爱尔兰数据中心产生的热量都去哪了？

Analysis: The energy from data centres ultimately becomes heat, but the question is how much of this ends up in somebody's radiator

Ireland has spent years debating how much electricity data centres use, their impact on the grid and the infrastructure they require. But far less attention has been paid to what comes out: heat. In 2025, Ireland's data centres used 23% of all electricity metered in the country, up from 5% a decade earlier. That one number has dominated the public debate, but almost every unit of that electricity comes back out as heat. What we do with that heat is a question Ireland has barely started to ask.

Inside a data centre, most of the electricity is used by the servers. The rest goes to power conversion, backup systems and the cooling plant: the fans, pumps, chillers and cooling towers that move heat away from the processors.

Engineers measure this with a ratio called power usage effectiveness, or PUE: how much extra electricity the building needs beyond the computing itself. A PUE of 1.0 would mean nothing at all goes on overheads. Averaged over a year, the best modern facilities come close to that, while older halls can spend considerably more. The commercial data centre we studied in Dublin averaged 1.27 over five years: 27 extra units of electricity for every 100 the computing used.

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From RTÉ Radio 1's The Business, Liz Carolan of The Briefing on the role of data centres in Ireland and how they're using a significant share of the country's electricity

Very little of this is published for individual sites, so it is hard to tell which facilities are efficient. That is beginning to change with EU rules now requiring larger data centres to report their energy use and environmental impact every year. Reporting will not save a single kilowatt-hour by itself, but it is hard to improve something nobody measures.

Ireland's climate is an advantage here. In Dublin, the outside air is below 17°C for more than 90% of the hours in a year, cool enough to remove that heat without much mechanical refrigeration. Warm weather changes the equation: as outdoor temperatures rise, more energy is needed to move the same amount of heat. There is still not enough operational data to say how much extra electricity individual sites use in warm spells.

The cheapest savings are also the least glamorous. Changing how the cooling equipment is controlled, letting the chilled water run slightly warmer and replacing ageing chillers can all cut energy use without compromising reliability. None of this requires exotic technology: these are decisions that can be made today.

From RTÉ Radio 1's The Late Debate, is it time to bring in a levy on data centres?

A much bigger challenge is arriving. A rack of servers built for AI training can draw many times the power of a conventional rack, in roughly the same physical space. Air can only carry so much heat away, so the industry is moving to liquid cooling: cold plates on the processors themselves, or whole servers immersed in fluid.

That shift is why we built the Cyber Physical Server Benchmarking Platform in the Thermo-Fluids and Energy Systems Research Group at TU Dublin. It is the only facility in Ireland built to test real servers and AI hardware under controlled conditions, measuring what they actually do rather than relying on manufacturers' datasheets. That matters because, as the air entering a server gets warmer, its own fans speed up and use more electricity, eating into the savings from running the cooling plant warmer.

Liquid cooling also changes what comes out. Air-cooled halls produce lukewarm air that is hard to use for anything. Liquid cooling produces warm water, and warm water is worth something: with a heat pump it can be lifted to around 70°C, hot enough to heat buildings.

From RTÉ News, Colman O'Sullivan reports on the Tallaght District Heating system which redistributes waste heat from an Amazon data centre

Ireland already has a working example. The Tallaght District Heating Scheme, which SEAI describes as the first large-scale district heating network of its kind in Ireland, uses waste heat from an Amazon data centre to supply County Hall, TU Dublin's Tallaght campus and 133 apartments. It has saved over 1,400 tonnes of carbon dioxide in 2025 and there are plans to extend it to thousands of homes.

So why is there one of these schemes and not 20? Partly geography: data centres are built where there is electricity, fibre and land, not where there are homes that need heat. Partly cost: pipes have to go into the ground, customers have to connect, and someone has to invest upfront for a return that takes years. And partly because waste heat is worth almost nothing to the operator: with no customer nearby, the simplest option is to reject it into the atmosphere.

EU rules already require data centres above one megawatt to reuse their heat where feasible and the European Commission has proposed a common rating scheme for data centres above 500 kW, taking account of energy and water use, waste-heat reuse and their contribution to the wider energy system. The first labels are expected in 2027 and a Heat Bill to regulate district heating is also on its way.

Data centres are built where there is electricity, fibre and land, not where there are homes that need heat.

But progress is slow: a plan to heat buildings in Blanchardstown with data centre heat is still at concept stage. Three things could change that. First, planning for large new sites should weigh nearby heat demand alongside electricity and fibre: if a site could one day feed a district heating network, that belongs in the decision from the start. Second, new data centres should be designed to be heat-reuse ready, because retrofitting heat recovery later costs far more than designing it in. Third, we need better site-level data, so independent researchers can test claims about efficiency, cooling performance and waste-heat potential.

Ireland will continue to debate how much electricity data centres use, and that debate is necessary. But we should also ask what happens to that electricity once the servers have used it. Almost all of it ultimately becomes heat but the question is how much of that heat ends up in somebody's radiator rather than in the sky above Dublin.

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The views expressed here are those of the author and do not represent or reflect the views of RTÉ