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Waste not, want not: How datacentre heat reuse projects can power ahead

The Nordics, Netherlands, Germany and Canada are progressing district heating initiatives that save energy and emissions, although obstacles remain

Excess heat extracted from hot air returned from server air cooling at Verne Global Finland’s The Air datacentre in Helsinki is transferred to water via heat exchangers and then accepted by the district heating company.

“Using heat pumps, the water is then primed from approximately 30°C,” says Kim Gunnelius, managing director of Verne Global Finland. “The required temperature depends on outside temperature, but is typically high, over 90°C and even above 100°C on cold days.”

For each MW of IT power, or power provided to the servers, the datacentre produces 1.3MW of heat, with heat pumps accounting for 300kW in additional electricity to prime up the temperature from 25-30°C to approximately 90°C. Energy converted to heat by the heat pumps can also be utilised, with the system sustaining energy losses of just a few percent, according to Gunnelius.

In Finland, getting permission for the project was “straightforward”, he adds, with the locally involved district heating company “very positive and proactive”, not least in reviewing the project and offering input on plans.

“The fact that there was already a district heating network in place, letting you plug into a utility, made it much easier,” he concedes, however, this meant they weren’t dependent on a single business or application as they had access to a city-wide service with ongoing energy demand.

The existing pipe was simple to plug into, given that it was right outside the Verne Global plot, too. In other places, you might need specific point services to integrate the datacentre with an industrial process to exploit the excess heat, says Gunnelius.

But he warns that such projects are not always economically viable, for instance, if electricity prices are high. “In our case, there were some subsidies available, and nowadays heat reuse is one option to reach a lower power tax class,” he says. “Some countries that mandate heat reuse don’t have existing infrastructure to plug into, and that can be a challenge. The same is true in remote areas and many smaller towns in Finland as well.”

Power prices

The energy crisis of 2022 caused power price fluctuations, which cannot always be fully mitigated by the purchase of fixed-rate electricity. At the same time, the required temperature in the district-heat network depends on the outside temperature.

“We have introduced automation for monitoring the electricity pricing, as well as the temperature requirement for the heat required from the utility,” he says, adding that district heat pricing is fixed on a monthly basis – causing problems if the project business case depends on selling heat.

Based on incoming customer requests, Verne Global expects to transition its highest density installations to liquid cooling, permitting the cooling system to run at higher temperatures, reducing power required and increasing efficiency – achieving 1MW of IT power plus 20% electricity instead of about 30% at present. Future efficiency may also be improved in future by implementing a reuse to return loop, lowering temperature further, says Gunnelius.

“Power companies may still be interested in getting excess heat into the return loop as well,” he adds.

The project already helps reduce emissions for the local power company, through using 100% green energy which is then reused by feeding it into the district heating network.

Although emissions reductions are “kind of a moving target”, if assuming today’s emissions per kWh and a full 50MW that could be implemented on the site – with maybe 70% average load and an average temperature – the emissions saving has been projected at around 30,000 tonnes per year, says Gunnelius.

Finland’s electricity grid is in “quite good shape”, including 97% carbon-free production in June, but district heating networks still have far to travel to reach their sustainability targets. However, with projects such as Verne Global’s, these can and are moving nearer.

Key elements

Drew Turner, head of sector integration at Danfoss, says we’re at the point where the key elements of an offering that enables heat recovery from a datacentre have been figured out, whether from an application or a systems service perspective.

But he says it can be much easier to realise such a vision with a hydronic – or water-based – cooling system, because water is more or less a perfect energy transport mechanism.

“Everything’s moving in the direction of integrated energy system designs, in general moving in the direction of more hydronics or more water,” says Turner.

The complications can often be associated with proximity for using it – how to deal with the need to cross property lines, and multiple different customers, from the datacentre customer to the reuse customer. The good news is that you can address some of those complications with the system design that you implement, says Turner.

“If it’s a hydronic-based cooling system for a datacentre, you can address the complications of getting that to a different customer by giving the datacentre a portion of the solution that fits with their business model, and then the heat reuse customer a solution that fits with their business model,” he explains. “Because datacentres don’t want to be in the heating business.”

Datacentres are typically interested in Power Usage Effectiveness (PUE) and free cooling, as well as removing barriers to building new datacentres. So any heat-reuse service that helps the datacentre operator advance those goals, without penalising them to boost the heat to a usable temperature for the next customer of it, can have great appeal.

“The solution can be pretty simple and elegant, because you’re, in effect, putting a heat exchanger in between the datacentre and the heat reuse customer, and then putting the onus of boosting the heat to a usable temperature on the customer,” says Turner.

Read more about heat reuse in datacentres

Danfoss first carried out related “lighthouse” projects on its own datacentre and headquarters, and has since designed “multiple systems” for other organisations, which are all at various stages of completion, he says.

The major datacentre hubs of London and Frankfurt appear further behind, which might be due to a lack of infrastructure. It’s mainly the demand side prevalence of existing district energy infrastructure and the need for heating that make the Nordics so attractive. “It just so happens that the average low ambient temperature also makes them attractive for datacentre locations, which by the way is no longer important if they are using 100% of the heat.”

For the business case, size does matter, which means a heat-reuse system must be designed appropriately for the business case. Also, it can be “arguably better” implemented as a retrofit, because if you’re adding heat reuse to an existing facility, you already have a cooling system to tie in with it, Turner tells Computer Weekly. “So, it’s not that complicated.”

Jakob Jul Jensen, head of datacentres at Denmark-based Danfoss, points also to implementations across Finland, including one at a big Google datacentre, and the Netherlands. In Denmark so far, however, one out of 10 datacentres can reuse heat – “but it’s probably not at the amount and scale we should have”.

Even though legislation can play a role in accelerating development, a lack of public funding, on the other hand, in terms of grants to operators, may not be so much of an obstacle. Hyperscalers are not typically interested in accessing public-sector support, he points out.

“If they’re going to do it, they’re going to pay for it themselves – I don’t think public funding is needed to do it,” says Jensen. “But some may need motivation to add the complication to their existing business model.”

Improve cooling, consider services levels

Tube or coil heat exchangers could give way to newer technologies with improved cooling efficiency, and more intelligent optimisation of datacentres with artificial intelligence (AI) and machine learning can help. Savings might also be made were datacentres to roll back on, say, five nines of availability and latencies for all customers that do not truly need them.

“Not all servers or CPUs are at a level where that is needed; network storage, network and storage don’t necessarily need to be liquid cooled,” says Jensen. “You might sell less, but be better for humanity.”

Also, colocations with anything under 10 racks typically see greater load fluctuations and therefore less predictable heat production. They might, however, benefit from some government support, and some Danfoss knows of are exploring partnerships other than with district utilities, with “off-takers” such as greenhouses, says Turner.

If used by district energy, scale is needed to invest in the interconnection and supply complication.

Long-term responsibility

Additionally, those few employees or consultants who are tasked with optimising energy systems typically think fairly short term, which also suggests a role for mandatory change, as well as considering hiring a specific person to drive heat reuse approaches, and has long-term responsibility for the whole lifecycle of the datacentre.

This would include the financial lifecycle cost of the datacentre, including accounting on embodied carbon as well as carbon emissions. Currently, such a holistic view is typically just not there from the start, says Turner.

And in the UK’s 456 datacentres, the potential for using excess heat has been overlooked and is in fact “extraordinary”, according to Kim Fausing, Danfoss chief executive. 

“If these were put to use to support heating across the country, the cost and emissions savings would be highly significant,” he says. “In London alone, there are 652 eligible excess heat sources, including datacentres, underground stations, supermarkets, wastewater treatment plants and food production facilities, with excess heat adding up to 9.5 TWh per year.”

That’s roughly enough to heat 790,000 households, says Fausing, with excess heat the world’s largest untapped source of energy with solutions available. Policy measures are urgently needed to accelerate such initiatives, across sectors, benefiting consumers, businesses and the climate. He asks: “What are we waiting for?”

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