Not long ago, I texted one of the top talk-radio shows in
Ireland during a discussion about energy and highlighted the potential for our
island to use geothermal energy for direct heating and cooling, which can help
reduce demand on the electrical grid. The show’s very well-known presenter read out my text and then followed it
with their view that geothermal energy could only be used for heating
and dismissed my comment as somewhat nonsensical.
In their defence, I get it – even if their lack of curiosity was disappointing! We usually talk about geothermal heat, so how can it help cool our buildings and homes? Is it, in fact, a practical solution to (a) cool our buildings and (b) reduce our electrical demand on the grid?
There is much discussion in Ireland about cooling for data centres - most of their electrical demand is for air conditioning to cool the computers. However, the demand for cooling is likely to increase more generally. I am writing this from a very warm Brussels which is (hopefully!) coming out of the recent heatwave across Europe. At least 12 countries broke temperature records and according to the WHO, it is estimated that 1,300 excess deaths are the result of the extreme heat, mostly vulnerable members of society. It is also clear that the regularity of these extreme events is only likely to increase in the coming years – a 1 in100 year heatwave doesn’t mean prolonged high temperatures will only happen once every 100 years; it means every year there is a 1% chance of that event recurring, and those odds are reducing all the time.
So how does geothermal energy cool your home?
It works, in simple terms, by reversing the geothermal energy heating system that we are more familiar with – instead of drawing heat from the warmer ground to heat a cold house, the heat from the air in your house is drawn out and transferred to the cooler shallow earth Warm indoor air transfers its heat to the heat pump fluid, which releases that heat into the cooler ground. The cooled fluid passes back through an expansion valve and is cooled further, allowing it to absorb more heat from inside and the cycle repeats. Here, the heat dissipates to the soil as the fluid circulates. As the ground temperature is typically about 10 degrees all year, this can be a very effective way to cool your home.
This can be scaled up to larger cooling needs and there are
new companies now providing large scale cooling solutions for manufacturing and
food processes, or data centres.
Opportunities for networked and seasonal heating and cooling
In some cases where there is a constant cooling demand (e.g. a data centre) alongside a user that needs heat 24/7 (e.g. a hospital) a direct supply is practical, for example in the Tallaght district heating system. However, cooling can also be integrated with subsurface geothermal systems where excess heat can be stored underground and drawn out again as needed later – this is sometimes called subsurface thermal storage. For example, government buildings in Germany use geothermal heat in the winter, but in the summer this system can be reversed to cool the building and replenish the subsurface heat resource. This means there is considerably more flexibility in the system to provide heating and cooling on demand to a wider neighbourhood and it is not essential to have a close neighbour that requires constant heating, nor does excess heat need to be vented during the summer.
The recent heatwave is a stark reminder that we need to
prepare for a future of more frequent extreme heat events across Europe. Geothermal
energy will be an efficient and effective part of the solutions needed to adapt
the impact of climate change.
Brussels, July 2026
