Exhaust vs. Filtration: Improving Air Quality for Process Cooling Applications
Controlling indoor air quality in a temperature-controlled environment can help process cooling equipment run more efficiently and improve worker comfort and safety.
Nearly every industrial process comes with its own indoor air quality (IAQ) challenges. Whether you are engaged in the production of food products, silica chips or chemicals and polymers, keeping workers safe from toxic, irritating or combustible dust and fumes is a necessary priority.
For some types of manufacturing, simply blowing contaminated air to the outside and pulling outdoor air in may be adequate. When you are engaged in processes that require strict indoor temperature control, however, an air filtration system usually is a better option. This article will look at what you need to know about controlling indoor air quality in a temperature-controlled environment.
Understanding Air Quality Options
No matter what kinds of processes you are using, IAQ mitigation options all fall into a few broad categories. You can think of these along a two-dimensional matrix:
- Filtration vs. exhaust.
- Source-capture systems vs. ambient.
Filtration vs. Exhaust. Filtration systems pull dirty air into a dust collector, where particulates are filtered out, before clean air is returned to the facility. Exhaust and makeup air systems push dirty air out of the facility and pull cleaner air in.
Filtration often is the better option for facilities with high volumes of particulates and temperature-controlled indoor environments. However, a minimal amount of exhaust and makeup air is important to maintain adequate oxygen levels and aid in correctly pressurizing different zones in a manufacturing environment. A skilled ventilation specialist will be able to guide you on the right combination of both.
Moving to air filtration can significantly reduce energy costs associated with heating or cooling makeup air for ventilation systems.
Source-Capture Systems vs. Ambient. Source-capture systems collect particulates close to the source — as they are generated — before they escape into the ambient air in the facility. Ambient systems turn over air for the entire facility. Ambient systems are sometimes used along with source-capture solutions for secondary air quality control.
Hidden Costs of Ventilation
Exhaust and makeup air systems are relatively inexpensive and easy to implement. However, they may not be the best fit for environments where indoor temperatures must be carefully controlled, or where process cooling equipment is in use.
If you were prone to leaving doors and windows open as a kid, you probably heard your parents say (perhaps many times), “Close the door already — I don’t want to air condition the great outdoors!” Homeowners know that running an air-conditioner or heater with the windows and doors wide open will quickly drive up energy costs. The same principle applies when using a ventilation system in an industrial environment.
Dust collectors that include integrated cooling can provide efficient spot cooling and reduce the pressure on process cooling and HVAC equipment in areas where temperature control is critical.
In an exhaust and makeup air system, air that has been heated or cooled to indoor temperatures by the HVAC system is vented to the outside. To maintain appropriate air pressure inside the facility, the air that is exhausted must be replaced by bringing outdoor air in. This air then must be heated or cooled to maintain appropriate indoor temperatures.
For shops engaged in light industrial operations and operating in mild climates, this may not be a big deal. For manufacturers engaged in processes where temperature control is critical, however, energy costs can quickly climb. For such manufacturers, using exhaust and makeup air systems may have disadvantages such as:
- Higher energy costs.
- More fluctuation in indoor temperatures.
- Additional stress on process cooling and comfort heating and cooling equipment.
- Environmental compliance issues (if exhausted air contains toxins).
- Decreased comfort for personnel.
An air filtration system keeps heated or cooled air in the facility while removing contaminants that are harmful to people or interfere with processes. This makes it easier to maintain a consistent indoor temperature, which in turn reduces stress on process cooling equipment. In fact, air filtration can reduce energy costs associated with running air quality systems by an average of 65 percent.
A traditional push-pull ambient filtration system creates air currents that pull dirty air into the dust collectors and push clean air back out to the facility.
Source Capture for Manufacturing Processes
Many options are available when it comes to choosing an air filtration system. The right solution depends on many factors, including manufacturing processes, facility layout and the toxicity of your dust or fumes.
If the manufacturing processes can be contained easily, source capture is always the most efficient air filtration option. The smaller the volume of air that must be captured and moved through the filters (measured in cubic feet per minute, or cfm), the less energy your equipment will use. Capturing fumes and dust close to the source also keeps toxic particulates from circulating throughout the facility, providing better protection for employees.
Some processes can be contained under a hood or in another form of enclosure. Hoods can be ducted to individual dust collectors or to a large centralized system that pulls air from multiple collection points. A centralized system can be placed inside on the factory floor or outside the facility (or even on the roof) to save floor space. These systems must be sized carefully and balanced by an air quality engineer to ensure that they provide effective capture from all collection points.
If processes cannot be fully enclosed, other options may be used to keep contaminated air from propagating through the facility. A combination of partitions or curtains and negative air pressure can be used to keep contaminated air contained near production processes.
Keep in mind that hoods and other types of enclosures may not protect people working inside the enclosed environment. Contaminated air will rise past the breathing zone of people working in the area before it is collected by the filtration equipment. If processes taking place inside the enclosure are entirely automated, this will not be a problem. But if employees need to enter the enclosed area for any reason, manufacturers should evaluate the exposure levels inside the enclosure and the toxicity of fumes and particulates and provide personal protective equipment (PPE) if necessary.
Computer modeling can identify how air current patterns impact air quality throughout the facility and help engineers optimize system performance.
Ambient Filtration Options for Manufacturing
For some manufacturing applications, source capture is simply not an option. If the fumes or particulates are widely dispersed through the facility, or particulate-producing processes cannot be easily enclosed, an ambient solution may be best.
When selecting an ambient air filtration system, manufacturers have three main options:
- Ducted push-pull systems.
- Ductless systems.
- Ductless ceiling-mounted systems.
Ducted push-pull systems rely on a system of ducts near the ceiling. The system creates air currents in the building that move air throughout the facility. This continually dilutes the contaminated air with filtered air, thus reducing the exposure to airborne particulates for personnel.
Ductless systems rely on standalone dust collectors that sit on the factory floor. Each dust collector creates its own circular local airflow pattern, pulling dirty air in and pushing clean air out. These are easier to install because they do not require overhead ductwork, but they do require some floor space.
A relatively new option is a ductless ceiling-mounted system. These systems combine the advantages of a ductless system with the floor space savings of a traditional push-pull system. They may work better in facilities where overhead cranes are used.
Finally, another option is to look for a system that combines cooling and air filtration. In these integrated systems, dust collectors provide both ambient air filtration and air conditioning in one unit. They can be used to augment HVAC equipment or to provide extra cooling in enclosed areas, reducing pressure on the process cooling equipment.
In conclusion, manufacturers using process cooling in their applications are already facing significant energy costs. An air quality solution should not put an additional burden on HVAC and process cooling systems or add unnecessarily to overall energy costs.
Moving from ventilation to air filtration may be the most important step manufacturers can take to control energy costs associated with air quality control. Enclosing or partitioning fume- and dust-producing processes to minimize the volume of airflow that must be treated will help reduce equipment and energy costs.
An experienced air quality system designer can help manufacturers further minimize costs through efficient system design and equipment selection. Sometimes, engineers use computer modeling to design the solution. Modeling helps companies avoid over- or under-engineering the air quality solution. With thoughtful system design, an air quality solution that keeps IAQ under control can be had without adding to energy worries.