Everyone’s up in arms about data centres right now. But one country’s found a way to use some of the negatives and turn them into positives for its citizens.

Meta's data centre in Odense, Denmark, sends its waste heat into the city's district heating network instead of venting it into the sky. Water from the network runs through the facility's cooling units, picks up the low-grade warmth coming off the servers, then goes to a nearby plant where ammonia heat pumps lift it to 70 to 75°C, hot enough for household radiators.

The system delivers about 45MW of heat, enough for roughly 11,000 households.

The scale of the waste is the starting point. Around 90% of the electricity a data centre draws comes back out as heat, and roughly 40% of its energy use goes to cooling, nearly all of which ends up as heat too. A data centre is, functionally, a very expensive radiator. The problem is temperature: server exhaust is warm but not hot, which is why it needs heat pumps before it can do anything useful.

Meta's energy specialist Lauren Edelman is straightforward that none of this is new physics, saying heat pumps are not a new invention and neither are coils for capturing heat, and that what is new is pairing them at hyperscale. The published home counts vary between about 6,900 and more than 12,000 depending on which phase and whose figures you use, which is worth knowing before quoting any single number.

Danish industry figures suggest 63% of the country's data centres plan to use their surplus heat.

ScienceBlog traced why the home-count figures differ across sources and phases. Ramboll, which designed the recovery system for district heating company Fjernvarme Fyn, describes about 45MW going into the network, 215,000MWh a year, and the largest heat pump installation in Denmark. Fjernvarme Fyn's Jan Strømvig is candid about why it works, saying the project is relatively unique because they have a very large distribution network and Meta placed the data centre completely inside it.

Strømvig named the constraint himself, and it is the reason this does not simply transplant. Denmark has widespread district heating, South Africa has none, and heat travels badly, so you cannot site a facility far from whatever it warms. We also do not have much demand for space heating. But the principle survives the climate difference.

The question is not whether you can heat homes; it is what low-temperature process load you can put next to the building: crop and timber drying, greenhouses, aquaculture, laundries, food processing. That matters now rather than later, because the GPU build in Centurion and MTN's 150MW plan are siting decisions being made this year, and heat offtake has to be designed in before construction.

It also cuts the cooling load, which is the point that connects to what the revised electricity pricing policy does to industrial tariffs. Nobody here appears to be planning this yet.

You might also like our piece on the Eskom distribution agency agreements, what the surge in South African M&A says about infrastructure appetite, and why South Africa's business regulation is more restrictive than China's.

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