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HVAC School - For Techs, By Techs

Oct 1, 2020

Sam Myers of Retrotec joins Bryan and Kaleb on the podcast to discuss building performance. He also answers some of our listeners' questions.

Checking airflow is important for building science as well as HVAC. However, "airflow" is vague and can refer to static pressure readings (which isn't actually "airflow" at all), air from whole-home ventilation systems, or CFM per ton. We can also look at total system airflow with flow hoods. Equipment settings also matter when it comes to measuring airflow as it relates to building performance.

Leakiness (of the ducts or structure) is a common building performance issue. Blower door tests can determine the building pressurization and are a great tool for determining leakiness. However, we usually only do comprehensive "airflow," duct leakage, and building envelope tests during renovations or other large-scale projects; we don't typically check "airflow" and duct leakage when we do small repairs like capacitor replacement.

When balancing airflow, we usually rely on room-by-room load calculations. However, Sam finds that finding a pressure differential between rooms can be a bit more reliable. The main drawback is that a pressure differential won't tell you if a room isn't getting enough air, but the opposite problem is far more common and can be addressed.

The duct system's location also has a lot to do with a building's ventilation or sealing strategy. If the attic is in an unconditioned space in a humid climate, it may be best to seal the area to control the dew point.

Sam, Bryan, and Kaleb also discuss:

  • Airflow measurement instruments
  • Total system airflow
  • Balancing and isolating rooms with comfort issues
  • Grilles, diffusers, and vents in zonal duct design
  • Using your senses during balancing
  • Ventilating vs. sealing the building envelope
  • Infiltration and air mixing
  • Split-level homes
  • Blower doors
  • Building performance in commercial HVAC

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