My Perfect Green Data Centre (4) – DC, Postscript 2 My Perfect Green Data Centre (5) – AC

My Perfect Green Data Centre (5) – Evaporative Cooling

I started thinking about this subject five years ago and, back then, I wondered if evaporative cooling would be useful in the humid tropics.

The form of evaporative cooling with which us humans are best associated is sweat. The reason sweat cools us down is not that we are covered in water, but that the water, when it evaporates, cools us.

In the dry air of Europe and North America, humidity is generally low, so evaporative cooling has not taken off. As it would seem that most HVAC engineers are educated in this tradition, whenever I mentioned evaporative cooling, I was steered quickly away. Even Dr. Hot, a consultant in thermodynamics, rubbished the idea. As he was the expert, I parked evaporative cooling in my bag of good-ideas-that-turned-out-to-be-rubbish.

Dr. Hot was dead wrong: so much for experts. A month ago I went to a data center fair in Hong Kong and came across Munters, a company that makes industrial-scale evaporative cooling for data centers. While I accept a certain amount of hype, their cooling system is the choice at Supernap’s new Tier-4 data centre in Thailand, and Munters claim that it saves so much power that, even in the tropics, a PUE of 1.2 is achievable – a massive saving on energy.

On the back of an envelope

IT Load PUE Cooling Power
2,500,000 2.0 2,500,000
2,500,000 1.7 1,750,000
2,500,000 1.3 750,000

So, the difference between a PUE of 1.7 and 1.3 is a 1MW generator set. A huge saving in capital cost (being green pays!), but also a significant reduction in the pollution that gen sets spew into the atmosphere, and the environmental impact of building, shipping and ultimately destroying the things.

That’s already good in a colo environment. In the self-contained pod that I sketched in my previous post, the idea would be to make the outer casing the evaporative cooler. Munter’s design re-circulates the air inside, so the idea would be to put the heat exchange on the wall, and the fans and pumps on the roof. Probably a rather expensive experiment, but I can’t help wondering if that may get the PUE down as far as it can go.

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