 n this live podcast episode, we have a fun conversation talking with Nathan Orr and Kevin Compass about grocery refrigeration. The most common types of calls are those where the machine is "not making temp." Usually, the cases can't maintain temperature due to frozen evaporator coils or backed-up drains. On low-temperature/freezer applications, we must rely on electrical or hot gas defrost to mitigate frozen coils. Hot gas defrost is a complicated but quintessential part of low-temperature grocery refrigeration because the coils easily freeze. The discharge gas has to go to the evaporator coil and merge back into the liquid line; that gas CANNOT make its way to the suction line without causing damage, so the liquid line pressure needs to remain lower than the discharge line pressure. Kevin sometimes recommends running the fans all the time in open cases because the fans aid in the defrosting process, especially when it comes to warming the drain pan. Another common issue that refrigeration techs encounter is starved coils. Clogged TXV screens often cause starved coils, but we don't usually replace the entire TXV in grocery refrigeration. Instead, we only replace the part that needs replacing (the screen). The same practice applies to other TXV components; we replace only the powerhead if the powerhead has an issue. Most grocery refrigeration systems use refrigerants that are quite different from residential HVAC refrigerants. Some of the most common refrigerants are propane and carbon dioxide. However, propane is flammable, and CO2 doesn't work very well in hot climates.  Nathan, Kevin, and Bryan also discuss:  Electric vs. hot gas defrost Walk-in boxes Bunker cases/coffin cases Hoarfrost Water heaters Defrost termination Offsets and thermistors Underground line sets Charging refrigeration systems for a wide range of ambient conditions Ammonia refrigerant    Learn more about Refrigeration Technologies HERE.      If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.     

Grocery Refrigeration Talk #LIVE

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In this short podcast episode, Bryan explains electronic expansion valve (EEV) types. EEVs perform the same function as TXVs, but they operate electronically, not mechanically. The EEV makes sure that the evaporator is full of the right amount of refrigerant at saturation; it doesn't just affect evaporator pressure. We don't want high superheat (due to inefficiency), and we don't want zero superheat (due to the risk of compressor failure). EEVs commonly have a stepper motor with a set of discrete settings depending on how many rotations the motor has made. It can be fully open or fully closed, and the number of rotations can set the valve at any value between fully open and fully closed; it's open or closed by a specific percentage. Instead of a bulb and external equalizer, a pressure transducer and temperature sensor report to the controller and give the controller the data it needs to open or close the EEV to maintain a specific superheat. Pulse-width modulation (PWM) allows an EEV to open and close rapidly. Unlike a stepper motor, PWM solenoids make an EEV stay fully open or fully closed for a specific percentage of time. It receives pressure information from a pressure transducer and temperature information from a thermistor or thermocouple.  As with a TXV, you would look at superheat and pressures to make sure the EEVs are operating correctly.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.  Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.” Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.  Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

EEV Types - Short #193

This episode of the HVAC School Live Stream covers the key concepts around heat pump efficiency and understanding the coefficient of performance (COP). Eric Kaiser from TruTech Tools and Jim Fultz from White-Rodgers provide valuable insights into how heat pumps operate and how to optimize their performance, especially in colder weather conditions. The discussion begins by exploring the COP of heat pumps and how it compares to the efficiency of electric resistance heat. A COP above 1 means the heat pump is delivering more heat for the same amount of energy input compared to electric resistance heat. Many homeowners mistakenly believe they should switch to emergency heat once the outdoor temperature drops, thinking the heat pump is no longer efficient. However, even at very low outdoor temperatures, a well-designed heat pump can still operate with a COP above 1, making it a more cost-effective heating option than emergency heat. The conversation then delves into the concept of the thermal balance point, which is the outdoor temperature at which the heat pump can no longer meet the heating load of the home. The guests discuss how to calculate this balance point and how to set up controls to optimize the use of the heat pump and any supplemental heating sources, such as electric resistance heat or a gas furnace in a dual-fuel system. They emphasize the importance of proper air distribution and avoiding blowing cold air directly on the occupants, which can be a common complaint with heat pumps. Key Topics Covered:  Coefficient of Performance (COP) and how it compares to electric resistance heat Efficiency of heat pumps at low outdoor temperatures Thermal balance point and how to calculate it Optimizing control settings to balance heat pump and auxiliary heat usage Importance of proper air distribution and avoiding blowing cold air directly on occupants Considerations for dual-fuel systems with both a heat pump and a gas furnace Best practices for programming thermostats and control systems to ensure optimal performance and comfort    Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.  Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.” Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.  Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).  

Heat Pump COP and Low Temp Lock Out

In this short podcast episode, Bryan talks about motor protection types, including overloads. The most common overload we see in residential HVAC is a built-in thermal overload, which is usually a bimetallic disk that flexes in response to heat (such as from a locked condition, electrical problem, or simply running hot) and opens the circuit. The two metals have different expansion and contraction rates, which causes the flexing; they will return to their original position once the motor cools down. In some cases, these can fail when they open and close too often; they are not designed for switching duty. Many circuit breakers have a similar thermal design and may be prone to nuisance tripping in the summer. A lot of commercial motors rely on external overloads; some are even built into the electrical box rather than the compressor. These external magnetic overloads are often integrated into the contactor, which turns the motor on and off; this type of contactor is called a starter. These starters may have adjustable overload settings based on current, not just temperature (which may also respond to nuisance sources of heat and require a cooldown period). Some circuit breakers also trip magnetically and are less likely to be affected by temperature. Thermistor-based overloads usually consist of a PTC (positive temperature coefficient) resistor; as temperature goes up, resistance goes up, which can take a motor winding out of the circuit. NTCs are in separate parallel circuits with relays; as the resistance decreases, it pulls in a coil that opens the circuit.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.  Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.” Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.  Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Motor Protection Types - Short #192

This podcast features a lively discussion on expansion valves, particularly thermostatic expansion valves (TXVs or TEVs), with a panel of expert guests - Corey Cruz (a market refrigeration tech), Matthew Taylor (head of refrigeration service at Kalos), and Joe Shearer (with Precision Air Conditioning). The conversation kicks off by busting some common myths surrounding expansion valves. The guests agree that minutiae like the precise clocking (rotational orientation) of the sensing bulb or whether it's mounted horizontally or vertically tend to be overemphasized. The key is ensuring good thermal contact between the bulb and refrigerant line. They dive into the operating principles of an expansion valve, explaining how it's essentially a balanced system of forces between the inlet (liquid) pressure, the outlet (suction) pressure, the pressure in the sensing bulb corresponding to superheat, and the adjustable spring force. Getting the superheat dialed in properly is crucial for efficient system operation. The experts share valuable insights on best practices like avoiding heat damage during brazing, using the right valve for the application, not adjusting the valve unnecessarily, allowing stable operation before making adjustments, and considerations like external equalizers. Real-world examples and demonstrations with failed valve components illustrate the importance of proper installation and maintenance. Topics covered include:  Common expansion valve myths and overemphasized factors How an expansion valve works and the balanced forces involved Superheat, hunting, and minimum stable superheat Recommended bulb insulation practices for different applications Proper bulb mounting, clamping techniques, and thermal contact When and how to adjust the valve (or not) Effects of plugged external equalizers and pressure drops Selecting the right valve size and type (bleed vs hard shutoff) Common installation errors like reverse flow direction Troubleshooting tips for various systems and scenarios Importance of airflow, load conditions, and other system factors    Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.  Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.” Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.  Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Expansion Valves - What Does and Doesn't Matter?

In this short podcast episode, Bryan answers an audience member's question and explains how to learn superheat & subcooling, two fundamental aspects of the HVAC/R trade. You can submit questions of your own at https://www.speakpipe.com/hvacschool.  Saturation is when a substance is in the liquid and vapor state in the same place. Eugene Silberstein likes to help us envision it by encouraging us to think of a horizon line on the ocean; anything below it is fully liquid (subcooled, what a submarine would travel through), and anything above it is a vapor (superheated, which a flying superhero would travel through). Superheat and subcooling can tell you a bit about how the HVAC system's main components are operating. High superheat indicates that there's more vapor in the evaporator, and you're not getting as much efficiency out of your evaporator as you probably could. High subcooling indicates that you're stacking more liquid refrigerant in the condenser, which can be good for efficiency but may also reduce the area of the condenser dedicated to condensing the refrigerant. Superheat and subcooling are NOT just there to help you set the charge; they can tell you a lot about a system and its components.    Ty Branaman has a great webpage about superheat, subcooling, and saturation at https://www.love2hvac.com/saturation-superheat-subcooling. You can also visit his YouTube channel at https://www.youtube.com/@love2hvac.  Craig Migliaccio (AC Service Tech) also has an excellent book on the topic, which you can learn more about at https://www.acservicetech.com/ac-book. You can also visit his YouTube channel at https://www.youtube.com/@acservicetechchannel.   Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.” Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.  Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Grocery Refrigeration Talk #LIVE

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