Server power densities have increased dramatically over the last five years, from 800 W/ft2 to 1600 W/ft2. Also noteworthy is the fraction of data-center energy consumption by non-IT loads, which has grown to more than 50% of the center's energy budget. These significant increases in power density and energy use are pushing the energy component of cost-of-ownership to more than $5 million for a 500-kW data center over a 10-year life. This provides an opportunity to assess new technologies that enhance energy efficiency and reduce the lifetime cost of ownership.
Power use in large computing systems comprises four main categories: IT loads, the power supplies for the IT infrastructure, cooling equipment, and the heat-transfer systems that circulate air through racks and individual boxes, frames, and card cages within a rack.
Consider the data center's rack blowers and air-conditioning compressors and fans. By switching from brush or brushless dc motors with trapezoidal drive to permanent-magnet ac (PMAC) motors with sinusoidal drive, peak motor efficiency can improve from between 65% and 85% to 90%. Additionally, PMAC motors with sinusoidal drive maintain their high efficiency with increasing torque load while efficiency falls off in brush and brushless dc motors with trapezoidal drive.
Sinusoidal-drive PMAC motors also generate less noise and vibration, with low-and mid-band peaks 10 to 20 dB below their dc counterparts. This helps when siting a facility and improves reliability while reducing unscheduled maintenance.
These higher motor efficiencies can cut energy costs by up to $160,000 per year. Also, the more efficient motors dump less heat into the data center, reducing the load on the heat-transfer system and saving roughly $60,000 in the example 500-kW data center. The technologies required to power these systems are available today without the need for complex algorithm programming by using an integrated design platform.
Technologies coming online during the next few years will deliver similar energy savings for the power supplies that feed IT loads and associated system electronics. The greatest power demands within large IT systems come from the many parallel microprocessors that provide the enormous data throughput that such a site must provide.
The supplies powering these processors today operate at about 88% efficiency in best-in-class systems. Within three to five years, this efficiency will increase to about 95%. Similarly, the ac-dc power supply that feeds an entire server rack can improve from present efficiencies of 85% to 94%.
These advances will not come from a single technology breakthrough but rather from a systemic approach that takes advantage of advances in silicon devices, power conversion and management topologies, and advanced packaging. This three-pronged power-technology strategy will save $440,000 in energy costs for the data-center model described here and another $140,000 per year due to the reduction in the cooling system's thermal load.
Even greater savings are possible as system architectures take better advantage of emerging power-feedback and load-control methods, such as those that PMBus and similar power-control communications protocols enable, to centrally and intelligently control power supplies and fan motor systems.
Combining the savings from cooling and heat-transfer systems attainable through these technologies will save as much as $800,000 in energy costs over the 10-year model lifetime. Current estimates put the cost of achieving these improvements at about $9000 per data center—an increase of 20% in the bill-of-materials cost—and falling.
Consequently, these technologies promise benefits approaching 1000% return on investment per year of operation as they pave the way for practical increases in functional density while control and IT technologies themselves evolve.