Is UVGI the best choice for air sterilization?

Coronavirus pandemic is the biggest “Black Swan event” this year, the number of people infected has reached 7 million on 13th Sept., 2020.

Hand sanitizer, social distance, facial masks do help.

But how to kill the viruses transmitted by aerosol at home and in public spaces?

UVGI is the most frequently recommended technology on all media outlets. Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (ultraviolet C or UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions. UVGI is used in a variety of applications, such as food, air, and water purification.(https://en.wikipedia.org)

Does UVGI really kill viruses?
Surely it does.

YET Is UVGI the best choice solution for air sterilization?
Hmmm, maybe not, it depends.

Let's see from how UVGI works. UVGI disinfects where it could effectively illuminate, which means it couldn't work for the whole space.

But maybe if we keep the air circulating, then it will disinfect the whole inner space?

Not really! It needs time long enough to illuminate the surface of the object and then could break the organizational structure of viruses. Data speaks louder than words, here we go:

At 6mW/cm2, the UV light needs to shine for at least 12.5s to kill >99.9% of the virus.

At 16.8mW/cm2, viruses need to be exposed to the UV light for 4.46s to kill >99.9% of the virus.

Obviously it cannot effectively disinfect the air by itself, because the air blows very quickly though the UV illuminating area, makes it almost useless.

Normally it works with HEPA filter, the media filters in traditonal air purifiers or in central air conditioning systems. Actually the mechanism is media filters capture the viruses in aerosol or particles, and UVGI disinfects on the filters. This is the most popular conventional solution but still has some shortness:

UV is NOT safe (Reference)

Ozone generation is inevitable

Long time UV irradiation may impact on the physical and chemical properties of media filter, which leads to worse purification efficiency (Reference)

Particles/dust come along with air flow will quickly cover the UV lamp and shorten its service time (Reference)

High pressure drop HEAP filter inherently possessed results in low purification efficiency and high energy consumption of AC system

High cost incurs for both UV lamp and HEPA filter replacement

Users need to timely monitor and solve the problem. It will definitely raise the maintenance cost.

In contrast, MESP air sterilizing purifiers is a better choice.

99.9% Virus-killing rate

Permanently Washable Filter for 10 years

Ozone-free

Low energy consumption

Low pressure drop

Safe and easy to maintain

MESP Air purifiers for AHU, FCU
At Hospital, School, Office, Hotel…

We must agree that UVC has been and will continue to be a big player in the disinfection field, lucky to have it in hospitals, clinics or food restaurants. Yet it's still disputable for its application in the HVAC system for commercial buildings which accommodate large populations.

We must weigh the pros and cons of this UVC+HEPA air sterilizing solution carefully, aside from extra cost from regular replacement for both UVC and HEPA, how to handle the disposed HEPA filter and mercury-contained UVC lamp will be a huge challenge to our already overwhelming environment-protection task.

It's an opportunity now for us to bring in a MESP filter solution amid this pandemic as it perfectly caters to the air sterilizing purification needs of both residential and commercial buildings and the spare environment of any further waste burden.