What is true hepa and how do you tell the difference between hepa filter ratings?

When it comes to True HEPA (True High Efficiency), we have to talk about what is the filtration efficiency of air purifier filters. Many people will say "I use the filter filtration level is H13", then what is the judgment standard of H13? According to the European Union EN1882 standard, the 0.3μm particle size particles filtration efficiency is higher than 99.97% of the filter called H13. And on the current domestic statistics,目前国内空气净化产品的净化效率依然在90%~95%@0.3μm, at best, is considered to be a sub-high-efficiency filter.

Generally in accordance with its filtration efficiency, HEPA is divided into five levels: coarse filter, medium filter, sub-high-efficiency filter, HEPA high-efficiency filter, ultra-high-efficiency filter. Details are shown in the following chart:

High-efficiency particulate arrestance is short for HEPA high efficiency particulate arrestance (HEPA) filters, often called HEPA filters or high efficiency air filters, are widely used in medical facilities, automobiles, airplanes, and home furnishings.The HEPA standard is set by the U.S. Department of Energy (DOE) and is designed to provide filtration efficiencies of 99.97% or greater for particles of dust up to 0.3 microns in size.

The following is Wikipedia's explanation of HEPA

Understanding the HEPA, the next with you to clarify the HEPA filter and PM2.5 common misunderstandings

Myths 1: HEPA on the 0.3 micron microparticle purification efficiency can reach 99.97% or more, then it is not sure about the purification effect of 0.1 micron particles, right?

This is actually a conceptual error. Think about it, why is the HEPA effect measured by 0.3μm particles instead of 0.1μm? In fact, PM0.3 is more likely to break through the protection of HEPA filter because it is less susceptible to van der Waals force, so the filter with 99.97% effect on PM0.3 is even 99.99% effective on PM0.1.

Myth 2: The smallest particle our HEPA can filter is PM0.1

Similarly, PM0.3 is more likely to break through the HEPA protection compared to PM0.1, so it's problematic for individual manufacturers to say that the smallest particle they can filter is PM0.1. Or someone said he can only filter PM0.3 can not filter PM0.1 is also unreasonable.

We are talking about filtration, that HEPA filtration is divided into which forms? What is the principle?

HEPA filtration is divided into four forms: interception, gravity, airflow, Van der Waals force

1, the interception mechanism that we commonly understand the sieve, 0.5μm, 10μm of large particles are intercepted "sieve" down.

2, the small size and high density of dust particles in the effect of gravity, when passing through the HEPA speed reduction, like sediment sinking to the bottom of the river as the natural settlement in the HEPA.

3, the filter weave uneven thus forming a large number of air vortex, small particles adsorbed in HEPA under the action of the cyclone in the air flow.

4, ultra-fine particles to do the Brownian motion to hit the HEPA fiber layer, by the Van der Waals force. Fiber layer, by the influence of van der Waals force to get purified. Such as less than 0.3μm virus carriers are purified under the influence of this force.