HVAC School - For Techs, By Techs

Matthew Taylor delivers an expert-level presentation on EPRs, building on his previous work on parallel rack systems. While his earlier content focused on the similarities between air conditioning and refrigeration, this session explores what makes commercial refrigeration unique—particularly the critical role of EPRs in maintaining optimal operating conditions across multiple evaporators running at different temperatures. This presentation was shared at the 6th Annual HVACR Training Symposium.
The discussion begins with a fundamental review of the refrigeration cycle in a typical supermarket setting, where 30 to 80 evaporators may share a common suction line. Matthew explains why EPRs are essential: when multiple cases need to operate at different temperatures (ranging from -13°F for frozen foods to 24°F for fresh products) but all connect to the same compressor rack, EPRs become the solution that makes this possible. Without them, cases would cycle on and off constantly, creating efficiency nightmares, oil management problems, and potential food safety issues.
Matthew walks through the mechanical principles of various EPR types, from the high-efficiency Sporlan SORIT valve with its pilot-operated design to the Parker A8 valve that can be installed directly in the store. He also addresses the industry's shift toward electronic EPRs, particularly the CDS modules that offer temperature-based control rather than just pressure regulation. Throughout the presentation, Matthew emphasizes practical considerations: how EPRs affect compressor staging, oil system pressure, defrost cycles, and ultimately, the core product temperatures that determine food safety. The session includes real-world troubleshooting insights and addresses common misconceptions about setting superheat on systems with EPRs.
This technical presentation provides HVAC professionals with the knowledge needed to understand, diagnose, and service EPR-equipped refrigeration systems confidently. Matthew's approach demystifies a component that many technicians find intimidating, breaking it down into understandable principles while highlighting the critical role EPRs play in modern commercial refrigeration efficiency and reliability.
Topics Covered
Basic Refrigeration Cycle in Supermarket Applications – Understanding parallel rack systems with 30-80 evaporators sharing common suction and liquid lines
Oil Management Systems – Oil separators, oil reservoirs, oil regulators, and the critical pressure differential required for proper oil flow
Compressor Staging and Capacity Control – How parallel rack compressors operate as multi-stage units to match system load efficiently
Saturated Suction Temperature (SST) – Why racks are designated by temperature (e.g., "13-degree rack" or "-13 degree rack") and how this relates to the coldest evaporator requirement
Temperature Difference (TD) Engineering – The relationship between evaporator temperature and case leaving air temperature, typically 10 degrees in traditional systems
EPR Fundamentals – Why EPRs are necessary to maintain different evaporator pressures on cases operating at various temperatures while connected to a single rack
Mechanical EPR Types – Comparison of Sporlan SORIT valves (pilot-operated, low pressure drop) versus Parker A8 valves (self-contained, higher pressure drop)
Electronic EPR Systems – Modern CDS modules and other electronic controls offering pressure control, temperature control, or hybrid approaches
System Stability and Load Management – How proper EPR settings prevent compressor hunting, reduce energy consumption, and protect oil management systems
Subcooling Requirements – Why liquid receivers eliminate natural subcooling and how mechanical subcoolers restore it before expansion devices
Core Product Temperature – The critical relationship between runtime, EPR settings, and food safety in refrigerated cases
Dual-Temperature Applications – Converting medium-temp cases to low-temp operation (like holiday turkey displays) using EPR pilot solenoids
Superheat Setting Procedures – Why EPRs must be overridden to 50-100% open position when setting TXV superheat
High Glide Refrigerants – Special considerations for setting EPRs with refrigerants that have significant difference between dew point and bubble point temperatures
Troubleshooting Philosophy – Understanding EPRs and TXVs as independent systems that don't directly affect each other due to non-critically charged liquid receiver systems
Pressure Drop Considerations – How EPR pressure losses (0.5-2 psi depending on type) affect compressor suction setpoints and energy efficiency
Electronic Control Integration – Various controller brands and approaches to managing electronic EPRs, from pressure transducers to temperature sensors and PID algorithms
 
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.
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In this short podcast episode, Bryan covers the history of the great heating debate: furnaces vs. heat pumps or combustion vs. compression. He also gives a breakdown of each other's strengths and gives his two cents on the winner of the debate.
Fire kept humans warm for much of history, but engineers developed a way to move heat by manipulating refrigerant pressures. Early heat pumps got a bad rap because they didn't live up to the hype; they had frequent operational issues, didn't heat effectively, and were largely unable to be serviced effectively by technicians.
However, heat pumps have evolved and now outperform furnaces in many areas. Ones with COPs between 2 and 5 can be anywhere from 200-500% efficient in terms of watts in, BTUs out. They also have many safety benefits over gas furnaces, including no risk of flame rollout, carbon monoxide poisoning, and gas leaks; removing the gas meter and all its risks entirely is a possibility. 
Nevertheless, some people still insist that combustion is king due to its comfort, as furnaces' heat is more intense than that of heat pumps. Furnaces also require little electricity, making them more sensible in markets with weak or dirty electrical grids. Combustion appliances also only need to work part of the year, meaning they run fewer cycles and experience less mechanical wear over the same period of time as heat pumps (thus may have longer lifespans).
Dual fuel allows you to get the best of both worlds; it allows the heat pump to handle the cooling and most of the heating for the energy efficiency benefits, and the furnace can step in when more intense heat is needed. Ultimately, the "winner" of this debate, at least to Bryan, is the most sensible solution for energy costs, safety, comfort, and reliability; the real answer will depend on the climate, infrastructure, and other factors.
 
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.
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In this engaging episode of the HVAC School podcast, host Bryan Orr sits down with Leo and Paul Sharkey, a father-son duo of mechanical engineers who made the leap into the HVAC business. Leo and Paul share their remarkable journey of purchasing an HVAC company in September 2020 and quadrupling its revenue within five years. Their engineering backgrounds bring a refreshing, data-driven perspective to an industry that often relies on rules of thumb and outdated practices.
The Sharkeys operate in the challenging Northeast market, where homes can date back to the 1600s and 1700s. They discuss the eye-opening discovery that traditional HVAC sizing methods—like the simplistic "one ton per 400 square feet" rule—fail dramatically in older housing stock. Their commitment to running thousands of Manual J calculations has transformed their approach, often resulting in smaller, more efficient systems than competitors propose. The conversation dives deep into the unique challenges of working with centuries-old New England homes, including extreme infiltration rates, non-linear heat loss curves during harsh winters, and the complications of mixing modern additions with ancient construction.
Beyond sizing, Leo and Paul tackle the practical realities of heat pump installations in cold climates. They explain why turndown ratio is critical, how they handle homes with heat loads that triple their cooling loads, and when backup heating systems are truly necessary. Their consultative approach rejects the "one-size-fits-all" mentality that has flooded the market with incentive-chasing installations. They candidly discuss the problems created by Massachusetts' generous rebate programs, which have attracted fly-by-night operators who prioritize rebate qualifications over proper design and long-term performance.
The episode also explores the balance between ductless and ducted systems, revealing when each approach makes economic and technical sense. The Sharkeys share fascinating case studies, from a 1748 house with the equivalent of a full-size door's worth of air leakage to underground concrete dome homes requiring specialized dehumidification. Their willingness to take on complex projects that other contractors avoid demonstrates how engineering thinking, combined with trade expertise, can solve challenging HVAC problems. This conversation is essential listening for anyone serious about understanding cold climate HVAC design, building science principles, and what it takes to deliver quality comfort solutions in real-world conditions.
Topics Covered
Engineering background transition to HVAC - How mechanical engineering experience in semiconductors and manufacturing informed their HVAC business approach
Manual J calculations and proper sizing - Running 7,000-9,000 Manual J calculations over five years and why they typically specify smaller systems than competitors
Old New England housing challenges - Working with homes from the 1600s-1700s, extreme infiltration rates, and heat loss characteristics of ancient construction
Heat load vs. cooling load imbalances - Managing homes where heat loads can be triple the cooling loads and how this affects system design
Heat pump turndown ratios - Why equipment turndown capability is critical for shoulder seasons and preventing short cycling in cold climates
Cold weather performance and derating - Equipment capacity loss at low ambient temperatures and the importance of proper backup heat sizing
Ductless vs. ducted system economics - When to choose multi-zone ductless over ducted systems based on home layout, infrastructure, and cost
Retrofit complications in mixed construction - Dealing with homes that combine 200-year-old sections with modern additions on the same heating system
Massachusetts incentive programs - How Mass Save rebates (up to $25,000 financing + $10,000 rebates) have impacted market quality and contractor behavior
Installation challenges at low temperatures - Field issues including undersized ductwork, poor equipment placement, defrost cycle complications, and electric backup heat requirements
Building science fundamentals - Blower door testing, weatherization impacts, infiltration effects on heat load, and wind loading considerations
Consultative sales approach - Rejecting one-size-fits-all solutions and customizing system recommendations based on home characteristics and homeowner needs
Backup heating strategies - When and why fuel-based backup systems are necessary, including power outage considerations and client comfort levels
Complex project examples - Case studies including underground concrete dome homes, storage closet air handler installations, and severely under-designed retrofit corrections
 
Learn more about Leo and Paul's business, Jay Moody HVAC, at https://jaymoodyhvac.com/. 
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.
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In this short podcast, Bryan answers a listener-submitted question and explains why heat pumps get a bit weird: when it comes to superheat in heat mode. He also explains how we can move heat from outdoors to indoors, even in temperatures below freezing (cold temperatures just have less heat, not zero heat).
In order to move heat in very cold conditions, we need very low suction pressures and cold coils, which gives us a high compression ratio. Superheat will be affected by these conditions. Remember: superheat that is too low can cause floodback, and superheat that is too high can cause the compressor to overheat.
Superheat is easy to check in cooling mode, but it's harder in heating mode, especially since the suction line is at the outdoor unit. In heating mode, we can only measure superheat between the coil outlet and the reversing valve inlet, which is a very short run of tubing.
The superheat will also be less stable in heat mode in cold weather, and it will have a wider range of "normal" values than cooling mode, depending on the conditions. Superheat could even drop to zero with some fixed-orifice metering devices (which would cause floodback). That's why many of these heat pumps have accumulators, which collect liquid refrigerant to protect the compressor. Even though TXVs attempt to maintain superheat, you may still see some variation in heat mode during cold weather. EEVs are common in ductless systems and are highly controllable but maintain relatively low superheats by design; fast metering control, intelligent logic, accumulators, and low refrigerant charges allow them to avoid floodback in low temperatures.
In any case, spikes and drops in temperature can cause the superheat to jump or collapse because the load changes (as the outdoor coil is the evaporator). Frost buildup on the coil also inhibits airflow and heat transfer, causing the superheat to change as the evaporator pressure and temperature drop. Defrost also introduces chaos to the equation. All of these should influence your judgment when checking superheat to diagnose or commission a system in heat mode.
 
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.
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Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this engaging and informative episode, Bryan sits down with Elliot to discuss his recent training experience with the National Comfort Institute (NCI), covering two intensive courses on duct system optimization and residential air balancing. The conversation offers valuable insights for HVAC professionals looking to improve their technical skills and provide better service to their customers. With a mix of technical expertise and practical field experience, this episode breaks down complex HVAC concepts into actionable strategies for contractors and technicians.
Elliot shares his key takeaways from the NCI training, emphasizing how the courses filled critical knowledge gaps about the "invisible stuff" in HVAC systems—the air itself. The discussion reveals a common industry problem: most HVAC professionals focus heavily on equipment while neglecting proper duct design and air balancing. Elliot explains how he learned to move beyond guesswork in duct design, discovering that flex duct has actual CFM ratings and that proper system design requires understanding static pressure, equivalent length of fittings, and the science behind airflow. The conversation highlights the importance of oversized return air systems—a point both hosts stress repeatedly—and explains why Florida (and possibly the entire nation) suffers from chronically undersized returns. The hosts discuss various duct system approaches, from traditional trunk lines to the flex-and-fitting systems, acknowledging that different markets require different solutions based on climate, building construction, and supply chain availability.
Throughout the episode, Bryan and Elliot tackle practical installation challenges that technicians face daily. They discuss the importance of proper flex duct installation, explaining how compressed or sagging ductwork dramatically reduces airflow efficiency. The conversation covers the critical role of balancing dampers in every branch run, the impact of proper duct strapping, and how simple adjustments like straightening kinked flex duct can immediately improve CFM delivery. The hosts also address the limitations of builder-grade installations, noting that most new construction lacks the dampers necessary for proper air balancing. They emphasize a practical, process-based approach to HVAC work that focuses on getting clients measurable results without requiring perfect conditions or unlimited budgets.
The episode concludes with a strong endorsement of the National Comfort Institute's training programs and tools, particularly the TrueFlow Grid and measureQuick technologies that simplify complex air balancing calculations. Bryan and Elliot stress the importance of ethical, high-performance contracting that delivers real value to customers rather than just marketing sizzle. They encourage HVAC professionals to invest in training and proper tools, acknowledging that while the initial investment may seem steep, the ability to provide superior service and reduce callbacks makes it worthwhile. The conversation serves as both a technical deep-dive and a call to action for contractors to elevate their skills and focus on the whole system—equipment, ductwork, and building envelope—to truly solve customer comfort problems.
Topics Covered
NCI Training Experience - Elliot's overview of the duct system optimization and residential air balancing courses, including instructor quality and course relevance to Florida's HVAC market
Duct Design Fundamentals - Moving from guesswork to calculated design using CFM ratings, square footage calculations, and proper system output considerations
Static Pressure Management - Understanding static pressure drop across coils, the importance of variable speed fans, and strategies to reduce total external static pressure
Return Air Systems - Why bigger returns are always better, the critical importance of oversized return grills, and the impact of filter face velocity on system performance
Equivalent Length of Fittings - How fittings add "phantom" duct length to runs, techniques to reduce equivalent length, and the dramatic impact of turning vanes on 90-degree turns
Flex Duct vs. Trunk Lines - Comparing different duct system approaches across various markets, the pros and cons of metal, duct board, and flex systems, and the flex-and-fitting methodology
Proper Flex Installation - The importance of stretching flex duct correctly, proper strapping techniques, and how sagging or compressed flex drastically reduces airflow
Air Balancing Techniques - The necessity of balancing dampers in every branch run, methods for achieving proper air distribution, and using velocity comparisons for troubleshooting
Throw and Mixing in Rooms - Understanding that grills, not duct size, control air throw and mixing, and the role of Manual T in selecting appropriate terminal devices
Practical Installation Tips - Simple improvements technicians can make during service calls, like straightening kinked ductwork and adding straps to reduce sag
High-Performance Tools - The TrueFlow Grid, measureQuick app, hot wire anemometers, and other technologies that simplify complex air balancing calculations
Building Performance Perspective - Moving beyond equipment-only focus to consider the entire system: ductwork, building envelope, and how they all interact
Ethical Contracting - Delivering real value to customers, avoiding the "all sizzle, no steak" approach, and providing solutions that work within real-world budgets and constraints
 
Learn more about NCI's training opportunities HERE.
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.