Data Center Energy Efficiency Project Wins Best of California Award

A project to improve the energy efficiency of the State of California Franchise Tax Board's data center has won a "Best of California" Award from the Center for Digital Government. Geoffrey Bell, Energy Engineer at Lawrence Berkeley National Laboratory's Environmental Energy Technologies Division, led the project team.

The research was funded by the California Energy Commission's Public Interest Energy Research (PIER) program, and other participants included Federspiel Controls, Inc., Emerson Network Power, and California's Department of General Services.

The Franchise Tax Board (FTB) is the California agency responsible for collecting state taxes. Its 10,000-square-foot data center in Sacramento was kept cool by 12 computer room air handling units (CRAHs), each one with a 22-ton capacity for chilling the cooling water. Data servers generate considerable heat, so data center designers tend to overdesign cooling capacity, typically providing more cooling capacity than is actually necessary. At the FTB, all 12 CRAHs were kept on all the time. There was no sensor system to coordinate the CRAHs cooling of the room. Consequently, there was no way to tell whether the room could be conditioned adequately with fewer CRAHs operating.

The project team did a complete evaluation of the data center's energy use, and installed a number of energy-saving retrofits, the centerpiece of which was a relatively inexpensive "wireless" control system for the CRAHs.

"This project demonstrated that a wireless sensing network could directly control computer room air conditioning devices, maintaining an optimum temperature, while saving energy," says Bell. The project team installed a wireless control system developed by Federspiel Controls, Inc., which included a wireless mesh-network of 46 temperature sensors at various locations around the center. The mesh network provided air-temperature feedback from the server-equipment air inlets to the control system that determined which of the 12 CRAH cooling units were needed to operate, and to reset the setpoints of the remaining operating units. The Federspiel technology is called a Data Automation Software and Hardware (DASH) System.

The DASH temperature sensors provided information that had not been available previously—real-time information on how cool various points in the center were. The DASH system could turn on and off the appropriate CRAH units to maintain the desired air temperature. This technology could also "learn" from operational experience: as it logged more and more data on how the temperature responded to the manipulation of the CRAH units, the DASH system actually further reduced energy consumption by managing these units more efficiently over time.

Once the control DASH system was working, the facility team learned that they could turn off eight of the 12 CRAHs, and keep the data center cool using just the remaining four units.

The project team also took other steps from an array of energy-efficient data center measures developed as a result of research conducted at Berkeley Lab. A simple one was to make sure that the floor tiles were correctly positioned for proper air distribution. The FTB server racks sit on a raised floor. The improved floor tile arrangement helped manage airflow to supply cool air to the server inlets within temperature limits recommended by ASHRAE, the Association of Heating, Refrigeration and Air Conditioning Engineers. They also installed fusible-link air curtains to isolate cold-air supply from hot-air return, and variable frequency drives to make the CRAH fans more energy-efficient. These efforts resulted in a decrease of chilled water use, and more energy savings.

In sum, the measures eliminated the use of more than 475,000 kWh per year, which is 21.3 percent of the data center's baseline energy consumption. This also represents eliminating more than 400 tons of CO₂ emissions annually. The wireless control alone was responsible for about 15 percent of these savings. Fan energy use decreased by 66 percent. All of the measures together will save about $43,000 per year in energy costs, so the cost of the work will pay for itself in about two years.

At a ceremony in Sacramento in December, the Center for Digital Government gave the Franchise Tax Board its 2009 Best of California Award in the Green IT category for this project. The Best of California Awards program salutes IT professionals and projects in California state and local government organizations and educational institutions.