HVAC School - For Techs, By Techs

In this short podcast episode, Bryan talks about blower taps in furnace systems. He explains how to set up their fan speeds and repair them. Before you even look at the blower taps in a system, you must know a bit about the system design. Is the system supposed to remove high amounts of sensible heat? What is the capacity? How quickly should the thermostat drop? When a system is supposed to move lots of heat and has a high capacity, it needs high airflow; to run optimally, the system needs higher fan speeds to move more CFM per BTU. Moreover, a Manual J calculation can tell you how much sensible and latent heat the system must move. Also, keep in mind that system tonnage does NOT always indicate the amount of BTUs a system is actually moving. Conversely, to calculate the airflow needed for heating, you must look at temperature rise. Ideally, your temperature rise should be near the middle of the temperature-rise range. So, how do you set the airflow and know how much you're producing? That's where you measure your static pressure and look at fan tables. Remember to make sure the blower is clean and to factor in additional resistance from components like heat strips or filters. Alternatively, you can measure airflow with a duct traverse or by using an airflow hood. Then, you set the fan speed accordingly. Overall, to set the blower taps, you need to be able to measure your airflow and read fan charts. If you're merely commissioning a new system, measuring airflow becomes less important; instead, you must ensure that the manufacturer's fan charts are correct. Remember, the airflow needs to be different for a customer's heating and cooling needs.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's podcast episode, Jim Bergmann covers furnace commissioning, including setting up furnace input, clocking the meter, setting temperature rise, and much more. The goal of commissioning is to optimize a furnace's efficiency; we want to make sure we correctly engineer the intake/exhaust system to extract as much heat from the flue gas as possible. The commissioning process for an 80% furnace is pretty similar to that of a high-efficiency furnace. Checking gas pressure, setting temperature rise, and combustion analysis are critical procedures when commissioning both furnace types. Moreover, you must know the heat content of the fuel and the amount of fuel going into the furnace before you can determine the correct input. There is an acceptable range for gas pressure, typically within 10% of the specs (usually 3.5" wc, so the acceptable range is 3.2-3.8" wc). Both the gas pressure and heat content let you know how efficiently the furnace is firing. When checking the input, you must clock the gas meter; you do that by timing a single revolution of the gas meter and determine how much fuel goes into the appliance during that time period. You can't have the water heater on at the same time that you are clocking the meter. When you clock the meter, you can start with a gas pressure of 3.5" wc and go up to 3.8" wc. When clocking the gas meter, you may realize that the orifices are incorrectly sized. Ideally, you want your temperature rise to be in the middle of the manufacturer-specified range. For example, if the range is 40-60 degrees, you would want your temperature rise to be close to 50 degrees). Jim also discusses: Weighing condensate Primary vs. secondary air Excess air Changing/resizing orifices Other gas lines in the home Ductwork sizing for temperature rise/CFM Filter considerations   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

This short podcast episode is about saturation and what it means. Bryan covers related topics, including boiling, evaporation, and condensing. Saturation refers to something that is "full" of something else. In science, "saturation" refers to a substance being in the middle of a phase change. (For example, boiling water stays at 212 degrees until it all boils off and becomes water vapor.) In HVAC, we often use the term to refer to refrigerant with liquid and vapor are present at the same time. The refrigerant is typically both liquid and vapor in the evaporator and condenser; phase changes occur in those two components as refrigerant changes from a liquid to a vapor and vice versa. Refrigerant tanks are contained systems, so the liquid-vapor mix remains at equilibrium, and the temperature and pressure will change at a predictable rate. That is why we can use the P-T chart to determine the refrigerant type; a given type of refrigerant that is changing state at a given pressure will always be a certain pressure. The process of changing state is where we can utilize so many more BTUs of heat. When a substance is at saturation, that substance will not increase in temperature so long as it remains in its current state. However, that substance will continue absorbing heat until it fully changes its state. We call the added heat that does NOT contribute to a temperature change "latent heat." Evaporators are so effective at absorbing BTUs of heat because refrigerants have relatively high latent heat of vaporization values; it takes a lot of added heat to make a refrigerant change from liquid to vapor. However, evaporation can occur WITHOUT boiling. Temperature is only the average heat content, and some faster-moving liquid molecules can still break free and become gas.   If you have an iPhone subscribe to the podcast HERE and if you have an Android phone subscribe HERE.

In this discussion with Bill Spohn from TruTechtools.com, we cover the practical steps and tools for YOU to start measuring airflow today, if not sooner. There are several ways to measure airflow; when measuring airflow, start with the "why" rather than the "how." Understand what the goal of the airflow is before you begin taking measurements in random places. You can take a bulk measurement at a return, but you have to be prudent to avoid human error. The best way to avoid error is to use a TrueFlow grid, which replaces the filter and uses a pitot array to measure airflow in the return. Another relatively easy way to get a bulk measurement is to use a flow hood. However, it can be easy to mess up the positioning of a flow hood (or not have enough room for it). Many techs misuse tools like vane anemometers and collect poor data. Vane anemometers can gather information throughout the duct (mini vane) or over the supply or return (larger vane). You want to pick up the micro-transitions in air velocity to get quality data; you can use either point or traverse measurements and average those readings to come up with your average CFM. We can take measurements INSIDE the duct with pitot tubes (although we have our reservations about using those), hot wire anemometers, and mini vane anemometers. In-duct measurements require multiple measurements and consistency during testing. A common system airflow measurement doesn't measure CFM at all; that measurement would be static pressure. However, you need to have the correct tables and understand all of the load requirements to measure static pressure effectively. Bill and Bryan also discuss: Pitot tubes vs. static pressure probes Air movement metaphors Point vs. traverse measurements Static pressure drop Total system airflow setup Ventilation airflow   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Today, Bryan discusses delta T (evaporator air temperature split) what it is, what it means, and how to avoid some common pitfalls. Delta T is NOT the air temperature rise on a furnace, and it is NOT the design temperature difference (DTD). Instead, delta T refers to the temperature split between return air entering the evaporator coil and the supply air leaving the unit. Typically, 20 degrees (Fahrenheit) is a desirable split, but there is still a range based on relative humidity, enthalpy, and airflow. The range can be as high as 24 degrees. To measure delta T properly, you need high-quality probes. (Don't use cheap dial probes if you don't want an inaccurate measurement.) Whenever you expose a probe to another probe via an air gap, they can affect each other's temperatures. Radiant heat transfer occurs between them, and you can get incorrect readings. In general, you want to keep your supply probe downstream of the coil. Do NOT use an infrared thermometer to measure the temperature split. Infrared thermometers are inaccurate and may also pick up duct gains. Delta T is not a fixed value, but it is still rather predictable. You can use our calculator to help get an idea of the measurement you're aiming for. Some factors that reduce the temperature split include high airflow, high relative humidity, and low capacity (and all of its possible causes). High temperature splits typically occur due to poor airflow. Dirty filters and coils are the main culprits of poor airflow and high temperature splits by extension. Dehumidification mode and lower relative humidity may also result in higher delta T values. (However, dehumidification mode is usually intentional and is rarely a cause for concern.)   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this simultaneously heavy and lighthearted discussion, Bryan Orr and Andrew Greaves discuss ego, Dunning-Kruger, insecurity, and apprenticeship in the trades. In the early days, apprenticeships were quite different from the way they are today. One-on-one mentorship used to be a much more significant component of early apprenticeships, but that style of training is uncommon for today's apprentices in all sorts of trades. As a result, many young technicians enter the field too quickly and don't have the training to perform a job skillfully. As such, many inexperienced techs become confident with bare-minimum work because nobody points out their mistakes. Moreover, many green techs also don't have the self-awareness to recognize their lack of skill. We call that disconnect between confidence and skill the "Dunning-Kruger effect." Another common scenario is when techs understand that they don't know something but are too embarrassed to admit it. Unfortunately, a tech's ego can get in the way and make them stick to their guns for no good purpose. However, old-timers are also part of the ego-ignorance equation. Many of them fail to explain the "why" behind their practices. Some old-timers share bad practices without knowing what they're doing. Moreover, when leadership breeds a culture of ignorance, the younger technicians will be set up for ignorance and ego problems. The way to move past the Dunning-Kruger effect and check your ego is to think about what you're thinking about. Question the validity of your OWN thoughts and ideas, and accept that you could be wrong or have a flawed understanding. Bryan and Andrew also discuss: Techs' behavior on social media Cognitive bias Metacognition Organizations that breed ignorance and ego issues   Check out AK HVAC on YouTube - https://www.youtube.com/user/akgreaves If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this short episode, we review the basics of the refrigerant circuit. The standard HVAC refrigeration circuit has four main components: compressor, condenser, metering device, and evaporator. The compressor squeezes refrigerant vapor into a smaller volume by applying lots of pressure. It simultaneously moves and compresses gaseous refrigerant. The more a compressor has to compress a gas, the less gas it moves. The more gas a compressor moves, the less gas it compresses. Then, the refrigerant leaves the compressor via the discharge line. The discharge line is very hot because the temperature increases with pressure. The hot vapor feeds into the top of the condenser. The condenser brings the gaseous refrigerant back down to a liquid. Condensers come in all shapes for various applications, but all condensers' main goal is heat exchange. Condensers desuperheat, fully condense (change vapor to liquid), and subcool. Subcooled liquid refrigerant leaves the bottom of the condenser via the liquid line. The liquid line leads warm, subcooled liquid refrigerant to the metering device. The metering device's goal is to drop the refrigerant's pressure. That pressure drop facilitates boiling in the evaporator coil. The evaporator absorbs heat from the space. Fans blow warm air over the coils, allowing that heat to come into contact with the refrigerant. The refrigerant boils when it absorbs enough heat. The last few rows of the evaporator are where superheating occurs. Superheat is the temperature above the saturation point; superheat indicates that the refrigerant is all vapor, no longer a liquid-vapor mix. Then, the vapor refrigerant travels back to the compressor via the suction line; the refrigerant circuit restarts. The suction line is rather cool; we use some of that cool refrigerant gas to cool down the compressor.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Jon Bennert from Air Oasis teaches us about PCO and Bi-Polar air purification and how it improves indoor air quality through ionization. Photocatalytic oxidation (PCO) is a technology field that uses catalyst metals, hydration agents, and lights to help remove pollutants from the air. These technologies shine a light source on a photocatalyst metal that reacts with pollutants in the air. These pollutants include volatile organic compounds (VOCs), viruses, mold, and other unwanted particles in the home. Some bacteria that are good for you in your gut are NOT good in your respiratory system. Bi-polar ionization causes reactions to occur with the pollutants. Ionization could potentially break down molecules or genetic material in VOCs and viruses, respectively. Other biological contaminants, including mold and bacteria, also have their proteins broken down and become unable to replicate or reproduce. Larger particles, like dust, are forced to clump together and become so heavy that they fall out of the air. The air motion in the Bi-Polar product line is the mixture of positive and negative ions that are splitting water vapor molecules. So, you can tell if the Bi-Polar products are working if you can feel airflow; you can tell that the product is generating ions. These ions work to break down harmful particulates in the air AND eliminate odors. Bi-Polar products that use ionization are desirable for people with allergies or homes with lots of shedding pets. Bi-Polar products are small and easy to install. They simply fasten to the shroud with magnets. These products also come in some voltage ranges, and they have a small energy footprint as well. Jon also discusses: Ionization history Petri dish tests Bi-Polar products and PCO usage Outdoor air standard qualifications Servicing Bi-Polar products Ice machine contamination   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's podcast episode, Eric Mele comes on to talk about reach-in coolers (refrigerators), freezers, and wine coolers with some mindset and technical tips. We mostly discuss self-contained equipment. Coolers are medium-temperature applications, while freezers are low-temperature applications. Wine coolers vary from normal coolers because they have slightly higher temperatures and controlled humidity. The cooler must control humidity to preserve the wine quality and prevent the cork from swelling. Metering devices vary with the size and type of equipment. We typically see capillary tubes in smaller reach-in coolers and TXV in larger ones and blast chillers. We typically use automatic expansion valves (AEVs/AXVs) for wine coolers. An AEV controls suction pressure in conjunction with a TXV, which controls superheat. Hooking up gauges is typically a last resort. We can chalk up most reach-in cooler problems to restrictions, which usually indicate cleanliness issues that are easy to solve. For example, dirty condenser coils can cause cap tube restrictions. Control strategies vary by size, application, and complexity. For example, simple reach-ins rely on manual defrost only. However, even higher-end blast-chillers recommend manual de-icing (although they DO have defrost controls). The main defrost types are manual, fan, and electric. Smaller reach-ins have a "cold control." Cold controls are relatively simple dials that stop the compressor when the evaporator coil reaches a set temperature. Most reach-in refrigerators are ONLY intended to hold products at temperature. With the exception of blast chillers, most reach-ins cannot bring a bunch of hot food down to temperature. These situations will result in poor performance, so customers should be aware of the refrigerator's appropriate usage. Eric also discusses: The troubles of charging reach-in cases Creating your own access ports Electric defrost in reach-in applications Thermal imaging cameras in diagnosis Manual defrost strategies Pump down   Check out Eric Mele on YouTube HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Stephen Rardon and Neil Comparetto join the podcast to talk about their headfirst dive into building performance as HVAC techs. They discuss jobs they do, how the transition has been, and important HVAC principles in building performance. Addressing duct leakage can help with indoor air quality and home performance overall, but it can also even help reduce noise. Building performance and HVAC both require the serviceperson to give the customer options and inform them of their specific situation. In both cases, you would give the customer a chance to improve their living situation by offering a personalized set of offerings. However, building performance allows us to give the customer control over their comfort. The main selling points of building performance solutions are health, comfort, and efficiency. Customer health is important because they want to make sure asthma, allergies, and other conditions won't be aggravated in their home. Comfort is important for many people, and efficiency is typically important for those with a green ethos. If contractors and technicians want to get into building performance, it pays to take time to learn the business. It's even better if contractors put training programs together for their technicians. However, technicians need to be able to care about the material; otherwise, the investment in training may not be worth it. You must care about why we need building performance before you enter that side of the industry. Stephen, Neil, and Bryan also discuss: Bringing building performance into HVAC business Blower door testing Sales packages System performance inspection Challenges of growing a company Precision manometers and other building performance tools Zonal pressure diagnostics Creating service departments within companies Thinking of the building as a system Expertise to combat automation   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.