Book - School of Science and Technology

Chapter 13VentilationThe act or art of ventilating is, according to the Oxford Dictionary, to `expose to fresh air'and to `cause air to circulate freely in an enclosed space' (L. ventilatio). As nowunderstood,the purpose may be either to supply the untainted air necessary for human existenceor to provide for dispersal of smells, noxious gases and dangerous concentrations of fumesand smoke. It has become practice to avoid the use of the definition fresh air, withits connotation of purity, and to refer instead to outside air leaving open the possibilitythat pre-treatment may be necessary.The need for a supply of outside air as a contribution to human comfort, the parallelrequirement for the removal of contaminants and some of the limiting considerationshave been touched upon in the first chapter of this book. The subject matter which followsis concerned primarily therefore with quantification of both need and requirement followedby consideration of some of the methods used to meet them.As mentioned in Chapter 3, for the first time the 2002 edition of Part L of the BuildingRegulations impose requirements on air conditioning and mechanical ventilation systems,in that if they are installed, they should be `reasonably efficient'.Clearly the most efficient approach to ventilation is by natural means. In BRE Digest399 Natural Ventilation of Non-domestic Buildings, natural ventilation is defined asventilation driven by the natural forces of wind and temperature. It is intentional and,ideally, controlled. It should not be confused with infiltration, which is unintentional anduncontrolled entry of outdoor air through cracks and gaps in the external fabric of thebuilding. This aspect is covered in Chapter 2 of this book.Natural ventilation may, in certain circumstances, provide tolerable comfort conditionsin the climate of the British Isles for office and other buildings provided that:. There will be, in the vicinity of the site, no excessive atmospheric or noise pollutionwhich will require the building to be sealed.. The purpose of the building is such that there will be no activities or processes whichrequire close control of the internal temperature or humidity.. The design of the building is such that excessive solar gains will not occur.. There will be no excessive heat gains arising from office machinery, etc.Considerable work has been under taken in to past few years to understand thecomplexities and variability of natural ventilation solutions mainly as a result of increasedconcern over the adverse environmental impact of energy use. This has encouraged thedesign and construction of energy efficient buildings, many of which are suited to naturalventilation because of the holistic approach in the design of the building fabric, the