The Industrial Ventilation series of documents discusses the elements of the exhaust system. There are two types of mechanical ventilation systems used in industrial settings: General industrial ventilation reduces the concentration of the air contaminants, or controls the amount of heat that accumulates in hot industrial environments, by mixing diluting the contaminated air with fresh, clean, uncontaminated air.
When used to control chemical pollutants, dilution must be limited to only situations where: the amounts of pollutants generated are not very high, their toxicity is relatively moderate, workers do not carry out their tasks in the immediate vicinity of the source of contamination, and the emission rate of contaminants is relatively uniform.
Figure 1. Figure 2. Figure 3. Figure 4 Figures 1 to 4: Examples of recommended dilution ventilation layouts. Figure 5 Example of not recommended dilution ventilation layout. As a method for protecting workers, it is important to know that dilution ventilation: Does not completely remove contaminants.
Cannot be used for highly toxic chemicals. Is not effective for dusts or metal fumes or large amounts of gases or vapours. Requires large amounts of makeup air to be heated or cooled. Is not effective for handling surges of gases or vapours or irregular emissions. This type of system is usually the preferred control method if: Air contaminants pose serious health risk. Large amounts of dusts or fumes are generated.
Increased heating costs from ventilation in cold weather are a concern. Emission sources are few in number. Emission sources are near the workers' breathing zones. A local exhaust system has five basic elements see Figure 6 : The "hood" or opening that captures the contaminant at the source. Ducts that transport the airborne chemicals through the system exhaust air and the air that is recirculated. An air cleaning device that removes the contaminant from the moving air in the system not always required.
Fans that move the air through the system and discharges the exhaust air outdoors. An exhaust stack through which the contaminated air is discharged. Does not completely remove contaminants.
Captures contaminant at source and removes it from the workplace. Higher cost for design, installation and equipment. Requires less maintenance. The only choice for highly toxic airborne chemicals. Requires regular cleaning, inspection and maintenance. Effective control for small amounts of low toxicity chemicals. Ineffective for dusts or metal fumes or large amounts of gases or vapours. Can handle many types of contaminants including dusts and metal fumes.
Effective control for flammable or combustible gases or vapours. Requires large amounts of heated or cooled makeup air. Requires smaller amount of makeup air since smaller amounts of air are being exhausted. Best ventilation for mobile or dispersed contaminant sources.
Each fan has its own unique properties and application, so it is important to place them in the correct space. In addition, selecting a fan with the proper CFM Cubic Feet per Minute is crucial to ensuring the fan operates as intended. A CFM that is too low will not be able to provide you with pristine air because it cannot move the air through the space efficiently.
If you have already pursued our inventory, please request a quote today. Otherwise, please contact our sales team with any questions you may have about our vast selection of intake air fans. Order Online or Call: Ventilation Fans As the name implies, ventilation fans are used to ventilate a residential or commercial space. Exhaust Fans When pollutants and contaminants enter the air, exhaust fans remove them in order to provide clean air.
Differences Between These Fans Both ventilation fans and exhaust fans work to create the freshest, cleanest air possible in the space they are installed. One concern with exhaust ventilation systems is that they may draw pollutants, along with fresh air, into the house.
For example, in addition to drawing in fresh outdoor air, they may draw in the following:. This can especially be of concern when bath fans, range fans, and clothes dryers which also depressurize the home while they operate are run when an exhaust ventilation system is also operating. Exhaust ventilation systems can also contribute to higher heating and cooling costs compared with energy recovery ventilation systems because exhaust systems do not temper or remove moisture from the make-up air before it enters the house.
Information courtesy of the EERE. Supply ventilation systems work by pressurizing the building. They use a fan to force outside air into the building while air leaks out of the building through holes in the shell, bath- and range-fan ducts, and intentional vents. As with exhaust ventilation systems, supply ventilation systems are relatively simple and inexpensive to install. A typical system has a fan and duct system that introduces fresh air into usually one—but preferably several—rooms that residents occupy most for example, bedrooms, living room, kitchen.
This system may include adjustable window or wall vents in other rooms. Supply ventilation systems allow better control of the air that enters the house than do exhaust ventilation systems. By pressurizing the house, these systems discourage the entry of pollutants from outside and prevent backdrafting of combustion gases from fireplaces and appliances.
They also allow air introduced into the house to be filtered to remove pollen and dust or to be dehumidified. Supply ventilation systems work best in hot or mixed climates. Because they pressurize the house, they have the potential to cause moisture problems in cold climates.
In winter, the supply ventilation system causes warm interior air to leak through random openings in the exterior wall and ceiling. If the interior air is humid enough, some moisture may condense in the attic or parts of the exterior wall, where it can promote mold, mildew, and decay.
Like exhaust ventilation systems, supply ventilation systems do not temper or remove moisture from the air before it enters the house. Thus, they may contribute to higher heating and cooling costs compared with energy recovery ventilation systems.
Because air is introduced in the house at discrete locations, outdoor air may need to be mixed with indoor air before delivery to avoid cold air drafts in winter.
An in-line duct heater is another option, but it will increase operating costs. Balanced ventilation systems, if properly designed and installed, neither pressurize nor depressurize a house. Rather, they introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air, respectively.
A balanced ventilation system usually has two fans and two duct systems. It facilitates good distribution of fresh air by placing supply and exhaust vents in appropriate places.
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