At this point in the evolution of data centers, use of economizer mode cooling technology is pretty much standard, at least for large data centers such as those owned by colocation and cloud providers as well as Internet Giants like Microsoft and Facebook. The only real argument is about what basic type of economizer mode to use: direct or indirect.
When air economizers first came on the scene, most companies favored the direct approach. Direct air economization, also known as “fresh air,” is when you take fresh outside air and send it through a series of filters and/or wetted media directly into the data center for cooling. The simple design of the direct approach makes it highly efficient from a power perspective because it takes only a series of fans and louvres to get the job done – at least while ambient outdoor temperatures are sufficient.
But direct cooling has a couple of downsides that tend to muddy the equation. Chief among them is the filtration required to ensure no airborne contaminants get into the data center. Those filters have a tendency to get clogged, requiring frequent maintenance. In areas that suffer from heavy pollution, that can be a deal-breaker. And if there happens to be a wild fire, chemical spill or other pollutant in the area, that can likewise require the data center to disable the economizer mode altogether and shift to mechanical cooling.
What’s more, direct cooling is highly subject to outside moisture changes. Overly dry outside air requires added humidification, while high humidity necessitates dehumidification – both of which reduce efficiency.
Indirect economizers, by contrast, address many of these issues. They use a heat exchanger to effectively separate the outside air from the data center, acting as an insurance policy against whatever contaminants may exist in the outside air – and eliminating the need for a filter. The indirect approach also eliminates concerns over ambient humidity conditions negatively impacting he data center. What’s more, the exchangers can be used in both dry and wet modes, so you can leverage both ambient dry and wet bulb temperatures to cool the data center. (For more on the various types of economizer mode, check out our free white paper no. 132, “Economizer Modes of Data Center Cooling Systems.”)
Today, more and more large data centers are gravitating toward the indirect economizer mode, especially as vendors have taken steps to make them more efficient. For the times when DX cooling is required, for example, Schneider Electric has developed proportional brushless scroll compressor technology that uses variable frequency drives to provide infinite capacity control. The design allows a 4:1 turn-down ratio of DX cooling capacity. In addition, when the compressor starts, the VFD performs a soft start to eliminate the in-rush of current normally required to start the compressor. That not only saves energy but it eases the burden on the entire electrical distribution and backup systems, which no longer have to account for that initial in-rush. When building a data center, that equates to lower up-front capital costs due to reduced electrical distribution and back-up system requirements.
Similarly, new motor technology uses electronically commutated fans that provide only as much power as is required at any given time, thus saving energy. Even the condenser coil takes advantage of micro-channel design to increase efficiency of the DX circuit.
Another advancement is in the heat exchangers, which are now made from a polymer instead of metal, making them more conducive to wet environments and less likely to foul. They can also be serviced in the field – which may be a first.
The overall point is, while direct air economization may be marginally more efficient than indirect, most owners of large data centers are finding the difference is not worth the risk with respect to air contamination, moisture intrusion and increased maintenance.
And the energy reductions they’re getting from indirect economizers are still quite impressive, on the order of 50% less power allocated to cooling, and 40% more power available for the IT space. What’s more, it reduces operating expenses up to 50% and even capital expenses by at least 5%.
The story will get even better soon, as Schneider Electric will be introducing new indirect economizer models in the first quarter of 2017. They were specifically designed to build on our previous models and to address feedback from some of our biggest customers in terms of efficiency, capacity and weight. You can look forward to two new models – 250kW and 500kW versions – that can be used together to create a highly scalable indirect cooling solution that can meet the needs of most any data center.
To learn more about indirect economizers, check out this short video. For a deeper dive into the differences between economizer modes, download the free Schneider Electric white paper no. 215, “Choosing Between Direct and Indirect Air Economization for Data Centers.”
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