What are the different kinds of anemometers? 

There are many different anemometer technologies for measuring air flow velocity. Some are better suited to measuring wind (outdoor airflow), while others are used in particular to measure indoor airflow: supply air, fresh air, recirculation air, or even air draughts, however slight, air leakage within a building, but also airflow within an air duct forming part of an air-conditioning or ventilation system. 

Here are the different types of anemometers and the areas in which they are best used: 

1. Vane anemometers (indoor and outdoor air): 
   These instruments use a vane to measure the speed of an air stream. These models are fairly versatile, the most sensitive being preferred for indoor measurements with a 4'' (100 mm) diameter vane. Some small-diameter portable vane anemometers are often used for outdoor wind speed measurements in some recreative activities, but professionals also use small diameters for duct measurements. 

2. Hot wire anemometer (indoor): 
   These anemometers measure air velocity using a simple thermal principle: the sensor is a wire heated by the Joule effect (low electrical current), and passing air flow cools it by convection. The cooling modifies the electrical resistance of the wire, making it possible to accurately assess the velocity and flow rate of an air stream, even a very weak one (blower door test measurement used to detect air-tightness defects in a building). The measurement accuracy of this technology is very high, but in return requires high quality manufacturing and calibration by the manufacturer. 

3. Pitot tube measurement (indoor): 
   These anemometers are in fact manometers whose pressure sensor is associated with Pitot tube technology: they measure the variation in pressure in a Pitot tube as an air flow passes through a duct or ventilation opening. The difference between the static pressure and the total pressure generated by the airflow is then used to determine the speed of an airflow fairly accurately, but with a sensitivity lower than that of the hot wire (above 394 fpm, 2 m/s) and only in ducts. 

4. Cup anemometer (outdoor, wind measurement): 
   These anemometers measure wind speed using cups attached to a vertical shaft. The wind rotates the cups, and the velocity of the air is calculated as a function of their rotation speed. These devices are still sensitive for measuring light breezes, but can also measure powerful wind gusts. 

5. Ultrasonic anemometer (indoor and outdoor): 
   Ultrasonic anemometers are versatile and extremely accurate. They are also very robust, as they have no mechanical parts. Used both indoors and outdoors, they are often found in weather stations, but also in certain specific industrial environments and in scientific research to study atmospheric dynamics. These devices emit sound pulses between 20 and 200 kHz, and are fitted with receivers that measure the propagation time of the sound waves, directly induced by the speed of the air through which they travel.  

6. Doppler or laser anemometers (indoor and outdoor): 
   These anemometers are very accurate but also very expensive. They are also very similar to radar anemometers (electromagnetic waves). Their advantage lies in their ability to take measurements in air as well as in non-gaseous fluids, and above all to do so non-intrusively, i.e. without disturbing the flow of the measured stream. They emit light or electromagnetic waves, and detect the frequency shift between a transmitted beam and its return. These devices are not generally used in HVAC applications. 

Which anemometer should I use in the HVAC-R field? 

For airflow measurement in the ventilation and air-conditioning sector, we recommend using a portable vane anemometer or hot-wire anemometer. These devices offer simplicity and an accuracy-reliability-price ratio far superior to other technologies for this type of use. 

You should also pay attention to the measuring range of the instruments in question, to choose the model best suited to the type of airflow to be measured. 

Flows of low and moderate intensity are best handled by a hot-wire anemometer. These instruments are suitable for insulation and air-tightness (blower door) tests in buildings (doors, windows, etc.), as well as for measurements in ventilation ducts. Thanks to their thinness, these probes can be inserted into a duct through a small opening, unlike a vane probe, which has a larger diameter. 

Vane anemometers are better suited to larger airflows and to measurements in the vent. These models also incorporate a temperature sensor to simultaneously measure the temperature of the air stream being measured. Vane-type thermo-anemometers are therefore ideally suited to measuring the temperature, speed and flow rate of a building's ventilation ducts or grilles in industrial environments. 

Pitot tube anemometers (which are in fact manometers fitted with a Pitot probe) are also used in the ventilation and air-conditioning sector within a duct. They provide reliable measurements, and some are equipped with a K thermocouple temperature probe to measure the airflow temperature at the same time. 

Measurement on the vent: the value of airflow measurement cones 

With a hot-wire or propeller anemometer, the most important accessory for studying airflow systems is the airflow measuring cone. This device makes it possible to obtain a very precise measurement of the actual air flow rate passing through a supply or exhaust vent. 

These measurement cones are essential for measurements that comply with current regulations (such as RE2020 in France), as they make it easy to obtain an accurate and reliable airflow measurement without having to carry out measurements by scanning or scaling (point-by-point zoning) at an air vent. The latter two methods provide a less accurate averaging result. The cones are also the only ones to provide a reliable flow measurement on multidirectional type diffusers, which do not blow a unidirectional flow of air. 

Measurement cones come in different sizes and shapes depending on the geometry of the diffuser in question. It is important to use a cone adapted to the vent in order to cover its entire opening. This is why Sauermann offers a multitude of cone models to cover the different types of air vents in a building. Some cones are designed for vane anemometers, others have a hole for inserting a hot wire anemometer. 

For vane anemometers, the latest generation of cones incorporates a flow straightener with a honeycomb structure that makes speed and flow measurement more reliable by eliminating turbulence and head loss due to the application of the cone to the wall around the ventilation outlet. This system re-establishes a laminar flow, whatever the type of air outlet. 

Note also that a balometer (electronic flowmeter) is also an excellent solution for measuring volumetric airflow in terms of accuracy and reliability on any type of diffuser. In addition, for permanent monitoring in a fixed position, the DEBIMO wing solution is also one of the best of its kind for monitoring airflow in a duct. 

Our blog articles to help you learn more about the subject: 

• Measuring air flow rate at an air vent: getting it right 

• The importance of indoor air quality for health is clearer than ever 

• Quick and easy HVACR inspections: choosing the right measurement instruments 

• VOCs: what they are, where they come from, and how to measure them 

• Using CO₂ concentration to measure air change rate 

• Indoor air quality matters in data centres too!