Data centers produce heat year-round. Here’s how to save it for winter

You have probably noticed it on a hot summer day: A basement feels cool even when the air outside is baking. The ground does not heat up and cool down as fast as the air does. A few hundred feet down, it stays close to the local yearly average all year, which can be around 50 degrees Fahrenheit (10 Celsius). In Verona, Wisconsin, the health software company Epic Systems has spent two decades turning that fact into infrastructure. It has drilled roughly 6,100 wells, 300 to 800 feet (90 to 240 meters) deep, that now heat and cool about 40 buildings on its own campus by using the waste heat from a 3.5 megawatt (MW) data center. What makes this setup unusual is not that Epic pulls heat out of the ground in winter—ordinary ground-source heat pumps do that in homes across the country. What’s uncommon is that Epic puts heat into the ground in summer and takes it back out months later. That matters more than it sounds because timing is what usually kills the idea of reusing a data center’s heat. Servers make heat every hour of the year. In most of the U.S., buildings need to be heated for only about four months. Piping it straight to nearby buildings works beautifully in February, but sol…