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 there’s a phone commercial. A guy is building a birdhouse and he says to someone else “I’m thinking of renting it out to get a better return on investment”. Now this guy understands what ROI is. He has an investment. He understands what it means. It’s how much he makes relative to what he put into it.
Investopedia defines ROI as the amount of net income returned as a percentage of shareholder equity. It further amplifies this definition to allow for different organizations to calculate ROI differently. ROI can be a cash amount, it can be a ratio, a percentage, or an annual yield. One thing clearly absent from this list of possible ways to calculate a return on investment is a time period.
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?
Many people make the mistake of confusing a Kilowatt (a unit of power) and a Kilowatt-hour (A unit of energy). The same could be said about Watts and Watt-hours, but the Kilowatt is much more commonly applied.
A kilowatt is power. Think of it as a rate of consumption. This is how fast you are gobbling up electrons from the grid.
A kilowatt-hour is energy. This represents the amount of electrons you have gobbled from the grid since your last utility bill, for example. (not really electrons, but you get the picture) Continue reading Kilawhat?→
PUElink - Saving Energy and Maximizing Capacity 