PRINCIPLES OF AIR AND CONTAMINANT MOVEMENT INSIDE AND AROUND BUILDINGS

7.1 INTRODUCTION

Proper selection and sizing of ventilation systems require knowledge of emissions from internal contaminant and heat sources and an under­standing of the mechanisms and characteristics of air and contaminant movement.

Major factors affecting air and contaminant movement inside ventilated space are summarized in Section 7.3 and can be classified as

• Sources of heat and contaminants (Section 7.2);

• Air currents produced by process equipment and moving people (Section 7.3);

• Forced convection or supply air jets introduced into the room by mechanical or natural ventilation systems, or their combination (Section 7.4);

• Free convection flows along heated and cooled vertical surfaces and above heat sources, covered in Section 7.5;

• Airflow created in the vicinity of local and general exhausts (Section 7.6);

• Airflow through intended and unintended openings and cracks in the building envelope (Section 7.8.2), and aerodynamic means of the large opening protection, described in Section 7.7;

• Airflow around the building under the influence of natural winds (Section 7.8.1); and

• Airflow between different building zones caused by pressure and temperature differences, or turbulent exchange, addressed in Section 7.8.5.

In some cases, the ventilation process in the room can be simplified and mechanisms of air and contaminant movement under the influence of each of the above factors can be described using simplified theoretical principles of fluid mechanics, empirical data, and observations from numerous research studies. In general, the ventilation process in a room is complex and different factors have a joint effect on airflow patterns and characteristics, in continued spaces and in industrial buildings particularly.

Though there are no ready recipes available, this chapter provides some guidance on

• How to select predominant factors affecting air and contaminant movement in ventilated spaces,

• How to account for their joint effects, and

• How to predict the airflow characteristics with an accuracy acceptable in ventilation design.

Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK