Talks about “green IT” are everywhere, no IT magazine without an article, no fair without new products, and advertisement all over the place. But I bet there are quite some small and medium-sized business around the world that ask themselves: “How are we to participate in this move?” Typically being the more responsible entrepreneurs, I’m sure they don’t put profit first, but cannot afford (or at least economically deploy) all those new & nifty water-cooled racks or set up “separated hot and cool zones in your data center”. Mostly, because there simply is no data center.
We were facing such a situation at a small office with a single-rack computing room. The office is in a zone of moderate climate (around -5 to 5 °C in the winter time with peaks down to -15 °C in tough years, and 20 to 30 °C in the summer time, despite some heat waves), the computing room is facing north (no sunshine heating things up), and a direct outside window front. The servers in the rack currently draw around 3,2 kW when under load.
In the first years, running with an open rack and fresh outside air was sufficient. But with time there came an increase in computing power and more servers in the rack. During an especially hot period, a typical mobile air conditioning was set up (you know the type, everything in a single unit and a nozzle to direct the hot air directly out of the window), but even with a permanently installed air outlet, that solution was soon coming to it’s limits.
Split air conditioning was out of the question (too much noise in the night, disturbing all the neighbors in the mixed office/living quarters), so it was time for some new ideas. I’d like to share with you what was created – you cannot only cut your A/C energy costs by two, but do so with spending only some hundred Euros!
First and most important was the realization that in that computing room, only the servers need cooling. Not all of the room needs to be cooled, not the backside of the servers, nothing else – cool air only needs to go to the front air intake of the servers to get them cooled.
It was helpful that the servers are in a closed 19″ rack – that’s different from many computing centers, where the rack fronts and backs are mostly open to allow free ambient air flow.
Secondly, it was decided that the servers will have to run with an intake air temperature of up to 27 °C – but you can vary that number to your liking (at least downward the scale… it’d be “depending on your willingness to take extra risks” when increasing that value). No special attention was to be paid to humidity – the servers ran with unconditioned exterior air for years without noticeable bad influence, so there was no motivation to spend money on that now.
Thirdly, the influence of television series of the 80es took its toll: Rather than spending big bucks on an industrial-grade super-duper custom-made air conditioning, MacGyvering a solution on a limited budget was requested. When it’s cold enough outside, take that air to cool the servers, and mix in some A/C-cooled-down air when necessary.
Key to success was the strict separation of hot & cool air zones inside the 19″ rack: the front of the rack, where the servers have their air intakes, was mostly sealed off from the area behind the front plates, making the front the “cool zone” and all of the back the “hot zone”. Fresh air is fed directly to the front area through an air pipe installed in the base socket of the rack, sucked in by the servers’ fans and pushed out to the back of the servers as warm (or even hot) air. That warm air (with typically 30 to 33 °C, but I`ve seen peaks up to 40 °C) is picked up by fans in the rack dome, partially transported out of the room by an extra fan and some air pipes, partially fed into the office rooms for heating during cold winter nights.
This hot/cold separation inside the rack alone took down energy costs by 25 %, as the air conditioning had much less running time than before, when cold air was simply fed into the rack (as done in typical data center installations with raised floors). It’s amazing: After some server works, a single height unit between two servers was left open – and the temperature at the servers’ intakes immediately went up several degrees, just because the warm air could (and would) flow back to the front side. Looking at it from the theoretical side, it’s all about what volume of air you need to cool down: When everything is open, you’ll have to add much more cold air to cool the resulting mix down to the desired intake temperature. When you separate properly, only the small volume between the server front and the front rack door needs to be cooled down. This makes a huge difference. (And you don’t need a coat to work in the computer room 😀 )
The other cost decrease occurred when a controlled fresh ambient air intake was added to the picture: An industrial-quality fan was added (the same build as the extra fan to transport hot air out of the building) to transport air from outside the building to the server rack, and both fans were hooked up to a custom-build, thermal-controlled fan control (that is also capable of switching the A/C on and off). This way, rather than only cooling down (warm) room air via the A/C, outside air is used to cool the servers and the A/C only kicks in when that air isn’t cold enough. About two thirds of the year the outside air is cool enough to reliably cool with it alone. If, in the winter time, the exterior air gets really cold, then the intake fan reduces its speed so the servers won’t get cooled down too much (and probably fetch condensed water or suffer from too wide temperature changes). If the outside air gets too warm to help cooling down (approx. 5 °C below the desired intake temperature), the fan is turned off so that the A/C doesn’t have to fight that, too.
So the complete solution consists of a regulated fresh air ventilation plus an A/C kicking in when things get too warm, fed into a climate-separated closed 19″ rack. All ventilation parts are industrial-grade geared towards low noise, the A/C is a standard mobile indoor unit, duct-taped to direct the air flow to the rack front and it’s temperature sensor relocated to the rack front (rather than sensing room temperature).
Both fans, noise-reducing air pipes, some installation material and the “mobile A/C” sum up to about 600 Euros. Add another 800 Euros for the custom control and you still are several times below the costs you’d face when you’d try to solve these requirements with standard components from typical data center suppliers. And unbelievably, the savings on energy required to drive the A/C more than compensated these costs, already in the first 12 months. Now that’s what I call “SMB-friendly green IT”.