Understanding Filtration Efficiency
There are many factors that affect the type of air filtration system that is best for your situation including CFM (cubic feet per minute) capacity, method of filtration, system design, and cost. One of the most important factors; however, is filtration efficiency. Filtration efficiency can be confusing to understand with different methods of testing, and technical jargon. This article will explain some of the common terms and how different types of filtration compare on efficiency.
Particle Size:
To understand filtration efficiency, you first need to understand particle size. MERV ratings use three different groups of particle sizes to rate a filter. 3-10 microns, 1-3 microns, and 0.3 to 1 microns. (ULPA filters are tested down to 0.12 microns). To better understand the scale of these particles, a human hair is about 70 microns in diameter, and a red blood cell is about 8 microns across.
This diagram shows the range in size of multiple different particulate types. Thermally generated oil smokes tend to range in size from 0.1 to 1 micron.
MERV Ratings:
One of the most important terms regarding filtration efficiency is the MERV rating. MERV stands for minimum efficiency reporting values, and is a standard used to describe the efficiency of many different types of air filters, from furnace filters to medical grade HEPA filtration. The MERV rating is given based on the percentage and size of the particles captured.
| 0.3-1 Micron | 1-3 Micron | 3-10 Micron | |
|---|---|---|---|
| MERV 1-4 | < 20% | ||
| MERV 5 | ≥ 20% | ||
| MERV 6 | ≥ 35% | ||
| MERV 7 | ≥ 50% | ||
| MERV 8 | ≥ 20% | ≥ 70% | |
| MERV 9 | ≥ 35% | ≥ 75% | |
| MERV 10 | ≥ 50% | ≥ 80% | |
| MERV 11 | ≥ 20% | ≥ 65% | ≥ 85% |
| MERV 12 | ≥ 35% | ≥ 80% | ≥ 90% |
| MERV 13 | ≥ 50% | ≥ 85% | ≥ 90% |
| MERV 14 | ≥ 75% | ≥ 90% | ≥ 95% |
| MERV 15 | ≥ 85% | ≥ 90% | ≥ 95% |
| MERV 16 | ≥ 95% | ≥ 95% | ≥ 95% |
| HEPA (MERV 17-19) | ≥ 99.97 | ≥ 99.97 | ≥ 99.97 |
| ULPA (MERV 20) | ≥ 99.9995% (0.12-1) | ≥ 99.9995% | ≥ 99.9995% |
Sometimes filter efficiency are listed as percentages instead of by their MERV rating. This can cause some confusion as there isn’t a standard size particle related to the percentage of capture. For example a 95% filter could be MERV 14, MERV 15, or MERV 16 depending on the size of the particle that it captures 95% of. To make sure you are getting the right filter, ask what the MERV rating is.
HEPA & ULPA filters
Filters that are over MERV 16 are commonly referred to as either HEPA or ULPA filters instead of by their MERV rating. HEPA filters are very common in both the industrial and medical settings as they are a great way to ensure a crystal clean environment. ULPA filters are not typically used in industrial settings as that level of efficiency is only necessary in extremely critical applications.
Some types of DOP panel filters are labeled as HEPA because they look similar and are interchangeable with HEPAs, but these filters do not have to be 99.97% efficient. These filters have their place, as they last longer than HEPAs, so if maximum efficiency is not needed they are a more cost effective solution.
Many types of air filtration systems designed for industrial use have HEPA filters as a final stage of filtration. Including Absolents, Donaldson Torit mist collectors, 3nines, Aeroex, and many others. That means that these types of air filtration systems are 99.97% efficient; however, if the previous filter stages are significantly less effective, the HEPA filter will have to be replaced frequently.
Electrostatic Filtration Efficiency
Electrostatic filtration is another common method of filtering wet particulate in industrial settings, especially oil smokes. When serviced properly electrostatic filtration is also a very efficient method of filtration. A single stage of Electrostatic filtration is 90% – 95% efficient on 0.3-1 depending on air speed and the model of electrostatic filter. Adding a second stage increases that to 99%+ efficiency. Some brands of electrostatic filtration even add third and fourth stages to further increase capacity, as well as adding redundancy in case one stage of filtration shorts out or otherwise becomes ineffective.
SmogHog, MistBuster, TriMist, Coolblaster, and Trion are all brands of electrostatic filtration systems.
Capture Efficiency: With any type of filtration, one of the areas that can be overlooked is capture efficiency. Capture efficiency refers to the percentage of particulate captured by the air filtration system, versus the smoke that escapes, due to poor duct design, undersized air filtration equipment, or plugged filters. If you are not collecting 15% of the smoke at the source, it doesn’t make much of a difference whether your filtration system is 95% or 99.97% efficient. That means focusing on capture efficiency is the most important step of creating an effective filtration solution.
If you have any questions about air filtration types and efficiency, give us a call. 888.451.0844.