529 episodes

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

# HVAC School - For Techs, By Techs Bryan Orr

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

Center-Tapped Transformers - Short #145

## Center-Tapped Transformers - Short #145

In this short podcast episode, Bryan talks even more about sine waves and center-tapped transformers.
Power is generated at the power plant when an energy source (such as steam) is used to drive a drive shaft. The resulting current can be mapped as sine waves, which actually represent points on a circle; there is a rotational magnetic field around stationary conductors, and the sine waves allow us to envision the positive and negative alternations as the rotation happens.
Center-tapped transformers use “neutral” as a reference point. The secondary winding on a center-tapped transformer may have 240v power, but the center tap splits that 240v power into two legs of 120v power. There are two sine waves completely out of phase with each other, so we get 240v from peak to peak. Both sine waves cross at neutral.
Even though the split-phase power consists of two separate sine waves, an oscilloscope would interpret the voltage as a single up-and-down wave with a higher peak and a lower valley. Center-tapped transformers do not necessarily create another phase of power; they merely turn neutral into a reference. If we were to measure that split-phase power as a single 120v sine wave with an oscilloscope, we would have to use neutral as our reference. To measure the separate sine waves for a total of 240v, we would need three probes: a reference at neutral and one reference on each side.
Many European countries only use a single sine wave; center-tapped transformers are not commonplace in those countries, and neither is split-phase power. However, the split-phase power in the USA allows for more versatility; we can supply power to 120v appliances where we would otherwise need to use 240v ones.

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• 11 min
Beer & Power Factor - Short #144

## Beer & Power Factor - Short #144

Bryan describes the tricky concept of power factor and why we should care about it. He also compares power factor to a beer mug to make the topic easier to understand.
Power is often represented on a sine wave, which is a curvy line that marks the state of electrical energy at different points on a circle. Power gets stronger and weaker, and it goes above and below the neutral line depending on the excess or deficit of electrons.
Unity power factor refers to a power factor of 1, indicating that voltage and amperage are perfectly balanced; there is no lag. However, an inductance (a form of resistance) opposes the current and causes an imbalance between current and voltage. Power loss or quality refers to the difference between the input and output power that results.
Apparent power refers to volt-amps, which we’d traditionally consider to be the wattage; however, in an inductive load, the true or real power (wattage) accounts for that power loss and comes from volts x amps x power factor. We can imagine power factor as a mug of beer: apparent power (VA) is the entire mug, the foam is reactive power (wasted), and the beer itself is real power. The power company only charges for the real power, not the reactive power. However, a power factor closer to unity can help prevent motor windings or wires from overheating.
To get closer to unity power factor, we need to make sure we have a run capacitor of the correct size. You can measure power factor with a power quality meter.
Bryan also covers:
Voltage and current Root mean square Inductive reactance Capacitance and how capacitors work Transformer VA ratings
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• 15 min
Motor Speed Facts - Short #143

## Motor Speed Facts - Short #143

Bryan lays down some motor speed facts in about 10 minutes in this short podcast episode.
We can figure out how quickly a single-phase motor (PSC) will run if we understand how many cycles it will make per second. In the USA, the standard hertz is 60 Hz (60 rotations or magnetic alternations per second). Motors are inductive loads that create an electromagnetic field with a spinning rotor and stationary stator; the amount of poles on the stator determines how quickly the rotor spins (RPM).
In the RPM counts, there are some allowances for slip. Slip varies depending on the load, with excessive loads causing more slip. Some multi-tap blowers have additional winding resistance and decreased current (due to the extra taps), which increase the slip. The rated load RPM usually accounts for the RPM at high speed, not medium or low speed with added resistance.
On the other hand, variable-speed motors or ECMs are powered by a variable frequency (sometimes a variable frequency drive or VFD). The motor control takes the incoming electrical frequency and converts it into a new frequency (turning AC power to DC and controlling the cycle rate). These motors also tend to be more efficient as a result. The RPM is more variable on these motors with VFDs, whereas we could only manipulate the RPM of single-phase motors by changing the number of poles.
When replacing a motor, you can’t use a replacement motor with a higher rated RPM than the original motor. The only way to change the RPM is to get a new motor with a different number of poles, increase slip to make it slower or decrease slip to bring it closer to synchronous speed, or adjust the frequency.

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• 9 min

Neil Comparetto and John Semmelhack of the Comfort Squad join Bryan to discuss high-quality value design in a high-performance home. They explain how they design HVAC systems (heat pumps) for low-load homes in ways that are affordable, efficient, and comfortable.
High-performance, low-load homes need to be energy-efficient AND comfortable, and it can be a challenge to get both. Manual J calculations aren’t as common as they probably should be, and it can be difficult to get accurate data about air leakage, power consumption, and radiant gains as well. So, John and Neil try to collect their own data and do aggressive load calculations to avoid the fudge factors that are all too common. The air velocity inside the ducts tends to be lower in these sorts of systems.
When you have relatively low airflow in the ductwork of high-performance homes, you don’t need as many ducts or for the ductwork to be particularly large. With minimalistic ductwork, supply register placement, face velocity, and throw become very important, especially because those factors are responsible for air mixing. When the duct design conditions are right and the load has been matched, you typically get long runtimes and good air mixing.
In many cases, John and Neil use variable-speed motors in their outdoor units that allow for high heating performance. The capacity ranges are wide, allowing the units to run even during exceptionally low-load conditions. They also use flex ducts due to their pre-insulation, noise suppression, and inexpensiveness; they just try to keep it sealed and avoid compressing the ductwork.
Neil, John, and Bryan also discuss:
Monitoring load conditions with software Design considerations for filter grilles and central returns Room pressurization and airflow testing Transfer grilles The Coanda effect and curved-blade registers Vent sizing Flex duct installation best practices Duct fittings ERVs
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• 53 min
Putting Contractor Success First w/ METUS

## Putting Contractor Success First w/ METUS

Lacey Dietz with METUS and Scott Arnold with Rycor HVAC join the podcast to talk about how the industry can start putting contractor success first. They talk about Mitsubishi Electric (METUS)’s commitment to contractor success and what that looks like.
METUS’s contractor program aims to provide training, support, and recognition to create a community of successful contractors. Support comes in the form of marketing, training, tech support, and customer service, and those services are available to contractors who sell and represent Mitsubishi’s products.
As a contractor who works with Mitsubishi, Scott has been able to specialize the labor in his business and grow his business as one that specializes in installing Mitsubishi systems. Mitsubishi also provided top-quality training and allowed Scott to streamline his training process and get his apprentices feeling confident and ready to go into the field quickly.
Adoption rates for Mitsubishi’s ductless technology have increased over the past couple of years, especially as people have spent more time in their homes and started re-thinking indoor comfort. Those who are educated about heat pumps also tend to appreciate the technology as well as the mini-split units’ small footprints in their homes. The mini-split units’ smaller environmental impact than unitary systems is also a plus.
Lacey, Scott, and Bryan also discuss:
Scott’s work with heat pumps in New York Programs that benefit contractors Mitsubishi’s products and supply chain management Diamond Contractor program and tiered contractors Mitsubishi’s lead generation program and referrals Ductless vs. unitary systems Bringing education into sales Dealing with business growth in a challenging labor market Overcoming objections
Learn more about Mitsubishi and its products, visit https://www.mitsubishicomfort.com/, and you can learn how to become a contractor at https://discover.mitsubishicomfort.com/contractors.
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Check out our handy calculators HERE.

• 36 min
Retrotec - IBS 2022

## Retrotec - IBS 2022

Sam Myers with Retrotec talks to Bryan about pressures in the home and why they matter for HVAC solutions at IBS 2022.
Technicians focus a lot on ductwork and airflow, but many of them don’t focus on how the building envelope impacts HVAC performance. A lot of the HVAC equipment’s performance is affected by the push and pull of air caused by leaky areas in the building envelope.
If you have a room with too much air and another room with too little, you will have unbalanced pressures. Unbalanced pressures may result in discomfort and latent load issues, especially when unconditioned air is pulled in through the attic. Sealing the envelope well and using dampers as necessary can minimize the comfort issues caused by pressure imbalances in the home.
Instead of just using manometers for static and gas pressure, we can also use high-resolution manometers under doors to pick up pressure differences. However, the manometer MUST be high-res to pick up those subtle (but palpable) differences in pressure. A blower door is also a great tool, especially when you use it with a thermal imaging camera; the blower door amplifies the temperature effects that a thermal camera will detect, especially if you also have a good delta T.

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.

• 8 min

## Customer Reviews

4.9 out of 5
799 Ratings

799 Ratings

Tiggibrar ,

### HVACR School

Thank you Bryan, re visiting all episodes, great resource for technicians. Delighted that you have quoted Douglas Adams. I thought I was the only one.

### Let me in on the conversation if you please get some questions

I’ve been doing eating eating heat ventilation and air-conditioning for 18 years plus recently a electrical company came in and did a pressure test for the duck work and the pressures are way off now they didn’t tape up none of the registers the supply they didn’t seal up the return was like a piece of cardboard in the hole cutting it with the flex running through it they weren’t 15 feet off the measurements were wrong the other the readings were off the charts so I will leave that all they did it incorrectly and there’s anyway I can join podcast and get down on it with you let me in I got some questions fellas

BluFox3 ,

### Hit and Miss

It’s not bad. There is some really good stuff contained within these talks. The problem is that it’s becoming harder and harder to find the gems within the ‘cast as a whole with so many fluff episodes. I would recommend this to someone who’s running an HVAC business, but for the boots on the ground tech? Not really.