Published August 28, 2026 at 05:55
The instrument measures six things: air velocity, air flow, relative humidity, wet-bulb temperature, dew point and carbon dioxide. Five of them describe what the ventilation system does. One of them describes something entirely different — namely whether what is being done is enough.
Carbon dioxide is produced by the people in the room. The level rises when more people breathe the same air and falls when the air is exchanged, which makes it a direct measure of the relationship between supplied air and actual load. A room can be balanced exactly according to the design documents and still be stuffy, if it is used by twice as many people as it was designed for — and it is only the carbon dioxide reading that reveals this.
What it is
A combined vane anemometer, psychrometer and carbon dioxide meter.
- 10 cm vane for more precise readings in larger ducts
- Air velocity, air flow, relative humidity, wet-bulb temperature, dew point and carbon dioxide
- Built-in air temperature sensor
- Multi-point and time-averaging
- Min/Max, Data Hold, automatic shut-off
- Supplied with NIST-traceable calibration certificate and hard case
The vane is the third measuring principle
A pitot tube measures at a single point, using pressure. A hot-wire anemometer also measures at a single point, using cooling — and it takes over where the pitot tube falls silent at low velocities.
A vane does something different: it integrates. The wheel is driven by the air across its entire swept area, and a ten-centimeter wheel therefore averages over a circle the size of a saucer. At a supply air diffuser or in a large duct, that is exactly what you want, since the velocity is never the same across the whole opening — it is higher in the middle and lower toward the edges.
The three principles therefore don’t compete. They belong in different places: pitot in high-velocity ducts, hot-wire for weak air movements and small openings, vane where a surface needs to be described with a single number.
The averaging functions solve what remains
Even a ten-centimeter wheel doesn’t cover a large duct. That’s why multi-point averaging exists: you measure in a grid pattern across the cross-section and let the instrument calculate the average, instead of writing down six numbers and calculating them afterward.
Time-averaging does the same thing in the other dimension. Flow in a system pulsates with dampers, with other zones and with the control system’s operation, and an instantaneous reading describes just that moment. An average over a period describes the operation.
Humidity gives three figures from one measurement
Relative humidity, wet-bulb temperature and dew point all come from the same sensor plus the temperature. However, they answer different questions: relative humidity is about comfort and how the air is perceived, while the dew point answers the one question that concerns damage — at what surface temperature does condensation begin.
This is why a commissioning engineer wants the dew point and not just the humidity percentage: a cold surface in an otherwise comfortable room is where moisture collects, and that assessment is made based on dew point versus surface temperature.
Three typical use cases
- Balancing: flows at diffusers and in ducts, with averages that hold up for a protocol.
- Complaint investigation: carbon dioxide versus occupancy, together with flow and humidity.
- Handover: documented values with a traceable certificate.
Why it pays off
Ventilation problems almost always fall into one of two camps: either the system is said to be poorly balanced, or the space is said to be used incorrectly. Without measured values, it becomes a matter of opinion between facility manager and occupants, and it’s usually resolved by turning up the fan — which costs energy and rarely solves the right problem.
With flow and carbon dioxide measured simultaneously, the question is settled: is the system delivering what it should, and is that enough for the people actually there. The two answers point in different directions, and it is only once you have both that you know which action is the right one.
Read more about the AN320 anemometer, psychrometer and carbon dioxide meter →
