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.
Ultraviolet (UV) systems are quite effective at maintaining the cleanliness of HVAC coils, drain pans, and other damp surfaces. 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 surface disinfection benefits.
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. 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 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.
The “Box Fan” fan with a Merv 13 air filter is effective and safe to use. It is economical, easy to assemble and is based on sound filtration technology. In short, it is a useful tool to help combat Covid-19 indoors and is highly recommended. When schools reopen after the coronavirus outbreak, ASHRAE also recommends a portable HEPA and UV air filter for each classroom, with at least two air rotations per hour. So how did our tests go with our “Box Fan with a MERV 13 Filter Cleaning Device”? In the tool room, the device removed 59.7% of one-micron particles and 86.4% of five-micron particles. Alternatively, you can upgrade the ventilation system itself, making it suitable for at least MERV 13 filters.
When considering air cleaning technologies that potentially or intentionally expose building occupants, safety data should apply to all occupants, including those with health conditions that could be aggravated by air treatment. MERV 16 is the tallest filter you can buy, but your air conditioning system may not be able to handle it. These products generate ions, reactive oxidative species (ROS), or chemicals in the air as part of the air cleaning process. On the other hand, resistance can be decreased and flow increased by changing the depth of the pleated MERV filter 13. For a residential filter in a slot that is a little loose, a simple piece of tape can be used, held in place and allowed the air flow to push the filter forward to engage the flat surface in front of it. At a minimum, when considering purchasing and using products with technology that can generate ozone, verify that the equipment meets UL 867 (Standard for Electrostatic Air Filters) certification for the production of acceptable levels of ozone or preferably certification of UL 2998 (Method of environmental claim validation (ECVP) for zero ozone emissions from air purifiers) which aims to validate that no ozone is produced. To help protect against the COVID-19 virus, ASHRAE changed its recommendation from MERV 8 filters to MERV 13+.
It's important to note that MERV and HEPA are two different types of air filters, although you've probably seen both related to air filtration. One of their recommendations is to use air cleaners with at least a MERV 13 rating or a higher HEPA rating when possible. There are no published laboratory studies demonstrating whether the SARS-CoV-2 virus can be re-aerosolized from ventilation air filters or other HVAC surfaces. It is also difficult for many existing HVAC (HVAC) systems to adopt a MERV 13 because of the greater fan load of finer filter media which can actually cause more harm than good and reduce airflow if your system is not designed to handle that type of filter.
Professional opinion from an HVAC engineer is highly recommended before attempting to upgrade any air filter.
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