With October marking Energy Awareness Month and with World Energy Day having taken place on October 22, energy efficiency is at the forefront of many data center managers’ minds. Although it’s an important consideration for professionals across many industries, it really hits home in the data center market today—especially for cloud-computing vendors, hosting companies and other IT-service providers who are opening multitenant data centers (MTDCs) at a rapid pace.
Thanks in no small part to the intense competitive pressures they face, large enterprise data centers, collocation facilities and MTDCs must maintain exceptionally high energy efficiency. In this article I’ll outline some of the unique energy challenges that face these types of facilities and then describe how the latest uninterruptible power systems (UPSs), air-containment solutions and economizers can help reduce power-related operating expenses without weakening reliability or agility.
Common Energy-Efficiency Challenges in MTDCs
To satisfy steep energy-efficiency requirements, MTDCs operate in ways that can create some notable challenges, including the following:
Extreme operating temperatures. The clients most MTDC vendors support use virtualization and blade servers extensively. Though both technologies radically increase a data center’s compute density, they also generate enormous amounts of heat in smaller spaces. Dispersing that heat can be a difficult and expensive task that requires rack-based power distribution units (PDUs) that are high density and high-temperature tolerant.
Inefficient cooling. MTDCs housed in older buildings often rely on so-called “chaos” air-distribution methods to keep temperatures within acceptable limits. In such cooling schemes, computer-room air-conditioning (CRAC) units around the perimeter of the server room pump out massive volumes of chilled air that both cool IT equipment and help push hot server exhaust toward the facility’s return ducts. By allowing hot and cool air to mix and recirculate, however, chaos air-distribution strategies decrease cooling efficiency and drive up electrical bills.
Low UPS loading. To preserve reliability, many MTDCs employ redundant UPS and/or 2N architectures in which multiple units operate at partial loads, so if one device fails or requires maintenance, the others can quickly compensate. Although such deployments guard against downtime, they also cut energy efficiency because lightly loaded UPSs waste more power and produce proportionally more heat than those that are fully loaded.
Best Practices for Maximizing Energy Efficiency
MTDC operators have a variety of options for coping with those and other efficiency challenges. A new generation of sophisticated UPSs can help them increase efficiency without compromising reliability. Such devices come in two basic types:
Variable-capacity modular UPSs. Many double-conversion UPSs now contain multiple power modules. The most advanced types also allow data centers to load those modules variably. Therefore, rather than distribute loads evenly across all modules at low levels, companies can load one or more modules fully and leave the other, unneeded ones on standby. Should a hardware failure or other issue cause load requirements to jump suddenly, the UPS can automatically and immediately activate the standby modules. The end results are greater efficiency under normal conditions, better mechanical reliability and continuous uptime when problems occur.
Multimode UPSs. Variable, modular UPSs function exclusively in double-conversion mode, whereas multimode UPSs offer two operating modes. In normal operation, the UPS runs in a highly efficient energy-saver mode, but if power conditions fall outside predetermined tolerances, they automatically and immediately switch to double-conversion mode. When power quality returns to acceptable levels, the UPS automatically switches back to energy-saver mode.
Though today’s double-conversion UPSs are often more than 94 percent efficient, multimode versions are up to 99 percent efficient—even at lighter loads. As a result, they offer MTDC customers the ultimate combination of low operating costs and high reliability. Some multimode UPSs also come with built-in harmonic-reduction capability. Harmonics are distortions in a data center’s voltage or current waveform, typically from nonlinear loads such as servers, variable-frequency drives and fluorescent lights. If left unaddressed, harmonics can reduce energy efficiency and reliability as well as shorten the life span of expensive electrical equipment.
In the past, data center operators concerned about harmonics had to devote precious floor space to specialized mitigation technologies. Today, they have the option of using multimode UPSs equipped with harmonic-reduction technology instead. Older devices with this capability decrease harmonics only while in double-conversion mode, but newer, state-of-the-art UPS models can mitigate harmonics, perform power-factor correction and balance loads while in energy-saver mode too.
Though most data centers continue to rely on them, CRACs take up valuable floor space, are costly to maintain and are a source of energy waste. As a result, MTDC owners are increasingly deploying smaller CRACs, moving them into the rack rows or eliminating them altogether, or using them only as backups for more-energy-efficient cooling technologies such as economizers.
There are two basic kinds of economizers:
- Water-side economizers take advantage of frigid outdoor temperatures to chill the fluid in a liquid-cooling system’s closed cooling loop.
- Air-side economizers pump hot server exhaust out of the data center and pump in naturally cool air from outdoors. Though they tend to be most effective when used in cold, northern latitudes, air-side economizers are a practical option for at least part of the day even in mild or warm climates, according to numerous expert studies.
Which kind of economizer an MTDC uses depends on variables such as where it’s located and whether it uses liquid cooling, but almost every MTDC will benefit from the “free cooling” that economizers provide.
A Comprehensive Cooling Solution
By deploying a strategy to organize, manage and protect IT equipment, MTDC operators can dramatically reduce their cooling costs. For a more enhanced solution, organize containment solutions with enclosed server racks in sealed structures that capture hot exhaust air, vent it to a CRAC or other cooling system and deliver chilled air directly to the server equipment’s air intakes. Operators can also manage a virtual environment with intelligent PDUs and UPS systems by using integrated power-management software for better efficiency.
Organizing and controlling air streams in this manner dramatically increases cooling efficiency. For example, to compensate for the effects of recirculated exhaust air, hot-aisle/cold-aisle containment schemes must often chill return air to 55°F (12.78°C). Containment-based cooling systems, however, completely isolate return air, so they can safely deliver supply air at a much warmer 65°F (18.34°C), measurably reducing cooling-related energy expenses.
As an added benefit, air-containment solutions improve reliability by protecting servers from thermal shutdown caused by hot exhaust air. They also enhance flexibility by giving facility operators greater freedom to position server racks in whatever way best suits their needs rather than in the rigidly aligned, uniformly arranged rows than hot-aisle/cold-aisle configurations require.
Tying It All Together
Operators who make energy efficiency a constant priority can reap many benefits. Using more-efficient UPSs, air-containment solutions and economizers can help MTDC owners reduce wasted power and ease cooling loads while also enhancing reliability and agility. As we look to wrap up Energy Awareness Month, it’s helpful for MTDC operators to understand how employing these benefits can help position themselves for long-term business success and growth opportunities.
About the Author
Ed Spears is a product-marketing manager in Eaton’s Critical Power Solutions Division in Raleigh, North Carolina. A 36-year veteran of the power-systems industry, Ed has experience in UPS-systems testing, sales, application engineering and training—as well as working in power-quality engineering and marketing for telecommunications, data centers, cable television and broadband public networks. Contact him at EdSpears@Eaton.com, or find more information at www.powerquality.eaton.com.