Fueled in part by the rise of cloud computing, multi-tenant data centers (MTDCs) are quickly growing in size, number, and popularity. Indeed, analyst firm 451 Research expects North American MTDC revenues to climb at a compound annual growth rate (CAGR) of 15.42% through 2015.

To succeed in an increasingly crowded market, MTDC providers must focus relentlessly on a demanding set of requirements, including:

  • Affordability. Though price isn’t the only variable businesses consider when evaluating third-party data centers, it’s one of the most important. MTDC operators must always offer competitive rates.
  • Efficiency. MTDC vendors that wish to earn decent margins despite those low rates must capitalize on every opportunity to conserve energy and floor space.
  • Sustainability. Profitability isn’t the only reason energy efficiency must be a top priority at MTDCs. Some 50% of Global 500 companies currently have written sustainability plans that require them to procure goods and services from environmentally responsible suppliers, and that figure continues to climb.
  • Reliability. To meet the terms of their stringent service-level agreements (SLAs), MTDCs must deliver near-continuous uptime.
  • Agility. Fast-growing businesses prefer MTDCs with the flexibility to deploy, modify, and scale applications rapidly.

To satisfy such steep requirements, MTDCs operate in ways that can create severe energy efficiency challenges. Read on to find out how MTDC operators should navigate these and other efficiency obstacles.


To preserve reliability, many MTDCs utilize redundant uninterruptable power supply (UPS) and/or 2N architectures in which multiple units operate at partial loads, so that if one device fails or requires maintenance the others can quickly compensate. While such deployment schemes guard against downtime, they also lower energy efficiency, because lightly-loaded UPSs waste more power and produce proportionally more heat than fully-loaded ones.

The solution: Use energy-efficient UPSs. A new generation of sophisticated UPSs can help MTDCs increase efficiency without compromising reliability. Such devices come in two basic types:

•Variable, modular UPSs. Many double-conversion UPSs now contain multiple power modules. The most advanced such devices also allow data centers to load those modules variably. 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 and continuous uptime when problems occur.•

Multi-mode UPSs. Variable, modular UPSs function exclusively in double-conversion mode. Multi-mode UPSs, however, support two operating modes. In normal operation, the UPS runs in a highly-efficient energy saver mode, but if power conditions fall outside pre-determined tolerances, the device automatically and immediately transitions to double-conversion mode. When power quality returns to acceptable levels, the UPS automatically transitions back into energy saver mode.

Though the newest double-conversion UPSs are often over 93% efficient, multi-mode UPSs are up to 99% efficient when running in energy saver mode. As a result, they offer MTDC vendors the ultimate combination of low operating costs and high reliability. Some multi-mode UPSs also come with built-in harmonic reduction functionality, which can help mitigate distortions in a data center’s voltage or current waveform. If left unaddressed, harmonics can reduce energy efficiency and reliability while shortening the lifespan of expensive electrical equipment.

In the past, data center operators concerned about harmonics had to devote precious floor space to specialized mitigation technologies. Today, however, they have the option of using multi-mode 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 models can mitigate harmonics, perform power factor correction, and balance loads while in energy saver mode too.


The clients most MTDC vendors support make extensive use of virtualization and blade servers. Though both technologies radically increase a data center’s compute density, they also generate enormous amounts of heat in smaller spaces. Dispersing and removing that heat can be a difficult and expensive task.

The solution: Utilize economizers. Though most data centers continue to rely on them, computer room air conditioning (CRAC) units take up valuable floor space, are costly to maintain, and are a significant source of energy waste. As a result, MTDC owners are increasingly deploying smaller CRACs, eliminating them altogether, or using them only as backups for more energy-efficient cooling technologies such as economizers.

There are two basic kinds of economizer:

  • Waterside economizers take advantage of frigid outdoor temperatures to chill the fluid in a liquid cooling system’s closed cooling loop.
  • Airside economizers pump hot server exhaust air 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, airside 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 must be based on variables like where it’s located and whether or not it uses liquid cooling, but almost every MTDC will benefit from the “free cooling” that economizers provide.


MTDCs housed in older buildings often rely on so-called “chaos” air distribution methodologies to keep temperatures within acceptable limits. In such chaos cooling schemes, CRACs 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 air towards the facility’s return air ducts. However, by allowing hot and cool air to mix and re-circulate, chaos air distribution strategies decrease cooling efficiency and drive up electrical bills.

In more effective versions of chaos air distribution, data centers position server racks so that only hot air exhausts or cool air intakes face each other in a given row. Such “hot aisle/cold aisle” arrangements allow convection currents to produce a continuous airflow that improves data hall efficiencies but still leaves data center operators with significant cooling burdens to offset.

The solution: Implement an air containment solution. Cooling is a major driver of data center energy costs, especially at facilities like MTDCs filled with dense, hot server racks. By deploying an air containment solution, however, MTDC operators can lower their cooling costs by some 30% or more.

Containment solutions enclose server racks in sealed structures that capture hot exhaust air, vent it to a CRAC or other cooling system and then deliver chilled air directly to the server equipment’s air intakes.

Organizing and controlling airstreams in this manner dramatically increases cooling efficiency. For example, to compensate for the effects of re-circulated exhaust air, hot aisle/cold aisle cooling schemes must often chill return air to 55ºF/12.78ºC. Containment-based cooling systems completely isolate return air, however, they can safely deliver supply air at a much warmer 65ºF/18.34ºC, 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 required by hot aisle/cold aisle arrangements.


Competing and winning in the market for MTDC services isn’t easy, but MTDC operators that make energy efficiency a constant priority can earn solid, consistent profits just the same. Utilizing new, more efficient UPSs, management software, air containment solutions, and economizers can help MTDC owners reduce wasted power and ease cooling loads while actually enhancing reliability and agility. MTDC vendors that wish to position themselves for long-term success should therefore work with their power system and cooling providers to investigate the suitability of the efficiency best practices described here for their environment.