Financial and technical obstacles hit Danish datacentre heat recycling plan

A datacentre project in Denmark is grappling with the challenges of reusing waste heat in local central heating systems

Demands for datacentres to pipe waste heat into central heating systems in people’s homes rather than the warming atmosphere have hit financial and technological obstacles in Denmark. 

Aspiring green datacentre operator Digiplex promised public officials it would redirect its waste heat to a district heating network after seeking permission in 2019, to build a large campus in Høje Taastrup, a suburb of Danish capital Copenhagen.

Local councillors had stopped the planning process, and declared that Digiplex should not be permitted to build its datacentre until it could guarantee its waste heat for local homes. 
Two years later, Digiplex has won approval to proceed building the first of five datacentres it intends for the Copenhagen campus. But it has still not guaranteed its waste heat will be reused and, Computer Weekly has learned, experts are still trying to work out whether much of it can be used at all. 
Denmark is geared for the task, having one of the most extensive heat-distribution networks in the world. But after years of planning, there is still a gap between public demands for datacentres to recycle their heat and what is yet possible. 
Astrid Birnbaum, director of Høje Taastrup Fjernvarme (HTF), the local district heating company, said that the municipality’s demand to take Digiplex’s waste heat had materialised into a plan for it to recycle heat from only one of five datacentres it plans to build on the campus. 
“HTF’s heating network is not strong enough here to use all the capacity,” said Birnbaum. “We can take the first datacentre, but we don’t want to take more because our network cannot take it, and we are not going to build a totally new network because that would be too expensive.”

Waiting on details

HTF was moreover still waiting for Digiplex to specify crucial details without which it could not invest in the infrastructure necessary to recycle the datacentre’s heat.

“We don’t know yet exactly how big the datacentre will be, and how much heat they are giving us. I don’t think they know. We have heard a lot of numbers,” said Birnham. “We are not going to make any investments until we know all that, because we have to make a business case to understand if we can use it, and that it will not be too expensive.”

She insisted however that this much progress was commendable. Without the municipality’s intervention, all Digiplex’s waste heat would just be blown into the air. Industry experts spoke of pushing technological boundaries to make it work. But HTF already supplied 70% of the town’s household and commercial heating, with established supply from sources such as waste incineration, wood pellets, and some gas burning. 

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Digiplex made heat recycling an option for town planners when it applied for their permission to build five datacentres carrying 100 MW of computer power in Høje Taastrup, in 2019, according to public records. That would use twice as much energy as used to heat the entire municipality of 50,000 people, according to Computer Weekly’s calculations, if it was ever fully built and utilised.

Høje Taastrup council’s planning committee pressured Digiplex into making a legal commitment last year to supply its waste heat to HTF. Local press and experts in the Danish engineering sector perceived this as a demand, which had been met by Digiplex, and which had set a precedent for Denmark.

But Line Marie Pedersen, a partner and green planning law expert at DLA Piper, said Danish authorities had no power to make such demands.

Peter Faarbæk, who as chairman of the council planning committee had led the calls for Digiplex to give its waste heat to HTF, said this had merely been his personal political conviction, and one that “wasn’t such a big problem” anyway, because Digiplex wanted to do it.

Planning records show that councillors used their power to stall the planning process, seeming to demand its heat be given, but formally only asking that Digiplex show it was talking to HTF with the aim of guaranteeing that its waste heat would be recycled.

Digiplex met this request with assurances of mutual interest and the promise of a legal commitment to supply its heat to HTF, that seemed to suggest it would happen. The commitment, however, pledged to supply only as much heat as HTF and Copenhagen’s regional heat distributor (VEKS) were able to take, and that it considered surplus. Dutch datacentre operators, courting public support by promoting the potential for waste heat recycling, claim that datacentres emit as waste heat 90% of the energy they consume.

The council and Digiplex’s agreement declared that what heat HTF could not take would be fed instead to VEKS. An executive at VEKS, who asked not to be named, said it wasn’t sure it was feasible to use the waste heat at all.

Waste heat

A datacentre would typically emit waste heat at about 30°C. HTF would install heat pumps to increase its temperature to the 70° needed to heat people’s homes, but VEKS’ greater-Copenhagen network needed to increase this to more than 100° for transportation over long distances.

“If we are going beyond 100°, we really need to test the business case and have the technology available to do that,” he said. “We are in that process at the moment, to see whether or not it’s feasible.”

Carl Ove Larsen, datacentres leader at Danish engineering firm Søren Jensen, said: “Using surplus heat from a datacentre is not that simple.

“That’s why we don’t have much surplus heating in the datacentre business. If you offer 5 MW of surplus datacentre heat for a year, at 35°, they have to heat it up for a year to 100° plus. There is some expense in doing that. Is it too expensive? It depends,” he said.

The district meanwhile needed the heat only in winter, whereas the datacentre had greater need to give it in summer, when the outside temperature reached about 33°.

Digiplex would not comment. 

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