What Does Ventilation Involve?
Also known as HVAC or mechanical ventilation, ventilation is the process of replacing indoor air with outdoor air in any space. The purpose of ventilation is to provide high indoor air quality. This includes controlling temperature, replenishing oxygen, as well as removing pollutants such as moisture, odours, smoke, heat, dust, airborne bacteria and carbon dioxide.
Effective ventilation systems remove unpleasant smells and excessive moisture, introduce outside air, keep air in the interior of the building circulating, and prevent stagnation and pollution of the interior air of the structure.
How is Effective Ventilation Accomplished?
Ventilation is a two-way process. It includes the exchange of air from the inside of the building to the outside and the circulation of air within the building itself. Methods for ventilating a building may be divided into types of ventilation including forced or mechanical, natural ventilation and combinations.
When architects are designing buildings, they pay close attention to using both mechanical and natural ventilation. When older buildings are being renovated, proper ventilation is an important factor in the reconstruction. Builders must adhere to regulations set by occupational health associations..
Why is Ventilation Important?
Indoor air quality has become an important health and safety concern. Ventilation concerns include:
- Improper or inadequately maintained HVAC and/or ventilation systems
- Air contamination of such construction materials as glues, fibreglass, particle boards, paints, and chemicals
- Other contaminants such as: dust, mould, fungi, bacteria, gases, vapours, and unpleasant or irritating odours
- Increases in the number of people occupying a workspace and the number of hours the workforce spends in the workspace
For more on the growing importance of indoor air quality, check out Indoor Air Quality: The Invisible Hazard in Every Workplace.
Ventilation is one of the most important ways of maintaining acceptable indoor air quality in buildings. When people or animals inhabit buildings, ventilated air is necessary to dilute odours, as well as limit the concentration of carbon dioxide and airborne pollutants. These potentially harmful substances include: dust, smoke, and “volatile organic compounds” (VOCs). These VOCs are organic compounds that easily become vapours or gases. VOCs contain elements of carbon, hydrogen, oxygen, fluorine, chlorine, bromine, sulfur and/or nitrogen.
Ventilated air is often delivered to the interior of a building by a mechanical system. If this is an HVAC system, it will also heat, cool, humidify and dehumidify the air in the building. Unhealthy air can enter a building due to uncontrolled or inadequate filtration of outside air.
Advanced air filtration and treatment processes including scrubbing, can clean and recirculate air inside a building.
Whether in commercial buildings or homes, effective ventilation protects the residents or employees, and visitors from unpleasant odours, pollutants, and dangerous gases like carbon monoxide.
If a ventilation system is well designed and in good working order, it prevents the growth of mould and mildew. These dangerous substances can cause or irritate allergic reactions and lung problems, such as asthma and COPD.
Individuals that do not work outside, spend about 90% of their time indoors. Ventilation systems are critical because indoor air pollution can pose a bigger health risk than outdoor air pollution. Good ventilation not only protects the people in the building. It also protects the building itself from damage. Effective ventilation systems work to eliminate excess moisture, which can rot window sills and attic eaves. Excess moisture also speeds up paint peeling, and is an open invitation to insect infestation. Damp insulation in walls and ceilings results in lost heat, higher heating bills, and mould growth. Carpeting, wallpaper, electronic equipment, and furniture can all be damaged by the presence of moisture in the building.
How Can Proper Ventilation be Assured?
"Mechanical" or "forced" ventilation controls indoor air quality in businesses and homes. Excess humidity, odours, and contaminants are controlled by the replacement of air inside the building with outside, or “fresh” air. This is particularly challenging in hot, humid areas, as large amounts of energy are needed to remove excess moisture from the air. Although ventilation increases the energy required to heat or cool a building, heat recovery ventilation can ease energy consumption. Heat is exchanged between air coming in and going out of the building. Energy recovery ventilation also exchanges humidity.
Mechanical exhaust systems in such areas as kitchens and bathrooms control odours and humidity. Kitchen ventilation systems must also manage smoke and grease.
Natural ventilation exchanges indoor air with outdoor air by way of non-mechanical systems like vents and operable windows. Natural ventilation can also occur through temperature and pressure differences from one space to another. Natural ventilation is not recommended for below-ground spaces like basements. The outside air will cause humidity and condensation issues. In more complex systems, warm air in the building can be allowed to rise and flow out of upper openings to the outside, forcing cool outside air to be drawn into the building naturally through openings in the lower areas. Natural ventilation uses little energy, however, high heat and low temperatures may make natural ventilation alone uncomfortable for the occupants.
Airside economizers act as natural ventilation, but these use fans, ducts, dampers, and control systems to distribute cool outdoor air if needed. Ceiling table and floor fans circulate air within a room, which reduces the temperature in an area where the fans are used, but does nothing to exchange indoor air with outdoor air. Some fan systems are effective in cooler temperatures at keeping a room warmer.
Hybrid, combined, mixed or supplementary systems make use of both mechanical and natural ventilation processes. Supplementary conventional air conditioning and heating systems may be required as backup in very high and very low temperature times during a day or season.
Infiltration, although not part of the ventilation system, is frequently used as a ventilation air source.
What Are Health and Safety Regulations?
Ventilation standards are stipulated for general industry, shipyard employment, long-shoring, and construction industry. The bottom line is: workers’ rights determine that the workplace is safe from air hazards due to poor ventilation. The law requires employers to provide the workforce with a safe, healthy work environment.
The ventilation rate, for CII buildings, is usually expressed by the volumetric flow rate of outside air coming into the building in cubic feet per minute (CFM) or litres per second (L/s). The ventilation rate may also be described per person or per unit floor area like: M/p or CFM/ft², or as air changes per hour(ACH).
Ventilation guidelines are based on the minimum ventilation rate required to maintain acceptable levels of bio effluents. Since it is the gas with the highest emission rate at a relatively constant level, carbon dioxide is used as a reference point. The constant value for carbon dioxide is 0.005 L/s.
ANSI/ASHRAE (Standard 62-89) has set a "comfort (odour) criteria are not to exceed 1,000 ppm CO2. OSHA has set a limit of 5000 ppm over 8 hours.