Data center DC power, power backup runtime, and free air cooling, a greener shade of green.

I’ve written previously here about the green, energy saving benefits of DC power in the data center, the reliability follies of super short run time power backup, and, of course, the well recognized benefits of free air cooling. In this post, I’m going to discuss making the best green use of all three of these together in the data center.

The “classic” data center power backup system is the double conversion UPS. In this scenario, commercial AC power is rectified to DC for the backup batteries and then inverted back to AC to supply the data center equipment. This configuration actually has three points of efficiency loss, the rectifiers for the AC to DC, the inverters for DC to AC, and the load power supplies for AC to DC again. The data center DC power plant does away with 2/3 of the efficiency loss by eliminating the DC to AC inverter and the AC to DC power supply in the load equipment.

The second part of this equation is the backup power itself. The trend to incredibly short run time backup power (such as flywheels with only 15 seconds of run time) is a foolish gamble that fallible generators are going to work perfectly every time. If there’s even a small issue that could easily be dealt with, there simply is no time and the facility is going down hard.

The third part is the free air cooling. It really goes without saying that using cooler outside air for cooling is far more efficient than any type of traditional data center air cooling.

So, how do these three things tie together to make the data center even greener than any one separately? Many data centers use load shifting to save power costs (such as freezing water at night when power is cheaper to cool with during the day). I call this technique heat shifting.

My data center is equipped with an 800A 48VDC modular power plant equipped N+1, a battery string capable of 8 hours of run time, and free air cooling. The idea is to simply pick the hottest part of the day (usually early afternoon) and remove heat load from the free air cooling by shutting down the rectifiers and running the facility from the battery string for 2 hours.

This shifts that part of the heat load of the data center to times when the free air cooling is operating more efficiently, allowing the free air cooling the elbow room to support more productive equipment load. Additionally, you have the side effect of exercising the batteries regularly, avoiding the ills that can plague idle batteries, such as stratification and sulfation.

As if there weren’t already enough great reasons to use green DC power, long run backup, and free air cooling in the data center, here’s another one.

Email or call me or visit the SwiftWater Telecom web site for green data center services today.


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