If chemical disinfectants are used, they should only be applied with the HVAC system turned off. In addition, disinfectants should not be applied to ventilation filters before continuing to use the filters within ventilation systems. The effects of disinfectants on filter performance are unknown. Filters should only be treated with disinfectants if they are to be removed from service and disposed of.
While UV systems are quite effective at maintaining the cleanliness of HVAC coils, drain pans, and other damp surfaces, properly designed systems can be quite effective in inactivating microorganisms in moving air streams on the fly. These systems generally require more lamps, so they can provide significant UV doses in a short period of time. A typical one-pass inactivation efficiency is 85%, just like a good particulate filter, but systems can also be designed for inactivation greater than 99.9%. In addition, a well-designed UV air disinfection system within an HVAC system, and located adjacent to the cooling coils, can also provide the surface disinfection benefits mentioned above.
Another way to install UV is in a “top air” configuration. Specially designed wall-mounted fixtures create an irradiated area above the occupant and disinfect the air in the space, as the air circulates naturally, mechanically or through the HVAC system. CDC has approved this type of system for use in tuberculosis control for nearly 20 years, and there is guidance from NIOSH on how to design them. Finally, mobile UV systems are frequently used for terminal cleaning and surface disinfection in healthcare facilities and other spaces.
Systems such as these are commonly used in unoccupied spaces due to occupant exposure concerns. The three types of systems can be relevant, depending on the type of building and the individual spaces within the building. The design and sizing of effective ultraviolet disinfection systems can be a complex process due to the need to determine the dose delivered to a moving air stream or to an irradiated region of a room. In-duct systems are further complicated by the configuration of the air handling unit and ducts and surface reflections that can help achieve higher irradiation levels.
Overhead air systems require proper air mixing to function properly while paying close attention to reflective surfaces that could cause room occupants to be overexposed to UV energy. Accredited manufacturers and system designers can help by making the necessary calculations and designing specific systems for individual spaces. With more than 57,000 members from more than 132 countries, ASHRAE is a diverse organization dedicated to promoting the arts and sciences of heating, ventilation, air conditioning and refrigeration to serve humanity and promote a sustainable world. In general, finding a filter with a higher MERV rating will correlate with greater efficiency in capturing particles and contaminants in the air.
HEPA filters are the most efficient for residential or commercial use, followed by MERV 13-16 filters. So if you want to filter the air in your home to improve indoor air quality and perhaps eliminate any coronavirus that is floating around, what do you need to know? Well, you need to know what particle size to filter and what type of filters will do it. Alternatively, you can upgrade the ventilation system itself, making it suitable for at least MERV 13 filters. The most commonly used filters are the MERV 13 to 16 range, which will capture everything mentioned above, including lead, humidifier, nebulizer, charcoal dust, legionella, insecticide dust and copier toner, sneeze cores, car fumes and bacteria.
Kevin, yes, the virus itself is too small for many filters to pick up, but it's mostly attached to other things in particles large enough to be filtered out of the air. Because HEPA filters are so efficient, they cause a greater pressure drop than MERV-rated filters. The following table summarizes the average stop and applications of filters along the MERV scale, and the typical particle size for which they are used. Therefore, using a high MERV filter to purify the air of COVID-19 can undoubtedly help reduce the spread in the office environment.
One of their recommendations is to use air cleaners with at least a MERV 13 rating, or a higher HEPA rating when possible. For the European standard, a True HEPA filter will filter the air and capture at least 99.95% of 0.3 micron sized particles. But if the filter has already captured the virus, it will die long before the filter is changed, so metal was not needed. MERV 14 and higher can capture particles that are even smaller than previous MERV ratings, ranging from 0.3 to 1.0 microns in size.
MERV 16 is the tallest filter you can buy, but your air conditioning system may not be able to do it. . .
