Anemometers

The anemometer is a measuring instrument for checking wind speed. First of all, in order to make the correct anemometer selection, the application should be clarified.

Hot Wire - Thermal anemometers

For accurate measurements of low wind speeds, thermal anemometers (Hot Wire) are often used. In the case of a thermal anemometer, also referred to as a hot-wire anemometer, an electrical resistor is heated with a defined current and constant voltage. If air flows past the anemometer’s sensor element, this resistor is cooled. By measuring the electrical variables of current and voltage, the resistance can be converted into a corresponding flow velocity. In thermal anemometers, temperature is also often measured via a separate sensor element. Thermal anemometers are often used to measure airflow or to measure flow velocities in ducts. Measurement with a thermal anemometer is often intended for directional flows.

Vane Anemometers

Vane anemometers have an impeller that is rotated by the wind. Depending on the model, the actual measurement is then performed either via a Hall sensor that records the individual revolutions or via an optical sensor that scans a reflective mark attached to the impeller.

An important difference compared to hot-wire anemometers is that moving parts are required here to measure the wind. A disadvantage is that a certain wind speed is required before a measurement can be taken. This starting flow is often between approx. 0.4 m / s ... 0.6 m / s, depending on the model. Therefore, it is not possible to measure very low wind speeds with vane anemometers.

Cup Anemometer

Another type of moving anemometer is the cup anemometer. Anemometers of this type are used when wind or flow must be measured independently of direction. These anemometers are often used for fixed wind measurement and wind monitoring.

Pitot Tube Anemometer

A special design of an anemometer is the Pitot tube anemometer. A Pitot tube anemometer calculates the flow velocity based on the difference between two pressures. Using a special Pitot tube probe, the anemometer measures the ambient pressure in a duct and the incoming pressure acting on the probe. The difference between the two pressures gives the flow rate. Pitot tube anemometers are often used at very high flow velocities. These anemometers are known from racing or aircraft construction.

There are anemometers that have the ability to transmit measurements to a computer. In addition, there are anemometers that can calculate, in addition to wind speed, the volumetric flow in ducts. The user only needs to enter the duct cross-sectional area into the device and the anemometer displays the volume flow directly. In addition to anemometers that consist of the entire measurement chain, i.e., sensor + display, sensor-only versions are also available. Anemometer sensors usually have a signal output that can be evaluated by external evaluation devices such as data loggers, alarm units, displays, or PLC. These anemometers are often used for fixed wind measurements. Depending on the application, we would like to recommend the following anemometer types. This overview can help you find the right anemometer for the current application.

Anemometer Applications

• Low wind speeds in ducts with limited access: Hot-wire anemometer (Hot Wire)
• Wind speed in ducts at the ventilation outlet: Vane anemometer
• High flow velocity in a duct: Pitot tube anemometer
• Checking air conditioning systems: Hot-wire or vane anemometer
• Leak test / airflow measurement: Hot-wire anemometer
• Wind assessment for wind farms: Cup anemometer
• Wind test in sailing: Cup anemometer

Using an Anemometer

In many models, together with the cross-sectional area, for example of a flow duct, the flow rate (Volume Flow) can also be displayed directly on the screen. This eliminates complex conversion. When using the anemometer, always ensure that you hold the probe of the measuring device (the impeller, the Hot Wire, or the Pitot tube) centrally in the middle of the flow and absolutely perpendicular to the flow direction.

Please always follow the operating instructions. If you hold the sensor in the wrong direction, it may be damaged. This also applies to devices with an impeller. The impeller wheels have a predefined direction of rotation. In the case of an anemometer with a thermal operating principle, make sure that the air you want to measure does not contain dust particles, because the thin vane can easily be damaged by microscopic impact particles. Since the sensor is the most important and most expensive part of the device, the entire anemometer cannot be repaired.

DIN specifications for anemometers

Every HVAC system must meet current requirements, and in particular DIN EN 12599, which means that the equipment must pass a series of tests before full commissioning and regular operation. The methods applied, as well as the measuring instruments used for the purposes of the test, must meet all requirements and be approved. European standards undergo revisions and tend to change over time, which is why it is particularly important for manufacturers and users to stay up to date so that the equipment always operates in accordance with the standards. DIN EN 12599 refers to the test procedures before delivery of the ventilation system. The test can vary from the simplest to the most detailed and comprehensive, if there is a need for it. This means that systems must be checked during the manufacturing and installation process, before and after commissioning, and of course during operation. Only with the help of certified auxiliary devices, such as, for example, the Pitot tube anemometer PCE-HVAC 2 and also the anemometer PCE-PDA 10L, can the inspection be carried out professionally and quickly. Such devices are able to effectively determine the most important characteristics for the HVAC system: air flow, air pressure, air velocity, ambient temperature, and detect whether there are deviations from the required parameter ranges. The use of these measuring tools provides assurance that the ventilation system under test is able to operate and provide the best and most comfortable environmental conditions.