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The HVAC industry's ongoing shift towards eco-friendly solutions continually introduces new challenges and learning opportunities. A2L refrigerants are at the forefront of this transformation, offering a lower global warming potential (GWP) than many of the refrigerants we’ve been using. They’re also mildly flammable, meaning they require some enhanced safety measures. One of these is the […]

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this educational session, Adam from National Comfort Institute (NCI) delivers a comprehensive deep dive into Fan Law 2 and its practical applications for residential HVAC systems at the 6th Annual HVACR Training Symposium.

Adam begins by establishing the fundamental concepts of CFM (cubic feet per minute) and static pressure, explaining how these measurements relate to system performance. He shares a humbling personal story about learning to measure gas pressure from a homeowner, emphasizing that even experienced technicians can benefit from understanding basic measurement principles. The presentation focuses heavily on Fan Law 2, which allows technicians to predict how changes in airflow will affect static pressure in a non-proportional relationship – a critical concept for equipment sizing and replacement decisions.

The core of the presentation revolves around practical applications of Fan Law 2 in real-world scenarios. Adam demonstrates how to calculate pressure drops across filters, evaporator coils, and entire duct systems when airflow changes occur. He emphasizes that static pressure increases exponentially when airflow increases, which explains why oversized systems often perform poorly. Through detailed examples using actual field measurements, he shows how a 16% increase in airflow can result in a 33% increase in static pressure, highlighting the importance of proper system sizing.

Perhaps most importantly, Adam presents a systematic approach to equipment selection that goes beyond simply matching tonnage. He demonstrates how contractors can “back into” total external static pressure calculations by carefully selecting low-pressure-drop components like evaporator coils and filters. This methodology allows technicians to predict system performance before installation, preventing the common scenario where new equipment sounds “like a rocket ship” due to excessive static pressure. The presentation concludes with a compelling comparison showing how proper component selection can reduce system static pressure from over 1.0 inches to 0.64 inches while maintaining the same capacity and airflow.

Topics Covered

Static Pressure Fundamentals
- Definition and measurement using manometers
- Inches of water column explained
- Relationship between static pressure and system performance
Fan Law 2 Mathematics
- Breaking down the intimidating formula into simple terms
- Step-by-step calculation examples
- Common mistakes when squaring numbers in calculations
Practical Applications
- Filter pressure drop calculations at different airflows
- Evaporator coil pressure drop analysis
- Total External Static Pressure (TESP) predictions
- Duct system pressure calculations
Equipment Selection Strategy
- How to select evaporator coils based on pressure drop ratings
- Filter sizing for optimal pressure drop
- Using manufacturer data sheets effectively
- AHRI matchup considerations beyond just capacity
Real-World Problem Solving
- Preventing “rocket ship” installations
- Retrofitting existing systems with proper calculations
- Downsizing benefits for static pressure reduction
- System commissioning and performance verification
Professional Development
- Moving beyond equipment replacement guesswork
- Using measurement tools like True Flow Grid
- Understanding manufacturer specifications
- Elevating installation quality through proper system design