What is the ideal temperature inside a data centre?
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends that server inlet temperatures be between 18 and 27 degrees Celsius (64.4 to 80.6 degrees Fahrenheit), with relative humidity anywhere between 20 and 80 percent. The Uptime Institute, however, recommends an upper limit of 25 degrees C (77 degrees F).
But, many data centres - especially older ones - keep everything much colder than that to be on the safe side and definitively avoid overheating equipment. Don't be surprised if you see some data centre staff wearing heavy jackets inside at all times! This is why many data centres require so much electricity - as much as 40 percent of all energy used in some data centres goes just to cooling, according to some research.
Data Centre Cooling Arrangements
Data centres need a way to keep servers from overheating. In a very basic facility, a fan or standard air conditioning unit can be employed. But, more often than not, a data centre will have a much more reliable and effective cooling arrangement in place. According to APC, there are 13 common ways to remove excess heat in these kinds of IT facilities.
Source: "The Different Technologies for Cooling Data Centres" by Tony Evans
What does the most traditional data centre cooling arrangement look like? According to The Uptime Institute, "Cold air from a computer room air conditioner (CRAC) or computer room air handler (CRAH) pressurized the space below the raised floor. Perforated tiles provided a means for the cold air to leave the plenum and enter the main space—ideally in front of server intakes. After passing through the server, the heated air returned to the CRAC/CRAH to be cooled, usually after mixing with the cold air. Very often, the CRAC unit’s return temperature was the set point used to control the cooling system’s operation."
Hot Aisle Containment
Over the past decade or so, hot aisle containment has become increasingly popular, as a way to more cost-effectively and efficiently cool servers. Under such an arrangement, heat escapes through a dedicated system, whilst cold air is channelled specifically where it needs to be. This way, only part of a server closet is kept cool - and not all of the data centre. Cold aisle containment works in a similar fashion, except cool air is kept just where it's needed in dedicated channels between the hottest components within server rooms.
Another increasingly common method is evaporative cooling, which uses water to selectively remove heat from the environment. According to GCN, in a so-called adiabatic system, “ambient air is passed through a wet filter that cools it. The air then enters the cooling system at a lower temperature, which allows for more efficient operation."
In an open-air cooling system, temperature and humidity inside the facility remain as consistent as possible with the outside environment, so that less energy is required to cool equipment. These kinds of systems only work in certain locations though, like near the Arctic Circle, in a cave or in a pod at the bottom of the ocean.
Some data centres are taking a closer look at direct liquid cooling. Under such an arrangement, some or all IT equipment rests in a pool of liquid (not water). The benefit here is that the liquid naturally cools the infrastructure, removing the reliance on a HVAC system for cooling. It's not yet a common arrangement, but it's poised to be one of the biggest data centre cooling trends in 2019 and beyond.