This Tuesday morning, data centers made a big splash in the media. Every data center professional in the UK was woken up by friends and relatives outside the industry, saying "Hey, you know those things you work on? They're on the news!"

The BBC reported that an immersion-cooled micro data center "the size of a washing machine" was heating a public swimming pool in Devon. The man behind the project, Mark Bjornsgaard, appeared on the early morning Today program, and the BBC's lunchtime news, offering to heat every swimming pool in the country with data centers cooled with oil.

The story quickly appeared in a host of other mainstream and technical publications (including ours).

An immersive experience

The UK has a couple of thousand swimming pools available for public use. They are fantastic resources for health, since swimming is very good for you. Pressure group Swim England reckons they save the health services nearly £360 million ($430m) a year, staving off conditions including dementia, strokes, and depression

Despite this, they are chronically neglected and underfunded. 400 have closed in the last dozen years, and that rate of closure has accelerated, Leisure centers were hit badly during the pandemic. Now they face a massive increase in the energy cost of keeping their pools warm enough to use, at the same time as public services are suffering cuts. Heating costs at the Exmouth pool which is now heated by servers reportedly went up from £18,000 per year to £80,000 in a year.

Swim England says 79 percent of pools are at risk of closure, and I would bet that pretty much everyone in the country will know of a pool that's either closed, struggling, or else was somewhat on the chilly side when you last visited. My local gym recently closed its pool permanently because of heating costs.

So Bjornsgaard's company Deep Green got a big reaction by heating one pool (or at least providing 60 percent of its needs), and boldly saying that every pool in the country could do the same. "Companies that have green ambitions and want to support their local pool - please get in touch,".said Bjornsgaard.

Britain's recent cold weather only added to the buzz, and the story has a nice symmetry. Servers and swimmers are both happily immersed in a warm bath - the servers cooling down, while the swimmers warm up.

The time is now

The idea is not entirely new of course. It combines some major existing strands from recent data center engineering, into a newly-viable form. And it applies them to a genuine and urgent need. "Servers for swimming pools!!" could be a rallying cry.

Heat reuse has been held up as a green goal for many years, but has always been fraught with difficulty. Data centers cooled by air simply don't produce a concentrated enough form of heat to make this really attractive, and as they are mostly far from the people who need the heat, the idea is rarely put into practice.

It's been known for some time that immersion cooling is more efficient than air-cooling, but data center operators have balked at the disruptive change (and the huge change in capex investment) when their facilities are designed for air-cooling. There are exceptions, when the physics simply demands liquid cooling, as in the HPC sector- and of course in cryptocurrency mining.

Taking the data centers to the customers, and installing small "digital boilers" has also been proposed for ten years, with France's Qarnot pioneering the idea of installing servers in homes where they can act as heaters, with Qarnot paying for the electricity and giving the heat for free. Qarnot has done the product development, building in second-user servers and adopting oil-based immersion cooling. In the UK, Heata is offering compute-based water heaters.

They have even reached swimming pools before: another French digital boiler company, Stimergy, actually heated one in Paris five years ago.

Meanwhile, in the wilder shores of cryptocurrency, YouTube can show at least two videos of crypto miners heating their own pools with immersed servers, One reports a somewhat-too-hot temperature of 100oF (38oC) for a giant back-yard pool using servers immersed in the sector's own brand of coolant, BitCool.

At the same time, a few years of hype for Edge services has acclimatized the industry to the idea that big hyperscale server barns aren't always best Deep Green is currently aggregating HPC loads on the servers in the Exmouth hot tub, so it's not technically an Edge application, but the company is seeking more workloads and pools could be a good Edge hub as they are in populated areas.

Bite-sized and quick to install, Deep Green's tubs make immersion cooling easy to adopt, provide an instant customer for the heat, and could become Edge platforms.


How far can this go? If the company could somehow put a 40kW tub in every pool in the country, that would provide a (possibly fanciful) upper limit of around 80MW. This sounds a lot - and it would represent a big shift for a somewhat-conservative sector, but consider that CBRE expects 120MW of new capacity to be built in large data centers in London during 2023 - and it's been well-publicized that these data centers are finding it increasingly hard to get access to electric power.

The next thing Deep Green needs is compute customers. There's a demand for their tubs' waste heat, but the company needs a wave of cloud customers wanting to put their workloads in the swim. So far, Bjornsgaard says, the company is adding workloads somewhat anonymously, through aggregators, but in future, it wants direct customers.

In terms of the UK's overall net-zero goals, things may not be so clear. The scheme could potentially shift tens of MW of swimming pool heating from gas to electricity. That represents decarbonization - if there's green electricity there to cover it (and Deep Green could do its bit by paying a green tariff).

If it keeps open pools that would otherwise close, that actually increases energy used by the country (albeit for a significant benefit). And a holistic view of the green benefits would also have to ask the value of the workloads being carried, and measure that against whatever emissions they produce.

All told, the media splash is well justified, and we will want to know more about the project as it progresses.

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