European Raised Flooring Systems now fall into two main Specification Categories. Those being PSA MOB PF2 PS/SPU and the New European Standard EN 12825:2001. The MOB Standard was set up by the Public Services Agency and was compiled in 1992 and became the definitive Raised Flooring Standard. The EN 12825 standard was designed to allow all European manufacturers to be able to classify their systems under one standard whatever the performance of their Products.

Zinc whiskers are tiny crystalline structures of zinc that have been found to sometimes grow on the surface of electroplated steel. Electroplating is a commonly used method of galvanizing steel and has been used on a variety of steel products now present in data centers and other computer controlled environments. In recent years, whiskers have been found growing on electroplated components of computer hardware, cabinets and racks; as well as on some galvanized-pan access floor panels.

The finished floor height (FFH) is defined as "The nominal vertical dimension from the specified sub floor level to the specified finished floor level".

The popularity of UFAD is understandable. Using the space under the raised access floor as a pressurized plenum rather than relying on overhead or underfloor ductwork is attractive because of the potentials for lower first costs, easier coordination between HVAC and other systems, and minimized labor to modify supply Air Distribution when changes are made to the occupied space.

However, UFAD systems with pressurized plenums have not performed as expected in recently completed buildings. Lessons learned from the review process illustrate plenum air leakage is an architectural design and general construction issue. It is a mechanical engineering concern to the extent that the capacity of the air-handling unit must be adequately sized to compensate for the leakage at design load, and controls must be designed to compensate for the air leakage at partial loads. Category 1 and 2 plenum air leakage tests at design static pressures conducted in six federal buildings and courthouses have ranged from 30 to 200 percent of the design airflow rates. Some of the consequences of such air leakage include complaints of being cold around the feet and legs from Category 2 air leakage during partial-load conditions, or when the thermostatic setpoint was satisfied; energy wasted because AHUs were required to run at higher-than-expected airflow rates, static pressures and longer periods to compensate for Category 1 and 2 air leakage; operations and maintenance difficulties in accessing equipment in the plenums; the need to reseal Category 1 leakage pathways because of changes in electrical, communications and plumbing penetrations; and IAQ issues and housekeeping difficulties caused by accumulation of inert and biological matter and pest infestation in the raised- floor plenum.

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