12.4.1 Introduction

One of the methods used for the determination of airflow in large spaces is model experiments. This method is also useful in the study of local ventilation around a working area in the industrial environment.

Large ventilated air spaces—e. g., shopping arcades, industrial buildings, atria, and exhibition buildings—have for a decade been built in large num­bers. It is not possible to use full-scale experiments in the design of air distri­bution systems due to the large dimensions of such buildings. It is also difficult to use simplified design methods like those based on throws of jets and pene­tration depths of nonisothermal jets because of the complicated geometry present in many situations. Several sources that produce air movements, such as diffusers, pressure difference around buildings, cold downdraft, and ther­mal plumes, also make the use of simplified methods difficult. Computational fluid dynamics (see Section 11.2) and scale-moaei experiments are two possi­ble methods for the determination of mass transport, contaminant transport, and energy transport in large buildings.

The ventilation of a working area in an industrial environment is estab­lished by a combination of a general and a local ventilation system. The gen­eral ventilation ensures the air quality and comfort far away from the contaminants, whereas the local ventilation—often as exhaust hoods—ensures the contaminant transport close to the emission sources and protects the peo­ple working there. It is very important that the contaminant control system be efficient because it represents one of the first elements in a chain process that might bring the contaminant out into the room. A well-designed local ventila­tion system will reduce the energy consumption of the total system because it is an energy-saving method to remove the airborne pollution as close to the emission source as possible. A local ventilation system can be efficiently opti­mized by model or full-scale experiments.

Scale-model experiments have been used to study a variety of ventilation problems as air movement in a room, air movement around a building, energy flow in a building, contaminant distribution at an operator’s workplace, and smoke movement in a building on fire. The theory is discussed at a general level in the references.1-^