The Basics of Air Velocity Sensors

Stainless Steel Pitot Tube, Series 160

Dwyer Instruments offers a multitude of sensors for monitoring air velocity in HVAC systems. Some of this instrumentation has a simple construction (Pitot tubes, for example) while others are more complex, such as hot-wire anemometers.

The initial term and first “hot-wire anemometer” was developed back in 1914 by Louie Vesso King. He is also accredited for King’s Law, which mathematically describes heat transfer in air flows using a heated wire. As the air moves over the wire, it causes a loss of temperature in the wire and removes some of the wire’s heat energy. Continue reading “The Basics of Air Velocity Sensors”

Characteristics of Thermal Anemometers & Why They’re Well-Suited for Low Flow Applications

There are two common ways to measure air velocity: by using pressure-based instrumentation or by using temperature-based instrumentation. Before we discuss the different technologies available for measuring velocity pressure, it is important to understand the basics of air velocity.

Continue reading “Characteristics of Thermal Anemometers & Why They’re Well-Suited for Low Flow Applications”

Velocity Measurement and Environmental Effects

Differential pressure measurement can be beneficial in a wide variety of building automation system (BAS) applications.

One of these applications involves determining if a filter in your system needs to be cleaned or replaced. Filter health can be established by monitoring the pressure on the primary and secondary sides of a filter. A clean filter will typically have a baseline differential pressure generated as air flows through it. As the filter becomes dirty, this differential pressure increases.

When using a mechanical flow sensor, such as a pitot tube, differential pressure can also be used to determine flow velocity and volumetric flow. Continue reading “Velocity Measurement and Environmental Effects”