Nestled away in the heart of Queen Mary University in London (QMUL) is a data center. The facility, a vital resource for particle physics research at CERN, the home of the Large Hadron Collider, harbors a secret that is only apparent when you step inside its humid halls.

Walking into the data hall, you are struck by the heat resonating from the numerous server racks, each capable of handling up to 20kW of compute. However, rather than allowing this heat to dissipate into the atmosphere, the team at QMUL had another plan. Instead, in partnership with Schneider Electric, the university deployed a novel heat reuse system.

The system captures the warmed water used to cool the server racks and transfers it to three water-to-water heat pumps. Here, the temperature of the water is increased from a balmy 23°C (73.4 °F) to a steamy 65 – 75°C (149 – 167°F), with the water then piped directly into the university’s district heating system. Large water cylinders across campus act like thermal batteries, storing hot water overnight when compute needs are constant, but demand is low, then releasing it in the morning rush. As one project lead put it, there is “no mechanical rejection. All the heat we generate here is used. The gas boilers are off or dialed down – the computing heat takes over completely.”

At full capacity, the data center could supply the equivalent of nearly four million ten-minute showers per year. This provides both a financial boost, saving the university around £240,000 ($324,163) annually in gas bills, as well as an environmental benefit, in the avoidance of more than 700 tons of CO2.

Walking out, it’s easy to see why Queen Mary’s project is being held up as a model for others. In the UK, however, the project is somewhat of an oddity, but through the lens of QMUL you can see a glimpse of the future, where compute is not only solving the mysteries of our universe but heating our morning showers.

The question remains, though, why data center waste heat utilization projects in the UK are few and far between, and how the country can catch up to regions such as the Nordics, who have embedded waste heat utilization into the planning and construction of their data center sector.

Heat of the moment

District heating systems are now commonplace around the world, especially in more frigid regions such as the Nordics.

Connection with data centers is a more recent development, but a logical one. With servers producing steady amounts of low-temperature heat as a byproduct of cooling, there is plenty of warmth that can be captured through water-cooling loops, upgraded with industrial heat pumps to reach the higher temperatures required, and then fed into district heating networks.

Heat pumps are essentially the same technology used in air conditioning, but in reverse. They take low-grade heat, usually between 23-26°C (73.4-78.8°F), and raise it above 50°C (122°F), making it usable for heating systems and hot water. As data centers run continuously, they can provide a steady year-round heat source to various offtakers, from universities, like QMUL, and entire housing developments.

However, as Noah Nkonge, senior manager, sustainability, heat export, at Equinix, says, deployment has been sporadic, with success often dependent on “either a supportive national policy, a mature network with lots of existing data centers, or a proactive local authority convening the pieces.” As a result, we have seen uneven deployment of these systems across Europe.

A unique opportunity or a catalyst for change

The UK is not a country known for adaptive infrastructure practices, and the development of district heating systems tied to data centers has lagged significantly compared to other regions.

District heating itself has not seen significant uptake, with a penetration rate of around 2-3 percent across Britain. A major factor in this has been years of cheap gas from the North Sea, along with a housing stock built around individual gas boilers. Subsequently, until very recently, there has been no economic/consumer regulation concerning district heating, nor a zoning regime that mandated the use of waste heat, as seen in the Danish capital, Copenhagen.

But as gas prices have risen due to geopolitical uncertainty, the UK government has launched a concerted effort to develop heat networks. Last year, the Department for Energy Security and Net Zero (DESNZ) selected six towns and cities to develop England’s first heat network zones connected to data centers.

The first project to officially get off the ground through the initiative is the Old Oak and Park Royal Development (OPDC) in West London. Embedded in the development is an integrated heat network, known as the Old Oak and Park Royal Energy Network (OPEN), which UK district heating firm Hemiko will construct.

OPEN will capture waste heat from local data centers, upgrade it with industrial heat pumps, and feed it into a district heating system. At full build-out, this will serve more than 9,000 homes and businesses in the area.

Davena Wilson, director of projects at OPDC, accepts that the UK has been slow to adopt these practices, especially in comparison to Scandinavia. “In places like Denmark and Sweden, the data centre is providing heat as a service,” Wilson says. “Here, it’s a byproduct we’re trying to make use of. It’s almost serendipity when it happens.”

Indeed, OPEN is in part a project of opportunism, with the data centers, including a nearby Vantage facility set to be connected to the network just 100 metres (328 feet) from OPDC-owned land, reducing the length of the pipe network and subsequent energy losses. Yet it still faces significant challenges, namely digging through congested streets and coordinating with work on the HS2 rail link.

Indeed, these systems are significant infrastructure projects. Even QMUL’s small-scale deployment required shoehorning pumps, tanks, and pipework into tight quarters. These issues are compounded even further on larger projects such as the OPDC.

Though barriers remain, major policy shifts could make projects such as OPEN easier in the future. Wilson points to the forthcoming heat network zoning, which will mandate developers in designated areas to connect to the lowest-carbon source. “That’s a game-changer for the market,” she argues. “It removes the uncertainty about whether schemes like ours will find customers.”

This view is supported by Noah Nkonge, who argues: “In the UK, heat-network zoning will mark areas where networks are viable and give operators decarbonization targets. That doesn’t mandate DC heat export directly, but it creates the conditions for it to work.”

It is hoped that OPEN could be the catalyst for a more concerted strategy embedded within planning for both data centers and future housing developments. For planners and legislators, it will help to look further afield to see how district heating networks powered by data centers have become a crucial part of urban planning.

A Nordic Model

Nowhere has the district heating model been more effectively adopted than in the Nordics, and in particular, Finland.

Nkonge says Finland has had “district heating ingrained in society for 50–70 years,” and adds: “It’s far easier to plug into an existing network than to guess where a new one will go and who the customers will be.”

The city of Espoo’s district heating system is a microcosm of this. In operation since 1954, the system connects approximately 250,000 people through 900 kilometers (599 miles) of underground pipes. Until around a decade ago, it relied solely on fossil fuels, but operator Fortum committed to eliminating the use of fossil fuels by 2030 as part of Espoo’s Clean Heat road map.

To do this, Fortum looked to data centers. It had already connected a handful of facilities, but in 2022, it partnered with Microsoft for what has been touted as the world’s largest data center heat-recovery project.

The Microsoft data center region tied to the project is expected to have a combined capacity of at least 615MW and has been designed with heat recovery in mind. Its two dedicated data centers, Kolabacken and Kera/Hepokorpi, are adjacent to the district heating network. To utilize the waste heat, Fortum is already at work constructing massive new heat pump plants, including a 20,000 m³ hot water storage tank and large electric boilers.

This will enable low-temperature waste heat from Microsoft’s servers to flow via underground pipes into the heat pumps, which will upgrade it to the 75–120°C (167-248°F) required for Espoo’s district heating supply. Once fully operational, the recovered heat is expected to cover about 40 percent of Espoo’s heating demand.

Teemu Nieminen, director of project execution at Fortum, says: “This works best when you plan it before a data center is built. Building district heating infrastructure is hard and capital-intensive—our 900km network took seven decades. To get projects flying, you need contracts and heat-use plans agreed up front.”

Culture and policy are also important. “The Nordics have had district-heating networks for more than 50 years in major cities,” Nieminen says. “Cold climate makes reliable heating essential; culturally, we don’t like wasting anything. We also have strong heat-pump know-how and affordable, low-carbon electricity.”

Government support has also reinforced this approach. In Finland, data centres that reuse heat and meet efficiency standards qualify for electricity tax benefits, while municipalities like Espoo and Kirkkonummi actively partner in planning and permitting. ”

Heating on the Edge

Given that the UK has limited legacy district heating infrastructure, a more modular approach, such as that seen at QMUL, could be a better fit.

It is here that companies like French vendor Qarnot see an opportunity. Instead of treating server heat as waste, the company created a liquid-cooled computing unit that captures warmth straight from CPUs and GPUs, producing water at around 65°C (149°F) that can be funneled directly into heating systems.

“We are focused on high-performance computing (HPC) because it is the part of computation in data centers that is very intensive and dense in energy, and generates a lot of heat,” explains Paul Benoit, Qarnot’s CEO.

This means Qarnot’s deployment model avoids hyperscale facilities and instead opts for smaller-scale 1MW Edge sites that can be located closer to urban centers. A benefit of this approach is the speed of deployment, with Qarnot claiming that it can set up a new site in four to six months, compared to the eight years it might take for a hyperscale facility in France.

Its deployments have ranged from residential and public buildings in France, where Qarnot’s “digital boilers” supply domestic hot water, to a partnership in Brescia, Italy, with A2A, where the hot water feeds into a district heating system.

The system also claims to have significant environmental benefits, reducing the carbon footprint of compute workloads by up to 80 percent. “The same energy is used twice – for computing and for heating,” Benoit says.

For the UK, which is pushing to expand its HPC and AI capacity rapidly, the distributed model offered by Qarnot could be compelling.

“Compute is becoming much more compact,” says John Andrew, technical sales manager of Advanced Power Technology. “A 1MW data center that used to require 300 racks can now fit in 12. That allows you to rethink location – why not embed compute where the heat is needed?”

The QMUL project could serve as a test case in demonstrating how small-scale liquid-cooled data centers can efficiently locate with respect to heat demand. The project’s success in delivering consistent hot water, reducing CO2 emissions, and achieving cost savings serves as validation of the feasibility of distributed heat reuse in regions like the UK.

For Professor Jonathan Hays, head of the Particle Physics Research Centre at QMUL, the growth of AI in the UK could be a catalyst for the growth of this model. “This is the start of something bigger,” he says, “As AI and HPC grow, colocating dense compute near heat demand – homes, hotels, hospitals – becomes not just possible, but essential.”