It's clean, abundant, and will outlast humanity — so why aren't more buildings tapping into the heat beneath our feet?

That question was on Curious Canberran Don Fletcher's mind, after learning about the Geoscience Australia building in the ACT, which is heated and cooled using ambient temperatures in the earth's crust.

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"I had this vague memory that Geoscience had done this thing that seemed unusual 20 years ago of drilling all these holes to heat their building from ground heat exchange," he said.

Concerned about Australia's energy future, Don wanted to know why such systems weren't used in other large buildings in the city.

"Here we've got another supply of heat that's constant … it's continuous, it's free, it's clean, there's no surface infrastructure to speak of - it sounds wonderful!"

Geothermal vs geo-exchange

Anthony Budd says the system at Geoscience Australia doesn't rely on "true geothermal" energy. ( ABC News: Jordan Hayne )

To learn more, Don and I met with geoscientist Anthony Budd and Geoscience Australia's acting property operations manager Hanna Slattery, at their Canberra headquarters.

Curious Canberran Don Fletcher at the Geoscience Australia building speaks to acting property manager Hanna Slattery in the building's plant room. ( ABC News: Jordan Hayne )

Beneath the earth, in the bowels of the heating system, Anthony brought up an important point: the heating at Geoscience Australia doesn't draw on "true geothermal" energy.

"This sort of system, a geo-exchange system, isn't really what I call a geothermal system," he said.

"We're just taking an average annual ground temperature, there's no extra heat from deeper within the earth coming into that system.

"There's a pretty big difference in concepts there."

Ok, so how does the system work?

On damp winter days, pipes full of warm water dry the ground above. ( Supplied: Anthony Budd )

Hanna gave Don and I a guided tour of the system's features, and a dummy's guide to geo-exchange systems, which are also known as ground source heat pumps.

"This is probably the largest closed-loop geothermal system in the Southern Hemisphere, it certainly was at the time of construction," she said.

"In essence, the system uses the earth at a constant temperature [of] about 17-18 degrees, down at 100 metres below the surface."

350 sets of pipes service the building and circulate water beneath the ground, where the temperature is always constant.

In winter, that water is warmed to 17 degrees Celsius, then brought back up to ground level where heat pumps extract the heat and circulate it through the building.

In summer the process is reversed —heat is extracted from the air and the pipes are used to sink it into the ground.

"In summer we can cool the air temperature by rejecting heat into the ground, and in winter we can pull that heat back out," Anthony said.

Why do it?

The plant room at Geoscience Australia, where the building's geothermal system operates. ( ABC News: Jordan Hayne )

Ground source heat pump systems are much cheaper to run than gas or electric heating - and they're environmentally friendly.

Geoscience Australia property employee Hanna Slattery in the building's basement. ( ABC News: Jordan Hayne )

"They did do some costing at the time of construction, and they gave us projected savings, which they believed to be approximately $1 million over a 25-year life span," Hanna said.

"That's probably fairly conservative, considering how energy has increased in price over the last 20 years."

As the building was being constructed in the 1990s, the system was also seen as an experiment for Geoscience Australia to champion.

"It's a purpose-built building, and I think the decision was that we could use a ground source heat pump to be a demonstrator for the technology," Anthony said.

"Being a bunch of geoscientists and whatnot, the opportunity to drill 350 wells was too good to pass up."

What are the drawbacks?

An underground corridor with piping at the Geoscience Australia headquarters in Canberra. ( ABC News: Jordan Hayne )

In my research I tracked down Zhenjun Ma from the University of Wollongong's Sustainable Buildings Research Centre, who told me the upfront cost of installing the systems was prohibitive for many buildings.

"You need deep holes, deep boreholes, so this borehole drilling cost is very high, especially in Australia where the labour cost is very high," he said.

At Geoscience Australia, Anthony explained that ground source heat pump systems were best suited to climates with hot summers and cold winters.

A ground source heat pump system being installed at a residential property in Bowral, NSW. ( ABC News: Jordan Hayne )

Zhenjun said much of Australia simply did not get cold enough to make the systems efficient.

"Ground source heat pumps really have a high performance under heating dominated climate conditions," he said.

"In Australia … we are cooling dominated, which means we have a relatively low performance."

But he said there was room to grow in places like Canberra and Melbourne.

Demand on the rise as gas prices soar

Systems can also be installed just a few metres below the surface. ( ABC News: Jordan Hayne )

Yass businessman Touie Smith is at the forefront of that growth, as one of the only people installing geo-exchange systems in the Canberra region.

I met him at a property at Bowral in southern NSW, where he told me that in the past, the biggest thing holding this kind of heating back was the low cost of more established heating methods.

Touie Smith says he has been inundated with interest in his heating systems. ( ABC News: Jordan Hayne )

But as the cost of gas and electricity has risen, so too has the demand for his business.

"Classically in Australia we have had low energy costs, and we've seen a massive shift in the last 5-10 years," he said.

"As more people are conscious about energy conservation and efficiencies and are building better houses, we're seeing a massive uptake."

Touie also agreed that skilled labour was hard to come by.

"Demand is exceeding what we're able to produce at the moment," he said.

"Our single biggest problem is finding skilled people that want to work in the industry."

Could this go mainstream?

Curious Canberran Don Fletcher reads a pamphlet about geothermal energy at the Geoscience Australia headquarters in Canberra. ( ABC News: Jordan Hayne )

Before Don and I left Geoscience Australia, Anthony told us there was growth ahead for both geothermal energy and ground source heating in Australia.

"It is happening in Australia. There's a new power plant which is due to be built at Winton in Queensland," he said.

"There's a housing development in Sydney, there are 800 houses being built by a single developer, and that developer took the decision to install a ground source heat pump in every dwelling."

Afterwards, Don told me he was keen to see more investment in heating systems like the one used in Canberra.

"Canberra seems to be an ideal place ... where this is going to work most easily."

"So in Melbourne and Canberra and perhaps Sydney, why aren't we doing this?"