The works of famed Odense writer Hans Christian Andersen depict Danish winters as literally the stuff of fairy tales — but in reality they are cold, wet, and dark. Now, thanks to Facebook’s data center in Odense, the third-largest city in Denmark will get some relief from the cold.

The custom-built Odense Data Center has been online since September, but its sustainability mission began years ago. The facility was located and designed with heat recovery in mind from the outset. The current goal is to recover and donate 100,000 MWh of energy annually from its servers — enough to warm 6,900 homes. This heat is donated to warm a local hospital and thousands of other buildings in the surrounding community. Like all Facebook’s data centers, this one is supported by 100 percent renewable energy. In Odense, a new wind project is adding more electricity annually to the Nordic grid than the data center consumes. 

The qualities that drew us to Odense include the ability to connect to a highly reliable Nordic electric grid with opportunities to add new sources of renewable energy, good access to fiber, and the talent needed to build and operate the data center. But what really differentiated this site from others was the opportunity for heat recovery.

Odense heats its buildings via a district heating system. The system, operated by Facebook’s partner for this project, district heating company Fjernvarme Fyn, sends hot water to the city’s homes and other buildings, most of which use radiators for heat. A multidisciplinary team of Facebook engineers, architects, designers, facility operators, and energy professionals embarked on the journey with Fjernvarme Fyn to make it possible for the two-building, 50,000-square-meter facility to capture and recover the low-temperature heat generated by the thousands of servers and to deliver this heat for free to the community.

Rather than releasing the warm air from the servers into the atmosphere, the Odense facility directs it across copper coils filled with water. The process starts with Fjernvarme Fyn routing water from its brand-new heat pump facility through insulated steel pipes to the roof of the data center, where it’s directed into copper coils located inside each of the 176 cooling units. There, the warm air from the servers heats up the water that flows through the coils.

Once the water is warmed in the coils, it’s pumped back to the heat pump facility, which Fjernvarme Fyn owns and operates. Inside Fjernvarme Fyn’s heat pump facility, the heat from the incoming warm water is used by the heat pumps to efficiently raise the temperature of the water loop that provides hot water to radiators throughout the community to warm homes.  

Because bringing awareness to environmental efforts is a priority, the facility is equipped with a glass wall to let visitors, from schoolchildren to energy engineers, view the scale of the energy-efficient infrastructure that supports the local community. The entire process, from powering the servers to delivering heat, is supported by 100 percent renewable wind energy. Heat pumps are not new — they are a very big part of the Danish heating strategy to phase out coal and natural gas — and neither are coils to recover heat. It’s the pairing of these two at hyperscale that is innovative.

Similar projects in Denmark have used recaptured heat from smaller structures, such as supermarkets, to supply a nearby building or two. The Facebook project scales the technology to a level not yet reached in the world by producing up to 25 MW per hour of usable heat. 

“Facebook opened their new data center in Odense,” said Denmark’s Minister of Climate, Energy, and Utilities, Dan Jørgensen, on Instagram. “It’s based on renewable energy only (from their own wind farm) and feeds their surplus heat into the district heating system. Good news for the transition to green energy!” 

As a nation, Denmark has set a goal to eliminate the use of coal by 2030. The heat recovery project supports Odense’s even more aggressive goal to phase out coal (which 30 percent of the city still depends on for heat) by 2023 — a modern feat for a city that just celebrated its 1,031st anniversary. Facebook’s data center is estimated to reduce Odense’s demand for coal by up to 25 percent.

“It’s amazing because every time we post pictures of our pets, family, and whatever on Facebook, it will produce heat that will heat up to almost 7,000 houses,” Odense Mayor Peter Rahbæk Juel said. “That is a good, green side effect of building the data center in Odense.” He adds, “I think that the data center in Odense will be a model for a lot of data centers around the world.”