HVAC School - For Techs, By Techs

Latest Episodes:

Myth: Path of Least Resistance - Short #154 Oct 04, 2022

Show notes

In this short podcast, Bryan debunks the myth that electricity only takes the path of least resistance.

It is true that more current will typically take paths of lower resistance; it's much easier for more electrons to flow through a path with lower resistance, which is consistent with Ohm's law. Ohm's law states that a circuit will have higher current with you have lower resistance so long as the voltage stays the same.

In most cases, the voltage stays relatively constant; transformers don't often need to limit their currents, so there usually isn't a voltage drop. When power supplies are regulated, the voltage is usually fixed, not the amperage. As a result, dropping the resistance in a circuit will increase the current.

Ohm's law holds true for both resistive and inductive loads. Inductive loads, however, are a bit tricky because the resistance isn't constant. As motors spin faster, they create back EMF or impedance, which is magnetic resistance. The resistance only shows up once a motor, solenoid, or another electromagnetic component is energized; the resistance is much more dynamic.

An electrical current takes ALL parallel paths, not just the path of least resistance. The current also stays proportional to the resistance, even when it takes paths of many different resistance values. Our bodies are also parallel paths, so there's a risk of electric shock even though our bodies usually have much higher resistance than loads. Wet skin has less resistance than dry skin, so that's why electricity and water are so dangerous to us; lower resistance means that more current can flow through our bodies.

If electricity ONLY took the path of least resistance, we wouldn't be able to operate all the appliances and electrical components in our homes. The only prerequisite is an electrical potential (voltage).

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.

Dehumidification in Shoulder Seasons w/ Nikki Sep 29, 2022

Show notes

Nikki Krueger from Santa Fe Dehumidifiers returns to the podcast to talk about dehumidification equipment and strategies in the shoulder seasons (spring and fall). The shoulder seasons (and the weeks leading up to them) are when many homeowners begin to notice moisture problems in their homes.

HVAC units and dehumidifiers should have a king-queen relationship. The HVAC unit is the king and controls the bulk of temperature and humidity during the day, but the dehumidifier can take care of the humidity when the king needs help. To remove moisture optimally, an HVAC unit needs longer runtimes and a cold evaporator coil. However, there will still likely be gaps in performance, and that's when the dehumidifier can step in.

Proper equipment sizing can help us achieve better runtimes; we want to avoid oversizing the HVAC equipment, but oversizing is a bit less critical when it comes to installing dehumidifiers. The actual install configuration is more important when it comes to dehumidifiers (i.e., whether it takes supply or return air and ties into the supply or return).

Dehumidification can be coupled with ventilation and filtration; ventilating dehumidifiers bring in outdoor air and should filter it before dehumidifying. The air mixing tends to occur in the dehumidifier, and the mixed, dehumidified air then moves into the supply airstream.

Nikki and Bryan also discuss:

Condensating vents, walls, and equipment
Modern homes, energy efficiency, and HVAC
Infiltration and the building envelope's effect on humidity
Effects of equipment sizing and wall/duct insulation
Fan speed, air mixing, condensation, and humidity
Andy Ask and Ken Gehring's contributions and legacies
Humidity from household habits and behaviors
Santa Fe Oasis 105 features and operation

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.

Time Management - Short #153 Sep 27, 2022

Show notes

In this short podcast episode, Bryan gives some quick tips for time management. You can save a lot of time by prioritizing what really matters and delegating tasks.

One of the simplest but most effective ways to manage your time is to use a calendar. You can even apply the calendar to your personal life; you can get into a habit of scheduling important appointments, deadlines, and tasks. Google Calendar also allows other people to see and interact with your schedule, so it's a great tool for scheduling performance reviews, interviews, and meetings.

When you prioritize things, think about the negative and positive impacts of each thing. The ones with the highest positive and negative impacts should take priority over things with less significant positive or negative impacts. Many of the major business initiatives take place in the slow season, and many of our urgent client issues take priority during the busy seasons.

Delegating is also a critical task. Just because you can do something, that doesn't mean you should do it. So, it often makes more sense to give someone a task if they're uniquely qualified for it. If someone is uniquely qualified to do a task, then you can delegate that task to them. Delegating is NOT the same as passing work to someone else because you don't want to do it. To delegate effectively, you need to assess qualifications and prioritize.

On the management side, you can put processes in place that allow you to spend less time managing and more time doing meaningful things at work that you actually enjoy. Making videos and audio tutorials can make it easy to demonstrate processes and procedures within your company. Then, you can focus on leading by example, creating, and making everybody better overall.

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.

Become a Better Mentor w/ Eric Kaiser Sep 22, 2022

Show notes

Eric Kaiser returns to the podcast to talk about how to become a better mentor. He explains the topic from the perspective of a mentor and a mentee.

The goal of mentorship is to pass your knowledge on to someone else. When you give someone the knowledge to succeed in the HVAC/R trade, you move the trade forward and allow yourself to try new career opportunities when someone can replace you.

Some of the most effective mentorship strategies establish the mentor as a guide rather than someone who spoon-feeds the mentee. Mentorship is about supporting discovery, which also builds the relationship between the mentor and mentee. Mentors can also learn from their mentees when they allow their mentees to discover the answers to their questions.

Mentors can also benefit their mentees by talking about health, especially mental health. Those who have been in the trade a long time may know how to draw boundaries between their work and their personal lives; mentees can benefit from open discussions about those things, and it helps to know that their mentor cares for them. Good mentors help mentees prioritize their health and wellness and break mental health stigmas.

Mentors can also share references to other possible teachers with their mentees. Those relationships are especially important for mentors who don't have all the answers. Mentorship provides the context for training, and those connections provide as much context as possible. Mentors can also be mentees themselves, and those relationships are what really advance the trade.

Eric and Bryan also discuss:

Online education vs. in-person mentorship
The role of the apprentice or mentee
The Socratic method
Mentoring people about health and safety practices
Bryan and Eric's mentors
Recognizing who mentors are and treating them appropriately

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.

HVAC Measurement Types and Benefits Sep 15, 2022

Show notes

Eric Kaiser joins the HVAC School podcast to talk about HVAC measurement types and the benefits of taking each one. He also talks about point measurements and data trends.

Point measurements include static pressure, voltage readings, and readings provided by gauges. We only take those measurements once. However, when you track those on several occasions over time, you can build data trends. Single-point measurements give us information about what is happening at the moment, but they don't give us a long-term view of the system's health.

Absolute and differential measurements also have different purposes entirely. Absolute measurements require us to compare a reading to a specific, unchanging reference point, but differentials compare one measurement to another.

When we turn point measurements into trend measurements, we can see some degree of causation. Changes in data trends indicate that a problem occurred at a certain point in time and could be due to changes that coincided with the deviation from the norm. However, that's intermittent trending that relies on us to take point measurements at spaced-out points in time. Continuous trending allows us to use sensors and test instruments that map changes constantly.

At the end of the day, point measurements are like snapshots, and continuous data trends are like videos; the former only shows part of the picture, and the latter can help us solve more difficult problems by giving us a more complete idea of what's happening.

Eric and Bryan also discuss:

Qualitative vs. quantitative measurements
Filter restrictions and static pressure
Gauge vs. atmospheric pressure
Combined trend measurements
How tool usage and calibration impact measurements
Non-invasive testing
Recorded data and sample frequency
Comparative troubleshooting in spaces with similar equipment
Resolution vs. accuracy vs. precision

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.

Ventilation and 62.2 Intro & Rant w/ Genry Garcia Sep 08, 2022

Show notes

Genry Garcia joins the podcast to give an intro to ASHRAE Standard 62.2. He and Bryan also share a nice rant about accountability in HVAC design. Standard 62.2 is the ventilation standard for low-rise residential buildings, which dilutes airborne contaminants like VOCs and CO2.

Before coming up with a ventilation strategy, we need to assess the leakage rate of the building, such as via a blower door test. However, we also need to consider how bringing in outdoor air might negatively affect efficiency and comfort if we don't do it right.

Exhaust ventilation removes air from the structure and relies on infiltration to bring air back in. Instead, we can use controlled intake air, which is brought in from the outdoors instead of unconditioned spaces in the home.

Ventilating dehumidification is a strategy we can use to comply with 62.2; we can bring in filtered outdoor air and dehumidify it before injecting it into the supply ductwork. When we introduce ventilation in a Florida installation, bringing it in through the return is typically not ideal, especially if it's unfiltered.

People can go wrong with 62.2 if they remain shortsighted; when designing ventilation systems, we need to think about a lot more than the load calculations and CFM of fresh air needed. We need to focus on accessibility, ventilation strategies, and location-specific installation practices. Consulting tradespeople during the design process would likely make ventilation systems much more accessible, sensible, and effective.

Genry and Bryan also discuss:

Ventilation as an IAQ strategy
Infiltration credits
Pressurization
Continuous vs. spot measurement
Holding the right people accountable during the design phase
Intermittent vs. continuous ventilation
Automating ventilation with sensors
Controlling ventilation on a timer
Genry's ideal methods of controlling ventilation

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.

Pressure Enthalpy without Tears Sep 01, 2022

Show notes

RACT manual co-author Eugene Silberstein joins the podcast to talk about the titular topic of his book, Pressure Enthalpy Without Tears.

Pressure Enthalpy Without Tears is a book that introduces engineering concepts to HVAC technicians in a way they can understand and apply in the field. Enthalpy is a fancy way of saying "heat," and we use it to refer to the total heat content (BTUs).

The pressure-enthalpy chart shows the relationship between the refrigerant pressure and enthalpy in a system; it's like a P-T chart that shows the relationship between heat content instead of temperature.

Each refrigerant has its own pressure-enthalpy chart, but the points and lines on the chart usually form a right trapezoid. Dirty air filters and other less-than-ideal conditions can distort the trapezoid or shift it on the chart. Each side of the trapezoid represents the refrigerant inside a major component of the HVAC system: evaporator, compressor, condenser, and metering device. The pressure-enthalpy diagram allows you to get a look at individual components while keeping the entire system in mind.

To plot points on a pressure-enthalpy chart, you need the high side pressure, low side pressure, condenser outlet temperature, evaporator outlet temperature, and compressor inlet temperature. Pressure is usually measured in absolute units (rather than gauge units), but ballpark estimates are typically sufficient.

Entropy is another concept we need to consider. Compression theoretically leaves no additional entropy and is reversible. Crossing a line of entropy means that a process is no longer reversible.

Eugene and Bryan also discuss:

Technicians vs. engineers
Temperature vs. heat content
Psychrometric and pressure-enthalpy charts
Using the pressure-enthalpy diagram to assess operation costs
Electrical measurements
Predicting compressor failure
Putting passion into learning and trades education

You can visit https://www.escogroup.org/ to purchase Pressure Enthalpy Without Tears and access all of ESCO Group's resources. You can also use the code HVACSchool22 for a discount on ESCO Group's eLearning services.

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.

Total Heat of Rejection - Short #152 Aug 30, 2022

Show notes

In this short podcast, Bryan talks about THOR, total heat of rejection. He explains what it is and why we should care about it when working on HVAC/R systems. THOR is another aspect of pressure-enthalpy calculations, along with net refrigeration effect (NRE) and total heat of compression.

When we talk about system capacity, we're often referring to heat absorbed in the evaporator coil (NRE). Heating is on the opposite side of the coin; when we bring heat into a home, we care more about how much heat is rejected than absorbed. That's where THOR comes in.

More heat is rejected at the condenser than absorbed in the evaporator. The total heat content increases due to additional heat being absorbed in the suction line. Compressors also have motors that aren't 100% efficient, so a bit of inefficiency also adds a small amount of heat to the refrigerant (in a system operating normally). All of that heat adds up to the total heat of rejection (THOR).

Even though a higher total heat of rejection is desirable when we want heat pumps to bring heat into the home, we don't want our compression ratios and discharge temperatures to get too high. We have to avoid oil breakdown and other negative effects. So, modern heat pumps use variable frequency drive technologies or liquid or vapor injection to get a lot of capacity out of the compressor without overheating it.

The effective THOR only happens in the condenser. Some heat rejection may occur in the discharge line, but none of that is of use to us when we need to bring heat indoors.

Check out Eugene Silberstein's book, Pressure Enthalpy Without Tears, at https://escogroup.org/shop/itemdetail.aspx?ID=1445.

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.

Hard Start vs. Easy Start Aug 25, 2022

Show notes

Matteo Giovanetti from Micro-Air joins the HVAC School podcast to talk about the differences between a hard start and an EasyStart.

Micro-Air's "EasyStart" provides a soft start rather than a hard start. A hard start abruptly ramps up the voltage and current to the motor start; a soft start is a much gentler start that results from a gradual voltage and current increase on the start AND run windings.

The EasyStart marks a paradigm shift in how we think about "saving" compressors. It attempts to avoid drawing unnecessary inrush current, which is very common with hard starts. Hard starts may even lead to premature failure if the potential relay fails and can't take the start capacitor out of the circuit.

EasyStart has a different wiring configuration compared to hard start kits. A hard start kit consists of a start capacitor wired in series with a potential relay, which increases the torque on the compressor and removes the start capacitor from the circuit. The EasyStart has four wires; the black and white wires (L1 and L2) connect directly to the contactor, a brown wire that splices directly to the run winding, and an orange wire to the HERM terminal of the run capacitor.

EasyStart also records information about the compressor during the first few startups to optimize its performance. It also monitors overcurrent and fault conditions with phase detection; when it detects a stall, it shuts off the compressor and doesn't attempt to restart it until a few minutes have passed.

Matteo and Bryan also discuss:

EasyStart models
Solar, generator, and RV use
Impedance
Positive temperature coefficient resistors (PTCRs)
Compressors running backward
EasyStart's Bluetooth capabilities
Tech support and product education
Offering useful upgrades to customers
Running and starting watt specifications for generators

Learn more about EasyStart or purchase it directly from https://www.microair.net/. You can also contact the manufacturer by email at sales@microair.net.

You can view the EasyStart home installation video at https://www.youtube.com/watch?v=bp4U-husy1o&ab_channel=MicroAir.

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.

Heat of Compression - Short #151 Aug 23, 2022

Show notes

In this short podcast, Bryan explains what the heat of compression is and why we should care about it as HVAC/R professionals.

More heat is rejected in the condenser than absorbed in the evaporator coil, and that's because the compressor adds heat. That added heat is called "heat of compression." That heat does NOT contribute to the net refrigeration effect (NRE), as it doesn't contribute to cooling.

When we compress something, we increase the system entropy during that process. Entropy is the waste and disorder associated with work. There is some inefficiency, which we see in the form of additional heat. So, the HVAC system needs to reject that additional heat of compression, and we can plot and track reversible changes by following lines of constant entropy.

As the temperature increases, the molecules begin moving more quickly. However, the refrigerant doesn't absorb many more BTUs in the compressor (in a properly operating system). The temperature spikes, but the compressor doesn't typically add a significant number of BTUs to the refrigerant.

Heat also enters the system via the suction line, which also doesn't contribute to the NRE. Long, uninsulated suction lines can absorb a lot of heat without cooling the space at all. That heat also has to be rejected in the condenser. So, short, well-insulated suction lines tend to absorb less heat.

When plotting the heat of compression, we're looking at BTUs added into the system in the compressor, discharge line, and suction line. BTUs that don't contribute to the NRE may fall under the "heat of compression" label, though the actual definition may vary by organization.

Check out Eugene Silberstein's book, Pressure Enthalpy Without Tears, at https://escogroup.org/shop/itemdetail.aspx?ID=1445.

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.

Our TOPPODCAST Picks

Follow Us

Stay Connected

HVAC School – For Techs, By Techs

Related Podcasts

Links

Stay Connected