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The Raised Floor

Raised floor

Today, the raised floor is still an important element in many new data centers. But why? What is it for, what does it do? Below are a few thoughts on the subject of raised floors.

To loosely quote DIN EN 50600 (also see "Data centre standard DIN EN 50600 (VDE 0801-600) in brief"), the raised floor is a system consisting of completely removable and exchangeable floor grills fitted onto adjustable base frames, which are interconnected by beams. Its purpose is to make the space under the floor available for facility services.

Now as ever, precision air conditioning units (CRAC or CRAH) are still the first choice for air conditioning data centers, even now in the age of in-row cooling, rack cooling and air handling units. This article does not go into the reasons for this. Instead, it deals with the raised floor which, in conjunction with precision air conditioning units, ensures maximum reliability and efficiency.

In the past, the raised floor concealed "facility services" such as power cables, data cables and piping, and the cold air had to painstakingly find its way through these to the air outlets. A good deal has changed since then. It is now common knowledge that the primary aim of the raised floor is to convey cold air to the servers, and so wiring is mostly routed above the racks. In addition, these days the height of the raised floor is planned to ensure that the air in this supply air duct has sufficient space to reach its destination without major losses or resistance.

It is vital that a raised floor is leak-proof if it is to be used for air distribution. Care must be taken to ensure that the cold air only leaves the raised floor in the direction of the servers where planned and where most effective. Leaks in cable glands, beneath racks or at wall connections must be meticulously sealed. Raised floor grills that are removed for maintenance purposes are a hindrance to air distribution. This should be reduced to the necessary minimum.

The raised floor creates a path for the cold supply air from numerous precision air conditioning units, which blow the cold air into the raised floor, to the servers, which are in turn supplied with cold air by numerous openings in the raised floor. By regulating the pressure to ensure a stable, minimal overpressure in the raised floor, a supply of cold air from the raised floor in the data center is ensured everywhere and at all times, even if a precision air conditioning unit is switched off for maintenance purposes. Only this type of air conditioning can achieve this degree of reliability.

The openings in the raised floor, through which cold air is supplied to the servers in the racks, can be intelligently controlled to ensure maximum efficiency (also see "Improving efficiency through raised floor grills with controlled opening angle").

Controlled, adjustable air dampers vary their opening angle in line with the cooling needs of the server racks, which they are supplying with cold air. This way, the system only needs to circulate the amount of air that is actually required to dissipate the heat generated by the servers.


Now as ever, the raised floor has its raison d'être, and offers considerable advantages over other air conditioning systems when it comes to air distribution in the data center.

About the author

Benjamin Petschke was born in 1969 in Germany. After studying physics he joined STULZ in 1996 and worked since then in the R&D, Export and Marketing department on different positions. With 19+ years' experience in the Data Center cooling industry, Mr Petschke is specialised in Data Center cooling design, energy saving and acoustic issues.

He works closely with the Joint Research Centre of the European Commission for the Code of Conduct on Data Centres on the Best Practice section and recently with the German DKE in development of the DIN EN 50600, Information technology – Data Centre facilities and infrastructures.

Mr Petschke authored White Papers on subjects like Best Practice for Data Centre Cooling and Indirect Free Cooling with Dynamic Control Logic.