Humidity, Airflow, and Refrigeration

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 environments Condensation Prevention Strategies: Evolution from energy-intensive frame heaters to modern DOAS systems with reheat capabilities Airflow and Air Curtains: How Bernoulli's principle creates invisible barriers in refrigerated display cases and why disrupting these patterns causes problems Reheat Methods: Various approaches, including waste heat from refrigeration racks, electric reheat, and desiccant dehumidification systems Building Pressure Management: Importance of maintaining positive pressure while managing fresh air requirements and exhaust systems Radiant Heat Effects: How surface temperatures, not just air temperature, affect condensation on refrigerated cases Troubleshooting Humidity Issues: Systematic approach to diagnosing moisture problems, including pressure testing, dew point measurement, and identifying intermittent airflow sources Return 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.