The MERV rating scale is a numerical tool used by engineers and operators of industrial dust collection systems to measure the efficiency of their systems. The rating scale is an industry-standard established to measure the overall quality, effectiveness, and performance of air filtration systems.
MERV, the Minimum Efficiency Reporting Value, is a methodology that measures the single filter initial efficiency for air filtration devices by particle size. In other words, it is a numerical system that ranks filters for air quality. There are 16 MERV values assigned to the rating scale, numbering 1 to 16. Each value measures how well a designated air filter traps airborne particles, particulates, and pollutants. The higher MERV value, the better a filter’s efficiency at removing dust particles and pollutants from the air and reducing emissions.
What Is the MERV Rating Scale?
The MERV scale is a comparative system developed by ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, to help determine the most efficient filter for a specific application in a workplace or residence.
It is by no means the only system used to measure the efficiency of dust collection systems—ASHRAE Standard 199-2016 is another test method—but the MERV rating scale is one of the most important.
The History of MERV
ASHRAE first published MERV as a filtration standard in 1987 as, ASHRAE Standard 52.2: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. It is accredited by ANSI, the American National Standards Institute, and the publication is commonly referred to as ‘ANSI/ASHRAE Standard 52.2’ or simply ‘Standard 52.2.’ Since going into print, editions of the standard have been updated regularly and continue to be recognized as the single most important guideline to measure and evaluate air filtration performance.
In all air filtration systems, air filter performance is measured by particle counts upstream and downstream of the air-cleaning device being tested. MERV established a method of laboratory testing to measure the performance of general ventilation air-cleaning devices in removing particles of specific diameters to the size of microns. Why is this important?
Using the MERV Rating Scale for Dust Collection Systems
A filter’s efficiency is measured by not only how much dust it can capture, but by the size of the dust, it can filter. The size of dust is measured in micrometers, better known and more commonly referred to as microns. A single micron is one-millionth of a meter. For comparison, a fiber from clothing is approximately 10 to 50 microns. A human hair, on average, is 80 to 100 microns. A droplet of mist or spray is about 10 microns. In other words, dust, dust size, and how much of it can be filtered, will determine the efficiency of the filter in question. When it comes to the filtration efficiency of dust collection systems, how much media is used to collect particulates and emissions is of lesser importance than how well the media cleans it.
Dust collectors are important tools in any manufacturing or industrial operation. Selecting the correct dust collection application is dependent on the type of dust particles, pollutants, and emissions being generated at a facility. The MERV rating scale assists engineers and operators determine the standard in the application of particle-based containment removal systems, which in turn will provide a cleaner working environment for employees, eliminate any concerns of air quality, and ensure that companies meet environmental directives and remain in compliance.