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Many designers and operators attempt to optimize their new or upgraded site for the greatest amount of “free”, economized cooling operation. This has been given great emphasis in recent years by the publication of free cooling maps which show how surprisingly far south you can use ‘free’ cooling.
Unfortunately, given the improvements in compressor cooling efficiency in recent years, both from device efficiency improvements by vendors and the selection of more rational operating temperatures by designers and operators, more economizer hours does not equal better performance in many designs.
We have observed many designs and operating data centers where the free / mechanical cooling control optimization is far from obvious. At one extreme we know of real designs where the economizer system will actually increase the energy consumption and PUE.
More frequently we see systems where the compressor cooling is efficient enough that the transition from economizer to entirely mechanical cooling should be made much earlier. This may result in fewer “free cooling hours” but like many misleading pseudo-metrics this doesn’t mean lower cost or PUE. As we have pointed out time and time again, efficiency isn’t the be all and end all of running a data center, the key figure is what the Total Cost of Ownership (TCO) will be.
In fact, the improvements in compressor cooling efficiency have now reached a point where many economizer designs either have negligible energy performance impact or have no realistic prospect of recovering their capital cost.
As always, the complexity of your individual facility (particularly as its performance is linked to the local climate) means that this level of insight requires modeling your data center!
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