Subway tunnel heat-exchangers could heat and cool thousands of nearby apartments

Originally published at:


What is this science nonsense?!?! We all know those are the same whack-a-dos telling us vaccines are safe!!!



I love these types of articles. It’s evidence that there are still intelligent humans on this planet.


Roger That!


I don’t know if these guys have been in a subway system lately, particularly NYC’s. But those tunnels are anything but cool in the summer time, and anything but warm in the winter. And most cities spend an awful lot to heat and cool cars, or pressurize/ventilate whole systems in order to keep them cool in the summer and warm in the winter. Insult to injury if you’re pumping heat, it doesn’t disappear. It goes some where. If you’re pumping heat into the subway when its warm, and sucking heat out when its cold. You’re just moving the resources expended to heating, cooling or ventilating the trains and stations/tunnels. So it very well may jack up more modern systems that are carefully designed to keep air moving through them to prevent heat building up when its warm on the surface. And its probably not going to work at all on old systems like NYC.


In NYC we I wonder if we could use modified refrigerators that use cold air during the winter.

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L’Ecole Polytechnique Fédérale de Lausanne and the Swiss Federal Institute of Technology are one and the same, just in different languages.


Does it come with urine and rat smells? Because if it doesn’t, I don’t know if I want inauthentic subway heating in my apartment.


I’ve never seen a 1 train station that looks like that, and I’m pretty sure I’ve been to all of them.

(I get that it’s a concept illustration, but why not use a fake subway line instead of a real one?).


I can’t find it now, but there was a Car Talk episode where they discussed cooling a movie theater back in the day by tapping into adjacent mines.

I miss those guys.

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Lausanne has a Metro? It’s not even 150,000 people. That’s really something.

Doesn’t NYC sort of do something like this? I thought the steam used to heat buildings was a by-product of electricity generation.

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Nope. ETH (Swiss federal institute of technology aka Eidgenossiche Technische Hochschule) is in Zurich. (WOW was that hard to write with auto-correct) :stuck_out_tongue:. Not Lausanne.

Sort of.

The steam system doesn’t feed every (or even most) buildings in the city. And the bulk of New York’s power isn’t produced locally, but pulled down from the Niagra Falls hydro electric plants and some other areas. There’s something of a critical shortage of local power generation capacity in the New York Metro Area. It gives us some of the highest power costs in the nation, especially on Long Island and bits of Connecticut. And it makes brown outs common in the summer. To the point where the weather reports sometimes contain brown out predictions during heat waves.

What power is generated in the bounds of NYC is often produced as much for as the steam as for the power so you could view the electricity as the byproduct being put to use instead of the steam. They aren’t exploiting a natural heat disparity for free heat pump reasons. So much as just rerouting hot steam from a regular powerplant instead of condensing it to be reboiled.

And the sheer amount of buildings heated by steam in NYC instead of geothermal, electrical or other more modern systems is one of the least green things about New York. Its apparently massively inefficient woth tons of heat lost in transmission, and much more energy thrown at buildings than would otherwise be neccisary.

Having lived in a steam system building or two. It’s fucking awful. When its on its always on, no adjustments. And the entire building is basically at the same setting at all times. So its either way too cold, or swelteringly hot depending on the neighborhood (Queens hot as balls, Brooklyn cold as fuck). It cant really be turned on or off except at the building level, or at best by floor. And then only by cutting off the steam flow. When the heat is turned on in NY is dictated by statute on a fixed date too. Irregardless of weather, to keep land lords from freezing out tenants. So depending on the year you might get the full blast heat during 70+ degree days one year, and go weeks unheated during early cold spells. City wide PSAs not to try and use your oven to heat your apartment are wide spread.

Its the sort of thing that looks real green when you isolate it down to how it offsets the impact of the electricity cogenerated with the steam. And it was probably amazing 120 years ago when home heating by anything but fire was brand new. But its an awful way to do things. My college campus in Philly was run on a similar steam plant system. Same problems.

If there’s a benefit its that steam is basically covered by the whole city’s electric bills. So steam buildings heat and hot water are generally free/included in the rent. So from a public benefit, reduce the cost of living front its pretty good. I probably wouldn’t have been able to afford to stay in Brooklyn for as long as I did if I wasn’t in a steam building. And when I was dead broke I was really happy to be getting one less bill than most people.


Same in London. In fact, so much heat has been dumped in the last 117 years that the tunnels have gone up 36 to 45˚F !


And on top of that if I’m remembering my yearly “Why is the NYC Subway so fucking hot” articles right. The sheer volume of air contained in the tunnels of older systems prevents the sort of ventilation that would move that heat out. Sort of like trying to breath through a garden hose there’s just too much mass of atmosphere in there for there to be a practical way to push cool air in, and pull hot air out. Or vice versa. Meaning you can’t vent that heat out to elsewhere. Neither is there is there a particularly efficient way to add heat if you need it. What little air moves through these tunnels is pushed by the trains as they move, and with an open set of interconnecting tunnels (many of which got no trains) that doesn’t do much.

That’s why some of the most modern subway systems have been built sealed/pressurized tunnels, with much closer fit to the trains. It makes it practical to force ventilation and allows the trains to do a lot more of the work pushing air around. Which lowers costs to heat and cool the trains cars themselves and makes everything a shit ton more pleasant. But you can’t add that to 120 year old systems, and especially in NY. Where the subway tunnel system intersects with multiple other tunnel systems including other transit tunnels, disused sections and older systems, information infrastructure, the steam system and electrical tunnels, maintenance tunnels, the old air tube post system and a thousand other things. No way to block all of the holes, and impractical to dig an entirely new sequestered system. You got like 6 fucking surface rail lines running though tunnels in Manhattan on top of the subway!

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There seem to be some issues with this, based on how excruciatingly hot-in-summer and cold-in-winter the subway usually is. So, maybe to think about this a different way…

Geothermal - it works. This is just geothermal, but using the existing subway network to run the pipes, so you significantly reduce the major up-front cost of geothermal (i.e. drilling). Just run the PEG lines down the subway tunnel and tap into the bedrock at a convenient point. You’re not really using the heat/cold* from the subway, rather you’re using it from the surrounding bedrock.

*minor science nit-pick… you can’t really move cold, as the write-up here suggests. Only heat can be moved. What changes with a heat pump type system for cooling in summer and heating in winter, is simply the direction you’re pumping the heat. An AC takes heat from indoors and dumps it outside (or underground in this case). Geothermal AC works really well because the heat capacity of rock is a lot better than air. When running in heat mode you’re just taking the heat from underground and dumping it into the house. For those who say “how can this work in winter?”, your fridge does this every day - it takes heat from inside the fridge where it’s already cold, and dumps it outside. Same for your freezer - the inside is ice cold but the system still finds heat in there to export - that’s why the back/top/side of the unit feels warm.


ISTR that a few buildings in Chicago tied into the freight tunnels for that purpose.

But really, why not just drill down and use a ground source heat pump, and ignore the subway? The reason to use tunnels and mine etc is that they are big enough holes in the ground to run air directly through and not need heat exchangers. Once you’re using a denser working fluid you can easily run pipes in your own holes, and drill the deeper, have better contact with the earth, and not link your building to a big population of rats.

Along those lines, cool cave air from Luray Caverns in Va. was used to cool a sanatorium:

“The air drawn from the caverns being about 54 degrees, when forced into the building, cools the rooms to any degree comfort may demand, however intense the heat prevailing outside,” observed Hunner. In winter, the comparatively balmy air was given a boost by passing through a series of chambers featuring coils filled with steam. Humidity was regulated by a series of condensers year-round.

Not sure if they could hear the pipe organ over the sound of the fans…


Yah. I was gonna say: Boston’s Park Street station can already get miserably hot in the summer. Pumping excess heat down there seems like it’d produce a simulacrum of hell.

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I believe that open cave systems tend to be cool because in the winter, denser cold air sinks into the system. And in the summer, it tends to stay there because of the lighter warm air outside. Over many years, this cools down all the surrounding rock.

That works in the small scale, like a move theater or sanatorium, but for a large scale heat dump, it would probably be best if someone does the interesting math.

It’s not like there’s a magical cold source in the ground. Dig deep enough and you hit really hot iron.