From gigabytes to megawatts: Why residual heat is hotter than ever

According to the International Energy Agency, half the world’s energy consumption is used to heat buildings. It has also predicted that the amount of sustainably produced heating needs to double by 2030 to limit annual average global temperature rises from exceeding the UN’s target of 1.5 degrees Celsius. 
 
Part of the solution may be to make better use of the heat produced naturally by people and machines. How can this heat be used most efficiently? There are a number of projects in Europe and the US in which residual heat from places where large numbers of people are in motion – shopping centres, train and metro stations – is being reused to help heat nearby offices, homes and even hospitals. 
 
In parallel with these projects – and perhaps offering even greater potential – residual heat from data centres and server halls is increasingly being used in district heating networks and in industrial processes. As of 2022, IEA’s analyses show that, data centers were estimated to consume between 240 and 340 terawatt-hours (TWh) of electricity annually, accounting for about 1-1,3 per cent of global electricity demand. This figure excludes cryptocurrency mining, which adds another substantial layer to energy consumption in the digital infrastructure landscape.

EU requirements set to spur progress

Mattias Vesterlund, Research Data Specialist at Research Institutes of Sweden (RISE) and the ICE Data Center based in Luleå in northern Sweden, sees huge potential in the recovery of residual heat from data centres and other heat-generating activities to help create a circular society. 
 
Policies at EU level have recently begun to focus on the issue, and he believes that this will see residual heat recovery become more widely adopted. With data centres currently accounting for approximately 1.3 per cent of global electricity demand, the European Commission is taking steps to ensure that larger data centres are required to report how they use residual heat.  
 
“There is currently no set level for how much [residual heat] should be recycled, but I’m convinced that guidelines will be put in place in the near future. This will drive efforts to identify different applications for the use of residual heat,” Vesterlund says.  
 
A major challenge lies in how responsibility is shared when recycling systems are set up. The transfer of residual heat always takes place in co-operation between a supplier (data centre) and a recipient, which can be anything from an industrial facility, a district heating system, or a food-producing greenhouse. It is important to clearly define where system boundaries lie, otherwise there is a risk of confusion over which actors are responsible for what.  
 
“What we’ve seen with data centres is that there can be uncertainty about who owns the technology that enables heat transfer. Is it the data centre owner or the recipient of the heat? There are many different business opportunities for data centres in terms of residual heat, the question that often arises is who owns the ‘tech’ that does the actual heat transfer,” Vesterlund says.

Comprehensive solutions at planning stage

EcoDataCenter is one actor that is already building systems for recycling residual heat. The company built its first data centre in Falun in central Sweden in collaboration with Falu Energi & Vatten in 2019. Plans were put in place at an early stage to build the entirely fossil-free data centre right next to a wood pellet factory where excess heat could be used in the drying process. 
 
By reusing residual heat, EcoDataCenter’s partners were able to reduce their carbon dioxide emissions by 165 tonnes in 2023 (two tonnes more than in 2022), and the company is now looking for new collaborations to use residual heat even more efficiently. 
 
For John Wernvik, Chief Marketing Director at EcoDataCenter, it made sense to have a comprehensive solution from the outset. 
 
“The fundamental idea was simple: where should we have our data centre to benefit as many stakeholders as possible from a systems perspective? In Falun we could locate it close to a pellet factory; and our facility in Stockholm uses heat recovery to supply the district heating network,” explains Wernvik.  

Requires stakeholders to take greater responsibility

For heat recovery schemes to be as efficient as possible, the various businesses involved need to be located as closely as possible to each other so as to minimise heat loss between them. If plans for how residual heat is to be used are already included at the planning stage, it is also easier to ‘match’ temperature levels between different sites to minimise waste. 
 
“How do we design a system so that it matches temperatures efficiently and optimises sustainability? That’s the key question,” Wernvik says. 
 
At the same time, the technology offers so many advantages, according to Wernvik, who says: 
 
“This approach is becoming a new form of co-location of industries, in which you use critical resources together. That efficiency gain is considerable. By doing this, you can also establish industries in specific areas that would not otherwise have existed there.” 
 
Given that the greater use of AI will require even more computing power, and thus even more electricity, there is a need to continue to develop circular thinking around residual heat from data centres. 
 
“I believe and hope that heat recovery will be part of taking greater responsibility as an industrial player,” says Wernvik. “There should be greater interest in designing energy- and resource-efficient industrial solutions because in the future we’ll have to share resources to a greater extent.”