There is a lot of discussion lately regarding “free cooling.” It seems you cannot pick up a trade publication without reading about how company XYZ or engineering firm LMNOP deployed free cooling, saved a boatload of money, eliminated tons of CO2, and thwarted global warming.
Free cooling sounds appealing – if you can bring in cool outside air or bypass the compressor, that has to save energy, doesn’t it?
Well yes, and not exactly.
While pondering free cooling, I recalled a story my father told me about a king’s quest to understand the meaning of economics. I will cut to the chase: “There is no such thing as a ‘Free Lunch.'” Eureka!
There are many paths to free cooling, but they come down to two basic choices:
A. Airside economizer – introduce outside air when the conditions of entropy are better outside than in; or
B. Waterside economizer – bypass the compressor and use cool fluid from the cooling tower or drycooler system to reject heat directly when conditions permit.
In each case, the desired effect is to use less total energy to keep the data center within ASHRAE environmental parameters – without increasing the risk of failure.
Controlling risk is the dilemma, as outside air is not as pretty as it looks. Want an idea just how bad the air is – AIRNOW can tell you.
But this is strictly related to human health – not expensive IT systems. Their electronics and precisely manufactured pieces are electro-chemical food for certain airborne cocktails. One recent test by an IT OEM using airside economization found an 81 percent increase in IT equipment failures in an eight-month test versus a control site. Corrosion is an additive effect, so what should we expect over two years?
Oh sure, high-MERV air filters can help with particulates, but nothing prevents a runaway freight train or semi-truck from spilling hazardous cargo upwind of your data center.
Filters, automated dampers, bypass circuits, air-quality monitoring, and control systems all add significant upfront construction costs along with operation and maintenance expense. Not exactly “free.”
Don’t get me wrong – some “free cooling” technologies show promise. For instance, fluid side economization can reduce energy costs without the risk of contamination.
However, you need to seriously evaluate the pros and cons of free cooling for your specific site.
And remember – just as there is no such thing as a free lunch, there is no such thing as free cooling.
Jack Pouchet is director of energy initiatives for Emerson Network Power.