MERV is the primary classification system used in the air filter industry, providing a clear indication of a filter's ability to trap and retain particulates. However, it is important to be aware of filters with an excessively high MERV rating. Fortunately, you don't need to spend hours comparing FPR to MERV or make a long list of pros and cons of MERV vs.
MPR
.Instead, you can rely on each of these ratings, since they essentially measure the same characteristics of an air filter. In December, Owen and Kerr wrote the technical paper “What You Can and Can't Do with the ASHRAE Standard 52.2”, which was published in the ASHRAE Journal. In this paper, they clarified the misconception that there has ever been a MERV greater than 16 and explored why some filters increase efficiency over time while others decrease. Given that particles containing COVID-19 can remain in the air long enough to pass into the respiratory space and air conditioning systems, there is a strong desire to filter these particles from the air. ASHRAE recommends using MERV 13 filters whenever possible, preferring MERV-A 13-A or MERV 14 filters.
This is driving the use of higher-efficiency filters in many buildings. For locations that cannot improve the HVAC filter or increase outdoor air during the winter, it is recommended to add room units with high MERV or better filters to remove most of these virus-loaded particles. Air filters are also needed to clean the air and help people inhale fewer particles due to global warming and the wildfires seen on the West Coast, as well as for people with allergies and asthma. The use of appropriate filters can reduce the need to introduce outside air, thus reducing heating, cooling and outdoor air conditioning costs. The filter used and its pressure drop will be important in determining how much energy savings can be achieved. It is necessary to use the air conditioning system to take advantage of the filter; if the air supply does not pass through it, it cannot capture particles. It is also important to make sure that the filter is sealed in place; if air is circulating around it (called a leak or bypass), it will not be cleaned.
In addition, particulate filters do not remove volatile organic compounds (VOCs) or ozone. Filter efficiency below 0.3 µm is completely irrelevant since the virus is almost always embedded in particles that are much larger, and recent reports indicate that much of the COVID-19 virus can occur mainly in particles with a size of 1 µm to 5 µm. Therefore, filter efficiency below 0.3 µm is completely irrelevant. When a filter is stated to have an efficiency of 99%, this means that 99% of the particles that enter the air are continuously removed; this is not equivalent to another technology eliminating 99% of the particles in two days. Control technologies should be compared on the same basis, for example, their equivalent rate of supply of unpolluted air. Another way filtration can be misapplied is in air filters that combine HEPA filters with other technologies that eliminate or inactivate infectious aerosols. A well-sealed HEPA filter has an efficiency greater than 99.9% for particles of all sizes; adding other technologies in series cannot add more than a very small amount of additional performance to the air filter. If you're trying to replace your filter with a higher MERV filter, make sure it fits and seals into your system.
Look for a filter with a pressure drop similar to what you have, or make sure your system can adapt to the upgrade. If possible, look for the MERV-A 13-A filter if you can get that information; if not, try a MERV filter 13 or higher. When replacing filters potentially contaminated by viruses, use rational personal protective equipment (PPE), including gloves and a mask; place the filter in bags immediately before you dispose of it. Order your replacement filters early this year due to COVID-19 demand; always change filters according to manufacturer recommendations to ensure that they work as specified. In cases where an HVAC system cannot handle a MERV 13 or higher rating due to airflow problems with older units, a MERV 11 air filter can provide additional benefits and capture a wider range of particles that would pass through a MERV 8 filter. Newer units shouldn't have airflow problems with higher MERV ratings.It's too early to know what will end up being done regarding environmental benefits from using higher rated FPR or MERV filters; however, people should check in from time to time to keep up to date with any new developments.
