HVAC School - For Techs, By Techs

Amrit Robbins of Axiom comes on the podcast to discuss how we can use data science to transform grocery and cold storage. Axiom Cloud uses cloud analytics and AI to map data and analyze trends on refrigeration racks. It can be particularly useful to keep track of readings all the time because it’s impractical to rely on a human to take and record readings 24/7. Grocery stores are unique because they have so much product at stake and are relatively inflexible in their usage of energy. If something goes wrong on a rack, thousands of dollars worth of products may be lost.  If we could collect and review data at our fingertips, we could spot potential problems before the store loses money. These systems may also have alarms for case temperature problems, floodback conditions, and even some less immediate issues, such as a lack of floating suction. Axiom Cloud also monitors when systems go into defrost, so you can assess the cycles of case groups and figure out if they correspond to any issues.  When you have data collection, you’re not relying on a “virtual technician” to automate HVAC work. Instead, data science can empower HVAC technicians and help them do their jobs more efficiently so that they can respond to issues before they become emergencies and serve customers better. After all, computer-based systems can’t repair or clean units! Amrit and Bryan also discuss: Generating value on behalf of the customer Compressor failures Technician labor shortage Creating sustainable working hours Developing more flexible energy usage Monitoring temperature rise across cases Thermal banking Preparing for data analytics to come to the industry   Learn more at axiomcloud.ai. 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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this short podcast, Bryan goes over the basics of superheat and explains why it matters to us. Superheat is the temperature increase above a substance’s saturation temperature or boiling point. When a substance is superheated, that means it is 100% vapor; there is no liquid at all. We can look at our superheat to determine how much refrigerant is feeding our evaporator coil. A lower superheat indicates that our evaporator is more full of refrigerant than a high superheat, meaning that the refrigerant is feeding the evaporator coil well. Generally, a lower superheat value will be more efficient, but if the superheat gets too low, we can get liquid in the suction line and compressor. An evaporator can maintain roughly the same temperature throughout the bulk of the coil because the temperature stays the same during a phase change. As the refrigerant boils off from its liquid state, it remains at the boiling point. You generally want to see no less than 6 degrees of superheat, especially at the compressor. Zero superheat indicates that you have some liquid refrigerant (or that the system is off). Superheat can get tricky when we use refrigerant blends with glide. The different refrigerants in a blend have different boiling points, so the evaporator temperature can drift up. When determining the superheat of blends, we use the dew point to calculate the superheat (and bubble point for subcooling). We get superheat in the evaporator (suction line at the evaporator outlet) and the compressor (suction line at the compressor inlet). The latter will be higher because some sensible heat will be absorbed in the suction line.   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this podcast episode, Bryan and Eric Mele talk about sight glasses, the significance of subcooling in refrigeration, and liquid quality. While we measure subcooling quite often in HVAC work, we rely on sight glasses and liquid line receivers far more often in refrigeration. You need a sight glass to determine the liquid quality in a refrigeration system. Subcooling is one way to assure liquid quality without a sight glass or a receiver.  Subcooling refers to the temperature drop below liquid saturation. Head pressure can dictate subcooling, and several other factors can dictate the condensing temperature, including stacking. We use sight glasses because a clear sight glass can tell us that we have a full column of liquid (therefore subcooling) without hooking up gauges.  In HVAC, we care about having a certain level of subcooling because we want to make sure the refrigerant is fully liquid when it reaches the metering device; no bubbles should be present by the time it reaches the metering device. Like the suction line, the liquid line is a place where heat can be absorbed into the refrigerant. So, some manufacturers recommend insulating the liquid line to prevent heat from transferring to the refrigerant in the liquid line. Unit orientation also affects subcooling. For example, you can shorten the liquid line sizing if your liquid line goes downhill to the air handler. Conversely, longer lines and uphill liquid lines require special considerations when it comes to subcooling. Eric and Bryan also discuss: Liquid line receiver fill standards Subcooling and efficiency Sight glass placement Stacking liquid in the condenser Pump down strategies Mechanical subcooling Flash gas “Free” subcooling Ambient temperatures   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this short podcast, Bryan explains the basics of repairing aluminum, such as on coils or tubing. Repairing aluminum can save lots of time on mission-critical calls and can help stop refrigerant leaks that lead to ozone layer depletion or global warming. Soldering makes almost all of the aluminum repair work we will do. (Brazing is possible, as aluminum has a melting point of 1200 degrees, but that’s still a bit too close to the brazing threshold.)  When working with aluminum, we need to recognize that it melts at a lower temperature than brass, steel, and copper, and it doesn’t change color. Aluminum is also thinner and almost fades away under excess heat. First, you’ll want to figure out how to get the base temperature to the right temperature, usually with a flux. (Some fluxes require cleaning, some don’t; either way, we recommend cleaning.) The powder flux should go clear, and then you’ll be ready to apply the rod. In many cases, indirect heating can be difficult if not impossible. After you choose your alloy, you need to choose your torch. We recommend using a swirl-tip air-acetylene torch. (It’s good to use a 3 tip for microchannel.) When working with an air-acetylene torch, you will run lower temperatures than oxyacetylene torches, but you will experience more convective heat. (Heat control is the key!) When doing a repair, you want products that will make a solid bond to the outside of the joint. Make sure your products are for repairs, not for joining aluminum tubing. If you do aluminum repairs on an evaporator or condenser coil, cut the fins out of the way. Make sure your work area is exposed and clean.   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this short podcast, Bryan goes over energy transfer and heat, specifically specific heat. BTUs per ton is a common measurement; a BTU (British thermal unit) is the amount of heat it takes to raise the temperature of one pound of water by one degree Fahrenheit. 12,000 BTUs per hour is equal to one ton in heating or cooling technology. It takes one “ton” of heat to melt a ton of ice, but we kept the measurement and terminology as we moved away from using ice in industrial refrigeration. When it comes to specific heat, we have to remember that one BTU has a different heating or cooling impact on different substances. Most fluids have a specific heat lower than water, meaning that one BTU of heat will result in more heat transfer in that substance than water. Air is one such fluid that has a lower specific heat than water (0.24 vs. 1); it’s easier to heat air than water. However, the specific heat of vapors can change with temperature and pressure. When we change a refrigerant from a liquid to a vapor in the evaporator coil, it will reach saturation before boiling. As the refrigerant boils, the temperature will stay the same because the absorbed heat will all contribute to the phase change as latent heat. Even though most refrigerants have low specific heat, direct expansion systems can still move a lot of heat because it takes a lot of latent heat to complete a phase change. In other systems that don’t use direct expansion (using glycol or water instead), specific heat is more integral to the effectiveness of heat transfer because latent heat isn’t a factor in heat capacity.   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this podcast, Steve Rogers from The Energy Conservatory explains some pro tips for pressure measurement. There are three common types of pressure measurements: absolute, gauge, and differential. Absolute pressure is the pressure in a particular space in reference to a complete vacuum. (All absolute measurements use the zero point as a reference.) Gauge pressure uses atmospheric pressure as a reference point (which varies with altitude and location). Differential pressure relies on two connections (one of them is a reference point to the other). The Energy Conservatory recently designed a manometer (DG-8) that differs from the standard manometers. The purpose of that manometer is to make pressure measurements in a more cost-effective way. Most manometers have similar sensors (diaphragms move with pressure, and the measurement read is the resulting difference in resistance). However, the DG-8’s methodology can help it yield much more accurate measurements.  When dealing with small pressure measurements (like Pascals), the DG-8 is one of the most accurate manometers you will find on the market. When you look at room pressure, keep in mind that pressurizing one room will depressurize another. Temperature differences also impact the pressure, and the HVAC unit can cause differences in pressure to arise as a result of temperature differences. When you run the kitchen or bathroom exhaust and expel a lot of air in your home, you can also bring the home under negative pressure; that can even cause your water heater to backdraft. Steve and Bryan also discuss: Blower door manometers vs. DG-8 manometers Pascal scale Room pressures and air paths Infiltration and its effect on load calculations Dominant duct leakage Combustion appliance zone (CAZ) testing Mechanical ventilation and pressure Orphaned water heaters DG-8 and the TrueFlow grid   Learn more about the DG-8 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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

Trevor Matthews from Refrigeration Mentor comes on the podcast to talk about Copeland reciprocating CS compressors. He and Bryan cover Bulletin AE4-1433 (found HERE) as they look at the operating envelopes for the CS compressor. The CS compressors are hermetic reciprocating compressors that can work with some of the newer refrigerants. You will likely see these compressors in applications with smaller tonnages. You’ll usually want to charge these compressors with liquid refrigerant. If you have more than 6 pounds of charge in the system, using an accumulator is recommended. Under those charge conditions, the system also needs a check valve between the receiver and the condenser. Suction line pressure drop is one of the most important things to pay attention to in the system. Make sure the suction line is of an appropriate size, that filter-driers don’t have restrictions, and that accumulators aren’t clogged. Overall, many manufacturers recommend removing the duction driers to keep the pressure drop minimal. The recommended runtime for these compressors is also very short, only 5 minutes. CS compressors should cycle no more than 12 times per hour, and the off-time between cycles should be a minimum of 10 seconds. Before returning or replacing a compressor, make sure you check all of the electrical components, including the capacitor. If the compressor hums but has power, you could simply have a capacitor or potential relay issue. Trevor and Bryan also discuss: Return gas temperatures Discharge line temperature Compressor superheat and flooded conditions with refrigerant blends Crankcase heaters Pump-down recommendations to stop short cycling Initial charge vs. recharge Metering devices Line sizing Electrical shorts Sticking relays Single-phase vs. three-phase power Megohm testing Purging with and flowing nitrogen Burnout cleanup procedures Locking/tagging out equipment Hard start kits, potential relays, and start capacitors   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this short podcast episode, Bryan explains the science behind adiabatic cooling. Adiabatic cooling occurs in specific HVAC/R applications and in our environment as air temperatures and pressures change. When we think of cooling, we refer to the loss of heat; we are either referring to the change in the total BTU content of the air mass or the temperature change. Adiabatic cooling takes sensible heat and transforms it into latent heat. The most simple forms of adiabatic cooling can be seen in cooling towers and swamp coolers. In evaporative or swamp coolers, you have a pad saturated with water, and air moves over it. When air moves over the media, some of the energy helps evaporate the moisture on the pads, so the air loses sensible heat and becomes cooler. The thermal enthalpy (total heat content) stays the same, but some of the sensible heat has transferred to latent heat. Air that goes through a swamp cooler goes in with higher temperature and lower humidity, and it leaves with a lower temperature and higher humidity. The BTU content stays the same; the energy merely transforms. As a result, we usually only use swamp coolers in arid environments where higher humidity is desirable. You also can’t compare these to compression-refrigeration systems because compression refrigeration aims to change the BTU content and is NOT adiabatic. When we run air over an evaporator coil, some of the water vapor in the air condenses to liquid water in the drain pan. Some of the energy in the refrigerant changes the state of the water vapor to liquid water instead of changing the temperature. You’ll see a lower delta T when your return relative humidity (RH) is higher.   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.

In this short podcast episode, Bryan shares his top tips for fighting boredom at work. You can use these tips to help you get out of a rut if you don’t feel productive or get bored easily. The first tip for fighting boredom is to see the art or creativity in your work. Even in the HVAC industry, there are plenty of opportunities for artisan skills and craftsmanship. When you see your work as an art that you need to refine, it’s easier to get engaged in your work and feel proud of it. That's especially true of tasks like duct strapping and brazing. Another way to stop from getting bored is to do more things that challenge you. Being constantly challenged and being out of your comfort zone keeps you interested and can even spark a new passion. Pursuing mastery allows you to focus on one particular skill or subject to become an expert. When you master a skill, you also become a marketable job candidate and can carve out a niche within your organization. Mastery is about going deep rather than wide, and more people will feel enriched by working towards mastery than others. If you’re a social person, finding a community can keep you from getting bored. When you have a community, you will be around people who have the same interests and experience the same challenges as you. So, you won’t get bored from feeling alone. Mentorship is another way to rekindle your passion. When you choose to invest in and guide less experienced people in the trade, you can feel a renewed sense of purpose in your work. And if you’re REALLY bored, you can change everything up entirely and try something new.   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. Check out information on the 2022 HVACR Training Symposium at hvacrschool.com/symposium/.

In this podcast episode, Bryan goes through the addendum to the book Review of Vacuum for Service Engineers. He and Jim Bergmann had the honor of revising the latest edition in 2020. You can get the latest edition of Review of Vacuum for Service Engineers from TruTech Tools HERE. Pulling a Schrader core before evacuation makes a big difference in the speed of the evacuation. You can use a core remover tool to pull the cores when the system is NOT pressurized. There are three common types of ports to access the system: the Schrader core, high-flow core (CoreMax), and the multi-position service valve. You can mid-seat the multi-position service valve for high flow, but you need to remove or depress cores on the other two port types. (You must use a special CoreMax CRT to remove high-flow cores.) Three factors limit the speed of evacuation: the conductance speed of the pump, of the connecting hoses, and of the system. The hoses and manifold can severely impact evacuation. TXV and piston metering devices have short orifices and have very little impact on the evacuation time; on TXVs and EXVs, the valve should be fully open. When pulling a vacuum, make sure the vacuum pump works properly and has clean oil. Once you know that the pump is working, only pull on a tight system (no leaks) and make sure the seals are in good shape. Bryan also discusses: Micron gauge and hose placement Core depressors and CRTs Refrigerant holding charge When core restrictions are helpful Single-hose vs. two-hose evacuation speed Moisture removal One-hose evacuation of a split air conditioner Decay testing Hard shut-off valves How to solve micron gauge issues Nitrogen sweeps for wet systems   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. Check out information on the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.