HVAC School - For Techs, By Techs

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Short #40 - Specifically Relative Feb 05, 2019

Show notes

In today's short podcast episode, we talk about specific gravity, also known as relative density. We explain why it matters to technicians.

When we talk about specific gravity, we're actually talking about density. We're actually using that value to assess how a vapor or liquid's density compares to air or water, respectively. Regardless, we are working with the pressure conditions of 14.7 PSIA, or atmospheric pressure.

In the case of liquids, we're relating them to water is at its densest, which is 39.2 degrees Fahrenheit. You may have noticed that ice cubes float in water. That's because water becomes less dense as it gets colder than 39.2 degrees and when it freezes. Ice is less dense and more buoyant than water.

So, specific gravity requires a reference. Because it requires a reference, it is also a relative measurement, so "relative density" is another appropriate term for specific gravity. Regardless of units, we are still comparing one thing to a constant in the form of a ratio. (For example, a liquid with a specific gravity of 0.85 is equal to 85% of the density of water at 39.2 degrees Fahrenheit.) The relative density also explains why some liquids sink and others float when mixed together.

Gases can also rise or sink based on how much lighter or heavier that gas is when compared to air. If the specific gravity of a vapor is less than one, it will rise to the ceiling. Natural gas is an example of that. If the specific gravity of a gas is greater than one, it will sink. LP is heavier than air and will sink. Therefore, LP is a bit more dangerous than natural gas because of how it takes up space due to its interaction with the air.

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.

R290 (Propane), What you need to know w/ Embraco Jan 31, 2019

Show notes

In this episode, we speak with Embraco about R290 (Propane) refrigerant, hydrocarbons, and what you need to know about them. Embraco is primarily focused on compressors and is involved in the residential and light commercial market.

The greater demand for natural refrigerants or hydrocarbons has made R290 popular. Hydrocarbons have hydrogen and carbon chains; although these refrigerants are very similar to grill propane, they are much drier and purer. R170 is another hydrocarbon for very low-temperature refrigeration. In some European countries, R290 and CO2 are becoming much more prevalent than synthetic solutions. China has invested a lot in hydrocarbon technology, and the United States has shown interest in using hydrocarbons for auto coolers and natural refrigerants for grocery refrigeration.

R290 is flammable, but most techs' aversion to working on those systems likely stems from a fear of the unknown. These systems have several safety controls that prevent gas leakage from getting in contact with sparks. So, these systems rarely ever catch fire. Embraco also has a commitment to putting safety first when they design compressors.

You can also vent R290 to the environment, which you can't do with many other refrigerants. Unlike other refrigerants, R290 has a very low global warming potential. R290 and CO2 are not perfect, but they will be the future as we move away from ozone-depleting substances and greenhouse gases.

R290 is also making its way into the residential sector. You can find it in smaller applications, such as mini-fridges and even some other domestic refrigerators.

We also discuss:

Overloads and why systems aren't as flammable as they seem
Terminal venting
Embraco's design goals and philosophy
Contamination and evacuation

Links:

http://refrigerationclub.com/

http://naturalrefrigerants.info/

http://embraco.com/Default.aspx?tabid=40

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.

Short #39 - Tricky Amperages Jan 29, 2019

Show notes

We talk about measuring tricky amperage on a blower and condensing fan motor. We also cover why you may be measuring inaccurately, resulting in a misdiagnosis.

When measuring amperage on a PSC blower motor, you may have noticed that amperage on the common is higher when the panel is off. Conversely, on ECM or X13 motors, the amperage is generally lower with the panel off. When measuring amperage, we recommend using a Bluetooth ammeter to take readings without letting the panels interfere with your measurements.

Anytime the amperage is low, the more difficulty the ammeter will have in measuring an accurate value. In cases where you're dealing with a very low amperage, you will need a higher-resolution ammeter for accurate measurements. One old-school way that you can increase your resolution is by using the 10-wrap method and putting that in series. Then, you take the amperage measurement and divide it by 10.

We don't recommend doing the under-load test on a blower; a bench test is much safer. However, the compressor and condenser fan motor capacitance can be measured under load. Outdoor tests can be a bit challenging because there is a greater possibility for interference. Current drawn outside of the clamps can indeed affect the reading, and several other nearby conductors draw current inside condensing units.

Sometimes, technicians replace perfectly fine run capacitors because the amperage seemed too high on an under-load test. To avoid interference, perform a bench test and check the actual microfarads. Tricky amperage interference also leads techs to condemn condenser fan motors when they really just picked up amperage outside the clamp. So, keep in mind that your meter could be running high or picking up interference. Any possible fail parts should undergo further testing to confirm that there's something wrong.

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.

Beacon 2 Refrigeration Talk Through Jan 24, 2019

Show notes

In this service manual talk-through episode, Eric Mele helps us discuss the Heatcraft Beacon 2 refrigeration system. We talk about what it can do and what it entails.

The Heatcraft Beacon 2 is a refrigeration system with more electronic controls than electromechanical. However, it is quite user-friendly, and it allows you to see what the system is doing at almost all times. The monitor doesn't allow you to adjust anything in the system, but it lets you see valve position, superheat, time until defrost, and more as the system is operating.

The Beacon 2 has a suction pressure transducer that maintains superheat. You can dial in the superheat on the control, and the system should control it almost exactly as long as all the components are working properly. You can also manipulate the wiring to run multiple evaporators off of one condenser. (There are master and slave evaporators, and you must differentiate them when configuring the controls.)

When it comes to parameters, you have to set your defrost type to air or electric. In general, you use electric defrost for freezers. You must also set your refrigerant type accordingly. Then, you set your box temperature. Medium-temperature applications tend to be around 35 degrees, and many low-temperature applications tend to be around -10 degrees. You also have control over defrost settings and temperature units (Fahrenheit or Celsius). You can also find frequent parameters on the evaporator panel for more information.

Most errors will be sensor errors. Many sensor issues are easy to test because of the user-friendly monitors. You can compare your reference sensor to the data to check the accuracy of what's being reported to the board.

Eric and Bryan also discuss:

Forcing pump-down and defrost
Schematics and wiring practices/applications
Headmaster valves
Setting pressure controls
Defrost frequency and failsafe

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.

Short #38 - Low Ambient Cooling Jan 22, 2019

Show notes

This short podcast episode covers the why and the how of low ambient cooling and refrigeration.

Low ambient cooling refers to operating A/C equipment during low outdoor ambient conditions. Typically, the cap of operation is around 55 or 60 degrees. However, some commercial facilities need cooling when the outdoor temperature is cold. For example, those facilities may have to cool electronics or large volumes of people. In buildings that don't have economizers, running the A/C in cold ambient conditions may be the only option. The same applies to restaurants, which always need to run freezers and coolers.

When the outdoor ambient temperature drops, the condenser rejects more heat to the outdoors. Head pressure drops, and there may be an insufficient pressure drop across the metering device. We also can't run A/C evaporator coils below 32 degrees, as there is no defrost mechanism in straight-cool A/C systems. So, the strategy to get around those issues is to focus on raising the head pressure by modulating the condenser fan motor.

A fan cycling control can turn the condenser fan on and off based on pressure. So, we try to maintain a fixed pressure in the condenser by allowing that control to shut off the fan when the pressure drops too much. However, fan cycling can be a bit jarring for the system.

Motor master controls help modulate the motor by decreasing voltage to the motor. However, that fluctuating voltage isn't necessarily good for the motor. In those cases, you must have a ball-bearing motor. Unlike the motor master, a refrigeration headmaster is a valve that allows discharge gas to enter the drop leg.

Variable frequency drives can work with a three-phase motor to vary the speed of the motor. When the speed can vary easily, you can manipulate the pressure.

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.

VRF in Real Life w/ John Oaks Jan 17, 2019

Show notes

In today's podcast, I talk to John Oaks about his experience as a VRF tech in the field, including branch boxes and two-pipe vs. three-pipe technology. John primarily works on the troubleshooting and service side rather than the installation and programming side of the field.

Variable refrigerant flow (VRF) systems, also called VRV systems when manufactured by Daikin, are commercial HVAC systems. VRF systems work best in commercial buildings with some degree of fragmentation, like offices and medical facilities. These systems are similar to multi-zone ductless systems, but they operate on a much larger scale. VRF systems have a branch box, which acts to direct traffic between the various zones of a building and parts of the system; the branch box allows the unit to heat and cool simultaneously.

A 24v signal drives most of the controls. These controls are "daisy-chained," as VRF systems are very interconnected, and a defrost signal can have up to about 50 destinations to various components. The entire VRF installation process requires careful attention to detail, not just on the programming side.

When it comes to common issues with VRF systems, the refrigerant charge is one of the most critical problem areas. These systems mask issues with the charge, so it is difficult to find out if a system is undercharged or overcharged. In addition, you can't weigh out the charge in the same way that you would in a residential system.

John and Bryan also discuss:

Metering device placement
Industry improvements and upgrades
Inverter boards
Line set length and charge issues
Flares, brazing, and ZoomLock
Condensate removal and drainage strategies
Diversity of zones and efficiency
Two-pipe vs. three-pipe configurations
Cooling mode, heating mode, and mixed conditions

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.

Short #37 - The Trade Skills Gap: A Manifesto Jan 15, 2019

Show notes

This is a voice-over audio presentation of the article of the same title on the HVACRschool.com website ("The Trade Skills Gap: A Manifesto).

The manifesto discusses the value of technicians and the trades in modern society. It also covers the plague of snobbery that we are all too familiar with in the world.

You can read "The Trade Skills Gap: A Manifesto" HERE.

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.

Furnace Sequence Of Operation Jan 10, 2019

Show notes

Jason Obrzut comes on the podcast and talks us through his furnace sequence of operation training: "Take It Slow, It's Gonna Blow!"

There are 6 main steps in Jason's furnace sequence of operation training. The phrase, "Take It Slow, It's Gonna Blow!" should help you remember the sequence (Thermostat, Inducer motor, Safety switch, Igniter, Gas valve, Blower motor).

The first component in the furnace sequence of operation is the thermostat, which initiates the call for heat. So, the thermostat has to send the signal to the circuit board. After the board receives that signal, it sends 120v out of the board to the inducer motor.

Next, the inducer pulls the gas combustion air into the heat exchanger. That air will then be deposited into the exhaust. The inducer is what aids the venting action and is a critical part of a furnace.

The safety switch is a general term for a negative pressure switch with a hose connected to the inducer housing or heat exchangers. Negative pressure from the inducer motor will close that switch. When that switch closes, 24v goes back into the board.

Then, the board sends a signal to the igniter. Now, you will finally begin to see heat delays. Silicon carbide and silicon nitride are common igniter materials nowadays, but they are fragile.

Once the igniter has worked long enough, the gas valve opens. We get 24v from the board to the gas valve, which brings on the gas flow and starts a timer.

When the timer expires, the blower motor will come on. This component is the LAST one to come on.

Jason and Bryan also discuss:

Pressures on the flue
Cracked heat exchangers
Safeties not closing
Hot-surface vs. intermittent-spark vs. direct-spark ignition
Flame sensors and proving flame
DIP switches

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.

Short #36 - Stack Effect Jan 08, 2019

Show notes

In this short podcast episode, we talk through stack effect. We explain what it is and what sorts of comfort issues it can cause in a home.

Most of us understand that hot air rises even though heat itself doesn't rise. The stack effect is precisely a version of that piece of common knowledge; hotter air is less dense than cooler air, so it floats above the cooler air. In hotter air, the molecules move a lot faster than they do in cooler air, so they can start to separate from each other, which reduces the overall air density.

For the most part, we don't work pressurize air in HVAC work (not refrigerant), but we do change the temperature. The temperature changes cause the difference in air densities to emerge.

If we're dealing with a furnace system in a two-story house or a home with high ceilings, we see that stack effect in action. When that hotter air rises and cooler air sinks, the hotter air makes way for a vacuum that draws colder air into the building. While that hot air rises, the colder air comes in under doors and through low cracks. Although the air that's coming out of the appliance is warm, it can't do much to heat the space before rising.

The reverse stack effect can also happen. When you have poorly sealed can lights or cracks in the ceiling, the colder, denser air will sink and create negative pressure near the highest point of the room. When we have that negative pressure, hot air can get pulled in from the attic or other undesirable locations. In Florida, we have to worry quite a bit about the reverse stack effect, whereas the stack effect is more of a concern for colder climates.

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 Future of App Based Diagnosis w/ Jim Bergmann Jan 03, 2019

Show notes

Jim Bergmann gives us a year-end review of all that is happening at MeasureQuick and his predictions for the future of app-based diagnosis. He also covers what's been going on with Redfish, BluFlame, BluVac, Supco, Testo, and Fieldpiece.

Diagnostic tools only work if the buyers understand how to use them. When apps can assist the tool buyers and users with diagnosis, the tool manufacturers can focus more on improving the technology; they can leave the software and education to mobile applications. Implementing gas appliance diagnostic education has been a challenge for Jim and other app developers. However, they are attempting to take app-based gas appliance diagnosis to the next level. The goal of diagnostic apps is to educate technicians about tools and readings and to make diagnoses more comprehensive.

From the start, one of MeasureQuick's major focuses has been accessibility and ease of use. A diagnostic app that gives technicians a seamless way to take readings, store data, and learn about their measurements should be easy to use, so Jim has put a lot of work into making a user-friendly app. So, the next step for MeasureQuick in terms of accessibility will likely be to allow users to share data for remote viewing.

MeasureQuick has incorporated education on the basic refrigerant circuit, electrical components, gas appliances, and vacuum within the app. Soon, Jim would like MeasureQuick to expand into the refrigeration and geothermal sides of the HVAC/R world; he'd also like to implement project notes.

Jim and Bryan also discuss:

Monetizing diagnostic apps
Tying tools into diagnostic software
Wireless range and BlueTooth considerations
Working with programmers
How much might I invest in an app-based diagnosis app?
Third-party quality control
Future-proofing
Project or process-based functions
Integration
Electronic accessibility and pricing

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.

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