Raising The Lid On Computer Room Floors

When it comes to installing uninterruptible power supplies within a server room or data centre white space, there are two choices. The first is to install the UPS within the server cabinets as a rack mount device and the second is to install the uninterruptible power supply as a stand-alone system.

Where the UPS system is to be a stand alone unit, the installation plan should consider the raised access floor design in terms of system and point loadings (weight), the use of spreader plates or plinths, installation ease and access for maintenance.

There are two types of raised access floor. The most commonly used in an IT environment is one based on the use of floor tiles and pedestal heads. The tiles are held in place by their weight and lateral location and sit on four pedestal heads, each of which is secured to the floor. A lock down/screw down raised floor is a second alternative but less common in a computer or datacentre environment where ease of access and reconfiguration is important.

Floor tiles vary not just in size but thickness, finish and weight (dependent on whether the tiles are to be used in computer rooms or general public access areas). The floor tiles themselves are graded from Extra Heavy grade to Heavy, Medium and Light grade dependent upon the Concentrated loads and Uniformly Distributed loads they are designed to support. Loads are measured in kN (Concentrated loads) and N/m2 (Uniformly Distributed loads). The general construction is a mixture of a high-density particle board encased in galvanized steel with a vinyl (anti-static or static conductive) or other finish; for non-computer room environments these can include: linoleum, rubber, carpet, wood, marble, stone. The tile construction, as well as providing a solid support structure, should also provide good fire suppression and acoustic performance.

A typical server room floor tile measures 500×500mm, sat on pedestals that are themselves secured to a sub-floor and designed to meet a required floor height (typically range from 70-1200mm). The space between the sub-floor and raised floor is referred to a void or plenum. Above 600mm, stringers are generally used to provide additional lateral support and stability. Stringers are 30mm deep and their usage reduces the void/plenum space available.

When planning a raised access floor it is important to consider the sub-floor and overall environment. The room itself should be dry and watertight, with temperatures above 5 degrees Centigrade and with a relative humidity below 75%. The sub-floor must be capable of accepting pedestal fittings (mechanical or adhesive or both) and should be flat and sealed (no holes or joint lines) in order to prevent floor sealer leakage to the ceiling level below. The sub-floor must be strong enough to support the raised access floor and overall room capacity (infrastructure, systems, people and so forth). The overall design and installation of a raised access floor must also comply with the BSI standard BS EN 12825 and the National Building Specification K41.

A raised access floor provides several benefits. Under the floor the void or plenum provides a ‘hidden’ space through which to route room infrastructure including cabling and pipework: electrical power cables, data and telecoms cables, security, environmental control and air conditioning (HVAC), water and where necessary drainage. The void makes room layout management easier and provides easy access for socket connections, maintenance and cable routing. The tiles can be lifted using a lifter/puller with lockable suction cups. The floor tiling system allows new systems to be installed fairly easily or moved in the room.

The raised access floor void can also be used as an air plenum for heating, cooling and general ventilation. In a server room or datacentre such usage is almost always for cooling as part of the air-conditioned output flow. Where a raised access floor plenum is used for cooling, its design must include certain specifications including air pressure differentials and consider leakage control at panel joints. Both are factors of the overall design, quality of installation, floor tile construction and pressure rating (high, 25-30pa or low, 7-15pa) of the HVAC system installted. In high-pressure air conditioning environments, neoprene or similar type gaskets may be fitted to tile edges to form a tighter seal. Airflow into the room itself is managed via the strategic placement of vented floor tiles. The use of easy to lift floor tiles also allows for ease of maintenance of the floor tiles themselves which can be replaced if damaged. The floor panels themselves should have a minimum life of 25 years with the supporting components a lifetime of 50 years.

In terms of raised access floors, an uninterruptible power system and its battery cabinet can be considered a static load. Once installed it will only ever be moved for replacement or refurbishment. Some thought has to be given to the initial installation in terms of logistics, as the UPS system will need to be placed (lifted) onto the floor. A specialist logistics company should be able to provide this as an additional service using at least a two-man team and suitable lifting gear.

For new datacentre facilities, the size and weight of a UPS system will generally be considered as part of the overall design. For existing computer room installations, this may not be the case. Examples can include server rooms that were reliant on multiple UPS installed within server racks, opting to move to a centralised uninterruptible power supply to protect the entire room. Here the size and weight of the UPS system has to be considered against the floor loading of the raised access floor. Will the floor be able to support the weight of the UPS which could be up to several hundred kilograms and in a concentrated area?

The UPS system may have feet or casters each of which concentrate the weight of the system into a set of point loadings (measured in Kg/m2). A suitably sized spreader plate can be used to distribute the weight of the uninterruptible power supply over a wider area and number of floor tiles and pedestals. If this is not an option a metal plinth may provide another solution and more appropriate for heavier weights. The plinth is designed to sit on the sub-floor within the space of a certain number of floor tiles and provide a base to sit the UPS onto. Air leakage can be an issue here if as it is almost impossible to seal the join between the plinth and the floor tiles. Worst case is to install the UPS onto the sub-floor but again this poses problems. The system has to be lowered into position using suitable lifting gear and the space available may not provide suitable access for maintenance.

If you are considering installing a UPS system onto a raised access floor, it is always better to check on the floor loading capability with a building structural engineer. They should be able to make a calculated assessment based on the point loading of the uninterruptible power supply and the grade of floor tile and pedestal installation.

For more information on raised access floors or other aspects of a datacentre UPS installation please contact the Eco Power projects team on 0800 612 7388.

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