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Do HVAC UV Systems Really Work?

UV System, Credit: Molekule

During the Covid-19 Pandemic, there has been a surge of interest over ultraviolet air purification systems.  ASHRAE has even recommended UVGI systems as a way to prevent the spread of infectious disease.  The real question is, do UV systems really work?

In short, ultraviolet air purification systems do work; however, their efficacy is based on their ability to adequately entrap and expose microbes to radiation. UV systems are best used in combination with other purification products (such as filters).

The History of Ultraviolet Disinfection Systems:

Using ultraviolet light to disinfect is not a new concept.  The idea has been around since 1878.  The majority of ultraviolet purification systems are used in water treatment plants.  Massive water treatment plants use ultraviolet rays to kill dangerous microbes in water.  

Ultraviolet systems have also been used in healthcare facilities.  These systems have been proven to successfully disinfect.

How it Works:

Ultraviolet rays “disinfect” fluids by breaking down microbial DNA.  Dangerous bacteria and other microorganisms live in the air and water.  Like any lifeform, in order to live, these creatures need to produce proteins.  Proteins are the building blocks of organic structures.  The instructions for producing proteins are stored in an organism’s DNA.  If a lifeform’s DNA is destroyed, that lifeform will no longer be able to produce proteins effectively and will eventually die.  Powerful UV rays warp DNA and render a cell unable to produce its necessary proteins.

That being said, UV light can be extremely dangerous, especially to the skin and eyes.  UV purification systems use UV-C light (the most powerful kind of UV light) to disinfect.  People typically get sunburnt after hours of exposure to UV-A light from the sun; UV-C light can do that same damage in a matter of seconds.  That is why it is very important to ensure that UV disinfection systems have proper shielding to reduce radiation exposure to humans.

Use in Air Purification Systems:

As stated above, UV light has long been used in water treatment systems.  It is considered a fail safe when used in conjunction with chlorine (which some pathogens are resistant to).  When it comes to air purification systems, however, disinfection is a little trickier.  In order for a UV system to adequately destroy microbial DNA, it must shine on microbes for a certain amount of time.  Microbes suspended in air tend to move erratically so hitting them with enough UV light to destroy their DNA is a bit tricky.

If a UV purification system is somehow able to trap infectious particles and hit them with UV light for a significant amount of time from multiple angles, then it could properly disinfect. So, simply putting UV lights in a building’s duct work would probably not do much in the way of destroying bacteria and viruses.

In the fight against Covid-19, UV purification systems can help, but they should not be our only solution.