With the recommendation of a MERV 13 or higher, does this filter meet your needs? A MERV 13 filter is a step in the right direction and captures more particles than a typical MERV 8 filter. However, it's not as effective at capturing small virus-sized particles as a HEPA can. A MERV 13 will trap less than 75% of air particles that are 0.3-1.0 microns in size (coronavirus is 0.1 microns). It is also difficult for many existing 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.
On average, many installations are limited to one type of MERV 8 or MERV 9 filter. ASHRAE recommends that MERV 13 filters be used whenever possible, with MERV-A 13-A or MERV 14 preferred. This is driving the use of higher efficiency filters in many buildings. For locations that cannot upgrade the HVAC filter or increase outdoor air during the winter, in-room units are recommended to add cleaning capacity. These units must include high or better MERV filters to remove most of these virus-laden particles.
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. Filter technology has grown by leaps and bounds over the years, and Merv ratings are designed to help us determine the most effective and efficient air filter options for heating and cooling systems and more. MERV ratings determine the capabilities of an air filter and its level of filtration efficiency.
The table below provides approximate relationships between ratings under ASHRAE, MERV and ISO 16890 test methods. It's best to comply with oven manufacturer's recommendations or consult an HVAC professional to determine exactly which MERV rating is best for your specific system. Well, MERV ratings range from 1 to 20, with 1 being the lowest level of filtration and 20 being the highest. Therefore, filters that are above 13 in their MERV rating can filter particles closer to the 0.3 micron size.
The worst percentage of the six tests is selected as the official measure used to determine the MERV rating of a filter. Filters with higher MERV ratings should be changed more frequently (at least every three months) to avoid restricted airflow that can cause your system to operate inefficiently or even damage it. The higher the MERV rating on a filter, the less dust particles and other contaminants can pass through it. A higher MERV rating often means lower airflow, which can make the system work harder and use more energy to do its job.
An air filter with a higher MERV rating can block microscopic particles, such as smoke molecules, due to its tighter mesh fabric.
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