Most data centers are located in areas that don’t experience warm weather all the time. (If yours is at the equator, you can stop reading this right now. There’s nothing here for you.) In climates that experience at least some cold weather, companies can save significant money by operating their data center cooling system in economizer mode – nearly 80% in some instances.
Operating in economizer mode saves energy by using outdoor air during colder months of the year, allowing components such as chillers and compressors to be shut off or operated at a reduced capacity. In some climates, data centers can run primarily in economizer mode, allowing the refrigerant-based modes to serve as the secondary mode of operation or backup. Economizer mode works so well that it is now becoming a requirement to meet efficiency targets and standards, such as ANSI/ ASHRAE Standard 90.1-2010, Energy Standard for Buildings Except Low-Rise Residential Buildings.
It’s helpful, then, to learn more about what economizer mode means, the various types of modes and why they’re beneficial.
Using economizer mode helps to offset the differential between cooling systems designed to work under full data center loads and high outdoor temperatures, and actual data center conditions which are often less demanding. At lower data center loads and cool outside temperatures, the system does less work to cool the data center but various devices in the cooling plant wind up being underutilized and not operating efficiently. Even cooling devices that include variable speed drives, staging, and other functions still require significant power. Economizer modes help reduce the power used by these cooling systems during conditions of light data center load and cool outdoor temperatures.
Cooling systems can use air, water or refrigerant to move heat from inside the data center to the outdoors. A compressor moves heat from within the data center to the outdoors when the outdoor temperature is greater than the data center temperature. When the outdoor temperature is sufficiently below the data center temperature, economizer mode can be employed to allow the heat to naturally flow to the outside, bypassing the compressor and saving significant energy. Some systems also use cool outside air to indirectly cool data center chilled water.
Historically, building an economizer mode into a data center cooling system was costly and complex, making it justified only in locations with extremely favorable weather conditions, such as high latitudes. But now economizer modes are considered advantageous in almost all locations for the following reasons:
- Operating data centers at partial load increases the benefit of economizer modes and more designers recognize that data centers spend a considerable amount of their life at light load. The trend toward dynamic power variation of IT equipment will amplify this effect.
- The trend toward operation of data centers at higher IT air return temperatures has a dramatic effect on the percent of time economizer mode operation is possible, especially in warmer climates
- Most newer economizer mode implementations can operate in a “partial” economizer mode, which greatly increases the amount of energy saved in almost all cases.
- The tools available to quantify the energy savings by using economizer mode have improved and frequently predict significant savings with excellent ROI.
- Real-world experience with economizer modes and improvement of controls and monitoring systems have increased confidence that these modes do not adversely affect the reliability of data centers.
Except for most extreme climates, all the economizer modes provide cooling energy savings over the baseline cooling system. One economizer mode, called air conditioner bypass via air heat exchanger, provides the lowest cooling energy consumption in nearly all climates with an average savings of 79% as compared to baseline cooling.
If that sounds like a savings worth pursuing, check out the APC by Schneider Electric white paper, “Economizer Modes of Data Center Cooling Systems,” to learn more about the various types of economizer mode.