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HVAC School - For Techs, By Techs

HVAC School - For Techs, By Techs

Auteur(s): Bryan Orr
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À propos de cet audio

 HVAC School is the ever growing online source for real training topics for technicians in the Air-conditioning, Heating and Ventilation Fields. In the podcast, we will share recorded training, tech ride alongs, share challenging diagnostic scenarios. All to help make the industry, your company, and your truck a better place to be. Développement personnel Gestion et leadership Réussite Économie
Épisodes
  • When Ammonia Ruled the World - Short #270

    When Ammonia Ruled the World - Short #270
    Dec 16 2025

    In this short podcast episode, Bryan takes us on a history journey back to when ammonia ruled the world.

    In the mid-1800s, before R-12, many inventors and scientists experimented with vapor-compression refrigeration systems to make ice. They used a variety of refrigerants in their patents, including ether, ethyl ether, carbon dioxide, sulfur dioxide, methyl chloride, and ammonia. Each one had tradeoffs, but ammonia was the favorite because it was inexpensive, very good at moving heat, and useful because its odor made leaks obvious (although it was toxic and irritated the lungs and mucus membranes).

    Toxic refrigerants, particularly sulfur dioxide and methyl chloride, were common refrigerants but had plenty of negative press due to the many deaths they caused. In response to the public's reservations about toxic refrigerants, Thomas Midgley from General Motors (who developed leaded gasoline) teamed up with Charles Kettering and DuPont to find a refrigerant that was non-toxic, non-flammable, and non-corrosive. In 1930, they announced dichlorodifluoromethane, also known as R-12 (a CFC) and trademarked as Freon. This refrigerant was non-toxic, non-flammable, and had no odor, and it effectively replaced the methyl chloride, sulfur dioxide, and ammonia.

    However, many decades later, scientists discovered that chlorine-bearing compounds were destroying the ozone layer. To combat the environmental damage, many nations signed the Montreal Protocol in the 1980s, which would effectively phase out R-12, R-11, and other CFC refrigerants. Over time, the regulations have tightened on HCFCs and high-GWP HFCs, leading us to where we are now with lower-GWP A2L HFCs and HFO blends. As with the old refrigerants, each refrigerant had a tradeoff.

    Meanwhile, this whole time, ammonia never became truly obsolete and quietly remained the lifeblood of industrial refrigeration, and it also had no global warming potential OR ozone-depletion potential. Ammonia systems run with relatively little charge, especially when paired with CO2, and ammonia is still a powerhouse today because of its chemical formula (NH3), good compression ratio, and excellent latent heat of vaporization.



    Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

    Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

    Subscribe to our podcast on your iPhone or Android.

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    Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.
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    11 min
  • Humidity, Airflow, and Refrigeration

    Humidity, Airflow, and Refrigeration
    Dec 11 2025
    In this episode of the HVAC School podcast, Bryan and Nathan dive deep into the challenges of humidity control in grocery stores and other refrigerated environments. While the conversation takes several entertaining detours (including discussions about morning radio shows, Indian weddings with elephants, and imaginary lava-heated homes), the core content provides valuable insights for HVAC and refrigeration technicians dealing with condensation and moisture issues in commercial refrigeration spaces. The hosts explain why humidity management is critical in grocery environments, where refrigerated cases and displays must maintain cold temperatures while preventing condensation on doors, frames, and floors. They discuss the evolution from traditional solutions—like energy-intensive frame heaters that kept surfaces above dew point—to modern strategies involving dedicated outdoor air systems (DOAS), strategic use of waste heat from refrigeration racks, and various dehumidification approaches. Nathan emphasizes that the key is maintaining proper dew point levels (typically targeting 45% relative humidity at around 72°F) while keeping the building under positive pressure to control moisture infiltration. A significant portion of the discussion focuses on airflow management and its impact on refrigeration equipment. The hosts explain how air curtains in display cases work on Bernoulli's principle to maintain cold temperatures, and why even minor disruptions to airflow patterns can cause product spoilage or increased energy consumption. They stress the importance of understanding building pressure dynamics, especially considering makeup air requirements for exhaust systems in sculleries and loading docks. The episode concludes with practical troubleshooting advice for technicians dealing with sweating cases and humidity problems. Nathan recommends systematically checking building pressure with a manometer, measuring dew point at multiple locations throughout the store, and verifying that door and frame heaters are functioning properly. He also suggests looking for intermittent fresh air sources and exhaust fans that might be disrupting the carefully balanced airflow patterns that keep moisture under control. Topics Covered: Dew Point vs. Relative Humidity: Why focusing on dew point (50-55°F typical target) is more important than relative humidity in grocery environmentsCondensation Prevention Strategies: Evolution from energy-intensive frame heaters to modern DOAS systems with reheat capabilitiesAirflow and Air Curtains: How Bernoulli's principle creates invisible barriers in refrigerated display cases and why disrupting these patterns causes problemsReheat Methods: Various approaches, including waste heat from refrigeration racks, electric reheat, and desiccant dehumidification systemsBuilding Pressure Management: Importance of maintaining positive pressure while managing fresh air requirements and exhaust systemsRadiant Heat Effects: How surface temperatures, not just air temperature, affect condensation on refrigerated casesTroubleshooting Humidity Issues: Systematic approach to diagnosing moisture problems, including pressure testing, dew point measurement, and identifying intermittent airflow sourcesReturn Air Placement: Benefits of pulling return air from underneath cases to capture the most humid air for dehumidification Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.
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    51 min
  • The Finned-Tube Coil - Short #269

    The Finned-Tube Coil - Short #269
    Dec 9 2025

    In this short podcast episode, Bryan explores the history of the finned-tube coil, which is what we use for heat exchange in air-source air conditioners and heat pumps.

    Air-source HVAC systems have copper tubes threaded through thin metal fins. This design was optimized to ensure the greatest possible surface area for heat exchange to occur. However, prior to the finned-tube coil, HVAC coils looked more like plumbing projects with bare copper loops, which were heavy, costly, and inefficient.

    In the early 1900s, HVAC was essentially plumbing with higher expectations; capacity was dictated purely by size and charge. In the 1910s and 1920s, early air conditioning pioneers were already attempting to increase surface area with metal discs or pipes, which evolved to continuous sheet fins. The tube would move refrigerant, and the fins would collect heat from the air and pass it into the tube; the finned-tube coil was born. The added weight was minimal, but the contact area was increased by almost 3000%, meaning coils and charges could be smaller with added efficiency.

    This move was necessary because while we already knew that heat can indeed move without touching molecules (radiant transfer), radiant cooling had a unique challenge: dew point. Finned-tube coils rely on convection and only have temperatures below the dew point in a small area, which allows us to have a small drain pan. Aluminum was also plentiful after WWII, enabling finned-tube technology to evolve to louvered fins and reach the masses. By the 1960s, finned-tube coils were in all sorts of applications. However, it became clear that aluminum was fragile, and we have since innovated to overcome that challenge.

    There are three barriers that heat transfer must overcome: air-side film resistance (air is a poor conductor), wall conduction through the tube and fins, and refrigerant-side film resistance (oil inside or laminar flow). The fins help with air-side film resistance, so we want to clean and straighten them as much as possible.

    Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

    Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

    Subscribe to our podcast on your iPhone or Android.

    Subscribe to our YouTube channel.

    Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.
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    13 min
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excellent in every way, down to earth, straight forward decent people trying to make their part of the world better by sharing their knowledge and experiences.

excellent

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