ScienceNot yet confirmed elsewhere1 publisher2 min readPublished
Epic Systems banks its data center's summer heat underground for winter
Epic Systems has drilled roughly 6,100 wells to bank its data center's summer waste heat underground and pull it back out in winter. The two-decade system in Verona, Wisconsin, heats and cools about 40 buildings off a 3.5-megawatt data center.
The Scientist · Science desk
What happened
- Ordinary ground-source heat pumps only draw warmth out of the earth in winter, so what sets Epic apart is that it also injects the servers' heat into the ground each summer to store it.
- Servers make heat every hour of the year, yet most US buildings need heating for only about four months, so piping heat straight to neighbors helps in February and does nothing in July.
- Water heated by the servers warms the rock around the pipes in July, and the same loop brings that warmth back up in January, with no tank buried below and no battery being charged.
- The heat Epic recovers warms offices, supplies hot water to the dining halls and melts snow off the campus sidewalks.
- The boreholes reach 300 to 800 feet down, into rock that holds near the local annual average, about 50 degrees Fahrenheit, all year round.
Why it matters
- capability At about 140 degrees Fahrenheit the recovered heat is too cool to drive a turbine. But a heat pump moves it with little electricity, so a data center's low-grade waste heat becomes usable winter warmth.
- constraint Store more heat each summer than you withdraw each winter and the rock keeps warming until the field can no longer accept heat at its design temperature. Epic answered the squeeze by drilling more boreholes and finding more uses for the heat as the campus grew.
- precedent A documented twenty-year installation gives other data-center operators and energy planners a concrete seasonal-storage case to point to when weighing whether to build one.
Rock conducts heat badly, and the storage depends on it [11]. Push warm water through a pipe into a large enough block of rock and most of the warmth is still there months later, because heat escapes only through the edges of the warmed zone [11]. The phys.org explainer makes the point with a snow pile. A thin layer on a driveway melts by afternoon. But the mound a plow shoves into the corner of a lot can last into April, because it has less surface area for its volume [12].
Epic's wells do a different job from the geothermal projects that have shared the headlines [10]. According to the same account, Google is purchasing 115 megawatts of geothermal power in Nevada, and Meta has signed a contract for 150 megawatts from a plant in New Mexico [9]. Both drill for heat the Earth already holds, hot enough to make electricity [10]. Epic drills the same kind of rock for the opposite reason: the heat comes from its own servers, and the ground only has to hold it [10].
Temperature sets what the stored heat can do. The water Epic sends down returns lukewarm, and comparable Dutch systems surface theirs at around 59 degrees Fahrenheit [14]. The researcher who wrote the account describes separate work that packs far more heat into a well. Surplus solar and wind drive a heat pump up to about 284 degrees, a grade that can later turn a generator [16].
Two numbers are missing from the explainer: how much of July's heat Epic draws back in January, and what the field cost to drill and run. This is one campus watched over two decades. No one has measured it against a set of sites [4].
What to watch
- A published figure for how much of its stored summer heat Epic actually recovers in winter.
- Whether other data-center operators adopt borehole heat storage, not only the electricity-grade geothermal deals Google and Meta have signed.
- How Epic manages long-term heat buildup in its borehole field as the campus and the data center keep growing.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence45
- Adoption15
- Hype gap0
- Incentives45
- Confidence50
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
If more heat goes into the ground each summer than comes back out each winter, the rock around the boreholes gets warmer year after year, until the field can no longer take heat at the temperature it was built for.
- [2]
As Epic's campus grew the company drilled more boreholes, and the two ways to fix the imbalance are to use more of the heat, such as preheating boiler water or melting snow, or to give the heat more room by drilling more.
- [3]
A few hundred feet underground, rock stays close to the local yearly average temperature all year, which can be around 50 degrees Fahrenheit (10 degrees Celsius).
- [4]
In Verona, Wisconsin, the health software company Epic Systems has spent two decades using the ground to store and recover heat.
- [5]
Epic has drilled roughly 6,100 wells, 300 to 800 feet (90 to 240 meters) deep.
- [6]
The wells heat and cool about 40 buildings on Epic's campus using the waste heat from a 3.5-megawatt data center.
- [7]
Ordinary ground-source heat pumps only pull heat out of the ground in winter; what is uncommon at Epic is that it puts heat into the ground in summer and takes it back out months later.
- [8]
Servers make heat every hour of the year, but in most of the US buildings need heating for only about four months, so piping the heat straight to nearby buildings works in February and solves nothing in July.
- [9]
Google is buying 115 megawatts of geothermal power in Nevada, and Meta has contracted for 150 megawatts from a geothermal plant in New Mexico.
- [10]
Those geothermal projects drill for heat the Earth already holds, hot enough to generate electricity; storing heat underground is the mirror image, where the heat comes from the building and the ground's job is to keep it.
- [11]
Rock is a poor conductor of heat, so warmth pushed into a large enough volume of rock stays close to where it was stored, escaping only through the edges of the warmed zone.
- [12]
A thin layer of snow on a driveway melts quickly, but a snow pile has less surface area for its volume, so less is exposed to warm air and it can last into April.
- [13]
In July water heated by the servers is pumped underground to warm the rock, and in January water pumped back through the pipe returns to the surface warmer; there is no buried tank and no battery, the rock is the storage.
- [14]
The water that comes back up is lukewarm; similar systems in the Netherlands surface their stored water at around 59 degrees Fahrenheit (15 degrees Celsius).
- [15]
A data center's servers produce heat at about 140 degrees Fahrenheit (60 degrees Celsius), which is not enough to drive a turbine to generate electricity but is efficient for warmth because a heat pump can move large amounts of heat with relatively little electricity.
- [16]
In the author's own research, surplus solar and wind power runs a heat pump that heats material packed into a well to as much as 284 degrees Fahrenheit (140 degrees Celsius), and that heat later drives a generator.
- [17]
At Epic the recovered heat warms offices, supplies hot water to the dining halls and melts snow off the sidewalks.
Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgData centers make heat all year long—here's how the ground can hold onto it until winter
1 article · October 9, 2026
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