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As much as we might fantasize about it, we can\u2019t air-condition the New York subway\u2019s platforms. It would cost billions to partition off every one so you\u2019re not pouring cold air into the tunnels, and then billions more for the electricity per year. It\u2019s money better spent on almost any other need, starting with repairs and rehabilitations of the most dilapidated parts of the system. (Have you seen the state of the Chambers Street station<\/a>? It is finally, mercifully slated for renovation<\/a>.) New elevators and better signals and new cars deserve priority over five or ten minutes of air-conditioned comfort any day.<\/p>\n And yet: Those platforms are really hot in the summer, and more so than ever. Even setting aside the changing climate, our air-conditioned trains contribute quite a bit to the sauna conditions, as they ever more efficiently expel hot air. Their compressors fire up when in the stations, cycling as the doors open and close. Relief doesn\u2019t come even when the hot weather ends. In my experience, the temperature down there lags the outdoors by a month or so. Place your hand on a tiled subway wall on a warm day in May, and it will be cooler than you expect. Do the same in November, and it will still be warm.<\/p>\n A version of that phenomenon lies behind a plan, newly under exploration by the MTA, to pump some of the heat out of its stations and put it to productive use \u2014 and the proving ground will be that very Chambers Street station as it\u2019s rehabbed. To laypeople, this scheme may sound bizarre, and, admittedly, it\u2019s at an extremely early stage\u00a0\u2014\u00a0little more than an agreement between state and city to look into whether it might be worth looking into. But a few experts I spoke with this week suggest that it is not only possible but realistic; similar systems exist around the world, though not in transit systems, and their benefits are real. \u201cI do think it\u2019s a plausible idea,\u201d says Jeffrey Pepin, a hydrologist at the U.S. Geological Survey. \u201cI mean, the science is there.\u201d<\/p>\n It\u2019s called a thermal energy network, or TEN, and it takes advantage of a natural phenomenon: Drill several hundred feet into the bedrock, where\u00a0the temperature stays around 55 degrees Fahrenheit, summer or winter, north or south. It gradually gets cooler the deeper you go (before things start to warm up again, but that\u2019s many miles down). So here\u2019s what the MTA would do: Drill a deep borehole \u2014 actually a big grid of boreholes \u2014 down into the Manhattan schist. \u201cUsually it\u2019s 100 to 200 meters deep \u2014 you design how deep you want to go to reach the target temperature,\u201d says Wanju Yuan, a research scientist at the Geological Survey of Canada.\u00a0Then you run pipes around the walls of the station and into those wells, fill the whole business with fluid (probably water), and pump that liquid around and around, down and up, in a sealed loop. When it\u2019s in a hot subway station, the liquid soaks up heat. When it\u2019s down below, the cold rock drinks up that heat energy, and the fluid gets chilled. Around and around that water goes, pulling heat out of the station on each cycle and warming up the bedrock.<\/p>\n When winter comes, it works the opposite way. The local bedrock \u2014 which has been soaking up heat all summer, and might be up to 70 or 80 degrees in the vicinity of those wells \u2014 now warms the water rather than cooling it. When it\u2019s pumped back up, that heat can be used to either warm up the station or (more likely) to heat the buildings above. The result would not be like a fully climate-controlled space, but even if all of this just takes the edge off in the summer, that\u2019s worth considering, especially if it\u2019s a source of warmth in winter. The agency could sell that heat energy to the buildings above, which would bring in a bit of money and potentially take a little pressure off Con Ed as well. If you couple a system like that with a heat pump, explains Guangdong Zhu, a researcher at the National Laboratory of the Rockies, you can get a lot more out of the energy you have to buy: With a borehole\u2019s boost, \u201cone kilowatt\u2019s energy can provide four kilowatts of heat.\u201d<\/p>\n A perhaps obvious question that comes to mind: Doesn\u2019t the heat just dissipate into the earth while it\u2019s down there? Not so much, explains Pepin: \u201cYou lose some of it,\u201d he says, but \u201cwhen they design these systems, it\u2019s common for the wells to be maybe ten feet from each other,\u201d so there is a concentration and it stays put. \u201cWhen you don\u2019t have a lot of ambient groundwater flow\u201d \u2014 which Manhattan does not, once you get down into the schist bedrock \u2014 \u201cit\u2019s not that big of an issue.\u201d<\/p>\n These systems are not new; lots of buildings use this borehole technology, notably in Europe and Canada, though some use it just to drain heat into the ground without actively trying to pull it back later on. The most prominent system was probably at Drake Landing, a planned community in the suburbs of Calgary, which for about 15 years took solar-generated power and stashed it underground during the long, cold Canadian winters. (The solar equipment aged out of efficiency and was recently decommissioned<\/a>.) In New York, these systems are rarer. At 1515 Surf Avenue in Coney Island, a 2019 condo building sits atop 153 geothermal wells. At least one Manhattanite tried to install one, too: The late Ted Kheel, the labor lawyer (and occasional New York contributor), spent several years in the 1990s trying to install an experimental system under a building his foundation was putting up on East 64th Street. It was a huge headache to get online<\/a>, although it finally did in 1999. And there are lots of small private systems. \u201cI have one colleague who used to run a geothermal program here years ago,\u201d says Zhu, \u201cand he retired and built a new house in the mountains with\u00a0a borehole coupled with a heat pump. It\u2019s beautiful \u2014 it worked really nice.\u201d<\/p>\n There are a ton of questions left unanswered in the MTA\u2019s announcement, probably because this is so early in the process. Zhu notes that \u201cthere\u2019s a couple of derivative additional things you can do to improve efficiency, technical performance, economic performance, things like that.\u201d There are also real obstacles. Boring into the ground is a lot easier on an empty lot in the countryside than on a station platform built in 1913. A drilling rig is not small; you\u2019d have to get it in there, and then there are cables, sewers, and God knows what else underneath. \u201cBut it\u2019s just more expensive,\u201d Zhu says, \u201cnot that it cannot be done.\u201d (For example, he mentioned to me that if you can\u2019t drill straight down, you can do it at an angle; the bedrock doesn\u2019t care.) \u201cIt\u2019s not mission impossible.\u201d<\/p>\n Sign Up for the Curbed Newsletter<\/p>\n A daily mix of stories about cities, city life, and our always evolving neighborhoods and skylines.<\/p>\n Vox Media, LLC Terms and Privacy Notice<\/p>\n