Who called it a waste?
As we all realise that our laptops are heating our legs when we use them while sitting on the sofa, one can imagine how much heat is generated from thousands of powerful servers racked together in a data centre. IT equipment (ITE) in a data centre transforms almost the entirety of energy supplied to it into heat. All other auxiliary elements present in a data centre are also mostly electrical energy based and eject heat as well. While a laptop could require around 100W of power,  typical servers employ 5 to 10 times more.
When putting many servers together and cooling them commonly, we could gather a very valuable amount of heat. Thermal energy could be extracted and supported in a fluid, usually water. That warm water can then be easily transported and reconducted to be used for an application that has need of heat.
We hence need to grow accustomed to seeing a data centre as an important thermal source, rather than as a huge electricity consumer. For roughly a century, heat recovery has been applied to industrial processes, and especially as a byproduct of electricity generation. While heat reuse from data centres is not a frequent practice, it is currently gaining a lot of attention and several projects have been already developed, particularly in Europe. Heat reuse in data centres might soon become a necessity since some local legislations are exploring the idea of mandating to consider this feature in data centres.
Excess heat from data centres can be of different qualities and quantities but there are numerous potentials offtakers of that heat:
- Residential: heating and domestic hot water
- Industrial: preheating, cleaning, drying processes among others
- Agricultural: greenhouses, fish farming
- Others: adsorption and absorption cooling, water treatment
Although some processes in the industry could employ elevated temperatures, floor heating for agricultural or residential purposes can work with temperatures around 30ºC which is the typical low-grade temperature of the excess heat generated by a classical air-cooled data centre. Heat pumps for increasing the temperature and storage tanks to sync the heat generation with the heat demand of the offtaker could be a plus.
The offtakers, regardless of whether they are a utility or not, are moving towards the electrification and decarbonisation of their heating needs, which is increasing the usage and promotion of heat pumps. These will be more energy-efficient when working against a 30ºC temperature (from the data centres) than working against lower variable ambient temperature.
In addition to the economic benefits of reduced cooling and heating efforts required by data centres and offtakers respectively, excess heat reuse has clear advantages towards carbon emissions: less energy required for cooling results in reduced electricity usage and hence less associated emissions, while less energy required for heating results in lower demand on electricity, gas, or other fuels typically used for heating at the offtaker and hence also lower emissions.
It is shown that the best approach towards effective heat recovery is to form partnerships with utilities or industrial partners at the conception of a project, with partners who have heating necessities that could benefit from the waste heat of a data centre. This, in turn, results in heat being turned from a liability into an asset for both parties. The matchmaking between both activities requires good intersectoral communication (which is a challenge) and will require collaboration at different layers and will probably require the involvement of public authorities to set standards of communication and working methods.
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