The Hidden Heat Beneath Our Feet: Thermal Energy Networks
Think about how absurd our heating infrastructure truly is. We spend years probing the Earth, figuring out where oil might be, then we begin drilling, deeply, extracting oil, shipping the oil to be processed, shipping the processed gas around the world, then pumping it into your house where you burn it, to heat up some air once and leave behind some carbon gas to float up in to our atmosphere. What kind of Rube Goldbergian madness is this?
From Fossil Fuel Follies to Heat Pump Magic
This is partially why there is so much hype around heat pumps. Rather than burning something to produce heat, they literally use electricity and just pump heat and air around, taking advantage of the differences between them. From an efficiency standpoint the differences are staggering.
Efficiency in heating systems is measured by something known as Coefficient of Performance (COP). For something like a natural (fossil) gas furnace that COP might be somewhere between 0.8 and 0.95, which means that for every unit of energy (e.g. a liter of gas burned) you would get 0.8 units of heat back. Natural gas is seen as being more clean burning and efficient, but that’s efficient for fossil fuel heating. For something like an air-to-air heat pump (like you see on many new homes) you can see COP values closer to 3 or higher (again for every unit of energy put in, you get 3x heat units back (also note efficiency drops in colder temps, but still not below 1)). While this sounds like magic, you already have a heat pump in your house that you use every day, it’s called a refrigerator. A COP of 3+ with air-to-air heat pumps is magic, but what if we could do better than that? What if we could tap into the warm Earth beneath our feet like a climate conscious Bond villain? This is the promise of Thermal Energy Networks.
Reinventing Heat: The Promise of Thermal Energy Networks
Broadly the idea here is you use a heat pump, which again basically just moves hot air from one place to another to heat or cool your house, and connects it to the Earth’s natural, molten core. This is achieved by drilling bore holes into the ground, but not actually to the core, typically 100 to 750 feet deep depending on region (though some folks are looking at going much deeper), and then pumping water into them. This water is heated by the Earth to around 55-degrees Fahrenheit and contained within pipes that are connected in a loop to several houses and other buildings that each have a ground source heat pump. This means you can pump heat through the system, but also potentially shift heat out of one building, like say the refrigeration unit in a grocery store, and into another building, like a daycare. If you’re having trouble picturing this, see the diagram below provided by the great folks at HEET.
Given the efficiency of air-to-air heat pumps, why would we bother with the drilling and piping of thermal energy networks and their ground source heat pumps? At the core it’s about efficiency and scalability. This tech is still fairly new, but from the networks that already exist, they’re seeing Coefficients of Performance above 5, sometimes closer to 7! So now you’re taking an already efficient technology and almost doubling the performance. That is insane, if someone doubled the horsepower in your car you would struggle to keep it on the road!
This efficiency gain is primarily due to two factors, first you’re using a liquid as the heat medium, rather than air. If you need to cool down on a hot day, a cold bucket of water is going to work better than a fan (always ask before dumping water on someone). Second there is what I mentioned above, in a network you can shift heat from one building to another. That heat doesn’t need to be generated, it's just reused. And when you need additional heat, you have the boreholes. The Earth is at a pretty constant temperature regardless of wind, clouds, winter, summer or whatever.
Turning Waste to Wealth: Capturing Data Center Heat
I didn’t fully grasp the potential of using excess heat at first, but Zeyneb Magavi of HEET really opened my eyes to this. Think about all of the heat sources that humans generate. It could be natural sources like a city harbor that has been warmed by climate change or local industrial sources like steel or cement production. But also most of our digital world generates lots of heat. We’re talking of course about data centers. Note that many large data centers (e.g. 100+ MW) target a PUE of 1.2 to 1.5 (PUE: Power Usage Effectiveness = Total Energy Usage / Total IT Equipment Energy Usage), which means about 16% to 33% of their energy usage is not dedicated to the actual data processing, but instead on server cooling, distribution losses, lighting, etc. This is the energy we’re going after, let’s do a quick back of the envelope exercise to see how this might pencil out:
How Much Excess Energy?
400 TWh (Terawatt Hours): The estimated the global data center energy usage for 2023 by the International Energy Agency
1.5 PUE (Power Usage Effectiveness): [Total Energy Usage / Total IT Equipment Energy Usage] → 33% of power usage is overhead
133 TWh (Terawatt Hours): Potential excess energy available for heating → 400 TWh * 33% = 133 TWh
How Much Excess Thermal Energy?
480 PJ (Petajoules): 1TWh = 3.6 Petajoules of heat → 133 TWh * 3.6 PJ = 480 PJ
9.1M Households: 1 PJ = 19,000 households annually → 480 PJ * 19,000 households per PJ = 9.1M households
1.8M Households: Assuming we can capture 20% of the heat energy
In my example above I’m assuming we can only capture 20% of the heat energy from data centers due to transmission losses, location issues, inability to retrofit, etc, but still if we can provide sustained heat to another 1.8 million households that would be huge and let’s keep in mind that heat pumps have the COP of 5 or higher, so this heat might be able to serve even more homes. There is a sort of beauty to this in that we can finally recapture some of the heat and damage we’ve inflicted upon our environment and use it for good.
Economic and Social Ripple Effects: Equity and Opportunity
So clearly this has a lot of technical potential and is pretty exciting if you’re an energy nerd, but it also offers a lot in the way of economic equity and job stability. Thermal Energy Networks require folks with a deep knowledge (pun not intended) in drilling and laying / maintaining pipes. This offers a perfect transition for folks in the oil and gas industries and let’s face it, if you want them to embrace our electrified future you need to provide them with an economic future.
Beyond benefitting these workers, adding heat pumps to homes offers the promise of air conditioning for many that don’t currently have that option. Many homes in the United States were built before air conditioning was common, or they were built in regions where air conditioning wasn’t needed before global warming. Heat pumps change all of that, remember all they do is move heat, so that also works in reverse (again recall your refrigerator is a heat pump). This is a big deal given that we’re seeing a bit of an uptick in heat deaths and often air conditioning is a benefit that only goes to the global rich.
Navigating the Hurdles: Technical, Regulatory, and Financial Challenges
What are the downsides to Thermal Energy Networks? Seemingly the biggest blocker is that it’s a new technology and utilities are typically conservative entities that prefer things that are tried and true. Thankfully more test pilots are coming online and they are crushing it! Additionally, there is a big capital outlay to get these up and running as you need to drill the boreholes, lay the pipe, retrofit old buildings to work with heat pumps and integrate this into the grid. Yet, these systems are like most large scale clean energy projects in that they have a large upfront cost, followed by many years of savings versus a traditional system (a system that is already due for replacement in many areas of the country it must be said). Beyond these main two issues, there is still a skills gap to get our homes moved over to heat pump systems and of course not all regions will be well suited to these types of networks due to their geology. In essence, while thermal energy networks offer a tantalizing solution to our absurd heating infrastructure, moving from concept to widespread adoption involves overcoming both technical and institutional challenges.
A Sustainable Future: Reimagining Urban Heating
We finally have a chance to flip the script. By harnessing the latent heat in our environment—from the Earth’s steady warmth to the untapped surplus in data centers—we can reduce our dependence on fossil fuels, lower emissions, and pave the way for new economic opportunities. Thermal energy networks represent a paradigm shift: a move toward systems that recycle and repurpose energy rather than wasting it. They not only promise significant efficiency gains, but they also offer a pathway to a more equitable, resilient, and environmentally sound energy future. If we can muster the will to innovate and invest, thermal energy networks might just be the answer to both our environmental crisis and the economic revitalization of our aging energy infrastructure.