Data centers are satis­fying our ever-increasing hunger for data, but in doing so they are exac­er­bating the climate crisis. They produce heat that dissi­pates, divert millions of litres of water away from commu­ni­ties and agri­cul­ture, use fossil fuels or even nuclear energy and degrade the natural envi­ron­ment through soil sealing. It’s a depressing view of a vital industry. But it doesn’t have to be that way. Info­ma­niak, a leading Swiss cloud provider, has not only discov­ered a glimmer of hope but has built it in the form of D4, Europe’s most sustain­able data center. And Info­ma­niak is making it easy for other data center oper­a­tors: All they have to do is type “d4project.org” into their browser, take a look at the project’s open source docu­men­ta­tion  –  and repli­cate the whole thing.“

D4 is replic­able. And we are openly sharing this knowl­edge with the entire industry free of charge so that the neces­sary changes can finally be made,” says Boris Siegen­thaler, co-founder and strategic thinker at the inde­pen­dent Swiss cloud provider. “As a company that is not listed on the stock exchange but instead owned by its employees, we have always done what we believe to be right. Our vision is an ethical cloud that gives Europe greater tech­no­log­ical inde­pen­dence and makes no compro­mises when it comes to protecting data and the envi­ron­ment.” Since 2015, Info­ma­niak has rein­vested all its profits to this end, constructing its own data centers exclu­sively in Switzer­land. 

Invis­ible and inaudible

D4 is not situ­ated in an indus­trial area in the middle of nowhere. It is hidden under a park in ­Geneva’s eco-friendly resi­den­tial La Bisto­quette neigh­bor­hood, avoiding the need to seal any addi­tional surface area. When plan­ning the neigh­bor­hood, the local coop­er­a­tive decided to limit the number of cars and parking spaces for envi­ron­mental reasons. This freed up space under­ground, where a parking garage had orig­i­nally been planned. Because Info­ma­niak was looking for a data center loca­tion where the waste heat could be reused at exactly the same time  –  it was a win-win situ­a­tion!

(Image | Jordi Ruiz Cirera/Fotogloria)

In-house cooling

D4 took four and a half years to build, more than twice as long as normal. “We had to rethink a lot of things as we went along,” explains Boris Siegen­thaler. “The biggest chal­lenge was how to increase capacity by 25 percent while keeping the floor space the same.” This was neces­sary to meet the increased heat demand during oper­a­tion. This chal­lenge was mainly tackled by S +T Service & Tech­nique SA (S +T), a Swiss specialist in air condi­tioning, venti­lation and heating. The company had already worked with Info­ma­niak in 2013 on its first data center, which had no air condi­tioners and was cooled solely using outside air.

So Chris­tian Logean and his team already had a rough idea of what to expect with D4: “In prin­ciple, all the tech­nology we use in D4 is avail­able today. It’s the clever way it’s all put together that makes it so special.”  D4 uses the energy it consumes as effi­ciently as possible. And it uses the waste heat gener­ated to return the energy consumed. To achieve this, all the air heated by the servers and other elec­trical equip­ment must be reli­ably returned to the heat pumps, and cold air for cooling must be returned to the servers just as reli­ably.

S +T was looking for a solu­tion for a total of three fan walls, known as FanGrid: “One for the recir­cu­lated air, one for the exhaust air and one for the outside air. The fans had to be powerful to ensure air circu­la­tion at all times, but ideally run at low speed. Because there are resi­den­tial build­ings all around the data center, it was impor­tant that our solu­tion was absolutely silent,” explains Chris­tian Logean. S +T compared different suppliers and opted for ebm-papst: “The company is a leader in this field, which is why we wanted to work with them.” 

Because there are resi­den­tial build­ings all around the data center, it was impor­tant that our solu­tion was absolutely silent.

Chris­tian Logean, Head of Plan­ning Office S+T

Oper­a­tion guar­an­teed, no matter what

For Chris­tian Logean, the main advan­tage of FanGrids is their redun­dancy  –  even in the event of indi­vidual fail­ures or reduced capacity, D4’s oper­a­tions are never jeop­ar­dized: “And if the heat recovery system should ever fail, we can easily switch the FanGrid to outdoor air oper­a­tion so the servers will remain cool.” S +T did the perfor­mance calcu­la­tions itself. “We used ebm-papst’s FanScout to plan the systems precisely. We ordered 70 second-­gen­er­a­tion RadiPac in size 800  –  it was all very simple. The biggest chal­lenge was the instal­la­tion, because we had to lift the huge fans into the under­ground D4 facility using a crane,” says Chris­tian Logean. S +T also supplied Info­ma­niak with its own Digimat control system, which uses MODBUS to regu­late the fans around the clock according to demand. 

Driving the energy tran­si­tion

D4 has been in oper­a­tion since November 2024 and will grad­u­ally be ramped up until it reaches full capacity in 2028. It will remain in service for at least 20 years, demon­strating that data centers are not just power guzzlers but key players in energy tran­si­tion. To this end, Info­ma­niak moni­tors two specific indi­ca­tors: PUE and ERF. PUE (power usage effec­tive­ness) compares the total energy consump­tion of the data center to the energy consump­tion used solely for IT systems such as servers. Anything above 1 is consumed by the data center for air condi­tioning and other infra­struc­ture. D4’s PUE aver­ages around 1.09. This means that for every unit of elec­tricity consumed by IT, D4 only needs 0.09 units (9 percent) for other infra­struc­ture. The global average PUE is about 1.58, meaning that conven­tional data centers spend almost 60 percent of addi­tional energy on things like cooling. ERF (energy reuse factor) measures how much of the total energy consumed is reused outside the data center. D4’s ERF is just under 1, aver­aging 0.95, which means that 95 percent is reused in the form of heat. “Natu­rally, our goal is to get as close to 1 as possible in both cases and set new stan­dards,” says Siegen­thaler.

(Image | Jordi Ruiz Cirera/Fotogloria)

D4 has already received several awards, including the Swiss Ethics Prize in 2023 and the Energy Tran­si­tion Prize in 2025. But Info­ma­niak won’t be stop­ping at that. “To support our growth, we are actively looking for addi­tional district heating networks. We will need another data center with at least 3.3 MW by 2028. We will source our elec­tricity locally and supply our zero-carbon waste heat free of charge,” says Boris Siegen­thaler. Through D4, the company has demon­strated that this can work if you are willing to take action. “A different para­digm is possible.”