Analysis: Could using heat from beneath the earth to warm and cool buildings deliver low carbon heat and help to relieve pressure on our electrical grid?
Geothermal energy (in the form of hot underground water), and district heating systems have been with us for many centuries. The earliest version of geothermal district heating could well be from the 14th century in France. Natural geothermal springs at Chaudes-Aigues Cantal were channelled to up to 40 homes to serve as a heating supply. The system was maintained by all users to ensure consistent geothermal heating in their homes, making this potentially the first municipal district heating system on record.
Geothermal energy has been used through the centuries for recreation, manufacturing and heating purposes. But now, thanks to improvements in modern technology, Ireland can use this geothermal resource for its own purposes and assist in removing carbon from our heat market.
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From RTÉ Radio 1's Today with Claire Byrne, could district heating help Ireland reach its emissions targets?
There are only a small number of options in today's heat market. Gas and heating oil supply the vast majority of homes and businesses. While individual electrical heat pumps are slowly taking hold as an alternative to fossil fuels, they present a problem to the electrical grid and its ability to meet the demand of large number of these units. Renewable electricity supply has increased hugely with wind farm and solar development, though demand is increasing in the housing, transport and commercial sectors.
The strain on the electric grid to supply both electricity and heat is a challenge the country needs to consider. The source mix on the electrical grid can also vary from high levels of renewables when conditions allow, to high levels of gas or imported electricity when the weather across the island is less favourable. Can geothermal energy be the final piece in the jigsaw that delivers low carbon heat and helps to relieve pressure from our electrical grid?
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From RTÉ News, calls for more support for Dublin's district heating systems
The use of geothermal heat for direct heating and cooling could take significant pressure off the electrical grid and provide a direct, secure, local near-zero emission option for heating homes, businesses and public buildings. Geothermal systems are unaffected by hours of sunlight or whether wind generated energy is available so provide a constant, year-round temperature, which also makes the system more efficient. This form of energy also has the smallest physical footprint when compared to other renewable sources such as wind and solar energy, making it very attractive in urban built up spaces.
At TU Dublin, the use of geothermal energy is firmly in our plans to reduce our dependency on fossil fuels. Working with Geological Survey Ireland, we have drilled to a depth of 1 kilometre on our Grangegorman campus and have found a temperature of 38.5°C. By exploring further, as in the Paris Basin and Vienna, we hope to find temperatures approaching 60 to 70°C and use this heat reservoir to supply all buildings on the campus.
When the campus was being developed in the 2010s, the foresight was there to install a district heating system with a view to making the campus ready for new renewable heat sources. This highly insulated network of pipes is fed from one location on site. This gives the campus the opportunity to use this single point of supply to heat all the buildings across the estate. In this case, a deep geothermal borehole could be the source of carbon-free heat to TU Dublin buildings as well as Health Service Executive buildings and the neighbouring Dublin 7 Educate Together national school.
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From RTÉ Radio 1's This Week, what exactly is district heating - and how quickly could it be rolled out?
The level of carbon reduction is directly related to the level of heat found at the location. Lower heat levels of 15-20°C will need a heat pump or other source of energy to make the supply effective for use in buildings, while higher temperatures of 60 to 70°C will require little or no energy to supply homes or businesses. On average, temperature increases with depth by about 30°C per kilometre as you drill into the Earth's crust. Even having an input of 20°C greatly reduces cost and carbon emissions: it is similar to filling your kettle with warm water, thereby needing less energy to heat the water to higher temperatures.
Though our electrical system is steadily decarbonising, our heating sector has been left behind. The use of geothermal systems to feed district heating networks is a huge opportunity to decarbonise using a fully local, clean, heat source.
What is district heating?
District heating is like a home’s central heating system just on a larger scale with several buildings being heat from the same network of pipes. The heat source can be anything you have available, including a mix of gas boilers, water heated from industry, waste heat from data centres or incineration or geothermal energy. Highly insulated pipes are installed underground and deliver heat to homes or businesses. The heat is delivered from a central energy centre as required. Utilising geothermal heat to feed these systems can provide near zero carbon heat to users day or night through the year.
From RTÉ News in 2023, George Lee reports omn plans to drill for geothermal energy at TU Dublin's Grangegorman campus
There are many examples of similar systems in use internationally. Deep bore geothermal wells (more than 500m deep) supply up to 250,000 homes in Paris, removing thousands of tonnes of carbon that otherwise would have been emitted through fossil fuel systems. In Vienna, work is due to be completed soon on a deep bore geothermal project to supply 20,000 to 125,000 homes with near-zero emissions heat. This not only reduces carbon footprint, but also helps improve air quality. The University of Delft is approaching completion of a large geothermal/district heating system utilising energy for the university and surrounding housing.
Closer to home, IKEA in Dublin uses shallow geothermal energy to supply heat to its store reducing its carbon emissions by 65%. The Rubrics Building in Trinity College Dublin, which was recently refurbished, is now heated by 21 shallow boreholes and has seen a reduction of 75% of carbon emissions. In the capital's Temple Bar area, several buildings utilise geothermal heat including the Green Building, where the original heat pump is still in place 30 years after installation.
From RTÉ News in 2013, Colman O'Sullivan reports on how the Tallaght District Heating system is taking waste heat from an Amazon Data Centre and usingh it to heat the South Dublin County Council offices and local library
A recent study carried out by Geological Survey Ireland emphasised that geothermal heat can provide 400% of the heat demand in public and commercial buildings across Dublin city centre utilising shallow geothermal systems, where testing has indicated that there are positive geological conditions locally. These indications suggest that exploring the city area further could give us the opportunity to harvest local, carbon-free energy. This heat can be used for housing, hospitals, offices blocks, schools, horticulture, food processing and sports facilities - basically, wherever heat is required. Together, geothermal energy and district heating systems can combine to provide solutions in every sector.
To confirm the availability of heat, and at what depth, different types of geological surveys are required and one of these, a seismic survey, will take place in Dublin city centre in the near future. These surveys operate similarly to a medical scan where a sound wave is reflected off geological structures underground to try to image what lies beneath.
District heating is like a home's central heating system just on a larger scale with several buildings being heat from the same network of pipes
Establishing geological structures, and where best to develop deep (greater than 500m deep) or shallow systems (less than 500m deep) systems through these studies, will give organisations and government agencies a menu of the most suitable sites for new projects. This new, robust, data of the Dublin city region will further enhance the knowledge required to create geothermal energy resource maps, which can then guide developers in choosing the most suitable systems and localities.
This project is partially supported through the GEMINI project which is funded by the PEACEPLUS programme and managed by the Special EU Programmes Body.
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
