Measuring Airflow Podcasts w/ Jim Bergmann

In this two-part podcast series, Jim Bergmann covers measuring airflow in HVAC systems. He covers a wide range of airflow measurement instrumentation and readings.

In the HVAC industry, many techs confuse static pressure for airflow. Although you need static pressure to have airflow, it is NOT airflow and can fluctuate rather wildly depending on the duct conditions. Static pressure is an indirect airflow measurement. Airflow is actually a measurement of velocity (such as with pitot tubes) that you then convert to a volume measurement (CFM). Airflow hoods and vane anemometers can give you direct airflow measurements.

You use static pressure probes, not pitot tubes, to measure TESP. When measuring static pressure, you put the negative probe in the return and the positive probe in the supply. Then, you measure the TESP (away from wiring and airflow). However, air pressure fluctuates as that air moves in the duct. Velocity pressure occurs when air moves and creates turbulence. The blower moves air, which has weight. As such, density, volume, and mass are all important as well. As air density changes, the CFM remains constant at a variable mass flow rate.

When it comes to using any tool for measuring airflow, static pressure, etc., all tools are an investment of money and time; you must spend some time learning how to use those tools. You will discover those tools’ limitations and must learn how to work with or around those limitations.

Jim also touches on:

• ECM & PSC motors
• Sensor quality and resolution (pitot tubes)
• Bernoulli’s principle
• Filtration and pressure drop
• Standard air formula variations
• Air mass vs. volume
• Amp draw
• Measuring air velocity vs. volume
• Airflow hoods and vane anemometers
• Hot wire anemometers
• Air turbulence

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