the energy inputs of a less efficient building.”

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