Ductless enclosures collectively refer to ductless fume hoods, chemical workstations, and enclosure cabinets. These standalone, self-contained enclosures, available in a wide array of sizes and configurations, use carbon and/or HEPA filters to remove fumes, vapors, and particulates from air drawn into the device that is then recirculated into the laboratory. For proper and effective use, filters must be discarded and replaced when they reach their chemical saturation point.
Ductless workstations are intended to provide a cost-saving alternative to conventional ducted enclosures that are attached directly to a building exhaust system. Because of their features, they are considered to have the advantage of being environmentally friendly or “green” as compared to the more traditional ducted enclosures.
The “green” advantage
Unlike conventional ducted enclosures, ductless workstations do not require ducting to the outside and do not carry the initial expense and coordination of ductwork installation. Ductless enclosures allow flexibility of placement, including hard-to-vent areas such as the center or bottom level of a several-story building. They are portable to allow sharing among several laboratories or can be stored when not in use, and, because they have no make-up air requirements, they can be used in air-starved laboratories.
Ductless enclosures are generally equipped with features such as safety controllers that monitor airflow and filter conditions, real-time gas sensor technology to ensure protection from exposure to toxic chemical fumes and vapors, visible and audible alarms to alert users of filter saturation, and airflow sensors.
Cabinet airflow and face velocity protect users from exposure to fumes and vapors. In contrast to ducted enclosures, in ductless enclosures, air is pulled through a series of carbon and/or HEPA filters. Chemical pollutants are removed and adsorbed onto the filters before the air is recirculated back into the room.
Ductless enclosures do not require exhaust ducts or make-up air systems, and do not emit chemical pollutants into the atmosphere. They produce lower carbon dioxide emissions, and thus have a lower carbon footprint than traditional ducted enclosures.
Cost savings are realized with ductless enclosures since there is no ductwork to be installed; operating costs are well below those of ducted systems. They also use less energy, since heated or cooled air is not exhausted from the laboratory.
Maintaining the “green” advantage
To maintain the “green” advantage, the appropriate enclosure must be selected for a specific application. In turn, the filter chosen must be suitable for the chemicals or particulates that need to be separated. It must also have the required filter capacity—defined as the percentage of the chemical mass adsorbed compared to the total carbon filter weight. Filter capacity is unique for each chemical and is dependent on the chemical affinity for carbon.
HEPA and bonded carbon filters
Several types of HEPA and bonded carbon filters are available. A HEPA filter is a disposable dry-type filter constructed of boron silicate microfibers cast into a thin sheet. The glass microfibers form a complex three-dimensional matrix that traps particulate matter but allows gases to pass through. HEPA filters are used to filter chemical powders and particulates.
Bonded carbon filters are either standard carbon filters or chemically impregnated carbon filters for increased load capacity. Standard carbon filters are used to chemically adsorb organic vapors, while impregnated carbon filters are used to neutralize acids and sulfur-containing compounds, ammonia/amine compounds, formaldehyde, and radioisotopes.
To maintain filtration efficiency, the ductless enclosure must be equipped with a monitor that measures the airflow and chemical saturation point of the filter so that it can be discarded when it reaches its chemical saturation point and then replaced. HEPA filters should be checked for leaks and periodically changed to maintain high filtration efficiency.
Ductless enclosures coupled with advanced carbon filtration technology offer a high-performance, “green” alternative to conventional ducted enclosures for a broad range of applications. Advantages include effective airflow containment, filtration of chemical pollutants, lower carbon footprint, and improved energy conservation. Depending on the application, there are many possible ductless enclosures to choose from. For more information, visit https://www.aircleansystems.com/.
Lina Genovesi, Ph.D., JD, is a technical, regulatory, and business writer based in Princeton, NJ, U.S.A.; e-mail: [email protected]; www.linagenovesi.com