When it comes to heating, air conditioning, and fan ventilation one of the most important factors that gets overlooked is air velocity measurement. Also valuable to know with gas flow, process gas systems, and pneumatic conveyance, knowing the air velocity means that you can multiply it by the cross section of the duct and know exactly how many cubit feet per minute of air is being moved. In this article we are going to discuss why you need an air velocity sensor if you are running a building, as well as how they work, and provide you with a few examples of the technology so that you can see it for yourself firsthand. Let’s talk about the good old air velocity sensor.
The development of air velocity sensors
The history behind air velocity sensors goes quite a long way back. In 1914 a man named Louie Vasso King developed what he called the ‘hot wire anemometer’ and established a principal known as ‘King’s Law’, which states the process involved in the anemometer and how it may be used to determine air velocity. The way that this sensor works would prove to be efficient enough that we still use it today. Inside the sensor there are actually 2 sensors, one which determines the temperature of the air and another, which employs a hot wire that cools as air transfers over it. By comparing the readings from the two sensors and factoring in the size of the duct you are able to determine the cubic feet per minute that is being produced at any given time.
Other types of air velocity sensors
Aside from the hot wire anemometer style of air velocity sensor there are other sensor types available that are applicable to other mediums. The three main types of air velocity sensors are as follows:
- Air velocity transmitter – Most commonly employed in clean rooms where air flow needs to be closely monitored, these transmitters are typically of the ‘hot wire anemometer’ style but there are variations, employing complex circuits, sporting LED displays, and more.
- Vaneometer – Vaneometers are air velocity sensors which are generally portable and meant to measure low air velocity levels accurately but at a discounted cost. Applications vary, one example being that you might use a vaneometer to measure the air flow in laboratory fume hoods.
- Windmeter – Perfect for a weather monitoring station, these units are often portable and capable of measuring factors such as wind chill, velocity, and more. Models are available that can provide all of the calculated data or you can obtain a model which simply gets you a direct reading so that you may determine the details on your own.
Let’s take a look at a few examples of the different kind of air velocity sensors so that you can have a better idea as to how they work.
Model 480 Vaneometer™ Swing Vane Anemometer
Our first example is the Model 480 Vaneometer from Dwyer, Economically priced, this unit is specialized for low air velocities and features a spirit level for accurate readings which fall within +5 for 100 FPM and within +10 for 100 FPM and above. Designed to be user-friendly, it has large scales which are easy to read and may be read from both sides of the unit. The ‘swing style’ of the meter makes it very easy to determine the feet per minute, making this a popular budget model.
For further details on this unit feel free to click the link below:
Mark II Wind Speed Indicator
Ideal for weather monitoring stations, the Mark II wind speed indicator may be easily installed in your home den, office, or workshop, and provides accurate readings for both miles per hour (from 0 up to 80) and on the Beaufort scale from 1 – 12. This liquid filled scale comes with a plastic vane and white plastic
“This is a great unit for the home.”
with gold tones for the readings and if you prefer metric, you can obtain a Mark II that reads from 0 – 120 kilometers per hour as well. When it comes to weather monitoring on the fly, this is a great unit for the home.
For further details on the Mark II Wind speed indicator please feel free to click the link below:
Series AVU Air Velocity Transmitter
This air velocity transmitter is great for serious applications, such as clean room air flow monitoring, HVAC cubic feet per meter air flow assessment, pollution studies, and exhaust and supply fan flow tracking. Also excellent for building management in general, the Series AVU functions as an anemometer, employing a single sensor for obtaining surrounding temperature with a secondary sensor with a heated element which loses heat as air flow is conducted, allowing comparison of the gathered readings for an accurate assessment of air flow velocity. These units are practically immune from ‘drift’ as well, due to the nature of the comparison sensor flow determination technology. Available in +5 and +8% accuracy, if you would like to view more information about the Series AVU then feel free to click the link below:
Model 641B Air Velocity Transmitter
Our last example is the Model 641B Air velocity transmitter and it has a number of excellent applications. This model utilizes a heated mass sensor capable of detecting FPM of air flow in either 250 feet per minute (1.25 miles per second) up to 2000 feet per minute (10 miles per second) . Applications for this unit include the following:
- HVAC air flow measurements
- Cleanroom monitoring for ventilation
- Exhaust stack flow monitoring
- Exhaust and supply fan monitoring
For further information on this unit, feel free to click the link below:
Today we have discussed air velocity sensors, how they work, a bit about their history, and popular applications for this technology. If you are managing a building, laboratory, or even just want to monitor the weather from home then these sensors can give you the data that you need so be sure to check out the links for more information. You’ll be happy that you did!