Whatever is happening in the world of data centre cooling?

Floor space, higher density air-conditioning and better power efficiency are all challenges that need urgent attention in data centres. Space saving is achieved primarily through virtualisation and the installation of a new architectural infrastructure, consisting of high-density blade servers, high-density rack mount servers, high-density storage arrays and bladed network equipment.

Gartner predicts that more than 50% of data centres will incorporate high-density zones in their data centres by 2015. While most of these newer devices are designed with space saving and power efficiency in mind by virtue of their compact design, they generate more heat as a result, so much so that traditional cooling methods simply cannot cope.

Furthermore, business continuity and IT governance regulations (HA and DR) meant that business-critical system components inside data centres have been doubled. While this is intended to eliminate single points of failure to better guarantee system availability, more equipment simply means more cooling capacity is needed, which means that still more space and electricity is needed.

Additionally, the recent 32% hike in electricity price means data centres can simply no longer afford not to achieve maximum efficiency.

Traditional CRAC (computer room air-conditioners) or CRAH (computer room air handlers) are either perimeter-based or centralised units that use raised floors and plenums for cold air distribution to the equipment through vents or perforated floor tiles.

With CRAC/CRAH at best 3kW cooling per rack is achievable. For higher densities CRAC/CRAH units prove increasingly inefficient, as the biggest disadvantage lies in the sheer volumes of air that need to be cooled and the distance that air must travel, and the considerable fan-power required to reach all corners of the data centre in an effort to prevent hot-spots.

The latest data centre designs see air-conditioning units placed overhead or in rows among the rack enclosures. In-row cooling provides much higher cold air densities to deal with the heat loads that are generated by fully-populated racks - up to 15kW cooling per rack.

In-row cooling devices can meet these phenomenal cooling demands purely because the distance between the cooling devices and the computer equipment has been reduced.

Further control is provided by variable fan speed and automated chilled water flow regulation, all of which improves cooling potential.

In-row coolers can also be referred to as close-coupled cooling units and an added element of efficiency comes in the quicker capture of hot air close to the outlet at its source, thereby improving the net cooling footprint.

By delivering cold air close to the origin of heat generation, less fan power is needed to move cold air to the equipment, which also means the requirement for a pressurised plenum with a traditional air-conditioner is eliminated, and the set point can be higher.

The latest recommended approach in data centre deployment is to arrange cabinets into hot aisle and cold aisle configurations.

Racks are no longer placed front to back, but rather arranged back-to-back and front-to-front, and through aligning cabinets into hot aisle and cold aisle configurations, hot and cold air kept separate, to enhance cooling efficiency.

Aisle containment is an ergonomic way to further maximise cooling efficiency that uses barriers between hot and cold air to maximise air flow dynamics. Set-points can be higher in contained environments, because cold aisle containment focuses on cooling the IT equipment and not the rest of the room.

For ultimate efficiency, hot air must not be permitted to escape from the rack or pod. Solid doors force the air to be recycled and returned immediately into the air-conditioning unit to focus on cooling the load and not the room.

The features of in-row cooling mean better air-conditioning efficiency, which in turn means better energy efficiency and ultimately higher overall data centre efficiency.

What needs to be considered in order to overcome the current limitations of current data centre cooling systems is that the choice of technology will depend on a host of factors, unique and specific to each data centre.

MERIT TS supports both hot aisle and cold aisle containment and advises open-mindedness and flexibility when looking at the future needs of a data centre. For now, conventional CRAC/CRAH units could be complemented by in-row cooling units, which could, in turn, contribute to the ease with which containment is made possible. But the only way to efficiently and effectively provide for future computing requirements will be to build high-density areas either within a current data centre set-up or in a completely new environment.

MERIT TS has been designing data centres for more than 10 years. Please contact the company with your questions. info@meritts.co.za