Almost seven years have passed since the finalization and implementation of the ASHRAE 90.4 Energy Standard for Data Centers in 2016. Many within the industry are aware of its existence, however, less remain uninformed about its implications. In contrast, The Green Grid's Power Usage Effectiveness (PUE) metric, introduced in 2007, still has more widespread recognition. Initially based on power snapshots, PUE was refined in 2011 to reflect annualized energy usage, presenting a more meaningful efficiency assessment under various operational conditions. Despite criticism for lacking sophistication on facility and compute energy efficiency, PUE's simplicity facilitated its widespread adoption.
PUE has not only served as a benchmark for data center operators to help improve their facility's efficiency but also influenced the creation of the U.S. EPA's Energy Star program for Data Centers in 2010. While PUE remains the more widely embraced metric, ASHRAE 90.4, provides a more comprehensive standard for designing and operating energy-efficient data centers. It addresses additional aspects that PUE lacks, including IT equipment efficiency, power distribution, and differing cooling systems.
PUE attained ISO standard status in 2016 just as 90.4 was about to go live. Either way, most local and state building codes reference ASHRAE 90.1, the energy standard that was updated in 2010 and further amended in 2012 to include data centers. In 2016 the 90.4 Energy Standard for Data Centers became the new ASHRAE reference for energy performance requirements for data centers, eclipsing 90.1.
PUE remains helpful as a baseline for continuous improvement and has found applications in building design goals and colocation contractual agreements. In contrast, ASHRAE 90.4 is predominantly a design standard for new data center facilities, covering facility capacity upgrades of 10% or more. The complexity of the energy calculation methodology in the 90.4 standard surpasses that of PUE and includes a geographic adjustment factor, utilizing climate zones from ASHRAE Standard 169, leading to different values for identical data centers in varying locations.
ASHRAE's 90.4 proposed addendums, such as f, g, and h, aim to enhance efficiency requirements, particularly in UPS efficiency and cooling system energy compliance. These changes, effective in 2020, reflect a continued focus on advancing energy efficiency standards.
Fundamentals on PUE & ASHRAE 90.4:
Power Usage Effectiveness (PUE): Total Facility power / IT Equipment power
Importance: PUE is a fundamental metric for assessing how effectively a data center utilizes its power resources. It provides a quick and easy way to gauge the efficiency of a facility, although should always be regarded as inaccurate for actual contracts or calculations. A lower PUE indicates that a higher percentage of the total power is being used by the IT equipment rather than support systems, which is a key goal for energy-efficient data centers.
Challenges: Achieving a PUE closer to 1.0 is challenging, especially in older data centers with legacy infrastructure, as there is a point of diminishing returns on the amount spent to achieve better efficiency. Upgrading and optimizing existing systems may be necessary to improve efficiency.
ASHRAE 90.4: Energy Standard for data centers derived from Standard 90.1
Comprehensive Standards: ASHRAE 90.4 provides a more comprehensive set of guidelines for data center energy efficiency. It covers various aspects, including IT equipment efficiency, power distribution, and various options for cooling systems. The standard is regularly updated to reflect advancements in technology and practices in the data center industry.
Flexibility: ASHRAE 90.4 recognizes that different data centers may have unique requirements. It provides a framework that allows for flexibility in design and operation while still adhering to energy efficiency principles.
Cooling Efficiency: The standard addresses the crucial aspect of cooling, prescribing guidelines for temperature and humidity ranges that can optimize the efficiency of cooling systems while ensuring the reliability of the majority of IT equipment.
Compliance and Certification: Data centers that adhere to the guidelines outlined in ASHRAE 90.4 can seek certification, such as LEED, to demonstrate their commitment to energy efficiency and sustainability.
Adaptability to Technological Changes: ASHRAE 90.4 considers advancements in IT equipment and cooling technologies. This adaptability ensures that the standard remains relevant as the industry evolves.
Integration of PUE and ASHRAE 90.4 have a complementary nature as they are not mutually exclusive but can complement each other. Achieving a low PUE often involves implementing practices and technologies aligned with the principles outlined in ASHRAE 90.4. Knowing this may help when helping other stakeholders when deciding on a data center design approach.
While PUE and ASHRAE 90.4 serve distinct purposes, their integration allows for a comprehensive approach to data center energy efficiency by all stakeholders. Older data centers may face challenges in upgrading equipment for improved efficiency, but cost-effective improvements addressing basic issues can yield significant energy savings. As the industry evolves, understanding the pitfalls of PUE and applying the ASHRAE 90.4 standard become crucial for maintaining sustainable and efficient data center operations.
