HVAC School - For Techs, By Techs

In today's podcast, Bryan talks about voltage (volts) and resistance (ohms), specifically using a voltmeter and an ohmmeter for diagnosis. We also discuss voltage drop. In many cases, Ohm's law is impractical for field usage because of the additional resistance from inductive reactance. We also don't typically measure impedance and only care about resistance on the windings. However, Ohm's law is still a valuable concept because it teaches technicians the relationship between voltage, amperage, and resistance (ohms). Ohm's law states that volts equal amps multiplied by ohms (E = I x R). Therefore, if the volts stay constant, ohms will increase as amps decrease and vice versa. We distinguish lines from loads in circuits; we say that loads are the parts that "do" something due to resistance in a circuit. There are two kinds of loads: inductive and resistive. Inductive loads generate expanding/collapsing magnetic fields, which can also cause rotational force or activate a solenoid. Resistive loads generate light and heat, so heat and resistance are related. Of course, the diagnostic tools we use (multimeters, voltmeters, ammeters, ohmmeters, etc.) also have their limitations. A voltmeter merely determines a difference in charges between two points. When using a voltmeter on a low-voltage circuit, try to plant one of your leads on the common side and take readings throughout the circuit with your hot lead. Ground is also NOT a reliable reference point for diagnosis. The point of measurements is to prove what we suspect to be true; we must understand what our data mean for system operation and what our tools' diagnostic limitations are. For example, when we ohm out contactors, we check to see if they're open. Bryan also discusses: Fixed wattage or resistance Reading between wires Meter lead placement Amperage (dynamic current/electrons) Undiagnosed shorted circuits Contact points Voltage drop and resistance Infinite ohms Wire length   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Jamie Kitchen from Danfoss talks all about variable-speed motor technology. He discusses why those motors exist, what they do, and how to think differently about the future of HVAC/R. Most techs think about variable-speed motors as the X13 and ECM blowers in residential applications. Those motors can adjust their performance based on ambient temperatures and moisture levels. So, variable performance may result in better comfort and efficiency. ECM motors adjust airflow based on sensor inputs, especially dehumidification calls. The sensors may pick up both sensible and latent heat content. Sensible heat is what we can feel (dry-bulb temperature). Latent heat refers to moisture in the air (humidity, wet-bulb). ECM motors adjust their speed based on data from both, which is highly beneficial for greater comfort in the home. Human comfort is a lot more complex than feeling satisfied with a single number on the thermostat; ECM motors help control humidity and give you more leeway over selecting an acceptable dry-bulb temperature of a space. Variable-speed motors exist on the commercial side of the HVAC industry as well. Commercial HVAC equipment brings in more fresh air and is overall less restrictive than residential. A variable-speed motor can help manage the latent heat of fresh air and work as a form of air treatment. Variable-speed motors compare indoor and outdoor conditions to treat the fresh air and maintain the indoor conditions. These motors account for sensible and latent heat loads, just like the residential ECM motors, and they adjust themselves constantly. Jamie and Bryan also discuss: Capacity and heat profiles X13 motor controversy Having multiple variable-speed components in a system (compressor, blower, etc.) Sensible heat ratio (SHR) and heat load matching Complex human comfort Reheat coils Air treatment requirements   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Jack Rise returns to the podcast to share some duct design facts with us and talk about his Manual D book on the ACCA website. Before we can even start thinking about duct design, we need to think about the total effective length; even before that, we also need to think about finding the critical path. The critical path is the path with the greatest resistance to airflow (from the return to supply); the fittings in the critical path contribute to the duct's total effective length. Flex duct is a controversial and somewhat complicated building material. It's common in Florida, but Jack doesn't use it in his duct designs; he can't depend on others to install it properly. Very few people tend to install flex ducts as tightly as they probably should. Noise is a problem for ducts, and takeoffs on the plenum are a significant contributor to noise issues. Instead, Jack suggests having a takeoff from the collar that goes straight into the appropriately sized duct for the desired airflow. (It's also worth noting that noise is subjective and is difficult to measure.) It's also unwise to position two takeoffs directly across from each other, as noise travels across those. The rise of indoor air quality (IAQ) products also requires us to look at duct design facts. Filtration improves IAQ but increases static pressure and can impede airflow. We need to be able to plan for IAQ products when we design ductwork. Jack and Bryan also discuss: Selecting the equipment location and position Balancing damper placement and leakage Radial systems and symmetry Plenum sizing Why panning is not great (and illegal) Why bay jumping is a bad idea Duct design vs. truss positioning Airflow in the occupied zone   Check out Jack's book, Understanding Manual D, HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Nate Adams joins the podcast to describe the method behind his madness of removing gas meters and installing heat pumps in Ohio. Nate is in the home performance business, and he focuses on its intersection with the HVAC industry We typically find heat pumps in milder climates, so removing gas meters and replacing them with heat pumps is a bold move in cold climates. However, high-performance heat pumps have inverter technology, which allows them to run in colder climates without freezing over in the snow. Nate predicts an eventual switch to heat pumps from fossil fuels. Heat pumps that rely on geothermal, solar, and other renewable energy sources will be much better for the environment than natural gas and oil. Backdrafting and CO issues are also nonexistent in heat pumps. However, we also have to consider domestic hot water and other appliances that use natural gas when we switch homes over to heat pump technology. When colder climates embrace electric heat pumps, they will have to prepare for increased dehumidification needs due to the moisture in the air during the spring and fall. According to some tests run by Nate, fully electric systems model nicely and perform on par with gas furnaces in his Ohio climate. However, some people may object to heat pump installations because they prefer the comfort of gas furnaces. When you look at mean radiant temperature (MRT), surface temperature contributes most to human comfort. In that case, BTU output and load matching are what really matter, not the system type. Nate and Bryan also discuss: Equipment sizing for load conditions Split systems and backup heat Being theoretical vs. using real data ACH50 vs. CFM50 High-efficiency furnaces and combustion air Determining surface temps and MRT Startup and commissioning of high-performance heat pumps Dehumidification and reheat systems   Learn more at energysmartohio.com and natethehousewhisperer.com. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Bill Johnson is one of the great educators and writers of our time in HVAC/R. In this podcast episode, he shares some information about his career and some of his top tips on keeping systems leak-free. Bill began his work on leak-free solutions by using Glyptal on centrifugal compressors. The Glyptal would harden around leaks and seal them up. Nowadays, this is an ineffective approach to sealing leaks in higher-pressure systems. Bill got the idea to start manipulating pressures to minimize leaks with a standing pressure test for 24 hours at the highest test pressure recommended by the manufacturer. That is Bill's best practice, though it is not always feasible. Bill's rationale is that leaks become much more evident under those testing conditions. (Remember, pressurize the line set. Pressurizing the system can be a bad idea.) On top of that, Bill recommends pulling a deep vacuum and performing a standing vacuum check according to the manufacturer's guidelines. Fitting inspections are also critical; fittings may be sealed imperfectly, and they are common leak points. Check fittings with a mirror and a good light to look for imperfections and cracks. Leaks generally occur in piping, not the equipment itself. Moreover, vibrations and corrosion generally cause leaks. Begin a leak inspection by leak-checking the gauge ports BEFORE attaching gauges. In general, inspect the entirety of the equipment with your senses before attaching gauges. When leak-testing with soap bubbles, make sure to use one that doesn't need to be washed with water, as water can lead to corrosion. (We recommend Refrigeration Technologies Big Blu.) Most of all, don't leave a job until you find a leak or confirm that the system is leak-free! Bill also discusses: Being an HVAC teacher Critical charge leak detection Pressurizing with nitrogen Misleading leak detection equipment Torque wrenches   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Jim takes us all the way through the history of furnaces, from the Stone Age when he was a child to modern modulating condensing types. The goal of a furnace is to move heat, so a furnace uses heat exchangers to facilitate heat transfer. Furnaces have primary and secondary air. The primary air goes through the burner, and the secondary air goes around the flame and is pulled in around the heat exchanger inlet. So, the flame's heat creates a draft that pulls air in. Natural gas and oil (LP/propane) furnaces are common nowadays, but we initially burned wood and coal in furnaces. The first gas furnaces came into existence by modifying coal, not from the gas lines we see nowadays. Long ago, the flue gases were also exhausted to the basement; CO poisoning was less of a concern back then, as combustion was usually complete. Burning the building was a much more severe risk. The first "gas crisis" in the 1970s forced us to focus on gas furnace efficiency. In that time, we developed spill switches and retrofit kits that converted furnaces over to spark ignition. In the 1980s, we came out with the draft-induced 80% furnaces we see nowadays. We also eliminated standing pilots and draft diverters. Even though the appliances became more efficient, we didn't actually burn the gas any more efficiently. So, despite the technological advancements we've made over the years, we don't actually burn gas any more efficiently than we did in the 1930s. However, our modern furnace technology has eliminated standby losses, controlled ignition, and focused on the role of latent heat in combustion. Jim also discusses: Flame color and types Draft hoods and diverters Products of complete combustion Excess air: a double-edged sword Natural ventilation Efficiency percentages Furnace testing and ratings Turbulators Modulation   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

This podcast episode on electrical circuits is a class recording. In it, Bryan discusses transformers, ground, common, and line vs. load sides of a circuit. Transformers use induction to pass alternating current signals to electrical appliances. Alternating currents (AC circuits) are tricky because the current switches direction each time. Therefore, the current flow is difficult to visualize because the direction keeps changing. Electrons naturally want to go to the other side of the transformer, not to ground. So, we have to connect both sides of the transformer to ground to send electrons to ground. (In this case, ground refers to the metal body of equipment, not the earth.) A "short" is an undesigned path, typically taken at high current due to low resistance. The high current can blow fuses and cause equipment failure. Therefore, we connect to ground to prevent that high current from taking paths that will cause equipment failure. The part of the circuit that we call "hot" is on the line side of the switch. That part is the line that goes into the switch. The part of the line that leads from the switch to the load is called the load side. After the load, we have "common" or "neutral." When common is connected to ground, it will be electrically the same as ground. However, it's worth noting that "common" can mean several different things in electrical. (Typically, we call common "L2" in high-voltage circuits with multiple phases, "neutral" in 120v circuits, and "common" in low-voltage circuits.) Bryan also discusses: The downsides of memorizing wire colors for making connections "Common" misconceptions Switch types in electrical circuits Thinking of connections as a switch and load Various terminals and wires    If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In HVAC work, we deal with quite a few electrical components. But where does electricity come from? Why do electrons move? In this podcast episode, we talk about differential charges, sine waves, and some voltage measurement basics. A large chunk of electrical theory is centered on electron movement. We get electrons to move with differentials in charges or energy states. Nature tends towards equilibrium, so electrons will move to restore a state of balance. A battery or transformer does not create energy; they create energy imbalances that cause electron motion to occur. Alternating current (AC) creates a differential by reversing the direction of current several times per second. Transformers and motors use AC power and inductance to drive HVAC systems. When testing with a voltmeter, you're looking for a difference in charges. So, the probe placement matters. When you have no difference in charges, no electrical work is being done. Most of the power we use comes from power plants. At these power plants, rotating magnetic fields generate the power we use. Power generated through magnetism creates a sine wave. A sine wave is a variation of a circle; the wave goes up and down in a cyclical pattern. So, you can look at sine waves and determine exactly how legs of power are out of phase with each other. For example, single-phase power comes in and splits at the transformer, creating an opposing sine wave that is 180 degrees out of phase with the power leg (when one wave peaks, the other valleys). There is also some confusion surrounding "neutral" and "ground." Ground is merely a conductor for safety reasons and has nothing to do with electrical operations; the ground does not generate electron movement. Neutral is NOT the same thing; neutral is a circuit conductor, but we usually connect it to ground.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Do you think of the building envelope as a duct? Do you test it? In this podcast episode, Joe Medosh talks to us about envelope testing and why it’s the future of building health and comfort. The building envelope is the largest duct in the entire home. However, so many HVAC techs forget about it; they attempt to optimize comfort in the HVAC system and ducts, not the home itself. Techs use Manual J and S, but they don't use the infiltration rate in their calculations. Infiltration in the envelope is a major culprit of discomfort in the home, especially through and around windows. We use blower doors to determine leakage. During the blower door test, we depressurize the home by a pressure difference of -50 Pa, and we can then calculate the air changes per hour by taking the CFM, dividing it by the volume, and multiplying that number by 60. The pressure pan is another tool that we use to determine leakage. Pressure pans are semi-quantitative tools that help you figure out where leaks are coming from; you won't find out how much CFM leakage you have, but you will find out if there is CFM leakage. The commercial HVAC industry has already used "fresh air" in buildings via economizers. However, the residential HVAC industry does not bring fresh air in via the HVAC system. Joe proposes solutions to seal homes but allow fresh air to enter the home in a controlled manner; when we bring that fresh air in, we could implement dehumidification measures to avoid fungal growth. Joe also discusses: Windows and energy savings myths Measuring volume in the home Common sources of leakage in the home Gas appliances and combustion/CO risks in tighter homes Outdoor air and retrofit applications Backdraft Balancing ventilation   Check out Retrotec at retrotec.com or purchase Retrotec products from TruTech Tools at trutechtools.com/retrotec. (Use the code "getschooled" at checkout for a discount!) If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Ductless expert Jesse Claerbout talks about his best maintenance practices for ductless air conditioners and heat pumps. This episode is part 2 of the two-part series.  Ductless outdoor units tend to have clean condensing coils. The only real issues are grass clippings (and cottonwood, in some locations). which typically don't affect performance too sharply. Jesse likes to clean outdoor units with plain water; he does not use cleaners. Drain cleaning is a little more involved than condenser cleaning. When cleaning a gravity drain, Jesse uses a shop vac to get rid of standing water. He does not run water through the drain line until after he begins reassembling everything after cleaning. Three main lines need to be insulated: the suction line, expansion line, and drain line. A proper ductless maintenance procedure will include checking the state of those lines' insulation. Condensate pumps can be a necessary evil in ductless unit maintenance. The cleaning procedure is straightforward, but it requires a lot of work and leaves plenty of room for techs to cut corners. Much of the difficulty comes from exposing the reservoir, which is the component that truly needs cleaning. You can clean it from the poly-tubing, but you must use a shop-vac to clean it thoroughly. When you finish, make sure that the blower wheel sounds right and that no parts are rubbing against each other. Let the unit run for 15-20 minutes before taking line temperatures so that all the parts can dry. Check the charge (preferably without gauges), air temperature split, and your amperage to make sure that the unit works as it should. Overall, the most important goal of ductless maintenance is to establish a cleaning regime that works for your business and the customer.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.