Local UV-C recirculation units treat room air directly instead of going through the central HVAC system. Air is actively drawn through an enclosed UV module — physically this is a recirculation room pattern: a compact irradiation chamber inside the room, sized on an air-changes-per-hour (ACH) basis.
They are the right choice when:
- The building has 100 % fresh-air HVAC, so there is no recirculation and in-duct UV has nothing to disinfect.
- There is no HVAC, or it is too old to retrofit economically.
- Specific rooms need additional hygiene beyond what the HVAC provides.
- A fast retrofit without an installer is required (plug-in unit).
- Production halls carry a high microbial load (food processing, pharmaceutical packaging).
- Rooms see temporarily elevated microbial load (waiting rooms, classrooms during infection season).
Typical Deployment Environments
| Environment | Why a local unit? | Typical room size |
|---|---|---|
| Storage rooms | No HVAC, often closed, mould risk | 30–200 m² |
| Staff changing rooms | Humid, hygiene requirement, changing occupancy | 15–60 m² |
| Medical waiting rooms | Microbial load from patients, no rebuild possible | 20–80 m² |
| Small offices | No central HVAC, single-room ventilation | 15–50 m² |
| Server / utility rooms | Dust plus thermal load, UV supplements filtration | 10–30 m² |
| Sample laboratories | Hygiene zone without a cleanroom build-out | 20–100 m² |
| Classrooms | Supplement to window ventilation | 50–80 m² |
How the Units Work
- Enclosed housing with a fan that draws in room air.
- Internal UV-C chamber with low-pressure mercury tubes (254 nm) — the number of tubes scales with throughput.
- Built-in light trap: a baffle labyrinth or mesh prevents UV radiation from escaping the housing, which is what makes the unit safe to run in an occupied room.
- Pre-filter (HEPA or coarse filter) upstream removes dust and protects the quartz envelope.
- Air outlet returns cleaned, microbially reduced air to the room.
- Installation: ceiling, wall or floor-standing; only a 230 V outlet is needed, no HVAC ducting.
Why low-pressure mercury tubes: in low-pressure mercury lamps roughly 40 % of the electrical input is converted directly into 254 nm UV-C radiation, and lab testing reports lifetimes up to about 16,000 hours [source: Light Sources / Excelitas]. Because the unit is enclosed, a tube breakage does not release mercury into the room air.
Mounting Modes
There are three mounting types with distinct target situations and airflow physics.
A) Ceiling-Mounted
- Unit bolted to the ceiling, hard-wired or fed from a ceiling outlet.
- Airflow is horizontal or downward — air is drawn in near the ceiling and discharged forward or down.
- The room flow pattern resembles a compact HVAC duct suspended in the middle of the room.
- Safety advantage: the unit sits above head height, so no one can reach into the UV chamber access; the maintenance cover is only reachable with a ladder, which reduces tampering and accident risk.
- Use-case fit: production halls, large offices, schools, supermarkets, storage areas and clinics — anywhere the unit should run unobtrusively and continuously.
Ceiling-mounted recirculation units are commonly deployed in industrial and large-space settings because the above-head placement combines an enclosed UV chamber with an out-of-reach second line of defence.
B) Wall-Mounted
- Unit fixed to a wall at roughly 2–2.5 m height (above head height), usually with horizontal discharge.
- Similar safety profile to ceiling mounting, but simpler to retrofit.
- Use-case fit: single-room retrofits, consulting rooms, smaller offices, staff changing rooms.
C) Mobile / Floor-Standing
- Rolling or portable, a wall outlet is sufficient.
- Discharge is usually to the side or upward, intake at the bottom.
- Safety trade-off: within reach, so it must have stricter light-trap baffling; risk to children or pets if the unit is damaged.
- Use-case fit: temporary use (cleaning a consulting room after an infectious patient), small rented spaces with no option to rebuild, home use.
Which Mode When?
| Use case | A Ceiling | B Wall | C Mobile |
|---|---|---|---|
| Industrial production hall | preferred | supplementary | no |
| Permanent open-plan office | preferred | possible | no |
| Classroom (infection season) | preferred | possible | interim solution |
| Permanent medical waiting room | preferred | preferred | rarely |
| Cleaning after infectious patient | no | no | preferred |
| Rented space, no rebuild allowed | too invasive | preferred | preferred |
| Storage room with mould risk | preferred | possible | rarely |
Rule of thumb: permanent installation → ceiling or wall; temporary or mobile use → floor-standing.
Core Sizing: How Many Units for a Given Room?
This is the decisive question for the planner. The relationship is:
Number of units = (Room volume × Target ACH) / Unit airflow rate
- Room volume [m³] = floor area × ceiling height.
- Target ACH (air changes per hour). For portable air cleaners, REHVA guidance indicates an airflow capacity of at least 2 ACH, with a positive effect up to about 5 ACH [source: REHVA COVID-19 guidance]. Building-code and use-case requirements may set higher targets; operating-theatre and laboratory environments are governed by dedicated ventilation standards rather than by portable units.
- Unit airflow rate [m³/h] varies widely between products — values should be taken from the specific vendor datasheet rather than assumed, because they are not normatively fixed.
Worked Example
Waiting room 60 m² × 2.8 m ceiling height = 168 m³. For a target of 5 ACH: 168 × 5 = 840 m³/h of required airflow. A compact unit rated at 250 m³/h would mean 4 units distributed across the room — or a single larger unit covering the full required airflow.
UV Dose Per Pass
Unlike a single-pass HVAC duct, the room behaves in a recirculating way: the air is processed repeatedly, and the room microbial count approaches an equilibrium between microbial input (people) and microbial removal (UV).
A measured prototype recirculating UV-C unit reported a UV-C dose of about 11.6 mJ/cm² per single pass at 100 l/min, rising to roughly 104 mJ/cm² under recirculated operation, and delivered a 5-log reduction in pathogen particle-forming units [source: Garcia et al., Scientific Reports 2024 / PMC11302707]. For airborne viruses an average dose near 2 mJ/cm² can give a 1-log (90 %) reduction, while around 20 mJ/cm² is typical for 90 % reduction of directly exposed viruses [source: PMC9553962].
Because most filtration and UV air-disinfection devices remove or inactivate close to 100 % of airborne pathogens, the clean air delivery rate (CADR) is essentially equivalent to the airflow the device delivers [source: CDC ventilation guidance].
Safety
- The built-in light trap is the primary reason these units are approved for occupied rooms. UV irradiance from the unit must stay well below occupational exposure limits everywhere in the room under normal use. ISO 15858:2016 defines minimum protection requirements through an irradiance limit corresponding to an effective daily dose of 30 J/m² at 254 nm [source: ISO 15858:2016 / Opsytec]; ICNIRP publishes the underlying exposure limits for incoherent UV radiation between 180 nm and 400 nm [source: ICNIRP UV guidelines].
- Mounting height as an extra protective layer: ceiling and wall mounting above head height prevents accidental contact with maintenance covers — an out-of-reach placement is a second line of defence even when the enclosure alone would be safe.
- The maintenance access to the UV chamber carries a safety interlock: opening the housing switches the lamps off.
- On a low-pressure tube breakage, the enclosed unit contains the residues, so no mercury enters the room air.
- No ozone is produced by pure 254 nm emission. Ozone is generated by wavelengths below roughly 200 nm; standard low-pressure germicidal tubes emitting at 254 nm therefore do not produce ozone. Far-UV-C at 222 nm requires its own separate assessment.
Distinction from Upper-Room UVGI
Do not confuse these units with upper-room UVGI (ultraviolet germicidal irradiation):
- Upper-room UVGI uses open UV radiation in the upper portion of the room (from about 2.1 m height); convective air movement carries air upward where it is irradiated.
- It requires careful beam-angle calibration, a minimum room height and exposure-limit control measurements.
- It is widely used in healthcare settings as a supplemental control for airborne infection [source: CDC ventilation guidance].
Enclosed recirculation units are the simpler equivalent: the air is brought to the lamps inside a closed housing, removing the calibration effort and the open-exposure concern.
Distinction from HVAC In-Duct UV
| Scenario | In-duct HVAC UV | Room recirculation unit |
|---|---|---|
| 100 % fresh-air HVAC | not useful | main choice |
| ~50 % recirculation | useful | supplementary |
| Fully closed, 0 % recirculation | duct UV usually has no duct | main choice |
| No HVAC present | not possible | main choice |
| One specific problem room | hard to target a whole building | point-targeted |
Manufacturers Active in This Field (non-exhaustive, no endorsement)
Examples of suppliers offering recirculating room-air UV-C units or related modules include Nuvonic (formerly Heraeus Noblelight), UVDI, Signify/Philips, Sterylis, Novaerus, Genano, American Ultraviolet and UVResources. Several lamp makers, such as Osram and Heraeus, supply the low-pressure tubes used by many device builders. This list is for orientation only and is not a ranking or recommendation.
Cross-References
- UV Lamp Technology — low-pressure 254 nm characteristics
- Standards and Certifications — ICNIRP, exposure limits, medical-device rules for clinics
- UV Economics and ROI — filter-plus-UV versus filter-only arguments
- HVAC UV Chamber vs Duct — in-duct versus in-room placement
- HVAC Filter UV-C Recommendation — combining filtration with UV
Sources
- REHVA COVID-19 guidance document (portable UV-C air cleaners, ACH guidance for classrooms and offices)
- CDC ventilation guidance (upper-room UVGI, equivalent clean air delivery, CADR)
- Garcia de Abajo team / Wong et al., Scientific Reports 2024 — portable UV-C device for high-flow infectious aerosols (single-pass vs recirculated dose, 5-log reduction)
- COVID-19 pandemic lessons — critical parameters for UVC inactivation of viral aerosols (PMC9553962)
- ISO 15858:2016 UV-C devices — safety information, 254 nm exposure limit
- ICNIRP guidelines on limits of exposure to ultraviolet radiation, 180–400 nm
- Low-pressure mercury UV-C lamp technical documentation (Light Sources, Excelitas) — 254 nm conversion efficiency and lifetime