HVAC School - For Techs, By Techs Bryan Orr

This podcast episode is Part 1 of a Kalos class on rack refrigeration given by Matthew Taylor. This first segment focuses on the basic refrigerant circuit and oil management of a parallel rack system, common in market refrigeration.
Parallel racks follow the same general process as any other compression refrigeration system. However, they contain multiple compressors on a single rack. These systems have multiple suction lines that tie into one single suction header that feeds into multiple compressors. The suction side of the piping is usually a long distance with varying elevations; risers are vertical stretches of piping that carry oil and refrigerant up and pose a challenge for oil return.
The compressor takes low-pressure vapor on the suction side and turns it into high-pressure vapor on the discharge side. From there, the condenser rejects heat from the refrigerant, which brings the superheated vapor down to saturation temperature and further rejects heat to make the refrigerant fully liquid (subcooled). Metering devices drop the pressure of the refrigerant, and the cases contain evaporators that absorb heat and boil off refrigerant, which travels to the compressors via the suction lines.
Parallel racks come in multiple varieties, but the ones in this podcast are of the direct expansion (DX) variety. Saturation remains a critical principle in these systems: superheat, subcooling, and the pressure-temperature relationship all drive system operation. 
Matthew also covers:
Different types of rack refrigeration systems Customized variations between racks  Looking up case information and reading legends Oil return and controlling velocity Mechanical subcooling Full load amps (FLA) and locked rotor amps (LRA) Temperature glide: dew point, bubble point, and midpoint EPR installation Evaporator efficiency and superheat Compressor types Compression ratio and liquid or vapor injection Oil management components and controls  
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

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Standard 310 is a technical workflow created by ACCA, ResNet, and ANSI for grading the installation of HVAC systems, typically in new home construction. It plays a crucial role in obtaining Energy Star certification, which can qualify homeowners for tax credits under the Inflation Reduction Act. The five steps of Standard 310 are design review, duct leakage test, total system airflow, blower fan watt draw, and refrigerant charge verification.
In this podcast episode, host Bryan Orr is joined by guests Chris Hughes and Eric Kaiser to discuss Standard 310 and its implications for HVAC contractors.
The standard aims to ensure that HVAC systems are installed correctly and operate as designed. The process involves a third-party HERS rater conducting various tests and measurements, which contractors need to be prepared for. Proper duct sealing, airflow settings, and refrigerant charging are critical for passing the assessments.
One of the challenging aspects highlighted is the refrigerant charge verification step. The standard requires either non-invasive testing (which has temperature limitations) or weigh-in verification with geotagged photos. Chris Hughes suggests manufacturers could develop more consistent commissioning protocols to streamline this process.
Topics covered in the podcast:
Overview of Standard 310 and its five steps Importance for Energy Star certification and tax credits Role of HERS raters and HVAC contractors Duct leakage testing and proper sealing Airflow measurement methods Blower fan watt draw challenges Refrigerant charge verification options Need for consistent commissioning protocols Coordination and documentation required Future improvements to the standard  
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

Purchase your virtual tickets for the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. 

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In this short Q&A podcast episode, Bryan answers Gunther's question about kitchen exhaust and makeup air. Gunther asked if there were any studies that showed that makeup air should come very close to the hood to avoid infiltration. He also asked how to educate others who push back against the idea, particularly in kitchen exhaust systems of around 600 CFM.
Commercial facilities, especially restaurants, bring in makeup air to balance out the air being exhausted. There are costs associated with makeup air, but there are plenty of valid reasons to add it to residential structures. Being able to control the makeup air allows us to control where we bring air in from (especially when it comes to drawing in humid air or dirty attic air from gaps and cracks, particularly in vented attics).
Open-combustion appliances in the building envelope are also prone to backdrafting if the structure is under negative pressure. The structure is also more likely to have its dryer vents experience leaks under negative pressure. 
The International Residential Code (IRC) (section M1503.6.2) requires makeup air when you have an exhaust system >400 CFM. The Florida Residential Code (section M1503.4) requires kitchen exhaust systems exceeding 400 CFM to have makeup air at approximately the same rate as the exhaust rate. Furthermore, the Florida Mechanical Code (section 505.2) specifies that kitchen exhaust systems exceeding 400 CFM must have makeup air to balance the air pressure and ensure proper ventilation.
 
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

Purchase your virtual tickets for the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. 

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This episode featured Bryan Orr interviewing Sam Myers, the building science consultant at Retrotec. Retrotec manufactures products like blower doors and duct testers for measuring air tightness and leakage in buildings.
Sam discussed his role at Retrotec, which involves training contractors on using their tools properly, product design, software testing, presenting at conferences, and running trade show booths. He talked about the demanding travel schedule this requires but also the rewards of educating the industry.
The main topic was duct leakage testing - why it's important, how it's done, interpreting the results, and investigating and fixing duct leaks when problems are found. Sam explained that while a duct leakage test provides a number, that number alone doesn't indicate if the leakage is acceptable or problematic. However, it points technicians in the right direction for further investigating issues like comfort problems, indoor air quality concerns, or high energy bills.
He provided tips on using tools like smoke tests and thermal cameras to visually identify leaks, checking common leak areas like connections and return duct penetrations, and the value of testing before and after making repairs to verify the work. Sam also discussed using low-cost manometers for other tests, like checking room pressure imbalances caused by duct leaks.
Topics covered included:
Sam's role and work at Retrotec The importance of duct leakage testing How duct leakage tests are performed Interpreting duct leakage test results Common duct leak sources like connections and return penetrations Methods for pinpointing and verifying duct leaks Using manometers for other diagnostic tests Tips for contractors getting started with duct testing  
Learn more about Retrotec's resources at https://retrotec.com/. 
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

Purchase your virtual tickets for the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. 

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In this short Q&A podcast episode, Bryan answers Jeremy's question about checking the charge on rooftop units, and he gives some RTU tips.
Rooftop units often come in sets, so you can use a thermal camera to look at all of the RTUs and compare them. A thermal imaging camera may even show you where subcooling begins in the condenser, which can be a useful diagnostic hack. Try to avoid hooking up gauges each time you check the charge on a rooftop; RTUs have a fixed factory charge, and losses from your gauges can add up over time. Your senses will also come in handy; check for odd sights, sounds, and smells.
Checking suction pressure and superheat is less risky and imperfect, but it'll give you some diagnostic data. You can also check discharge temperatures to check for signs of compressor overheating (remember: 225 stay alive). 
Here are some tips for RTUs:
Get familiar with the service manual and wiring diagrams; these items will help you with the job and help you build on your knowledge of RTUs in general. Make sure you have all of your materials at the ready, including extra screws. Make sure you have access to the BAS system, if necessary. Safety is critical on rooftop units, especially when it comes to ladders, lockout/tagout, and ensuring that you have safe access to the unit (this burden is often on the client).  Pay attention to specialized equipment, including ERVs and economizers. Be mindful of curb installation, transformer taps, and phase monitoring, as those items may not be set up properly. Build up a basic working knowledge of variable frequency drives or VFDs (or know where to find information about them; THIS livestream is a good start), Keep systems clean to prevent overheating. Prevent oil logging whenever you have to replace a compressor.  
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

Purchase your virtual tickets for the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. 

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Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

This episode features an insightful conversation with Brynn Cooksey, an experienced HVAC contractor and trainer from Southeast Michigan. Brynn shares his expertise in conducting proper load calculations, sizing the equipment correctly, improving duct design, and addressing common issues contractors face.
Brynn emphasizes the importance of performing accurate load calculations, especially in older housing stock where equipment is frequently oversized by 50% or more. He discusses how oversized equipment leads to short cycling, poor efficiency, and increased utility costs for homeowners. His approach involves educating customers by involving them in the measurement process and using metrics like "duct deficiency" to demonstrate the inefficiencies of their current systems.
The discussion then shifts to heat pumps and the unique challenges of implementing them in cold climates like Michigan. Brynn advocates for a "dual fuel" approach, utilizing heat pumps for efficiency while supplementing with gas heat during extremely cold temperatures. He stresses the necessity of a tight, well-insulated thermal envelope and proper duct design to ensure optimal heat pump performance.
Topics covered include:
Conducting blower door tests for accurate load calculations Downsizing equipment and solving duct issues in retrofit applications The "duct deficiency" metric for demonstrating system inefficiencies Aeroseal duct sealing: benefits, limitations, and proper application Identifying and addressing cracked heat exchangers due to airflow issues Training sales teams on a hands-on, educational sales process The importance of building science education for contractors Overcoming hesitancy in trusting load calculation results Brynn encourages contractors to embrace building science principles, trust the load calculation process, and focus on system design rather than simply swapping out equipment. By proving these methods to themselves, contractors can transform their businesses and deliver true value to customers through improved comfort, efficiency, and cost savings.
 
Learn more about HVAC U and its course offerings at https://www.hvactrain.com/. 
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. 

Purchase your virtual tickets for the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. 

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.