Controlled natural ventilation for commercial and industrial buildings.

The Dutch organization for applied scientific research TNO in Delft developed asystem of Controlled Natural Ventilation (CNV). It is produced by the Dutchventilation fm Brake1 in Uden. The system controls ventilation grills and windows.Its purpose is:to compensate for fluctuating buoyancy forces (wind and temperature) so thatnatural ventilation flows are kept on set point value, independent of weatherchanges and changes in internal heat production;to optimize the air flow distribution over the building to get the highest possibleventilation efficiency;to restrict ventilation openings when draught risks occur.The CNV system is based on a computer program that simulates ventilation. A specialinverse version is derived that calculates the optimal ventilation openings for a specificbuilding on each weather condition and for each ventilation set point.The program needs input on local wind effects on the building. They are predicted withanother new developed simulation tool, called the 'Cp-Generator'. This specialcomputer program for prediction of wind pressure coefficients (Cp's) is build in as amodule in the main program.Extra features of the CNV system are:rain protection without decrease in flow rate,improved noise reduction,collaboration with mechanical ventilation,anticipation on opening doors,building leakage compensation,adjustment of both flow rate and direction to varying pollution or heat sources,smoother temperature control,special control for smoke ventilation.