This episode is a rebroadcast of a very useful episode from the Corbett Lunsford's Building Performance Podcast at https://buildingperformancepodcast.com/. Corbett talks to building moisture control expert Lew Herriman about moisture, ventilation, and what happens when you're drying "stuff."

When we think about humidity control, we have to ask if we're drying air or drying "stuff." Dehumidification is about drying the air, but many people think about it when they actually want to dry "stuff" like fabrics and other absorptive surfaces often found in residential applications. However, drying out "stuff" does affect how we would dry out the air.

Commercial buildings often don't have a lot of absorptive materials, as many have tile floors. Residences tend to have carpet and upholstery, making them challenging cases in building performance. The HVAC system controls moisture, whether they have a humidifier, dehumidifier, or neither. HVAC systems create pressure differences, which contribute to dry air infiltration. Homes heated solely by radiant heat would not be as good at drying the air, but good ventilation could supplement radiant heat.

When we have humidity control problems that affect comfort or moisture on absorptive surfaces, we might start thinking about controlling absolute humidity. Absolute humidity refers to the actual moisture content in the air, not the moisture relative to the temperature. However, most homes don't have the ventilation systems that would help dilute the humidity, including HRVs. 

Then, when drying "stuff," you have to put heat in to get the moisture out.

Corbett and Lew also discuss:

• Absolute vs. relative humidity
• Dry-bulb temperature changes and dew point
• Duct leakage
• HVAC and building performance strategies for mixed climates
• Energy-recovery ventilators (ERVs) vs. heat-recovery ventilators (HRVs)
• Exhaust at the source
• Dehumidifiers
• Dehumidifying incoming fresh air
• Hypothetical makeup air systems for residential applications
• Comfort metrics

Learn more about Corbett's work at buildingperformanceworkshop.com.

Restaurant HVAC and refrigeration tech Nick Messick comes on the podcast to talk about restaurant equipment, especially the "hot side." The "hot side" refers to equipment that heats the food; it includes often deep fryers but has a lot of variation. The "hot side" also includes specialty equipment for frying noodles and performing other unique functions.

In Nick's opinion, the worst service call has to do with fryer pumps due to all of the grease. The grease gets all over tools and your hands, and it can be quite difficult to work on equipment with fryer grease. Other things he dislikes working on are machines that are on their last legs, as many owners are reluctant to replace equipment.

Many fryers go through a melt cycle that turns the heat on and off to avoid burning the oil. The flames heat the bottom of the vat using a heat exchanger like a furnace; then, the gas vents into the flue and out the hood. These systems generally use spark igniters and may use either direct-spark or intermittent-spark ignition with a pilot. Nick's favorite call is when fryers make loud popping noises, as it's easy to diagnose and fix; the cause is typically either the ice cube relay or a bad igniter.

In grease-heavy restaurant environments, we clean equipment by using cleaners meant for electrical equipment. You want to avoid leaving residue on the equipment and ruining the control boards. The restaurant staff should be cleaning out the fryers themselves, but you may encounter some dirty equipment (and workspaces).

Nick and Bryan also discuss:

• Dishwashers
• Replacing equipment
• Flame rectification
• Circuit boards
• Electric fryers
• Drawing the line when it comes to sanitation in HVAC service

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P.S. - Don't pull the fire alarm

Phil Zito of Building Automation Monthly comes on the podcast to discuss building automation and what HVAC techs should know about it.

Automation essentially refers to control systems; we started off with pneumatic control systems, and then we went to analog and electromechanical control systems over time. Building automation refers to the process of automating controls on a larger scale, such as for an entire building. As long as you can read electrical and mechanical diagrams, you can work on automation systems; you don't need to know about IT or robotics. 

Large buildings like malls may require HVAC automation. In other structures like university buildings, you may also end up automating lights and other electrical functions. Automation makes other systems talk to each other, and it does that by controlling on/off schedules and set points. These building automation systems consist of sensors, switches, conductors, and decision-making logic (such as simple desktop servers).

Regardless of the automation system, the sequence of operation will always go in the following order: server, supervisory device, field controller, and input/output. A communication bus transmits messages between field controllers; it works like floating controls or pulse-width modulation. You don't need to know the binary communication of the computer; you just need to know how to measure voltage with your multimeter to work on a communication bus.

An HVAC tech may also be interested in knowing that building automation has an air side and a water side. These systems may also interface with package RTUs and VAV systems.

Phil and Bryan also discuss:

• How Phil got into building automation
• Servers
• User and web interface
• Resistance vs. analog values
• Barriers to getting into BAS careers
• Installation vs. service
• Taking initiative and being resourceful
• How BAS and HVAC workers can make each other's lives easier

Visit Phil's website HERE.

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In this podcast episode, Bryan and Mike Layton of Shore Distributors explain how HVAC contractors and distributors can build a great partnership. Shore Distributors is a wholesaler in Maryland that carries Carrier, Bryant, and Payne.

The job of a territory manager is to help HVAC contractors, so they're there to help contractors. The territory manager's job is to help set contractors and dealers up for success, so they don't feel burdened by questions because it's their job to answer them. Territory managers know that the goal of business is to make money, so they understand the importance of moving boxes and making sales. That said, contractors who move boxes tend to make the rules and have access to privileges.

Warranty returns are a bit of a touchy subject; distributors tend to give contractors the benefit of the doubt and are generally willing to replace the part as long as you supply the correct information. However, Mike believes that the 10-year parts warranty has been detrimental to business.

End-user satisfaction is a goal we can all strive for. HVAC contractors can be more thorough when completing their jobs and setting up equipment; when installers take their time and explain proper use to the owner, they increase customer satisfaction. When HVAC contractors succeed, distributors succeed and can keep providing service to top contractors.

Overall, a healthy contractor-distributor relationship has mutual trust built on dependability. Distributors need to be dependable and available to help the contractors they serve.

Mike and Bryan also discuss:

• A day in the life of a distribution role
• Ego vs. results
• Contractors that abuse warranties
• Vetting techs and holding them accountable
• Controls
• What installers can do better
• Inverter products
• Understanding each other

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this episode, Bryan talks with Jamie Kitchen from Danfoss about why and how thermostatic expansion valves (TXVs) fail and how they function in the first place.

As fixed orifices become a dying breed with the development of higher-efficiency systems, TXVs take over the mantle as the primary method of expansion. Expansion valves meter the flow of refrigerant by aiming for a certain suction line superheat value. Unlike a fixed orifice, which has an opening of a constant diameter, an expansion valve adjusts the opening size to the evaporator based on suction superheat readings.

TXVs have a sensing bulb, diaphragm, spring, and cap tubes. Various pressures act on these components: bulb pressure, spring pressure, and evaporator pressure. The sensing bulb picks up the suction superheat adjusts its pressure on the diaphragm based on the superheat it detects. Spring pressure and evaporator pressure act against the bulb pressure. The combination of all three pressures (bulb vs. spring + evaporator) dictates the opening of the TXV orifice into the evaporator. The bulb pressure is an opening force, and the spring and evaporator pressures are closing forces.

You can cause TXV failure by adjusting it or brazing it in improperly. When too much heat is applied to the TXV, the components inside can warp. Some TXV failures also occur due to contamination. Flowing nitrogen while brazing flushes carbon and oxygen contaminants out and reduces your risk of TXV failure later on.

Bryan and Jamie also talk about:

• TXV anatomy (powerhead, spring, etc.)
• Internal vs. external equalization
• Pressure drop across the distributor
• Subcooling and its relationship with the TXV
• Solenoid and ball valve (upstream) malfunctions
• Filter-dryer placement
• TXV assessment during commissioning
• Locating restrictions
• Residential system airflow

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this second part of the podcast, Jim Bergmann wraps up the steps to check a system charge without connecting a gauge manifold.

You can check the charge without gauges if you use the following process (and know your DTD, CTOA, etc.):

1. Take the dry-bulb temperature. (Let's say it's 70°F in this example.)
2. Subtract the DTD (35°F).
3. Add target superheat (10°F).
4. Check the suction line. It should be 45°F in this example. If your probe senses a temperature that is NOT within 5°F of the temperature you calculated, check the filter, evaporator coil, etc., for dirt.
5. If the system is not dirty, check the charge with gauges.

For a more extensive look at the process in writing, check out THIS article.

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In this episode of the podcast, we talk about gauges. Jim Bergmann from Redfish Instruments and the MeasureQuick app explains why you may want to check a charge without using a gauge manifold. (That's not clickbait; if you've already connected gauges to a unit once, you can probably check the charge of that unit WITHOUT gauges moving forward.)

HVAC units manipulate temperature and pressure in the refrigerant charge. Heat transfer occurs between the refrigerant and the environment, and various readings indicate the charge level WITHOUT necessarily connecting the gauges. So, you can check the charge if you know the unit's SEER rating, target superheat, DTD, CTOA, and if the unit uses a fixed orifice or TXV.

A large portion of checking the charge without gauges deals with "benchmarking" the equipment. You do that by evaluating the system's performance over time and comparing it to the performance when the system was first commissioned. Airflow WILL decrease over time due to components becoming dirty.

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In this episode, Jack Rise talks about duct design regarding ACCA manual D, friction rate, face velocity, duct velocity, and what is ACTUALLY wrong with flex duct.

Manual D causes a lot of confusion for technicians, and most techs have a limited understanding of it anyway. When determining a blower wheel for commercial ductwork, Jack Rise calculates pressure drops for all of his elbows in the ductwork and makes his decision based on those calculations. Residential HVAC is a bit trickier, and that's where Manual D calculations come in. Luckily, many software nowadays, including Wrightsoft, can calculate loads very precisely and help you with duct sizing.

Just as with heat and pressure, there must be a velocity differential if you want air to move. If you need to move more BTUs of heat, then you need to move more CFM of air. Air also tends to take the path of least resistance. Trunk and branch design velocities must be different if you want any control over where the air goes. Trunk duct velocity typically stays between 700-900 CFM, but branch velocity can change quite a bit when you change the locations of the registers and grilles. Branch velocity tends to be 400-600 CFM. Good face velocity can be achieved by choosing the correct register and putting it in an ideal location.

Flex duct is not a bad material, but it is controversial due to its reputation for being poorly handled. Manual D has an appendix on compression and sag, and techs who consult it will design a much better duct.

Jack also discusses:

• Available static
• Choosing a blower and factoring friction rate
• Oversized ducts
• Compression, sag, and bends in flex duct

You can find the book at http://www.acca.org/store

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In this episode, Bryan speaks with Eric Shidell about some of the basics of system freezing, what causes it, and what to do about it.

Freezing is a normal part of some equipment, such as low-temperature freezers and outdoor units on heat pumps. On straight-cooling systems, freezing is NOT normal and indicates poor operation. Ice formation starts on the evaporator coil and may spread to the compressor via the suction line. The best way to remove ice and defrost the system is to pull the disconnect on the outdoor unit but let the indoor fan keep running. Or, you could turn the unit off but leave the fan on.

The goal is to defrost slowly and steadily. Defrosting too quickly could potentially cause damage. Horizontal air handlers in the attic can flood the home if ice forms and melts off too quickly. In an upflow furnace, defrosted ice could damage the electrical components.

You will typically find low suction pressure on frozen systems. Many technicians who merely attach gauges and don't thoroughly inspect the unit for freezing will mistake the low pressure as a result of a low refrigerant charge. However, low pressures are a SYMPTOM, not the cause of freezing.

Freezing is generally caused by poor airflow over the evaporator coil. As frost appears on the evaporator coil, airflow will be further impeded. On top of that, the suction pressure drops even more. From there, all of these factors feed each other and cause the frost to snowball out of control (almost literally). Sometimes, coils may freeze due to low refrigerant, but the amount of ice will typically be minimal compared to freezing that occurs due to an airflow issue.

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Corbett Lunsford from the Building Performance Workshop and the Proof is Possible tour talks to us about the moral superiority of building performance testing, blower door testing, and much more.

Building performance and HVAC have been becoming much more closely linked lately. So, it's a good idea for HVAC techs to learn a bit about building performance.

In the HVAC world, we often see homes with extremely hot upstairs portions and cool downstairs questions. That is a complex building performance issue. A good contractor can troubleshoot the issue with the building and find cost-effective ways to improve the enclosure (air ceiling and insulation) and the HVAC. The construction and improvement industries will be utilizing diagnostics and metrics, much like most of the HVAC industry today. (Metrics that we use include static pressure, superheat, subcool, etc.)

The blower door is the most important tool for diagnosing issues with the enclosure. Many odor and comfort issues deal with ventilation, not just the HVAC. As such, blower door testing can help diagnose issues that don't go away after improving or repairing the HVAC system. Air leakage is the most important issue that occurs with the enclosure.

A blower door test replaces the front door with an airtight shroud with a fan mounted inside. That fan then hooks up to a manometer to measure pressure in the home with reference to the outdoor pressure. The blower door drags the pressure down to 50 pascals, and then you can see how much air goes through the fan at that constant pressure. The air that comes through the fan indicates a lack of airtightness in the home. However, blower door testing requires practice and repetition. If you get one, practice with it before you use it for diagnosis.

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