Industrial/Commercial Ventilation

Introduction

Industrial/commercial ventilation refers to the supply and exhaust of air from a room, building, or other area for the purposes of controlling airborne contaminants, heat relief, or removing dusts and other substances. The contaminants can include gases, vapors, dusts, cigarette smoke, or "stale" air. These substances may pose a fire or explosion hazard (flammable and combustible vapors), may create a health hazard (cigarette smoke or toxic fumes), or may prevent machinery from running properly (saw dust in a wood processing plant).

Industrial/commercial ventilation equipment includes fans, blowers, ducts, air cleaning devices, and hoods. Fans and blowers are "air pumps" which generate airflow by creating a pressure difference. Air handling units house a blower or fan, filters, and conditioning equipment in one self-contained unit. Air cleaning devices include electrostatic precipitators, fabric collectors, dry and wet dust collectors, centrifugal collectors, and various types of filters. Exhaust hoods provide the point of entry in local exhaust systems by capturing the contaminated air. Ducts provide the connection between the inlet, the fan/blower/air handling unit, and the exhaust.

There are two types of ventilation systems, general systems and local systems. General ventilation systems (also known as dilution ventilation systems) involve the "dilution" of contaminated air with uncontaminated air. These systems are most effective when the air contaminants are primarily gases or vapors, do not pose a high health risk, and are uniformly dispersed. A great deal of care needs to be taken in the design of general ventilation systems due to the fact that the inhabitants are still exposed to the contaminants. The level of exposure is controlled by the amount of dilution air.

Local ventilation systems control the contaminants directly at the source prior to their escape into the building. Local ventilation systems are effective in instances where there are a few, large fixed sources of contamination. Local systems may be the only option in certain circumstances such as when an emission source is directly in the breathing zone of the inhabitant(s).

This paper presents a review of the basic fluid mechanics principles which are used in designing a ventilation system. The relevant building and safety codes and practices which a designer must consider are also discussed. Finally, three case studies are presented. The first case study involves the design of an exhaust system for a wooden pallet manufacturing plant. This is a case where the primary function of the system is the efficient removal of sawdust from the equipment to prevent clogging. The second case is the design of a ventilation system for a flammable liquid storage facility. The third study involves the design of a ventilation system for a restaurant.

Basic Principles

In this section a brief review of some of the basic principles of ventilation will be presented. The topics include static, total and velocity pressure, conservation of energy, conservation of mass, capture velocity, transport velocity, static pressure losses, vapor generation, selection of a fan/blower, and system balancing.