Ventilation systems in buildings are generally designed to move out (exhaust) and bring in (intake) a specific amount of air at a particular speed (velocity), which results in the removal of undesirable contaminants from a space. The system may also be used to control temperature, humidity and odors, as well as protect equipment and personnel from fire, explosion and hazardous/flammable gases or vapors. The field of ventilation engineering is sometimes abbreviated to HVAC or HACR.
Ventilation is one of the most important engineering professional ventilation systems techniques for controlling indoor environment conditions. The selection, design and installation of ventilation systems is a complex process that should involve professionals familiar with comfort or hazard control. Incorrect ventilation design can result in the “sick building syndrome” or, in industrial applications, can have deadly consequences.
The primary ventilation system requirements are specified in the ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality and its published addenda, which are incorporated into many state codes and regulations. State and local building codes may also specify minimum energy efficiency requirements, air conditioning and ventilation controls, duct insulation and sealing, and system sizing.
Workplace investigations of ventilation system problems are often initiated by worker complaints, the discovery of flammable or toxic gases or vapors, or complaints about poor indoor air quality. The investigation usually includes a review of the ventilation system’s design and construction, as well as the physical condition and operating characteristics of the ductwork and hoods.
Most ventilation system problems are the result of either inadequate or excessive fan capacity, improper design, or incorrect operation and maintenance. The occurrence of these problems can be reduced or prevented by following the basic design guidelines described below and by keeping a systematic record of inspections and testing.
Ensure that duct dimensions, lengths and heights are correct and clearly shown on the duct plans, drawings and specifications. Hood and duct dimensions can be measured with a tape measure or, if the duct is constructed of 2 1/2 or 4-foot sections, counted (elbows and tees should be included in the measurement). Hood-face velocities outside the hood and at the hood face can be estimated by using velometers, smoke tubes or swinging vane anemometers.
The ducts, fans and other components of a ventilation system should be easy to access for cleaning, maintenance and repairs. Ideally, all components should be located within a well-lit area that is easily accessible to workers who will be performing the maintenance or repairs. Whenever possible, rooftop equipment should not require the use of a ladder or the removal of ceiling tiles.
Proper labeling of HVAC system components is an inexpensive but effective way to facilitate their operation and maintenance. Labels should be readily visible, permanent and durable. They should clearly identify the function of each component, e.g., the air handling unit (AHU), controls, exhaust fans and other components, and should match the descriptions in the HVAC drawings or specifications. Labels should be placed where they can be read when a worker is standing beside the equipment, and they should be located on a surface that is not subject to corrosion or damage.