HVAC School - For Techs, By Techs

Latest Episodes:

Critical and Triple Point w/ Rusty Walker Nov 15, 2018

Show notes

Rusty Walker with Hill-Phoenix comes on and talks about CO2 triple and critical points. He also covers some best practices for refrigeration techs working with CO2.

The triple point is the temperature and pressure at which a substance can exist in all three phases of matter. CO2 has a very high triple point, and CO2 refrigeration equipment can reach its triple point during operation, unlike most other refrigerants. Solid CO2 is dry ice, and it sublimates by becoming a gas and bypassing the liquid CO2 phase under low-pressure conditions. Therefore, the relatively high pressure applied in a CO2 refrigeration system keeps the refrigerant in a liquid state. We want to avoid reaching the triple point because solids can cause restrictions.

The critical point is the point at which a substance becomes a supercritical fluid and loses its pressure-temperature relationship due to densities equalizing. CO2 has a low critical point, only 87 degrees Fahrenheit. So, CO2 refrigeration systems will have supercritical or transcritical CO2 in their systems. You cannot calculate superheat under these circumstances, and you cannot condense supercritical fluid. So, you need to send the supercritical fluid through a gas cooler to reduce the temperature before it can change state.

Critical and triple points are important to keep in mind when working on a CO2 system. You want to control pressure to steer clear of the triple point and understand the necessity of gas cooling when dealing with supercritical fluid. Remember: all of the basic laws of thermodynamics still apply.

Rusty and Bryan also discuss:

CO2 leak detection
Bars and pressure conversions
Supercritical fluid as a solvent
Avoiding triple point on a service call
Recommended equipment and practices for working on CO2 systems
Vacuum
Booster system piping and brazing

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 #30 - Braze or Solder Anything Nov 13, 2018

Show notes

In this short podcast episode, we cover what you need to consider before you solder or braze any type of joint in HVAC/R work. We want to give special thanks to Solderweld; you can learn more about their products at solderweld.us.

When you braze or solder anything, you need to know your base metal. The base metal's temperature and composition will determine which type of flux you will use. For example, if you are working with steel, you can't use fluxing agents with phosphorus. Instead, you will need to use high silver rods and a separate flux. Copper rods with phosphorus don't require a separate flux.

The main difference between brazing and soldering is the temperature. When you work with temperatures above 840 degrees Fahrenheit, you're brazing. Anything below 840 degrees counts as soldering. In both cases, you use an alloy that differs from the base metals.

Copper is highly conductive and is one of the most common metals we use for brazing and soldering. So, it is pretty easy to draw the alloy into a copper-to-copper joint because the copper heats easily and evenly. Steel is nowhere near as conductive as copper, so it can be challenging to work with because the heat localizes. So, on copper-to-steel joints, you need to understand the different behaviors of the metals. It's also a good idea to know the melting point of your base metals to prevent overheating.

As we heat base metals, they change color. When those metals get to a cherry red, that's a great range for brazing; don't let the temperature rise or fall much below that.

We also discuss:

Soft solder
Metal expansion and contraction
Copper-to-aluminum brazing challenges and practices
Flux usage and best practices
Alloy-Sol and bonding
Preventing leaks

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.

Hot Gas Reheat Dehumidification w/ Eric Mele Nov 08, 2018

Show notes

Eric Mele is back on the podcast. This time, we cover hot gas as a reheat dehumidification strategy with all of the broad strokes you should be aware of.

One common dehumidification strategy is the hot gas bypass; this strategy allows you to operate under low load. Hot gas reheat is when you add discharge heat back to the conditioned space. When you use reheat for dehumidification, you cool for the purpose of dehumidification and then add sensible heat to remove moisture on the coil. So, you don't overcool the space to an uncomfortable level.

Hot gas reheat uses waste heat from the equipment to remove moisture. Using waste heat is not a very efficient process, but it is better than using electricity or fuel to provide a heat source. Common systems that use this reheat system are 100% outside air units and humidity-control applications. Systems that use hot gas reheat can divert refrigerant to a reheat coil or use a dedicated reheat circuit. No matter which strategy the equipment uses, the reheat always happens AFTER the evaporator coil.

Common issues with these reheat systems deal with the modulating valves. These valves can get stuck or end up in a different position than their controls say. You must confirm that the valves are in position. When working with these valves, you may work with DC controls, so that's something to keep in mind if you primarily work with AC circuits/controls. DC-signal sensors can also malfunction, so you have to check your outputs and can usually find a sensor-related problem quite easily.

We also discuss:

Overcooling to dehumidify
Fresh air requirements and equipment
Solenoids
Expansion line
Technician vs. manufacturer training
Confirming valve position
Stepper motors
Tools for circuits
Checking the refrigerant charge

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 #29 - 3 Quick Tips to Level Up Overnight Nov 06, 2018

Show notes

In this short podcast episode, Bryan covers three things you can do to level up and make you a much better tech tomorrow. Everyone will notice your improvement. Also, no matter what level you're on, you can become even better by remembering the following three tips:

1. Use a full-system diagnostic process. Every application should have a full-system diagnostic process, whether you're working on a residential ductless mini-split, a commercial chiller, or a walk-in refrigerator. Instead of focusing just on the primary problem, you'll be much more effective if you assess the entire system. You can also adopt a wide-narrow-wide approach to diagnosis where you start by examining the entire system (for example, look for oil and check the filter). Then, you focus on the main problem at hand and fix it. Before you leave a job, test the equipment and check it over once again to make sure that everything is working as it should.

2. Communicate better. In the commercial sphere, it's a good idea to write up equipment reports that customers can use to help them make informed choices about their equipment. For residential customers, communication is about courtesy. Send a text to let them know you're en route or send a follow-up email. When it comes to dispatch and leadership within your organization, communicate useful and helpful information for them. Report common things that you see in the field so that they can improve at their jobs.

3. Have a closing conversation with every customer. Before you leave a site, check in with your customer to make sure that there's nothing you or your company can do better. When you have these conversations, you show that you care and give the customers an opportunity to provide feedback.

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.

Combustion Analysis w/ Jim Bergmann Nov 01, 2018

Show notes

In this episode, Jim Bergmann does a deep dive into combustion analysis. He covers everything you need to know to keep a furnace running safely and efficiently.

When you go into a home, one of the first things you should do is perform an ambient CO test to check how much carbon monoxide is in the home. Combustion analyzers can typically measure CO, or you could use a dedicated CO meter. When it comes to checking for spillage, you'll want to make sure you check anything that is connected to an atmospheric draft appliance; these appliances, including water heaters, can create a pathway for CO.

First, you want to make sure everything is working properly before the combustion analysis. Set the fuel pressure according to the manufacturer's specs. Then, you go outside and clock the meter. When you do that, you merely verify that you have the correct gas input to the appliance; figure out how long it takes the one-foot dial to do a single revolution. After you verify the fuel and air, you want to see if you have an adequate amount of draft. Then, you set your temperature rise and verify that your CAZ zone is within the allowable limits.

When we do a combustion analysis, we measure the efficiency of the combustion process, not the overall furnace efficiency (AFUE). Combustion analyzers also help us account for stack losses. When doing the test, you must measure undiluted flue gas and take readings on fuel pressure, excess air, and stack temperature.

Jim and Bryan also discuss:

Fuel pressure and fuel orifice sizing
Fuel heat content
Excess air and condensing
Carbon monoxide thresholds
Stand-by losses
Contaminants
Temperature rise ranges
Net vs. gross stack temperature
Combustion efficiency
Duct leakage
Positive vs. negative pressure exhaust
Cracked heat exchangers
What to do when CO levels are high
AccuTools

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 #28 - The Magic Heat Absorber Oct 30, 2018

Show notes

This short podcast episode is about a simplified way to explain the basic refrigerant circuit to new techs. By explaining a component as an absorber, rejector, increaser, or dropper, you may help lock in the basic idea of absorbing and rejecting heat.

The goal of refrigeration is to remove heat from a place. Whether that place is a grocery case or a house, we're moving heat. The overall function is pretty straightforward, but the components can get a little bit complicated. At Kalos, we've found that HVAC/R apprentices tend to grasp the refrigerant circuit better when they can refer to the components by their functions. We move heat with a combination of heat absorption and rejection and pressure rises and drops.

For example, the compressor is the "pressure increaser," and the metering device is the "pressure dropper." Likewise, the evaporator is the "heat absorber," and the condenser is the "heat rejector."

When we understand that higher energy goes to lower energy, we can understand that the cold refrigerant inside the evaporator acts as a heat absorber. The evaporator coil is lower than the indoor temperature; it can do its job as a heat absorber even in relatively cool spaces. In air conditioning, we try to maximize efficiency by creating the proper temperature inside the evaporator (heat absorber). In many places, that temperature is about 35 degrees (F) below the indoor dry-bulb temperature. Explaining the component in this way encourages technicians to check the space of the temperature and relate it to the evaporator temperature.

The condenser is a heat rejector; it performs the opposite function of the evaporator. So, the outdoor temperature must be lower than the condenser (heat rejector) temperature. Then and only then can the condenser reject its heat to a cooler location.

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.

Do you even CAZ test? w/ Jim Bergmann Oct 25, 2018

Show notes

In this first part of the two-part combustion analysis series, Jim Bergmann covers CAZ testing or worst-case draft pressure testing in detail. He also explains why it matters to techs and customers. Once again, MeasureQuick will come in handy if you do CAZ testing in the field; Jim Bergmann is working on automating the testing process in his app.

CAZ (combustion air zone) testing will benefit the customer in both safety and efficiency. A proper CAZ test will also likely increase the furnace system's longevity. This test identifies if there is a high potential for flue gas spillage. We want to check if the appliance is installed in a space where it can easily and safely vent combustion gases. Other appliances can potentially give off exhaust, and they may impede a combustion appliance's ability to vent properly.

Worst-case draft pressure testing is a way of making sure that we have enough combustion air in a room for an appliance to operate safely. Some sealed combustion appliances can potentially suffer negative impacts of depressurization, which is dangerous despite the sealed combustion.

First, you want to measure the CAZ pressure with respect to the outdoors. Then, you turn the air handler on and measure that pressure again to identify possible duct leakage. After that, you close the interior doors and measure the CAZ again. Redo all three of these steps to produce the highest negative pressure. You can measure your pressures with a good manometer or the draft gauge on your combustion analyzer; ideally, your tool's resolution will read tenths of Pascals.

Jim and Bryan also discuss:

Pressurization and pathways
Radiant heaters and other appliances
Disconnected supply
Sealed and unsealed base pans
Exhaust pipe ventilation
Temperature-draft relationship
Water heaters
Resolution, accuracy, and precision
Measurement tools

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 #27 - Commissioning Mindset Oct 23, 2018

Show notes

In this short podcast episode, we talk about the commissioning mindset and what it REALLY takes to set up and commission a new system properly. We commonly check airflow and the refrigerant charge during commissioning.

There is a difference between mere startup and commissioning. When you commission a system, you ensure that it is working according to design. Think about how the system lines up with the manufacturer's specs and how appropriately it fits its application. In Florida, our designs typically maximize latent heat removal, so we want our systems to run optimally by those standards. We have to check sensible and latent capacity to avoid short-cycling and maximize customer comfort.

When comparing your equipment operation to the manufacturer's specs, you'll want to check the charge. You can check the suction pressure, outlet air temperature, and weigh in the charge with a proper scale. You should test the system to make sure that you don't have any leaks from the factory and that Schraders aren't causing any leaks.

Ductless units can be tricky, as there may seem to be little to check. However, you can certainly weigh in the charge and check your pressures to make sure that the unit is running well. You can even check the ductless system's delivered capacity as part of the commissioning process.

Communication with your installers is key. Tell the installers what your targets are so that they can make sure that the system delivers on the contractor's promises. Show your installers how to take the measurements so that they can confirm the operation.

Other procedures that are vital to the commissioning mindset include balancing the ventilation and ensuring that air moves through the supply and return vents correctly. The goal of commissioning is to make sure we deliver on our promises.

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.

3 Flavors of CO2 w/ Rusty Walker Oct 18, 2018

Show notes

In this podcast episode, Rusty Walker from Hill Phoenix talks us through the three most common types of market CO2 systems and how they work: secondary, cascade, and booster.

Carbon dioxide (CO2) is one of the oldest refrigerants; it is a natural refrigerant that came about when toxic refrigerants like ammonia were common. In the 1980s, we began to rediscover the benefits of CO2 in market refrigeration, including its high latent heat capacity, low costs, and low global warming potential.

Secondary systems use an HFO or HFC on top, which acts as the primary system and helps discharge heat. These systems have large receivers with both liquid and vapor CO2, and they resemble glycol systems quite a bit. The actual CO2 side of the system moves a lot more heat than the primary system alone; the CO2 side absorbs heat from open cases on the sales floor.

Cascade systems are two complete refrigeration systems tied into each other. Like secondary systems, these may use an HFC or HFO with the CO2 system. A heat exchanger exists between the two systems and serves as the evaporator for the upper cascade or the condenser for the lower cascade.

Booster systems have an upper side and lower side. These may have multiple medium-temp and low-temp compressors. They also have a high-pressure control valve. That controller looks at drop leg temperature and pressure to regulate subcooling. These systems also have a flash gas bypass valve that discharges into the receiver or the medium-temp suction line.

Rusty and Bryan also discuss:

CO2 and ammonia
Triple point
Supercritical fluid
Latent heat benefits
Metering devices
Thermal siphon
Heat exchangers and pressure drop
Upper vs. lower cascades
CO2 pressures
Compression ratio
Subcritical and supercritical modes
Adiabatic operation
Climates

You can also contact Rusty by email at rwalker@doverfoodretail.com.

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 #26 - Temperature Mistakes Oct 16, 2018

Show notes

Can you really trust that temperature reading? In this short podcast episode, we talk about some common mistakes techs make when making temperature measurements and what to do about it.

Many heat pumps use heat strips as a source of auxiliary heat. However, it takes some time for the heat strips to integrate with the air. So, your superheat, subcooling, and pressures will look fine on a system that isn't cooling well enough. When you take air temperature measurements in the ductwork, try to get as close to the center of the duct as possible or take a measurement farther down in the duct. Even so, you need to be careful with measurements in the center of the duct on gas furnace systems because radiant heat can give you an incorrect reading. You can also measure a few different points and average them out.

On gas furnaces with a coil on top, the coil can be in visual contact with your temperature probe. In those cases, the coil will absorb some of the heat from your probe via radiant heat transfer, so you could end up with a lower reading. Not accounting for small sources of heat transfer is one of the most common temperature mistakes that techs can make.

When measuring outdoor temperatures, you want to avoid using your probes in the sun. The sun can add radiant heat to your readings when you calculate CTOA, and you will get a high reading. Radiant heat gains also apply when you're working very close to hot, active pool heaters. The thermostat should also avoid being exposed to very high or low temperatures for maximum accuracy.

We also discuss:

Radiant heat gains
Air mixing
Line temperature clamps and copper cleanliness

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.

Our TOPPODCAST Picks

Follow Us

Stay Connected

HVAC School – For Techs, By Techs

Related Podcasts

Links

Stay Connected