UV light is regularly used on HVAC systems and water purification systems.

There are systems used in hospitals that are automated which will roll into an empty room and then turn on to disinfect the room. They are usually used in hospitals but I’ve seen them used in places like China during their zero covid crackdown on public transportation.

Some transit systems in China even converted a paint booths to disinfect with UV so they could drive buses through. All of which is probably overkill as prolonged exposure to sunlight will do the same thing.

Exposure to UV light that is intense enough to kill viruses within seconds is very bad for humans. I pulled the cover off a system I was taking marketing pictures for while it was turned on. Within a thirty to sixty seconds I could feel like I was getting a sunburn on my arm that was closest to the light. I wouldn’t want to risk a direct UV system turning on while someone is sleeping and burning them. As a result most systems are indirect and rely on a combination of UV and HEPA filters to disinfect airborne viruses.

There are other ways to disinfect surfaces. Bleach or chlorine is cheap, simple and won’t harm humans. Chlorine gas can be used to kill really bad viruses like anthrax. Chlorine gas was used to disinfect the Federal buildings that had been contaminated in the 2001 anthrax attacks. Many detail shops, rental car agencies and public transit systems in the US use Chlorine gas on vehicles to disinfect or more commonly remove nasty odors from vehicles. The gas can seep into all cracks/crevices and get into the HVAC system ductwork in ways UV light can not. If you ever get into a car that faintly smells like a pool, chances are it has been gassed recently to kill an odor.