Ventilation
control.
Exhaust fans in an enclosed garage are among the largest continuous electrical loads in the building. They do not need to be. Code allows garage ventilation to be operated automatically by carbon monoxide detection instead of running continuously, and that is what a properly commissioned system delivers.
How garage ventilation control works
Garage ventilation control ties the exhaust and supply fans to the gas detection system. Carbon monoxide sensors (plus NO2 sensors where diesel vehicles use the space) report to a controller, and the controller compares each reading against programmed setpoints and stages the fans or ramps their drives.
- Clean air: fans off or idling at low speed
- Rising readings: fans stage on or ramp up in steps
- Alarm setpoint: full ventilation plus horns and strobes
- Sensor or controller fault: a properly set up system fails safe and runs the fans
Most garage ventilation problems we find are control problems, not fan problems: sensors out of calibration, setpoints changed years ago, drives left in hand mode, or a controller bypassed to stop nuisance alarms. That is why we treat the sensors, the controller and the fans as one system.
What VFD integration does
A variable frequency drive lets a fan run at any speed instead of only fully on or fully off. Tied to CO detection, the fan idles at low speed, ramps as gas levels rise, and drops back when they normalize. In most facilities reduced-speed operation covers the great majority of the day. The saving is not linear either: fan power falls sharply with speed, so a modest speed reduction is a large energy reduction.
What we do
- Review the existing fans, starters and controls to see what can be reused
- Install and program drives, interlocked with the gas detection panel
- Set the ventilation sequence: idle speed, ramp thresholds, alarm override, minimum run
- Commission against span gas so the response is verified, not assumed
- Document the sequence and setpoints for the file
The safety half of the same job
On-demand ventilation only works if the detection is accurate. A drifted sensor either runs fans you do not need or, worse, leaves them off when exhaust is building. That is why we do not treat energy work and calibration as separate programs. Every drive we install is commissioned with calibrated sensors, and stays that way through annual calibration and testing.
If your fans run constantly today
That is a symptom, not a setting. Start with why parking garage exhaust fans run constantly, then call us and we will find out which cause you have.
See what this looked like in real buildings: our parking garage CO system case studies show fan runtime cut 84% to 94%, with the savings then and at today’s rates.
Common questions
How much can VFD control save?
Fans on continuous operation run 100% of the time. With working CO detection and VFDs, most garages need full speed only a small fraction of the time and run at reduced speed the rest, which is where the savings come from.
Is on-demand ventilation code compliant?
Yes. Enclosed garages must be mechanically ventilated, and the code allows the ventilation either to run continuously or to be operated automatically by carbon monoxide detection.
Can VFDs be added to existing fans?
Usually. If the motor and starter are serviceable, drives can be added and interlocked to the existing gas detection panel.
Why are our fans running all the time now?
Almost always failed or drifted sensors, or controls that were bypassed to stop nuisance alarms. It is the most common thing we find on a first visit.
Talk to a gas monitoring specialist
Tell us the building and how many sensors you have. We will tell you what service it needs and what it costs, no pressure.