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HVAC School - For Techs, By Techs

Oct 29, 2017

Do you think of the building envelope as a duct? Do you test it? In this podcast episode, Joe Medosh talks to us about envelope testing and why it’s the future of building health and comfort.

The building envelope is the largest duct in the entire home. However, so many HVAC techs forget about it; they attempt to optimize comfort in the HVAC system and ducts, not the home itself. Techs use Manual J and S, but they don't use the infiltration rate in their calculations. Infiltration in the envelope is a major culprit of discomfort in the home, especially through and around windows.

We use blower doors to determine leakage. During the blower door test, we depressurize the home by a pressure difference of -50 Pa, and we can then calculate the air changes per hour by taking the CFM, dividing it by the volume, and multiplying that number by 60.

The pressure pan is another tool that we use to determine leakage. Pressure pans are semi-quantitative tools that help you figure out where leaks are coming from; you won't find out how much CFM leakage you have, but you will find out if there is CFM leakage.

The commercial HVAC industry has already used "fresh air" in buildings via economizers. However, the residential HVAC industry does not bring fresh air in via the HVAC system. Joe proposes solutions to seal homes but allow fresh air to enter the home in a controlled manner; when we bring that fresh air in, we could implement dehumidification measures to avoid fungal growth.

Joe also discusses:

  • Windows and energy savings myths
  • Measuring volume in the home
  • Common sources of leakage in the home
  • Gas appliances and combustion/CO risks in tighter homes
  • Outdoor air and retrofit applications
  • Backdraft
  • Balancing ventilation

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