Spring is coming. Will your data center be a spring chicken or an old bird? As the weather begins to warm (hopefully) this is a great opportunity to take stock of your data center and it’s economizer system and operation.
We have this sensor, we call it the million dollar sensor. Now how can a single sensor be worth a million dollars? The answer is simple, really, it’s the outside air temperature and humidity sensor, and we have selected it such that many of the problems with other sensors, particularly humidity, are eliminated. By having a highly accurate sensor, we can reduce the margins for the economizer to engage ( for instance, return air temperature plus 2 degrees instead of 4) and have knowledge that we won’t be what I call “anti-economizing” where the air we bring in has more enthalpy than the air exiting the building.
Right now we’re having a bit of a debate on how to calculate PUE. We are all familiar with the GreenGrid definitions of PUE 1, 2, 3 etc but our debate is which is most valid. As a colocation provider we lease data center space. We also lease data center adjacent office space. Should this space count against our PUE? Some of our sites don’t have offices while some do. Comparing them to identify opportunities would require a similar metric wouldn’t it? The office really isn’t supporting the center, it’s its own entity. At the same time, we have been including office, so the historical readings will no longer be as relevant if we change PUE. I’d like to open up a discussion here if anyone is interested.
I’m not as obsessed with conforming to an industry standard as I am with providing useful standards for comparison and progress. Of course us in the know are looking at so much more than just PUE, we break down the load path, find out where our power is and where it should be, and look for opportunities or solve issues. Yet PUE is an important tool for executive level reporting.
What’s the best measurement of success in an organization when your talking about energy savings? Cash savings is great because it’s quantified in the most important business metric. Unfortunately it does not correct for changes in IT load and utility pricing. kWh gets at what is most controllable by efforts of the group trying to save energy, but again needs to be calibrated for IT loads. If we benchmark against expected energy spend (vice previous spend or trended spend) then we can use the actual IT load and the results can represent what the energy efforts actually accomplished. PUE doesn’t need any calibration, but it isn’t quantified. The statement PUE went from 1.77 to 1.65 is meaningless to a income statement. And those are the results with impact ( save $400,000 a year with a net present value of $2,500,000 and a first cost of $300,000 for improvement is a great victory to anyone in corporate finance). It’s a juggling act, maybe it depends more on who is seeing it. But when your getting evaluated for year end performance, which is most important?
So one of the big things I have been pushing for in my job has been VFDs on every motor >2 horsepower. VFDs can be incredibly useful tools. First of all, without considering energy implications, they give you finite control of the motor. Just being able to modulate capacity is huge, especially if you have a control system that can handle the input.
Energy savings, however, are really where its at. Most of our motors in the data center are connected to a fan or a pump. For the most part, fans and pumps are variable torque loads and (with the exception of some oddball positive displacement pumps) vary their consumption with the cube of the speed, per the fan laws. Continue reading VFDs Spend a little Save a LOT→
PUElink - Saving Energy and Maximizing Capacity 