Displacement flow air supply through a raised floor covered by carpet - possible mistakes by wrong design and installation

Large spaces with high thermal loads and high air flow rates air conditioned by displacement flowsometimes require air supply through the raised floor. One favoured solution is to cover the perforated floor by an air permeable carpet. Successful solutions of this type of air outlets exist in many buildings in Germany since many years and work successfully. But design and installation require some knowledge which partly may have been lost in recent years. In newer buildings many difficulties appeared. Typical mistakes were: No airtight plenum, leakages to other rooms, wrong perforation of the sheet metal, non performing fixation of the carpet to the floor, too low or too high pressure drop across the carpet.