HVAC School - For Techs, By Techs

Don Gillis joins us again to talk more about common types of CO2 systems and how they differ

In this episode, we are joined by three people who know a lot about heat pumps and cold weather. We also cover everything from the way technologies have changed, some of the pitfalls to keep away from, and why heat pumps work even in really cold climates nowadays. Chad Gillespie: Chad is a senior manager, part of Mitsubishi Electric’s Performance Construction Team. He currently leads a national team of business development managers tasked with growing the new construction market for high-performance heat pumps. He has also worked in the construction industry for 26 years and has been with Mitsubishi Electric for 9. Dana Fischer: Dana is a residential area manager at Mitsubishi Electric. He supports and promotes the installation of high-performance, ductless heat pumps in homes across Maine and New Hampshire. Prior to his work at Mitsubishi Electric, he was a program manager for the Efficiency Maine Trust. Scott Libby: Scott is the owner of Royal River Heat Pumps. He has over 35 years of experience and training in the residential HVAC industry. His team sells Mitsubishi Electric exclusively; they are one of the largest heat-pump-only contractors in the country. Heat pumps are becoming more effective and comfortable, so they are now more appealing for cold climates. Although we previously relied on gas and oil in colder climates, we have seen people using heat pumps with success in New England and even Norway. We partially have R-410A and high-speed compressors to thank for those technological advancements to heat pumps. Chad, Dana, Scott, and Bryan also discuss: Offsetting fossil fuel usage Compressor advancements Heat pump performance during the polar vortex Leaky vs. tight buildings Load calculations and equipment selection Seasonal loads Single-zone vs. multi-zone heat pumps Design software Flaring tools Triple evacuation Responsible refrigerant handling Auxiliary heat Mitsubishi Kumo station   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.

Trevor Matthews is back and dropping more compressor knowledge on us. This time, he talks about demand cooling and liquid and vapor injection. In low-temperature applications, the discharge temperature would get very high and lead to oil breakdown and thermal overload, so demand cooling is a means of cooling the compressor. Demand cooling injects saturated refrigerant into the compressor body to cool it down. You're not jamming liquid into the compressor; the refrigerant flashes, which achieves a cooling effect. A demand cooling system consists of a module, temperature probe, liquid line solenoid valve, and injection valve. On the Discus compressors, the sensor will go in the port in the compressor head. When installing these, it is important to make sure high-quality goes to the valve. It's normal to have some frost at the outlet during operation; look for frost to make sure the demand cooling system is working properly. Scroll compressors use liquid and vapor injection almost exclusively nowadays. However, there is a difference between liquid and vapor injection for scroll compressors. A liquid injection system helps the compressor avoid high discharge temperatures (and high compression ratios). The vapor injection improves capacity and efficiency. When troubleshooting demand cooling or liquid/vapor injection systems, you need to keep a few things in mind. For example, you need to make sure you have the right amount of tees when you retrofit a compressor with a vapor injection system. You may also have to repipe the vapor line and add a DTC (discharge temperature control valves). Trevor and Bryan also discuss: What happens when we change refrigerants Return gas temperature and mass flow rate Compressor head cooling fans Motor operation and spinning indicators Visual inspection Vapor injection vs. mechanical subcooling KVE vs. K4E Part replacement DTC vs. EEV w/ CoreSense diagnostics   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.

Don Gillis with Emerson joins us on the podcast to teach us the basics of CO2 as a refrigerant. He explains how it works and its applications. Carbon dioxide is a colorless, odorless gas that is becoming an important refrigerant for commercial refrigeration (R-744). It is desirable because it has a low critical point and high triple point, so we can use subcritical (below the critical point) and transcritical (above the critical point) CO2. Carbon dioxide also has a very low global warming potential (1), is inexpensive, and is very efficient at transferring heat. Above the critical point, we see transcritical fluid, which is a high-pressure fluid. Below the critical point, you get lower pressures. We don't see CO2 in our everyday air conditioners because it doesn't have the typical pressure-temperature relationship above the critical point (over ~88-degree ambient conditions). It is also more common in regions with colder ambient conditions like Canada. We rarely encounter the triple point in other refrigerants, but it is crucial in CO2 refrigeration. The triple point is the temperature and pressure at which a substance can exist as a solid, liquid, and gas. The triple point of carbon dioxide is very high, so we can come across it in normal equipment operation. We don't want dry ice in the system, so we want to charge the CO2 system with our pressure well above the triple-point pressure. Don and Bryan also discuss: John Gorrie's original machine Recovery (or lack thereof) Sublimation of dry ice (solid to vapor CO2) Risk of asphyxiation in confined spaces Leak detection Saturation and operation pressures of CO2 compared to HFCs Liquid vs. gas tanks Piping and fittings CO2 grades and moisture content Sales and distribution   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.

Sam Myers of Retrotec joins Bryan and Kaleb on the podcast to discuss building performance. He also answers some of our listeners' questions. Checking airflow is important for building science as well as HVAC. However, "airflow" is vague and can refer to static pressure readings (which isn't actually "airflow" at all), air from whole-home ventilation systems, or CFM per ton. We can also look at total system airflow with flow hoods. Equipment settings also matter when it comes to measuring airflow as it relates to building performance. Leakiness (of the ducts or structure) is a common building performance issue. Blower door tests can determine the building pressurization and are a great tool for determining leakiness. However, we usually only do comprehensive "airflow," duct leakage, and building envelope tests during renovations or other large-scale projects; we don't typically check "airflow" and duct leakage when we do small repairs like capacitor replacement. When balancing airflow, we usually rely on room-by-room load calculations. However, Sam finds that finding a pressure differential between rooms can be a bit more reliable. The main drawback is that a pressure differential won't tell you if a room isn't getting enough air, but the opposite problem is far more common and can be addressed. The duct system's location also has a lot to do with a building's ventilation or sealing strategy. If the attic is in an unconditioned space in a humid climate, it may be best to seal the area to control the dew point. Sam, Bryan, and Kaleb also discuss: Airflow measurement instruments Total system airflow Balancing and isolating rooms with comfort issues Grilles, diffusers, and vents in zonal duct design Using your senses during balancing Ventilating vs. sealing the building envelope Infiltration and air mixing Split-level homes Blower doors Building performance in commercial HVAC   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.

The great Ed Janowiak (Jon-Oh-Wok) joins us to talk about what correct airflow really looks like. He also explains how to design for it appropriately. The ACCA design series (Manuals J, S, and D) all go hand in hand to design HVAC systems properly for a given space. Correct airflow will depend on how a technician or designer uses the ACCA design series. When we say "correct airflow," we mean that the CFM per ton matches the sensible and latent load for a space while maximizing comfort for building occupants. In many cases, 400 CFM per ton is the rule-of-thumb baseline for many systems, but it's not a one-size-fits-all solution. The point of the ACCA manuals is to use math to determine solutions tailored to a specific space and avoid rules of thumb. Many technicians prefer higher airflow in the field because it leads to fewer technical problems. However, the occupied space can suffer from reduced latent removal when you have higher airflow. Variable-speed technology helps a bit to allow longer runtimes to help with dehumidification, but consumers may not be in the market to purchase those solutions. We can use airflow grids to determine the CFM on a running system. When those grids determine that the CFM per ton is below 300, that means the equipment is likely failing to match the required sensible BTUs. Airflow also affects pressurization, which you can measure with a manometer. Overall, you will want to track airflow trends and work to optimize the airflow. Ed and Bryan also discuss: Using software for calculations Friction rate Sensible heat ratio (SHR) Equipment selection and code compliance Relative humidity targets Intermittent ventilation Ancillary dehumidification Duct sweating Residential vs. commercial equipment design gap Blower door testing Testing delivered capacity and balancing Zonal pressure testing Extended performance data   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.

Have you ever heard a compressor that keeps changing in sound as it runs? Trevor with Emerson tells us more about what that is all about and how the digital compressor operates.

Joe and Eric join us, and we have a general conversation about small self-contained refrigeration units, including residential and commercial. Small refrigeration includes self-contained reach-ins and small walk-ins. These units typically use capillary tube metering devices. Some of the biggest failures that occur in small refrigeration systems happen because of dirty condensers and user error (leaving doors open, etc.). You'll also want to check that the fans are working, the compressor is running, the coil is free of ice, and that the airflow isn't blocked. Inspection is the key, and gauging up is typically a last resort. Refrigeration temperature measuring strategies can vary wildly by application. For example, open cases measure discharge air temperature. Systems with enclosed boxes (like walk-ins) typically sense return or box temperature. Small reach-in systems also typically have dial cold controls in a challenging location: buried at the end of the evaporator. There are straight and curly cold controls, but new equipment has made a shift towards electronic controls. On small refrigeration units, we don't usually see start capacitors or hard start kits; however, we do see PTC relays and thermal overloads. Domestic refrigerators also count as small refrigeration. They have independent controls that move air from the freezer to the refrigerator section of a normal household fridge; there is usually no cooling apparatus in the refrigerator. In systems with defrost timers, a bimetal defrost thermostat would open when the element detects no more ice on the coil, and defrost would terminate. Joe, Eric, and Bryan also discuss: Capillary tubes vs. other fixed-orifice metering devices Capillary tube restrictions and R-134A Leaky systems Vacuum Box temperature vs. coil temperature controllers Set point and customer expectations Safety controls Resistance in circuits Defrost fan delay and failsafe Hoarfrost   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. Check out our handy calculators HERE.

Kaleb, Joe, and Eric join us again to discuss some myths about single-pole contactors. We also cover some weird crankcase heater wiring configurations. When you have a single-pole contactor on a unit with no other resistance crankcase heater attached, the contactor energizes the compressor but is NOT a source of crankcase heat. That myth about single-pole contactors likely stems from a misunderstanding of Ohm's law and resistance heat. We care about crankcase heat because we want to prevent refrigerant from migrating into the compressor during the off cycle. A crankcase heater keeps the compressor shell warm and prevents vapor refrigerant from condensing in the compressor. Overall, crankcase heat helps prevent flooded starts and oil loss. Some crankcase heaters can be wrapped around the outside of the crankcase, and others can be inserted into the compressor. The crankcase heater and compressor winding can connect across an open contact to form a series circuit. (If you hook across L1 and T1 so that the other side has constant potential when the contact is open, a path can go to the crankcase heater.) The resistance in the compressor winding can contribute to the crankcase heat strategy, but Joe and Eric argue that the resistance is insignificant. Overall, we need to remember that resistive heat is resistive heat; in a resistive circuit, your wattage is your wattage, and you can convert that directly to BTUs. Kaleb, Joe, Eric, and Bryan also discuss: Two-pole and three-pole contactors Resistive heat Operating A/C and heat pumps in low-ambient conditions Ohming compressors Jumpering in place of a single-pole contactor Wire sizing Loud thumping when the unit shuts off Trickle current during the compressor off cycle Power factor, reactive power, and actual power Low-resistance circuits Capacitor purposes, wiring, and sizing Small charge and flood back prevention 3/8" lines   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.

Trevor Matthews with Emerson Canada comes on the podcast once again to talk about electronic expansion valves (also known as EEVs). He explains how they work, what they do, and how to diagnose them. Trevor compares electronic expansion valves to TXVs on steroids; they accomplish similar tasks, but EEVs have faster response times, better accuracy, and can improve system efficiency. The valve operates on a controller, which is the "brain" of the EEV that tells it to open or close. EEVs can come in the on-off variety (pulse-width modulation) and stepper valves, which rely on a motor to control the mass flow through the metering device. Pulse-width modulators are less accurate than stepper valves because they only have two operation settings. When installing EEVs or systems with EEVs, in many cases, the valve will point down. When brazing in stainless steel valves, you'll usually use a 30% (or higher) silver solder. It's also a good idea to wrap the valve and flow nitrogen while brazing. The bulbs of these valves MUST be insulated and strapped properly. The bulb and transducer need to be outside the refrigerated box in low-temperature conditions. When troubleshooting EEVs, the best thing to do is start off by reading the manual; you want to understand the valve and controller. Then, check the parameters and determine where the pressure transducer and temperature probe are located. Trevor and Bryan also discuss: Balance of forces and superheat control Solenoid valves How stepper motors control the mass flow Various refrigerants and EEVs Setting parameters on EEV controls Flux and flux-coated rods Evaporator feeding EXD-SH and EXD-U02 controllers Connections, cabling, and wire splices Expansion valve hunting Objectional current and electrical issues with controllers Battery backup vs. solenoids   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.