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Heating and cooling: (AI) data centres, water, geo

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    I’m surprised water consumption by data centres is an issue. Presumably, in countries with at least half-functioning planning systems, a centre could be forced to 1) use geo energy for primary cooling, and 2) build a closed circuit water circulation (with filtration) system for the needed-in-summer cooling fans, with a restriction on the amount of drinking water the centre be allowed to use per annum?

    My workplace - large hospital - achieves all cooling needs using geo energy - approx 100 holes approx 70m depth. We even heat space & water (almost) year round using same energy & some extra electricity to get the temp up from 40C to 68C

    If I wanted to build a data centre, I’d do this.

    However, I don’t want to build one :)
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      CommentAuthordjh
    • CommentTimeJun 6th 2026
     
    Posted By: minisaurusMy workplace - large hospital - achieves all cooling needs using geo energy - approx 100 holes approx 70m depth.
    My last workplace used a similar number of similar sized boreholes for all its heating and cooling, but it had nothing to do with geo energy. It was simply a ground source heat pump.

    Geo energy is not generally easily available and requires fairly particular conditions. So I don't think it's a good solution to the data centre problem.
  3.  
    I’m in Sweden so translated “geoenergi” which means heat from the underlying ground, mostly granite in Sweden. I’m not talking about Iceland-type “geothermal” energy. So I guess I should have said ground source heat pumps, maybe?
  4.  
    Green Building Forum, like all cloud based software, is hosted in a data centre somewhere.

    Occasionally I wonder how much energy is used there each time I post something like this - does anyone know?

    Of course every joule that is used by that computer for processing this post, requires exactly one joule of cooling, as they import energy but cannot export it.

    They don't need seasonal heating balanced by seasonal cooling in the way that a hospital or office does, so there's no point storing their waste heat into the ground.


    You could think of an integrated system with a datacentre to create heat, an underground store, and district heating to distribute it, but you run into the same economic problems as the 'heat a city with waste heat from a factory' proponents did.
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      CommentAuthordjh
    • CommentTimeJun 6th 2026
     
    Lets build our data centres at the seaside, or next to large rivers :devil: I'm sure they'll enjoy the scenery as much as power stations do. :bigsmile:
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      CommentAuthorfostertom
    • CommentTimeJun 6th 2026 edited
     
    Wonder if there's the same potential for development of direct conversion of 'weak' (small delta t) heat into electricity (which is used on a small scale for exceptional circumstances, like electricity to read while on a polar expedition, running on waste gaz-cooking heat) - as there was for the very weak generation from solar radiation (used for exposure meters), and the very weak light output from LEDs, to start with?
  7.  
    Carnot is not your friend for making power from small delta T..... only a few % recoverable, which means 95+% of the waste heat is still waste heat.

    Better to find how to reduce power consumed (= heat generated) by the computers by a few %, use them better or less, use more renewable power. Maybe there's something useful to be done with the waste heat but generally it's not very economic.
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      CommentAuthorfostertom
    • CommentTimeJun 6th 2026 edited
     
    Will, does Carnot apply when there's no mechanical action? Excited molecules (even slightly excited) directly creating an electrical potential? Why in that case does any of the heat need to be 'waste'? Does Carnot apply to direct PV conversion of radiant energy to electricity? whereas it certainly does if e.g. the radiant energy heats water which drives a turbine which drives a generator.
  9.  
    Carnot limit applies to any 'heat engine' where heat energy goes from a warm source to a cold sink and does work along the way. The work can be mechanical, electrical, magnetic, biochemical, etc

    A PV panel is not a heat engine as the source is not heat energy (is actually electromagnetic radiation, which is a kind of work already) and there's no cold sink, so no Carnot limit. Likewise a wind or hydro turbine.

    Carnot was a clever bloke but his theory isn't that jaw dropping nowadays - he just claimed that perpetual motion is impossible.

    He imagined putting heat through any kind of engine to generate motion, that drives an identical engine running in reverse as a heatpump, to pump the heat back up to temperature to use it all over again. If the two engines were very efficient then he could end up with more heat than he had started out with, free energy! He said that's impossible and so there is a limit on how efficient any engine can be. Doesn't matter if the engine is mechanical, electrical, whatever.

    (The idea of a heatpump was already familiar to him in 1824, there's no novelty about them!)

    So small delta T means we can have very efficient heatpumps but cannot have very efficient generators, and vv at high delta T.
  10.  
    so, getting back to the subject - Will has suggested that ground source is not economical for data centres (in the UK I assume?) So, having established that we're going to use "conventional" cooling roofs (and hopefully renewable electricity), I imagine in the UK one can keep the rooms below set point using outdoor air winter time and summer evenings? Thus reducing the need for the cooling system fans & eventually the cooling water.

    And the cooling water could be some kind of closed-loop filtered system, thereby significantly reducing water demand, instead of constant drinking water.

    P.S. ground source appears to be economical for data centres in Sweden, i.e. you can connect to district heating & sell the heat to your local authority - e,g, Glesys in Falkenberg, facebook in Karlix etc.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 7th 2026 edited
     
    Thanks Will - heat energy vs radiation. OK so Carnot applies. Taking the trouble to have a look for myself, https://tomorrowdesk.com/method/thermoelectric-generator - many present and poss future techniques, incl a few for low delta-t.
    "a critical technology for improving energy efficiency and harnessing waste heat in industrial, automotive, and renewable energy systems"
    "enable energy recovery from low-grade heat sources that would otherwise be discarded"

    So, minisaurus, I'd say this spot-on the subject, and full of promise for re-capturing/recycling free-release of massive waste energy into the biosphere by data centres and no doubt other future energy consumers. We focus on greenhouse gasses which increase resistance in earth's necessary dispersion to space of its core heat, received solar heat and almost as a footnote, human-generated heat. But if the latter increases, a time will come where it causes biosphere heating on its own, even if greenhouse gasses are brought back down.
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      CommentAuthordjh
    • CommentTimeJun 7th 2026 edited
     
    Posted By: minisaurusI imagine in the UK one can keep the rooms below set point using outdoor air winter time and summer evenings? Thus reducing the need for the cooling system fans & eventually the cooling water.
    That's one reason data centres are being built in places like Iceland. They need a LOT of cooling.

    Posted By: minisaurusground source appears to be economical for data centres in Sweden, i.e. you can connect to district heating & sell the heat to your local authority
    We don't have much in the way of district heating in the UK, nor local authority heating networks.
  13.  
    Thermoelectric generator from Tomorrowdesk:- "can recover 3–5% of the total fuel energy ... from a diesel engine exhaust"

    This is in line with Carnot efficiency of heat recovery generators, but having burned myself I know that a diesel engine exhaust runs a lot hotter DeltaT than a computer does! Hundreds of degC, which is 'low grade heat' from industrial perspective.



    human-generated heat other than from fossils - there is none. A datacentre running on solar or wind emits exactly the same heat as if there was no datacentres and the sun had just shone onto the ground and the wind just blew eddies over the sea. Aldebo is important, but that's 99% about ice and snow cover, solar panels have vanishingly little contribution.



    Waste heat reuse for district heating - in UK there is very little district heat distribution, despite 200 years of many GW of free waste industrial heat being available. It's always ended up more expensive than individual heat per building, given UK climate heating loads. I'd love to make it work and there are some successful networks including Aberdeen, but the competition is with air-air heatpumps per dwelling which are going to be very cheap.
    •  
      CommentAuthordjh
    • CommentTimeJun 7th 2026 edited
     
    And data centres need to operate 24x7 both for economic and computing reasons. So they need power and cooling 24 hours a day.

    Edit to add, looks like the Japanese are already thinking of data centres very near the sea (although the date is a bit suspicious):
    https://www.theregister.com/on-prem/2026/04/01/mitsui-osk-taps-hitachi-for-floating-datacenter-plan/5229981
    •  
      CommentAuthorfostertom
    • CommentTimeJun 7th 2026 edited
     
    Again Will, spot on - 'other than from fossils - there is none' - I hadn't quite registered that, and hadn't updated an old notion. So the demise of fossil
    provides a beneficial end to humans' dumping of extra 'unnatural' waste heat into the biosphere - except for other kinds of exothermic conversion of ancient minerals, like explosives, maybe fertilisers - and nuclear. Thanks
  16.  
    Posted By: WillInAberdeenhuman-generated heat other than from fossils - there is none. A datacentre running on solar or wind emits exactly the same heat as if there was no datacentres and the sun had just shone onto the ground and the wind just blew eddies over the sea.


    But surely there are localised effects? While the net influence into the global atmosphere might be negligible, there will be an intensity of heat energy output from the datacentre into the immediate neighbourhood that would otherwise have been dissipated by atmosphere.

    Like the urban heat island effect. No?
  17.  
    As I understand it the amount of power falling on the earth from the sun is massively more than the amount of power being used by humans (which turns into waste heat), like tens of thousands of times more.

    If we say built say 3 GW of solar panels in Lincolnshire to power datacentres in west London, that would remove 3 GW of heat falling on the soil of Lincolnshire and add 3 GW to the air over London instead.

    In principle this would make Lincolnshire colder and London hotter.

    But the average sunshine power falling on London (averaged over day and night all year round) is around 1,600 GW, so doubtful they'd notice an extra 3 GW!

    The urban heat island is caused by replacing solar heat-releasing and heat-reflecting surfaces (such as leaves) with solar heat absorbing surfaces (such as concrete) so more of the 1600 GW of sunshine gets absorbed.
  18.  
    Posted By: WillInAberdeenThe urban heat island is caused by replacing solar heat-releasing and heat-reflecting surfaces (such as leaves) with solar heat absorbing surfaces (such as concrete) so more of the 1600 GW of sunshine gets absorbed.


    Exactly, so I'm not sure you can say:

    Posted By: WillInAberdeenA datacentre running on solar or wind emits exactly the same heat as if there was no datacentres


    You are by definition creating a localised area of heat (and noise) which will have localised effects.

    I don't disagree that nature can make things several orders of magnitude more extreme, but you can say the same thing about wildfires vs domestic fires. I wouldn't want either happening next door to me.
  19.  
    Interestingly the government has just announced a Data Centre design ideas competition:

    https://www.riba.org/news/riba-and-government-design-ideas-competition-for-data-centres/
    •  
      CommentAuthorfostertom
    • CommentTimeJun 19th 2026 edited
     
    Posted By: WillInAberdeenthe average sunshine power falling on London (averaged over day and night all year round) is around 1,600 GW, so doubtful they'd notice an extra 3 GW!
    Yeah but that's exactly what everyone used to say about the environment's self-evident (rhetorical exclamation "!") ability to soak up whatever humans did - until 'carrying capacity' became a recognised thing, as raw quantity approached then overwhelmed it; new non-obvious mechanisms of harm (such as greenhouse effect) were identified; and subtle but serious effects of even small emissions (particular pollutants within the total) were found.

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