Simply operating America’s buildings uses more than a third of the country’s energy. A major chunk of that is temperature control — keeping the indoors cool in the summer and warm in the winter. Heating eats into families’ budgets and burns a tremendous amount of fuel oil and natural gas. But what if we could heat and cool buildings more efficiently, cleanly, and cheaply?
On this week’s episode of Shift Key, Rob and Jesse talk to Dulcie Madden, the founder and CEO of Dig Energy, a New Hampshire-based startup that is trying to lower the cost of digging geothermal wells scaled to serve a single structure. Dig makes small rigs that can drill boreholes for ground source heat pumps — a technology that uses the bedrock’s ambient temperature to heat and cool homes and businesses while requiring unbelievably low amounts of energy. Once groundsource wells get built, they consume far less energy than gas furnaces, air conditioners, or even air-dependent heat pumps.
Shift Key is hosted by Robinson Meyer, the founding executive editor of Heatmap, and Jesse Jenkins, a professor of energy systems engineering at Princeton University. Jesse is an adviser to Dig Energy.
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Here is an excerpt from our conversation:
Jesse Jenkins: We’ve been throwing a few different terms around here to describe this. We talked about geothermal heating and cooling, ground source heat pumps, geoexchange. There’s a little bit of ambiguity here in the language people used to talk about these things. What’s your favorite way to talk about this product and why?
Dulcie Madden: Ugh.
Jenkins: Or is this just an endless debate that is not resolved?
Madden: It is a great question. It’s a big debate. When I think of geoexchange, just so everyone knows, it’s really about, like, are you able to basically create a larger array, potentially, across buildings, more like exchanging heating and cooling, like both point source and — I think about it more in the context of Princeton, where it’s also across buildings, right? And that starts to move into what some people call a thermal energy network. And so there’s some work there.
There is a lot of back and forth between geothermal heat pump and ground source heat pump, and a lot of people will use them interchangeably. I think that there is technically a differentiation, but I don’t know if there’s a didactic, like, This is what it is. It’s just … you have to be interchangeable.
Jenkins: Yeah, I’m curious, I don’t know what the best marketing term is, what people actually resonate with beyond the technical crowd. I was describing what you guys were doing when you closed your seed series round on X or BlueSky, and somebody jumped into the replies. That’s not geothermal energy, it’s ground source heat pump. And it’s like, okay. And I guess the argument is that, because it’s basically just using it as a source for heat exchange in the heat pump operation as opposed to extracting heating out of the ground — which you can do. I mean, you can just do direct heating from geothermal.
Madden: Right.
Jenkins: Deep geothermal drilling, as well. It’s something that Eavor, which is an Alberta-based deep geothermal company that I advise, as well, is working on their first commercial project in Bavaria. That’s gonna go into a district heating system. So they’re going produce a little bit of power, but a lot of that is just direct heat. But again, they’re drilling, five, six kilometers deep and pulling out heat at high temperatures. And so it’s because it’s kind of back and forth, you’re using this kind of buffer for both heating and cooling. I think that’s why people might push back on the idea that it’s geothermal. But you’re using the heat in the ground.
Mentioned:
Dig Energy
TechCrunch: “Geothermal is too expensive, but Dig Energy’s impossibly small drill rig might fix that”
Princeton University’s Geo-Exchange System
Jesse’s downshift; Rob’s downshift.
This episode of Shift Key is sponsored by …
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A warmer world is here. Now what? Listen to Shocked, from the University of Chicago’s Institute for Climate and Sustainable Growth, and hear journalist Amy Harder and economist Michael Greenstone share new ways of thinking about climate change and cutting-edge solutions. Find it here.
Music for Shift Key is by Adam Kromelow.
