How to Balance Ambient Data Center Setpoints with IT Equipment Energy Use
For many years, data center temperatures were run cold enough to suit penguins and polar bears, resulting in greater energy consumption than necessary for safe, reliable data center operations.
The latest ASHRAE recommended operating temperature for data centers is between 17.7°C and 27°C (64 and 81°F). In fact, for every degree that the air inlet temperature is raised, a data center operator could save up to 4% on cooling costs. With that said, going outside the ASHRAE recommended range into ASHRAE A1 to A4, can result in increased power usage, as shown in the figure below, due to increased IT equipment fan usage. This is particularly true for high density data centers:
Because it doesn’t appropriately account for changes in equipment energy use, a metric such as power usage effectiveness (PUE) may not capture this overall additional energy consumption. For example, a data center operator decides to increase the air inlet temperature in a data center from 79°F to 84°F, which is above ASHRAE’s recommended range in their high-density data center environment.
The operator sees an improvement in PUE, but the 10% savings in facility cooling energy is more than offset by the 20% greater IT equipment energy use, resulting in 80,000 more kWh consumed. This is driven by the additional fan power needs in the IT equipment due to the higher air inlet temperatures in the data center and the products being optimized for up to 80°F operation. The overall data center energy use increases 8% despite the PUE reduction, ultimately raising operating costs and potentially decreasing resiliency.
Set your air inlet temperatures as high as is allowed by your equipment and the ASHRAE recommendations for operating temperature and humidity, but do not exceed those recommendations. Pushing long term air inlet temperatures past the ASHRAE recommended range, beyond 27°C (80°F) into ASHRAE A1 through A4 operating regions may improve your PUE score but will likely result in higher overall data center energy costs, especially for higher density data centers. Sustained operating temperatures above 80°F can also introduce longevity and warranty concerns for the IT equipment and reduce resiliency of the IT load when dealing with temporary cooling equipment failures, depending on the ASHRAE rating of your IT equipment.
Author: Ryan Fogle, ENERGY STAR Certified Products