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Air treatment

The ventilation system of a premises may be significant, in terms of the possibility of airborne contagion. The mechanical ventilation systems currently in use can be roughly divided into two parts: the ventilation machinery, and the ventilation ducts. At the same time, the cleanliness of a ventilation system can be divided into two parts: dirtying that occurs during installation, and dirtying that occurs during when the system is
operational.

When one considers the microbiological cleanliness of ventilation systems, the proper use of the system is important, as is the structure, materials and cleanliness of the system’s components and ducts. Also important are the cleanability and serviceability of the system. Ventilation systems have components, such as the terminal devices, in which the amount of airborne microbes can be reduced through the use of antimicrobial material.

Also a movable air purifier could be used. An air purifier is a device, which removes contaminants from the air. Devices are especially beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke. Air purifiers are manufactured as either small stand-alone units or larger units that can be affixed to an HVAC unit found in the medical, industrial, and commercial industries. Air purifiers are also be used in industry to remove impurities such as CO2 from air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.

Several different techniques of varying effectiveness can be used for air purification (1). These are described in more detail below, behind “More info”.

1. Thermodynamic Sterilization System – TSS technology works by heat sterilisation via a ceramic core with micro capillaries. The ceramic core is heated to 200°C/(392°F), consequently 99.9% of microbiological particles, i.e., bacteria, viruses, dust mite allergens, mold and fungi spores are incinerated. The air passes through the ceramic core by the natural process of air convection. The hot air is then cooled using heat transfer plates and then released. TSS is not a filtering technology, as it does not trap or remove particles but uses heat sterilisation technology to destroy micro- organisms. (2)

2. Ultraviolet germicidal irradiation – UVGI can be used to sterilize air that passes UV lamps via forced air. – Air purification UVGI systems can be freestanding units with shielded UV lamps that use a fan to force air past the UV light. Other systems are installed in forced air systems so that the circulation for the premises moves micro-organisms past the lamps. Key to this form of sterilization is placement of the UV lamps and a good filtration system to remove the dead micro-organisms. (3)

3. Filter – based purification traps airborne particles by size exclusion. Air is forced through a filter and particles are physically captured by the filter. High Efficiency Particulate Air filters (HEPA) remove at most 99.97% of 0.3-micrometer particles and are usually more effective for particles which are larger. HEPA must be arranged so that no air bypasses the HEPA filter. In dusty environments, a HEPA filter may follow an easily cleaned conventional filter (prefilter) which removes coarser impurities so that the HEPA filter needs cleaning or replacing less frequently. (4)

Filter for HVAC at minimum efficiency reporting values (MERV) 14 or above are rated to remove airborne particles of 0.3 micrometers or larger. A high efficiency MERV 14 filter has a capture rate of at least 75% for particles between 0.3 to 1.0 micrometers. Although, the capture rate of a MERV filter is lower than that of a HEPA filter, a central air system can move significantly more air in the same period of time. Higher-efficiency MERV filters are usually denser and increase air resistance in the central system, requiring a greater air pressure drop and consequently increasing energy costs. (5)

4. Activated carbon is a porous material that can adsorb volatile chemicals on a molecular basis but does not remove larger particles. Activated carbon is merely a process of changing contaminants from a gaseous phase to a solid phase, when aggravated or disturbed contaminants can be regenerated in indoor air sources. It is normally used in conjunction with other filter technology, especially with HEPA. Other materials can also absorb chemicals, but at higher cost. Carbon filtering is a method of filtering that uses a piece of activated carbon to remove contaminants and impurities, utilizing chemical adsorption. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped. The carbon is generally activated with a positive charge and is designed to attract negatively charged contaminants. There are two predominant types of carbon filters used in the filtration industry: powdered block filters and granular activated filters (6)

5. Polarized-Media Electronic Air Cleaners use an active electronically-enhanced media to combine elements of both electronic air cleaners and passive mechanical filters. Most Polarized-Media Electronic Air Cleaners use DC voltage to establish the polarized electric field. Airborne particles become polarized as they pass through the electric field and adhere to a disposable fiber media pad. The efficiency of Polarized-Media Electronic Air Cleaners increases as they load, providing high efficiency filtration with air resistance typically equal to or less than passive filters.

6. Photocatalytic Oxidation (PCO) is an emerging technology in the HVAC industry. PCO systems are able to completely oxidize and degrade organic contaminants. PCO uses short-wave ultraviolet light (UVC), commonly used for sterilization, to energize the catalyst (usually titanium dioxide (TiO2)) and oxidize bacteria and viruses. PCO in-duct units can be mounted to an existing forced-air HVAC system. PCO is not a filtering technology, as it does not trap or remove particles and is sometimes coupled with other filtering technologies for air purification. UV sterilization bulbs must be replaced about once a year and manufacturers may require periodic replacement. Drawback is high commercial costs.

7. Ionizer purifiers use charged electrical surfaces or needles to generate electrically charged air or gas ions. These ions attach to airborne particles which are then electrostatically attracted to a charged collector plate. This mechanism produces trace amounts of ozone and other oxidants as by-products. There are two major subdivisions: the fanless ionizer and fan-based ionizer. Fanless ionizers are noiseless and use little power, but are less efficient at air purification.

8. Ozone generators produce ozone and are sometimes sold as whole house air cleaners. Unlike ionizers, ozone generators are designed to produce significant amounts of ozone, a strong oxidant gas which can oxidize many other chemicals. The only safe use of ozone generators is in unoccupied rooms, utilising “shock treatment” commercial ozone generators that produce over 3000 mg of ozone per hour. Restoration contractors use these types of ozone generators to remove smoke odors after fire damage.

9. Titanium dioxide (TiO2) technology – nanoparticles of TiO2, is mixed into slightly porous paint. Photocatalysis initiates the decomposition of airborne contaminants at the surface. (7)

(1) https://healthybutsmart.com/air-purifiers/

(2) Insect Research Institute UK, “Report on the effectiveness on the Airfree air steriliser manufacture under license of US Patent 5874050 at reducing the levels of Der p 1 (A major house dust mite allergen) on allergen placed within it for varying lengths of time”, Phase 1, 2005.

(3) National Institute for Occupational Safety and Health “Word of the month: Ultraviolet Germicidal Irradiation (UVGI)”, NIOSH eNews April 2008, 5, 12.

(4) American Society of Mechanical Engineers, ASME AG-1a–2004, “Addenda to ASME AG-1–2003 Code on Nuclear Air and Gas Treatment”, 2004.

(5) AFA User’s Guide for ANSI/ASHRAE Standard 52.2-2012, “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size”, 2012.

(6) https://inspiredliving.com/airpurifiers/carbon-filters.htm

(7) AFA User’s Guide for ANSI/ASHRAE Standard 52.2-2012, “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size”, 2012.