Designing a More Energy Efficient Data Center
November 05, 2009
Appeared in Building Operating Management/FacilitiesNet
The average data center can be many times more energy intensive than an office building, according to a recent EPA study.
In response, EPA and the Department of Energy (DOE) have launched a joint national data center energy efficiency information program, which includes Save Energy Now, the Federal Energy Management Program (FEMP) and Energy Star. EPA also is working with end users to identify ways energy efficiency can better be measured, documented and applied in data centers.
Against this backdrop, data center operators are gaining an appreciation of sustainable design and high-performance buildings, and have successfully applied these concepts to their facilities. This has translated into a new generation of critical facilities that is more environmentally sound, more energy efficient and more cost-effective than before. These new facilities incorporate the best features of sustainability to reduce energy consumption without sacrificing reliability.
As with commercial building projects, creating sustainable data centers requires integrating ideas and objectives for building systems and sharing a vision with all of the project's stakeholders from day one. Success in achieving sustainable goals is driven by sensible decisions made early in facility programming, when the sizing of HVAC equipment, positioning of data center equipment, location and sizing of air openings and orchestration of large-scale airflow patterns are the most flexible. While some strategies may drive a higher first cost, they will lower operating cost over the facility's lifetime if they are properly applied. The following are a sampling of energy efficient design practices that should be explored in new data centers.
Managing Air Distribution
As in the legacy data center, managing air distribution effectively is a starting point for energy efficiency. Proper design and best operational practices will significantly increase the cooling capacity, reduce operating costs and allow for greater densities.
The widely followed hot/cold aisle configuration for IT racks is most effective when it is designed with ventilated racks and floor tiles (or supply/return grilles) matched to the space load. Designing to a higher difference between return and supply air temperatures will increase the achievable load densities. It should also reduce the relative size of the cooling equipment, thereby reducing first costs. While best practice traditionally calls for underfloor air distribution via a raised floor, a newer approach is to serve the loads via an overhead air distribution scheme that ÒdropsÓ air directly into the cold aisles. In some cases this can use less air and allow for a higher difference between supply and return air temperatures.
Customized central air handling systems have been demonstrated to perform more efficiently and provide advantages over the multiple distributed computer room air conditioning (CRAC) units that have traditionally served computer rooms. Larger systems will naturally have more efficient fans and motors, are better suited for variable frequency drives (VFDs) and perform better in variable volume operation and at part load. A centralized air-handling approach modulates air handler fan speeds in unison to maintain a uniform static pressure. It also offers individual cold aisle variable volume control by using motorized dampers and temperature sensors in cold aisles to constantly monitor the state of the thermal environment.
If the HVAC system must be designed around CRAC units, they should be specified with electronically commutated motors (ECMs) to drive the fans. ECMs are more efficient than regular AC motors and may be operated at part load without requiring a VFD. ECMs are also more efficient at lower speeds and more reliable because they have fewer moving parts. EC motors can receive the analog signal that controls the speed of the fan directly from a static pressure sensor and be linked together so that multiple fans will receive the same control signal. In an outside air economizer application, multiple fans can be similarly ganged together for variable exhaust flows, allowing for more efficient operation.
Make IT a Partner in Energy Efficient Design
Energy efficiency is not strictly beholden to infrastructure design. With heightened industry awareness, new strategies and technologies for IT equipment deployment are being aimed squarely at addressing power consumption and reaping energy savings. Given that IT equipment is the largest consumer of power in the data center (60 to 70 percent of the electrical usage typically comes from the servers and computers themselves), proper selection will contribute significantly to reaching overall energy efficiency targets.
Facility infrastructure systems need to be designed to support future IT technologies that may not necessarily be available on day one. It is vital, therefore, that IT be a partner in the design process. Some ways today's new data centers are doing this include purchasing high-efficiency servers with up to 85 percent more efficient power supplies, using server virtualization, and employing thin client network and massive array of idle disks (MAID) technologies.