Tunnel airflow monitors

Our Airflow monitors are considered crucial assets in any existing or new build tunnel system.

Product types :

Maintaining optimal airflow to minimise fan usage

Road and rail tunnels require continual fresh air flow to ensure that visibility is maintained and toxic gases levels are kept within acceptable limits. If levels exceed those limits, the tunnels’ ventilation systems will begin operating wall or ceiling mounted jet fans.

Because these jet fans are extremely expensive to run based on their enormous power consumption — which can fluctuate between 45 kW and 200 kW— having access to reliable, real-time and precise airflow measurements is considered best practice for efficient operation.

Ultrasonic airflow measurement is now the most commonly used technology in tunnels. With no moving parts, the system requires minimal servicing and can be fully sealed from the tunnel’s harsh environment. Measurements are independent of temperature, pressure and composition of the tunnel atmosphere. Other than a regular clean and check, it can be considered a ‘fit and forget’ solution.

Tunnel airflow monitor measurements can be used as part of an air quality management system for ventilation control within a tunnel or other confined space including traffic tunnels, rail tunnels and utility applications such as cable tunnels.

Cross bore tunnel airflow monitors versus single point solutions for ultrasonic tunnel airflow monitoring

Depending on tunnel design and conditions, you can choose between either a single point or cross bore ultrasonic airflow monitor. Typically, cross bore systems require more upfront investment and may be more complex to install, however they are considered to be highly accurate. While calculating an average airflow reading across the tunnel bore will provide more representative information, the system can only be installed if the tunnel’s design is suitable.

Limited head room above the traffic envelope, structural supports, cable trays and other obstacles may mean that a cross bore measurement system would not be viable.

In tunnels where cross bore instruments cannot be implemented, single point ultrasonic airflow monitoring systems are a practical alternative. When installed correctly with adequate clearance around the sensor, single point ultrasonic solutions will provide readings that accurately track the tunnel’s air velocity.

With easy installation, you can install a single point, reliable, ‘fit and forget’ tunnel air flow monitoring solution at a lower price.

At Acoem, we offer solutions for both cross bore and single point ultrasonic tunnel airflow monitoring and will work with you to ensure optimal performance based on your individual application or tunnel project requirements.

CROSSFLOW is an open path, cross bore air flow sensor (anemometer) designed to measure air speed and direction in multi-lane and bidirectional tunnels. The system uses reliable ultrasonic transit time measurements between a pair of transceivers which are mounted and aligned on either side of the tunnel.

AIRFLOW MkII is a single point airflow monitor for tunnels that provides consistent and accurate measurements of air speed and direction using proven, ultrasound time of flight technology. It is a dual axis monitor that can measure air speeds of up to 60m/s with a resolution of 0.01m/s.


Multi-lane, bidirectional tunnel anemometer



Fixed point anemometer for tunnel


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