Cutting data centre power costs

Multitenant data centres (MTDCs) are growing in size, number and popularity. In this increasingly crowded market, MTDC providers are discovering they must focus relentlessly on a demanding set of requirements, including affordability, efficiency, sustainability, reliability and agility in their bid to attract and retain customers.

The problem is, in order to satisfy such steep requirements, many MTDCs operate in ways that can create severe energy-efficiency challenges. To preserve reliability, for example, it is common for data centres to use redundant uninterruptible power supplies (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. 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 those that are fully loaded.

Client equipment, particularly virtualisation and blade server technologies, can also present challenges. Though both radically increase a data centre’s compute density, they also generate enormous amounts of heat in smaller spaces. Dispersing that heat can be a difficult and expensive task.

When an MTDC is housed in an older building, it may rely on so-called ‘chaos’ air distribution methodologies 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 air towards the facility’s return air ducts. However, by allowing hot and cool air to mix and recirculate, chaos air distribution strategies decrease cooling efficiency and drive up electrical bills.

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

Maximising efficiency

To address these challenges, there are a number of options available. The latest generation of 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 of these devices also allow data centres 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 and continuous uptime when problems occur.

Multimode UPSs: Variable, modular UPSs function exclusively in double-conversion mode, while multimode UPSs support two operating modes. In normal operation, the UPS runs in a highly efficient energy-saver mode, but if power conditions fall outside predetermined tolerances, the device automatically and immediately switches 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 95% efficient, multimode UPSs are up to 99% efficient when running in energy-saver mode. As a result, they offer the ultimate combination of low operating costs and high reliability.

Some multimode UPSs also come with built-in harmonic reduction functionality. Harmonics are distortions in a data centre’s voltage or current waveform typically produced by non-linear loads, such as servers, variable frequency drives and fluorescent lights. If left unaddressed, harmonics can reduce energy efficiency and reliability while shortening the lifespan of expensive electrical equipment.

In the past, data centre operators concerned about harmonics had to devote precious floor space to specialised 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 models can mitigate harmonics, perform power factor correction and balance loads while in energy-saver mode too.

Air containment solutions

Cooling is a major driver of data centre energy costs, especially at facilities like MTDCs that are filled with dense, hot server racks. By deploying an air containment solution, 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 deliver chilled air directly to the server equipment’s air intakes.

Organising 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 cooling schemes must often chill return air to 12.78°C. Containment-based cooling systems, however, completely isolate return air, so they can safely deliver supply air at a much warmer 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 required by hot aisle/cold aisle arrangements.

Use economisers

Though most data centres continue to rely on them, CRACs 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 economisers. There are two basic kinds of economiser: water-side economisers take advantage of frigid outdoor temperatures to chill the fluid in a liquid cooling system’s closed cooling loop; air-side economisers pump hot server exhaust air out of the data centre and pump in naturally cool air from outdoors. Though they tend to be most effective when used in cold, northern latitudes, air-side economisers 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 economiser an MTDC uses must be based on variables such as location and whether or not it uses liquid cooling, but almost every MTDC can benefit from the ‘free cooling’ that economisers provide.

Make energy-efficiency a priority

Competing and winning in the market for MTDC services isn’t easy, but operators that make energy efficiency a priority can earn solid, consistent profits just the same. Utilising the latest-generation, high-efficiency UPSs, air containment solutions and economisers are a good starting point when looking to reduce wasted power and ease cooling loads while actually enhancing reliability and agility.

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