Cooling solutions for high-density datacentres

Gautham Gnanajothi
Research Analyst at Frost & Sullivan
Visit website

Post date: Tuesday, 24th January 2012

Datacentre technology has arrived at a point of no return in recent times. The servers used in them have evolved and have reduced in physical size but have increased in performance levels.

The trouble with this fact is that it has considerably increased their power consumption and heat densities. Thus, the heat generated by the servers in datacentres is currently 10 times greater than the heat generated by them around 10 years back; as a result, the traditional computer room air conditioning (CRAC) systems have become overloaded. Hence, new strategies and innovative cooling solutions must be implemented to match the high-density equipment. The rack level power density increase has resulted in the rise of thermal management challenges over the past few years.

Some of the main datacentre challenges faced in the current scenario are adaptability, scalability, availability, life cycle costs, and maintenance. Flexibility and scalability are the two most important aspects any cooling solution must possess; this, combined with redundant cooling features, will deliver optimum performance. The two main datacentre cooling challenges are airflow challenge and space challenge. These challenges can be overcome with the use of innovative cooling solutions. Some of the cooling techniques used in datacentres are discussed below.

Aisle containment

Most datacentres have a standard hot aisle/cold aisle layout: the aisle containments are the refinements of these layouts. In these layouts each successive aisle is labeled either hot aisle or cold aisle. In the hot aisle, the banks of the server rack exhausts hot air. In a cold aisle, the server racks are aligned in such a way that the equipment inlets face each other in the opposite sides. There is usually a raised floor system known as the “plenum” under which the cool air from the CRAC or the computer room air handler (CRAH) flows to the perforated floor tiles. These floor tiles are located in the cold aisles and facilitate the cool air into the server inlets in front of the racks and exhaust via the hot aisle. By the hot aisle/cold aisle containment, the cool air can be directed closer to the server inlets, thereby increasing the latter’s energy efficiency.

High-density supplemental cooling

Data centre densities have increased from 2 to 3 kW per rack to an excess of 30 kW per rack. A different cooling approach needs to be implemented to meet the high-density requirements. This is when supplemental cooling comes into place. It uses two different approaches: “rear door heat exchangers” and “over head heat exchangers”. Rear door heat exchangers come to the rescue of the struggling CRAC by conditioning the hot air and returning it to the room at colder temperature. They require a chilled water source and a connection to a remote chiller unit. The over head heat exchangers, as the name suggests, are suspended above the server rows. They compliment the hot aisle/cold aisle containment by sucking the hot air from the hot aisle exhaust, condition it, and send cool air to the cold aisles. The supplemental cooling reduces the pressure off the CRAC unit.

Liquid cooling

As the name suggests, it brings the liquid (either chilled water or refrigirant) closer to the heat source for a more effective cooling. On contrary to a CRAC unit where it is isolated to a corner of the room, liquid cooling solutions are embedded in row of server racks or suspended from the ceiling or installed in a closed relationship with one or more server racks. There are two types of the liquid cooling – “in row liquid cooling” and “in rack liquid cooling”; both of them require chilled water (or refrigirant) and return piping. It is run either overhead or beneath the floor to each individual cooler.

Closed couple cooling

Another remedy for the high-density computing would be closed couple cooling where the distant air conditioner is moved closer to the computing load. The latest generation cooling products can be described by the term closed coupled cooling. Although their solutions vary in terms of configuration and capacity, their approach is the same. It brings the heat transfer closest to the source, which is the server rack. By doing so, the inlet air is delivered more precicely and the exhaust air is captured efficiently.

There are two configurations in which it operates – “closed loop” and “open loop”. In the open loop configuration, the air stream will tend to interact with the room environment to an extent. However, closed loop configuration is completely independent of the room in which it is installed. It creates a micro climate within the enclosure because the rack and the heat exchanger work exclusively with one another.

Energy and Environment