UV-C FAQ
Straight answers about UV-C.
How germicidal UV-C works, how exposure is controlled, where it fits in HVAC, water and surfaces, and how to tell it’s doing its job.
UV-C basics
What is UV-C?
Ultraviolet light is divided into three bands: UV-A (315–400 nm), UV-B (280–315 nm) and UV-C (100–280 nm). UV-C is the germicidal band. Most germicidal lamps emit at 253.7 nm, close to the wavelengths that microorganisms’ DNA and RNA absorb most strongly.
How does UV-C work?
UV-C is absorbed by the DNA and RNA of microorganisms and damages it, which stops them from reproducing. The effect depends on dose: the UV-C intensity a microorganism receives multiplied by how long it is exposed. Different organisms need different doses.
Can you see UV-C?
No. The 253.7 nm output of a germicidal lamp is invisible. The faint blue glow is a small amount of visible light the lamp also gives off. It tells you the lamp is on, not how much UV-C it is producing, which is why Cognituv measures UV-C output with sensors.
Does UV-C occur naturally?
The sun produces UV-C, but the ozone layer absorbs it before it reaches the ground. Germicidal UV-C comes from lamps and LEDs.
What does UV-C affect?
Bacteria, viruses, mold and other microorganisms all absorb UV-C, but the dose each needs varies widely. Spores and some viruses need much more than common bacteria. A sound design starts from the organisms that matter in your application.
How long does UV-C take to work?
It depends on the dose. A strong lamp close to a surface delivers a dose quickly; air moving through a duct may be exposed for only a fraction of a second, so in-duct systems need high output and reflective surfaces. Published dose data for specific organisms is used to size systems.
Can UV-C pass through solid objects?
No. UV-C is non-ionizing and doesn’t penetrate solids the way X-rays or gamma rays do. It only treats surfaces, air and water it can reach directly. Shadows, dust and soil block it.
What materials let UV-C through?
Very few. Quartz and certain fluoropolymer films transmit UV-C, which is why lamps use quartz sleeves and FEP coatings. Ordinary window glass and most clear plastics, such as polycarbonate, block it, even though you can see the blue glow through them.
Safety
How is UV-C exposure controlled?
Direct exposure to UV-C can irritate skin and eyes, so well-designed systems prevent it. Lamps sit inside air handlers, ducts or sealed chambers; upper-room fixtures direct UV-C above head height; and access panels, interlocks and switches turn lamps off when equipment is opened.
What happens if someone is exposed?
Overexposure can cause temporary skin redness and a painful eye irritation called photokeratitis, similar to snow blindness. Don’t look at operating lamps, and switch them off before servicing. Most clothing, and ordinary glass or plastic eyewear, blocks UV-C.
What if a lamp breaks?
In food and process applications Cognituv uses lamps with shatter-resistant fluoropolymer coatings that contain the glass if a lamp breaks. Germicidal lamps contain a small amount of mercury, so handle and recycle them the way you would fluorescent lamps.
Does UV-C damage materials?
Long exposure can yellow or embrittle some plastics, rubber and coatings. Cognituv builds fixtures from UV-resistant materials such as stainless steel and aluminum and places lamps away from sensitive components.
Does UV-C produce ozone?
Lamps that also emit at 185 nm produce ozone. Ozone-free lamps use glass that blocks 185 nm. Check the spec sheet: Cognituv’s DUCT modules, ICE fixtures and in-room purifiers, for example, are specified with ozone-free lamps.
UV-C in HVAC systems
Why put UV-C in an HVAC system?
Cooling coils, drain pans and ducts are dark and wet, so biofilm and mold grow there. That growth restricts airflow, insulates the coil and can release odors and microorganisms into the airstream. UV-C aimed at the coil and drain pan is designed to keep that growth from building up.
Can UV-C reduce HVAC energy use?
Clean coils move air with less resistance and transfer heat better. ASHRAE-funded field research (RP-1738) measured lower airside pressure drop and better heat transfer after UV-C was installed on fouled coils, with results that varied by site. Savings at your facility depend on how fouled the coils are and how the system runs, which is why Cognituv measures results against a baseline agreed for your site instead of promising a number.
Does UV-C replace filters or coil cleaning?
No. UV-C doesn’t capture particles, so you still need filters. It complements filtration and can reduce how often coils need mechanical cleaning, but it isn’t a substitute for maintenance.
Where does UV-C go in an air handler?
Usually on the leaving-air side of the cooling coil, aimed at the coil face and drain pan, where it runs continuously. In-duct modules treat moving air further downstream. Lamp count and placement depend on coil size, airflow and temperature, because lamp output drops in cold, fast-moving air.
Does UV-C run all the time?
On coils, yes. Continuous operation keeps growth from re-establishing. Lamps lose output with age, so they are replaced on a schedule, and UV-C sensors show when output falls.
What maintenance does a UV-C system need?
Lamp replacement, keeping lamps and sleeves clean, and checking that interlocks and ballasts work. Replace lamps on a schedule, or when Cognituv Connect UV-C sensors and lamp-status outputs show output has dropped. Cognituv Grid lamps are rated for 16,000 to 18,000 hours, depending on the environment and how they’re used.
How do you know a UV-C system is working?
Three ways: measure UV-C output with a radiometer or a permanent UV-C sensor; check results with surface swabs or microbial sampling before and after; and track system data such as coil pressure drop. Cognituv Connect records UV-C output alongside the rest of your facility data.
Air, water and surfaces
How does UV-C treat air?
Three ways. In-duct systems treat air as it moves through ductwork. Upper-room fixtures treat a zone above head height while room air circulates through it. Sealed in-room units draw air through an enclosed UV-C chamber and return it.
How does UV-C treat water?
Water flows through a stainless chamber past UV-C lamps in quartz sleeves. UV-C adds no chemicals and leaves no residual, so it is often paired with a disinfectant residual where codes require one. It works best on clear water, so it usually follows filtration.
How does UV-C treat surfaces?
Fixtures treat surfaces they can see directly: conveyors, tables, walls and equipment. Shadowed areas and soil block UV-C, so surface UV-C works alongside cleaning, not instead of it. Research on food contact surfaces shows results depend on the surface material and the organism.
Where is UV-C used?
Hospitals and labs, food and beverage plants, office buildings, schools, data centers, water and wastewater treatment, and oil and gas.
What are the advantages and limits of UV-C?
UV-C adds no chemicals and leaves no residue, it can run continuously instead of only when someone cleans, and its output can be measured. Its limits: it only treats what it can reach, it needs the right dose for the organism, and lamps need replacing on schedule.
What guidance covers UV-C?
Several organizations publish guidance on UVGI, including ASHRAE, NIOSH (upper-room UVGI in healthcare settings), the International Ultraviolet Association and the Global Lighting Association.
Working with Cognituv
What does Cognituv do?
Cognituv is a hygiene automation company for commercial, industrial and mission-critical facilities. We combine wireless sensors, treatment systems (UV-C, photocatalytic oxidation and filtration for air; in-line treatment for water and gas) and Cognituv Connect, a monitoring and measurement & verification platform. Every engagement follows Identify · Apply · Verify™.
What is hygiene automation?
Most facility hygiene is manual and periodic: coils cleaned once a year, filters changed on a schedule, a swab when someone complains, and no record of what happens in between. Hygiene automation makes it continuous. Sensors watch the conditions that matter, treatment runs at the source, and the result is measured against a baseline, so you can show it worked.
How does an engagement start?
With a no-cost assessment: a call with an engineer, then a written recommendation. When you want to see your own data before you decide, the next step is Cognituv Connect, scoped and quoted for your site: sensors on your equipment, a baseline, then every result measured against it.
Do you publish pricing?
No. Systems are sized to each facility, so quotes follow an assessment.
Do you help with installation and support?
Yes. We provide system design, installation guidance and technical support, and Cognituv Connect keeps reporting after commissioning.
Want the answer for your building?
Book a no-cost assessment: a call with an engineer about your coils, ducts and rooms, then a written recommendation.
Prefer to talk? Call 1-888-580-8738