A parking garage CO monitoring system runs the ventilation only when carbon monoxide rises, so sensor placement and setpoints decide both safety and the energy saved versus constant running.
Why Monitor CO
Vehicle exhaust in an enclosed garage builds CO, an odourless gas that displaces oxygen and harms health at modest concentrations. Running the extract fans 24/7 wastes energy when few cars are moving, so codes and good practice allow demand control: fans start when CO passes a setpoint and stop when it clears. The setpoint is tied to occupational exposure limits, commonly around 50 ppm for an 8-hour average and a higher short-term figure, and the monitoring system is what makes the limit enforceable automatically rather than by manual checks.
The system only works if sensors actually see the worst local pockets, which is a placement problem more than a sensor problem. A well-chosen setpoint on a badly placed sensor still leaves a dead corner where CO climbs unnoticed, so the two decisions, placement and setpoint, must be made together as one design.
Ventilation capacity has to exist before demand control can modulate it. Enclosed car park extract is commonly designed on an air-change basis, often in the region of 6 air changes per hour for normal operation and a higher rate for fire mode, with the design checked against a dilution calculation rather than the air-change figure alone. Where diesel vehicles are common the contaminant of concern shifts: nitrogen dioxide and particulate become the limiting factors and a CO sensor alone can under-report the hazard, so combined CO and NO2 detection is increasingly specified. Bus and lorry parks, and any level used for loading with engines idling, deserve that treatment even where the code names only carbon monoxide.
Placement and Setpoints
Sensors sit where CO accumulates: near ramps, low in the breathing zone (about 1.2โ1.8 m), and spread so no zone is far from a device, typically one per 200โ400 mยฒ depending on code. The controller starts fans at the alarm setpoint (often 50 ppm) and may step to high speed at a higher level (e.g., 100 ppm), then run a purge before stopping, so the air is cleared rather than merely held at the limit.
| Item | Specification | Note |
|---|---|---|
| Start setpoint | 50 ppm | Fan start on CO rise |
| High setpoint | 100 ppm | High-speed stage |
| Sensor height | 1.2โ1.8 m | Breathing zone |
| Coverage | 1 / 200โ400 mยฒ | Per code or design |
| Purge | Post-alarm | Runs until cleared |
| Normal ventilation rate | ≈ 6 air changes per hour | Higher rate in fire mode |
| Diesel-heavy sites | Combined CO and NO2 sensing | CO alone can under-report |
Placement must avoid dead spots behind pillars and not sit in the direct exhaust plume of a single car, which would chatter the system. A grid based on airflow, not just floor area, is the robust approach, because CO moves with the air pattern the fans create, and sensors should sit where that pattern actually carries the contamination.
Sensors are consumables, which is the part of the system most often forgotten after handover. Electrochemical CO cells drift and typically need calibration annually and replacement every three to five years, so the design should place them where a technician can reach them with a step ladder rather than a scaffold. The control interface matters just as much: fan start and stage commands, a local alarm, a remote signal to the building system, and a hard-wired override for fire mode all have to be defined, and fire mode must take priority over CO control so a smoke-clearance sequence cannot be overruled by a clean-air reading. Documented setpoints and a trend log turn the installation into something an inspector can verify.
Design Checklist
- Grid by airflow: Place sensors where CO actually pools, not by area alone, using the ventilation pattern as the guide.
- Set two stages: Start at 50 ppm, high speed at 100 ppm, with a purge that runs until the space is clear.
- Keep them low: Breathing-zone height, not near the ceiling where CO mixes and dilutes before it is read.
- Log readings: Trend data proves compliance and tunes the setpoints to the real garage behaviour.
- Avoid plumes: Keep sensors out of a single car's exhaust stream so one vehicle cannot fake an alarm.
- Size the fans first: Confirm extract capacity meets the dilution and fire-mode duty before adding demand control.
- Plan for calibration: Mount sensors within easy reach and budget cell replacement every three to five years.
Why Monitoring Pays
CO-based control typically cuts garage fan energy by half or more while keeping air safe, a clear compliance-and-cost win that also reduces nuisance noise from constantly running fans. Keruite supplies the jet and axial fans the monitoring system switches, sized for the garage's dilution and purge airflow so the fans can actually clear the space within the purge time.
Garage ventilation is judged on two very different days: the ordinary one where the objective is to use as little energy as possible, and the rare one where the system has to clear smoke. Jet and axial fans built in an 80,000 m² plant by a manufacturer with more than 30 years of experience are supplied with airflow, thrust, and where required a high-temperature class, so one installation can serve both duties. An in-house performance laboratory confirms the airflow behind the purge calculation, ISO 9001:2015 and CCC certification cover the build and electrical side, and units operate in more than 50 countries.
Our engineers respond to selection enquiries within 24 hours, including fan airflow and staging advice for CO-controlled garage ventilation.