Tag: hvac

First, let’s state the obvious and clear the air a bit. The photo above is SUPER CHEESY! But this story is about three bad techs who don’t know it so three models clearly posing in clean clothes makes as good of a proxy for a bad tech as anything else.

First off, I’m not being negative about the trade or making fun of people, the point of this story is to identify some traits that many of us may exhibit or see in others techs and it can be hard to identify our own issues or issues within your organization. See if any of these techs sound a LITTLE TOO FAMILIAR and maybe we can learn something. Before you ask… No, these are not real people…. probably… maybe

Randy the Drama King

Randy, like most dramatic people who work in the trades, doesn’t see himself as being dramatic. He just thinks he is being constantly disrespected by management and co-workers and customers are crazy and the dispatcher is out to get him and it’s always about to rain and that ladder (and every ladder) looks unsafe.  These things aren’t DRAMA they are FACTS in Randy’s world and if you question this reality you get added to the long list of people who are disrespecting him.

Randy starts conversations with customers with phrases like “you aren’t going to want to hear this” or “Do you want the good news or the bad news”. He also tends to pass blame to his coworkers or his company because they are just clueless and he knows what’s REALLY going on.

Randy is actually a good tech, but he get’s in a lot of conflicts with coworkers, customers don’t always like his negativity (or as he calls it “being honest”) and he is inefficient and largely unpopular with other techs and management. Randy knows people think poorly of him because everyone is conspiring against him with that blankety-blank dispatcher Donna!

Randy always feels persecuted by the people around him and usually has something negative or conspiratorial to share about every topic. Politics, The weather, customers, co-workers, spouses… you name it.

Here is a test you can take to see if you might be a bit of a Randy

  • You have more than 5 people you are ticked off with or avoiding at any given time
  • You consistently see “danger” around you that nobody else sees
  • During work hours you have multiple conversations over 5 minutes with others about things that are “wrong”
  • You use a lot of negative and fear-inducing language with customers

If you find you are allowing negativity and drama get to you the best practice is to give yourself a break from negative speech. Like your grandma used to say, “If you don’t have anything nice to say”. Negativity is a hard habit to break but the best time to start is now and the best antidote for negativity is gratefulness.

Bob the Excuseful  

Yes, excuseful is a word… I made it up and I like it.

Bob is confident that he would be able to do his job if he was just given the proper training and tools and enough time to do the job and enough sleep and wasn’t forced to work these ridiculous hours. Bob often wonders if he should go back to school and get his degree in …. something and all the courses he would take if his cheapskate boss would just invest in him.

Sure he was given a book and sent to a seminar last month but that was all THEORY, he is a hands-on learner and he CANNOT learn from books or videos or seminars or anything unless he can get his hands on it.  Once he DOES get his hands on it he can’t be held responsible for any mistakes he makes because he has to be SHOWN what to do and how to do it and if he isn’t SHOWN how can he be held responsible? Now, when he is shown, he is a hands-on learner so he can’t learn things by being shown… he needs to do it himself.

His truck may be a mess but he would clean it if he ever had time with these ridiculous hours but in the slow season that is his one time of the year to relax, you can’t expect him to take his own time during the slow season to clean his van can you?

Here are some indications you may be struggling with a bit of Bobish excusefullness

  • You feel jealous when others succeed  and immediately give some reason why they have an advantage over you
  • You read fewer than 5 books last year but still feel like your lack of education is someone else’s fault
  • You find yourself using “hands-on learner” as a reason for failing to understand something
  • When you don’t understand something you call or text someone rather than looking up an answer yourself
  • You have a sense that your lack of progress is due to a lack of “opportunity”

The best way to stop making excuses is to begin living and working with what old-timers called “grit” or “gumption”. This means doing whatever it takes to solve problems, making excellence a goal and going after it no matter the barriers. Start by reading and learning on your own, don’t wait for someone to show you or tell you, go get it yourself.

Todd the Careless

Todd knows he is just forgetful, he TRIES to remember to tie down his ladder and put the caps back on and close his back doors on his van but he just forgets sometimes OK!

Sometimes Todd get’s defensive when other techs call him out for leaving the panel off or “forgetting” to clean the drain, but usually Todd just apologizes and says he will do better next time, but he knows he won’t because he didn’t do it on purpose, it just …… happened.

Some of the “Grouchy” old techs have told him that doesn’t seem to care about his job, but they are WRONG! (in Todd’s mind) he does care, he just has other things going on in his life and in his mind and sometimes accidents happen… like the time he stepped through the attic ceiling, or the time he slipped on the ladder, and that one time he rear-ended that car in the parking lot… oops

You may be a Todd if ….

  • You regularly make mistakes where you “just forgot”
  • You find yourself looking at your phone, texting and using social media during the workday
  • Your mind is preoccupied with personal matters during work and while driving

We have entered a new era of carelessness due to the advent of smartphones, social media, and texting. Many of us find our minds constantly distracted by things other than work during the work day and it leads to poor outcomes, mistakes and safety hazards. everything from climbing a ladder, to driving, to filling out a service call requires ATTENTION and distraction can lead to costly and dangerous mistakes. The best advice is to put the distractions way during the work day… unless it is reading this article. Just remember to put the panels back on and run test the equipment when you are done.

— Bryan

 

 

 

 

 

 

Even though there will almost surely be a healthy demand for HVAC service businesses, any service business is still at risk of going under. Most of the trouble comes down to money mismanagement or misunderstanding.

The good news is that the risks are avoidable with proper education and care. We aren’t accountants or lawyers, but we have learned a few financial tips over the years. Here are some common financial mistakes for service business owners to avoid.

 

Mistake #1: Not treating owner pay as an expense

Many business owners make the mistake of not separating their pay from the net profit. We recommend treating the owner’s salary as an expense, not something that can be taken from the profit after all the other cost calculations are said and done. 

You’re free to determine the amount of money you want to take as a working owner. It can be as little or as much as you’d like, but you’re going to want to treat it like any other employee salary. As an owner, you probably won’t want to take out too much money for your salary because you’ll want to have a healthy net profit to fall back on. It’s better to have a financial buffer than to go into debt.

It’s good to separate your pay from the profits so you can use the net profit to grow your business and pay off business-related debt, not put food on your table.

 

Mistake #2: Not separating the cost of goods sold from overhead

When most people think of expenses in the service industry, they think of parts, labor, and tools. These costs are all directly related to service jobs, so they are factored into the cost of goods sold (COGS). These will probably make up around 60% of your company’s expenses over a given period, leaving you with a gross profit margin of about 40%. 

A 40% profit margin sounds great, right? It sounds great, but we haven’t finished determining costs yet. The building insurance and staples you purchased for the office staff don’t factor into your cost of goods sold, but they still cost money. Those fall under overhead costs. You can expect those to take up around 30% of your business’s expenses for many service businesses. Your net profit would really be around 10%.

To keep a realistic image of your business profit, keep track of your overhead expenses and subtract them from your gross profit. (And remember that the owner’s salary comes from either the cost of goods sold or overhead costs, not the 10% net profit!)

Depending on the segment of business you are in and your mix of service and install your COGS will need to be 70% – 50% in order to make a solid and sustainable profit and weather the storms of business. Keep those separate from overhead in your books and your mental math so you don’t sell yourself short. 

 

 

Mistake #3: Not distinguishing billable and non-billable hours

Your employees bring in your company’s revenue when they perform service jobs. However, they are also a significant source of your expenses. To determine the total cost of labor, you’re going to have to make some distinctions between billable and non-billable hours.

Billable labor is labor that directly brings in money. If a technician spends two hours on a job site fixing a customer’s heat pump, those two hours are billable because the customer pays for the service. However, a lot of your employee labor doesn’t fall under that category. Your employees don’t actively bring in money when they drive to and from job sites, stand by, or clean vans. Those tasks fall under non-billable hours, and your employees still need to be paid for them.

To get an accurate picture of your employees’ labor costs per billable hour, you’ll want to calculate your fully loaded labor costs. To do this, you can add up your employees’ total labor and payroll costs (including benefits and vacation time) over a set time period. You’ll then divide those by the total billable hours over that same period. 

It gets trickier to determine labor costs if you don’t keep track of billable hours. If you keep track of billable hours and calculate your fully loaded labor costs, you will have a clearer idea of how to set your service prices to make up for those costs in your pricing and efficiency initiatives. Many companies that struggle do so because they fail to look at non-billable labor expenses and their causes. 

 

Mistake #4: Improperly calculating markups

This is the big one. Unfortunately, it’s easy to go wrong here. Many business owners calculate a single job’s cost of goods sold by adding parts and labor. They’ll want to set a price that makes up for overhead expenses (30% for example) and leaves room for net profit (10%), so they’ll decide to apply a 40% markup. Intuitively, they multiply the cost of goods sold by 140% (1.40). 

However, they won’t get a 40% profit by multiplying the cost of goods sold by 1.40. When they multiply the cost of goods sold by 1.40, they only add 40% of the cost of goods sold. They don’t figure out 40% of the entire job cost. The markup won’t even add up to 30% of the total amount collected, meaning that those business owners lose money despite the marking up 40% if they NEED to make 30% to break even.

Instead of multiplying by a markup, you can calculate a gross margin. You can successfully determine a 40% gross margin by dividing the cost of goods sold by 60% (0.6). When you divide the cost of goods sold by a percentage, you turn the cost of goods sold into that percentage of the total price. The leftover portion of the total price equals your 40% gross margin, which accounts for the overhead expenses and desired net profit.

 

Mistake #5: Being afraid to raise prices

It’s not easy to start a business without any previous financial data. When you first get into the service industry, your prices will likely come down to guesswork because you don’t know what your employee efficiency and overhead costs will look like. 

The key to reaching your net profit goals is to adjust your prices to hit those targets. In many cases, business owners set their prices too low to make a desirable profit. It makes sense for them to raise prices once they know what their expenses are. However, they risk losing customers when they raise prices.

Losing customers is a valid fear. You can’t make any money without a solid customer base to support your business. However, the company will continue to bleed money if you don’t raise your prices and keep missing targets. Raising prices is a risk worth taking because many customers will understand and be flexible with pricing. Will you lose some customers? Almost certainly. Still, it will be impossible to build your business if you don’t take the risk of increasing your prices.

 

Running your own service business can be difficult if you don’t know how to manage your finances. Still, it can be a rewarding experience once you become aware of the common financial blunders and learn how to avoid them.

Most of the content in this article is based on Alex Meaney’s contribution to the HVAC School podcast in the October 2nd, 2020 episode: “How to Get The Most From Online Education.”

 

Attending a class from your bedroom or home office sounds very convenient, right? That was probably what many Americans would have thought several months ago. Now, many of us shudder at the thought of learning remotely. With distractions and technical difficulties galore, many students and trainees have struggled with online education. Maybe you are one of those people, but fear not! Rock Star HVAC design educator Alex Meaney addresses the challenges of online education and offers advice for struggling students and educators alike. He has provided some crucial tips for overcoming the obstacles of distance learning and getting the most from your online education.

 

Take advantage of early reading

 

It’s a good idea for educators to provide educational materials before an online training session or class. If students or trainees have access to readings and videos ahead of time, they may enter the class or training session with a basic understanding of the concepts. Educators, it’s on you to set your students up for success.

 

Students, I’m afraid you aren’t out of the woods yet. It helps to go into a class feeling prepared. You may want to familiarize yourself with heat gain/loss equations before entering a psychrometrics class. That way, you will be ahead of the curve and won’t have to waste valuable time memorizing formulas.

 

Meaney also stresses the importance of learning vocabulary before attending a class. It helps to feel like you “speak the language” of the topic before attempting to grasp challenging new material. For example, you don’t want to look like you’ve seen a ghost when the educator says a word like enthalpy in a psychrometrics course. 

 

Look for opportunities to tutor difficult subjects

 

Meaney also gives a seemingly counterintuitive piece of advice for students: seek opportunities to tutor confusing subjects. Tutoring increases a student’s investment in the subject by making them accountable for your classmates’ successes. 

 

Some of you may enjoy the added pressure, and some may not. Regardless, you will obtain a more in-depth understanding of the material if you teach it to others. It also feels great to help a friend grasp a tricky topic. Who doesn’t want to be a good person and benefit from the experience?

 

Take a class with a friend

 

Taking a class with a friend is also a good strategy for getting the most from remote education. Studying with a buddy is useful for filling the gaps in learning. One person may better understand a topic than the other and vice versa. 

 

Manhattan Institute lists a few other benefits of friendship in education. Even in the virtual classroom, friends provide comfort and security. You may feel more comfortable asking questions or requesting clarification if you aren’t afraid of being judged by your classmates.

 

Friendship is also a source of support in the learning environment, even in nontraditional, remote settings. Students reinforce their learning when they tell their friends what they found exciting or challenging about a class.

 

Educators: show your faces

 

Educators can create a more engaging environment for their students by adding a video of themselves explaining the content in videos or PowerPoint slides. Although these learning formats do not compare to lectures in real-time, it’s nice to see a human face among diagrams and charts.

 

Work in a clean, distraction-free zone

 

This is a big one. Maintaining an organized workspace is a must for students and educators. For most people, this means limiting distractions and maintaining the cleanliness of the workspace. 

 

Putting away cell phones is a good start. Putting the cell phone away minimizes the temptation to look at text messages or social media during class. The last several times I checked, #HVAC wasn’t trending on Twitter anyway.

 

It also helps to remove irrelevant documents and materials from the workspace. Paying bills is essential, but nobody wants to think about that while they’re trying to learn a new skill. Even if you just need to shove them on the floor for a bit, it’s better than keeping them in front of you.

 

Closing background programs and internet tabs on the computer eliminates clutter on the screen. We know you enjoy listening to HVAC podcasts and checking out family photos on Facebook, but class time is not the time for that. The webpages will still exist when the lesson is over. 

 

Meaney also recommends taking notes with a writing utensil, not on a phone or tablet. Involving the hands in the learning process is an excellent way to engage the body while taking in new information, especially for those fidgety hands-on learners. (If writing is not required, try squeezing a stress ball while you learn!)

 

Ensure a stable internet connection

 

Anyone who shares an internet connection with other people may consider minding their bandwidth usage. This means ensuring that other people in the home or office don’t stream videos or play video games online.

 

Many people love watching The Mandalorian and playing Grand Theft Auto V online, but heavy bandwidth usage strains internet connection. A spotty internet connection can result in long download times, buffering, and disconnection from online lectures. 

 

It would be best to let roommates and family members know when it’s class time. That way, they can do their part to respect and support your remote learning process. Netflix, Disney+, and the PlayStation Network can wait.

 

Set aside additional time to ask questions

 

Even with scheduled classes, students can benefit from managing their time. Students could consider reserving some time after a lesson to ask questions or do some independent learning. (For example, a student could set aside 2 ½ hours of their day for a 2-hour class.) If you don’t end up using the additional time, then it becomes free time. You can study some more, walk the dog, or take a nap. It’s your time. It is better to set aside more time than necessary than to plan poorly and need more time. 

 

Consider using the extra time to take advantage of the instructor’s availability. Ask questions! They love helping students understand their lectures. After all, they would not have chosen to teach if they did not enjoy helping others. There are plenty of jobs that pay better.

 

Don’t be tempted to skip material

 

It may be tempting to skip through sections of pre-recorded videos or speed up the playback, but it’s best to refrain from zipping through the first playthrough. Yes, the educator may talk slowly. Yes, you may already know what they’re talking about. That could change within seconds, and you don’t want to miss out on new information you’ll need later.

 

It’s okay to jump around and bypass some sections on subsequent playthroughs. You may choose to skip around the learning materials to focus on specific topics. Still, it would help to understand the terms and general subject before turning your attention to individual parts.

 

Take care of yourself

 

Not many people think about comfort in the learning environment, but it can significantly help the learning process. Exercising self-care is vital for getting the most from remote education. Hunger and thirst can ruin your mood and make it more difficult to concentrate. 

 

Bring a glass of water to class and have some snacks within reach. After all, eating or drinking during an online lecture is not as disruptive as eating in a classroom or auditorium.

 

Be aware of your microphone and webcam status

 

Students and educators can benefit everyone in the class by being mindful of their video and audio settings. 

 

Webcams are great because they can add a social component to distance learning. However, they can also disturb other students. Please wear appropriate clothing and monitor the activities of pets or other background distractions. Yes, everybody would love to see fido and tell him he’s a good boy. No, he is not helping anybody learn about the nuances of Manual J. . 

 

Students should ensure that they remain muted unless they have permission to speak. Even though we are strong proponents of staying comfortable in class, nobody wants to hear you crunch Doritos. Everyone’s online learning experience will improve if everyone makes an effort to be considerate and use technology appropriately.

 

Have faith that you will learn

 

The best thing students and educators can do to get the most from remote education is to remind themselves that we are all capable of learning. Distance learning is difficult for many people, and anyone who struggles with it is not alone. 

 

Getting the most from remote education primarily entails limiting distractions and temptations. Students can succeed with a healthy amount of educator guidance, discipline, and self-compassion.

 

The industry leaders are seeing positive trends and have faith in you, too. Dominick Guarino, chairman and CEO at National Comfort Institute, acknowledges that the HVAC industry is a little behind when it comes to online education. However, he and other industry leaders are optimistic about the progress contractors have made in distance learning over the past year. 

 

Educators can do the following things to maximize the effectiveness of their online classes:

 

  • Provide preliminary readings or vocabulary lists
  • Attach their face to the content to boost engagement
  • Make themselves available to answer questions
  • Be honest with what they do and do not know; follow up with students who ask difficult questions

 

Students can do the following things to get the most from their remote education:

 

  • Study materials and learn vocabulary ahead of time
  • Take a class with a friend
  • Seek opportunities to tutor difficult subjects
  • Set aside more time than the class itself
  • Ask questions!
  • Stay disciplined and committed to learning

 

Educators and students can benefit from:

 

  • Keeping a clean work environment
  • Minding bandwidth usage within their homes
  • Being aware of their microphone and camera usage

 

Remote education is efficient and cost-effective, but it presents a unique set of challenges for educators and students. 

 

To succeed in an online curriculum, students must hold themselves responsible for their learning. Taking responsibility includes limiting distractions within the workspace: putting away cell phones, closing unnecessary applications and tabs, and removing workspace clutter. 

 

Students should also challenge themselves and take advantage of opportunities to maximize their learning potential. These opportunities include tutoring other students, learning with a friend, asking questions, and setting aside additional time to learn the material. 

 

Students will learn to prepare themselves for class, manage their time, and take care of themselves in a challenging, unfamiliar educational environment. 

 

Educators can improve their students’ learning process by providing videos of themselves explaining the content, providing preliminary reading materials, and following up with students who ask complicated questions.

The biggest thing is to prepare and be intentional and learn how to learn in this brave new world we find ourselves in.

Nomenclature on HVAC/R equipment is a sequence of numbers and letters a manufacturer uses to speak directly to the technician. Lots of initial upfront information is handed to the technician by the manufacturer the moment the technician reads the nomenclature in the model and serial numbers.

So how do we make sense of these seemingly random sequences of alphabetical/numerical characters? Every manufacturer has developed its own “language” of sorts when it comes to their equipment. Let’s take a look at several different examples.

Carrier 

Goodman

Mitsubishi

Trane

Now let’s take a look at all the different information these model numbers can give us. Across the manufacturers listed as examples, we can find information about Product Series, Type of Equipment, SEER, Cooling/Heating Capacity, Grille Variations, Voltage, Configuration, Cabinet Dimensions, Type of Motor, Airflow Capacity, Refrigerant Type, Efficiency, etc.

Understanding the importance of the information in model numbers is essential, and can save a lot of time in diagnosis and installation. Serial numbers, too contain valuable information. Most manufacturers don’t publish the nomenclature for serial numbers, because it’s mostly used for warehouse and warranty tracking, but a few helpful tips per manufacturer are:

 

Carrier: The first 2 numbers in the serial number indicate the week of the year the equipment was manufactured. The 3rd and 4th numbers indicate the year of manufacturing. 

Goodman: The first 2 numbers in the serial number indicate the year of manufacturing. The 3rd and 4th numbers indicate the week of the year it was manufactured.

Trane: Typically has the year of manufacturing printed elsewhere on the data tag

Mitsubishi: The first number in the serial number indicates the year of manufacturing. The decade must be assumed. (an “8” could mean the equipment was manufactured in 2008, or 2018)

 

Bottom Line 

 

Always take a moment to familiarize yourself with the manufacturer model/serial number nomenclature. The information you find will help you understand the system more fully and can help speed up the diagnosis/installation process.

 

-Kaleb

I’ve seen a lot of guys recently who reach for the motor puller tool first thing when attempting to remove a blower motor from a wheel/fan blade. Motor puller tools are an awesome backup tool when needed, but that shouldn’t be the go-to method of removing a motor.

 

The main issue with using a motor puller for every single motor is its tendency to bulge out the shaft. Motor pullers work by clamping down on a hub and then twisting a small shaft against the motor shaft in order to push/pull the motor/wheel away from each other. Sometimes, when technicians don’t sand down a shaft and spray the area with WD-40 or other water displacement lubricants, the shaft will get stuck and a tremendous amount of force is required to crank the motor puller shaft against the shaft of the motor. These opposing forces can significantly bulge the motor shaft. If the technician is successful in removing the motor that way, they often find it more difficult to get the motor shaft back inside the bore of the wheel. 

My hope is every technician reading this understands that the cardinal rule of removing a motor is to never use any of the following methods:

  • Use a hammer/wrench/blunt object to beat the shaft out of the assembly
  • Use channel locks of set screws
  • Use channel locks on the motor shaft
  • Over tighten the set screw

Any of the above-mentioned sins can result in expensive problems.

Please note the two things that must be completed before using a motor puller: sanding the shaft and lubrication. Guess what…

 

That’s all you need to do to remove a shaft!

  1. Sand the motor shaft until shiny and smooth.
  2. Spray with water displacement lubricant
  3. Loosen the set screw (but don’t remove it. They are easy to lose)
  4. (Optional) Take an adjustable wrench and gently turn the shaft independently of the wheel
  5. (Optional) Slightly push the wheel down the shaft to sand the portion of the shaft that was previously unreachable, which may have a lip that needs to be sanded down.
  6. Gravity is your friend. Let the motor fall out of the assembly. A shake or two may be required.

 

Voila! Those are steps a technician needs to do before using a motor puller, yet 90% of the time, those steps are all that’s needed to do the job. 

 

One extra tip…Blow off the sandpaper/rust debris before applying the lubricant, and don’t apply lubricant before you sand the shaft. The debris can get stuck and make things even more difficult, and sandpaper that is saturated in WD-40 doesn’t do much good.

 

For a video on this method, we shared a post by Brad Hicks earlier this year of him demonstrating how it’s done!

The Surefire Way to Get a Blower Wheel Off

 

– Kaleb

 

Dielectric grease is an often misused and misunderstood product that could easily benefit HVAC/R technicians in a variety of ways. From food service to electrical connections, dielectric grease can help lubricate mechanical components and prevent corrosion on electrical connections. But we need to understand what it is to begin with, in order to properly apply it in the field.

Dielectric grease is silicone-based grease with insulating properties. Common uses for dielectric grease include electrical connections, spark plug wires, and mechanical connections. The most common misuse of dielectric grease relates to electrical connections.

I mentioned dielectric grease acts as an insulator, yet many technicians mistake silicone grease as conductive. For conductive grease, Conducto-Lube Silver or any carbon conductive grease will do. Conductive grease is for conducting electricity from one conductor through the grease to another conductor. 

 

To apply silicone dielectric grease properly to electrical connections, make sure the conductor mating surfaces are bonded before applying the grease. In coastal climates, low voltage wiring is particularly in danger of corrosion, especially right on the waterfront. 

         

To prevent corrosion and to protect the connections, make a solid connection with your exposed conductor wire with an appropriately sized wire nut. Then remove the wire nut and dip the exposed conductor into dielectric grease. Next, put the wire nut back on. If you really want to get crazy, you can then wrap the connection with electrical tape. For contactors and other connections, wire up the components as usual, then apply a dollop of Daisy…I mean Dielectric grease to the connection points.

         

Dielectric silicone grease can be used in a variety of mechanical applications, as well. The Refrigeration Technologies Silicone Grease is also food-grade and can be used in many refrigeration applications. 

 

Remember to always double-check your electrical and mechanical connections for the correct torque before applying the grease. If you’re not careful, things can get messy quick!

 

-Kaleb

Sensors, Measurements, and Physics

As HVAC/R Technicians, we use tools and instruments to make measurements every day. In fact, 90% of our job could not be done efficiently without some kind of measurement. 

“How do we measure?”

“With what instruments?”

“How accurate are these measurements?”

These are all questions a thoughtful technician should ask before spending money on a tool or implementing solutions to solve a problem. 

 

Tools are our primary resource for measurement. Measuring tapes, scales, pressure transducers, thermocouples; the list goes on. But how exact are these measurements? How precise must our measurements be for us to use them to make decisions regarding the mechanical operation, occupant comfort, and occupant health? To answer these questions, we need a crash course in a little bit of physics. 

Don’t worry; we aren’t going into the rabbit hole too deep. I simply want to introduce you to a concept called the Heisenberg Uncertainty Principle in quantum mechanics. The Uncertainty Principle states that the more precisely you determine a particle’s position, the less precisely you can determine that particle’s momentum. Basically, the Uncertainty Principle limits our ability to measure things exactly. In modern physics, there simply is no such thing. There is only the agreed-upon accuracy and precision everyone is satisfied with to make practical decisions. For example, if you asked me how tall I was, my answer might be 5’11”. But is that 5ft. 11in. exactly? The line on the measuring tape with which I measured my height has a thickness, doesn’t it? Where within the thickness of that line do I fall? This principle is, of course, much more noticeable in the quantum (atomic) scale than on the macro scale. However, when measuring airflow and trying to solve occupant health concerns by measuring indoor air quality, accuracy, and precision matters. Our margin of uncertainty matters.

A technician doesn’t have to lose sleep over the fact nothing can be measured exactly. In our trade, and most of life, it’s not necessary. We can use this knowledge, however, to be more critical about the types of tools to choose to use. A duct traverse with a rotating vane anemometer can provide a quick and dirty idea for system airflow. Still, it’s not accurate nor precise enough to make complex troubleshooting decisions based on its results. The margin of uncertainty is too high. A flow hood or The Energy Conservatory’s TrueFlow Grid would be required for more accurate measurements upon which to base airflow balancing solutions. So how do we quality check for accuracy and precision? First, here’s a diagram showing the difference between the two and various combinations of accuracy and precision:

It’s important to understand the differences between these different combinations of accuracy and precision. Take any three brands of micron gauges and do a vacuum pump test. It helps if you have a digital gauge on the pump itself. Pull only on the pump first, and record the level of vacuum achieved (a good vacuum with fresh oil should be able to pull below 50 microns). Next, add the gauges one at a time and pull a vacuum in three more separate tests. You will very likely record three different micron levels for each gauge. In this experiment, the pump was our reference. In reality, the pump gauge itself would also need to be scrutinized for accuracy and precision, but as a demonstration, this test works well. Looking at the recorded micron levels from the gauges relative to the pump, where on the graph would your test results lie? Most are either accurate, but not precise, or precise, but not accurate. 

When thinking about buying a measurement tool, first consider what you are trying to accomplish with that measurement. If you aren’t planning on making accurate and precise capacity calculations, then you don’t really need the more accurate and precise hygrometers and airflow measurement tools. You may not need a digital manifold to charge a system to proper superheat and subcooling, because the margin of uncertainty is forgiving in that context. But a more accurate and precise sensor for a digital manifold or probe sure makes a pin-hole leak during a standing pressure test a lot easier notice.

Sensors are another factor to consider when choosing a measurement tool. Sensors are responsible for most of what makes a tool more expensive (not always, but most of the time). The product data for any instrument can be found either in the manuals or through a quick phone call to the manufacturer. In a recent podcast with Aeroqual’s Bernadette Shahin, we discuss some points to look for when researching the quality of a particular sensor.

  • Selectivity
    • A sensor that can measure the target parameter only (humidity, pressure, CO, microns, VOCs, etc.)
  • Sensitivity
    • A quality sensor should be able to have low cross-sensitivity to other parameters and should be stable in its ability to measure the target parameter over time.
  • Speed
    • A sensor has a published response time to change, but a manufacturer can confirm how long a sensor takes to reach an acceptable range of accuracy and precision expected from the sensor

Home automation is becoming very popular in the HVAC trade, and many are using Indoor Air Quality monitors to determine when and for long a mechanical system will operate, in order to maintain a comfortable and healthy home. To do this effectively, the accuracy and precision of the sensors in that monitor should be scrutinized. AQ-Spec is an excellent resource for this specific type of evaluation. Other manufacturers may have done their own third-party testing, and results can be released upon request. 

Keep in mind we aren’t referring to this concept as the “margin of error,” as many often call it. There is hardly ever any ill-intent when it comes to making a measurement, and manufacturers are not trying to create poor quality products. There are simply varying levels of uncertainty when we are using the tools at our disposal, and picking the right tool for the job is essential for quality solution implementation.

Another principle in physics, which all technicians should be aware of, is the Observer Effect. This theory states that the very act of observing a property’s state of being will inevitably change that property’s state of being altogether. In other words, by the time you have made a measurement, the state of whatever property you are measuring has changed, and no longer holds the same state of being it held before you started to measure it. A good example of this would be connecting hoses to a system. The mere act of attaching your hose has let out a little bit of pressure from the system; therefore, the pressure you will read is different from the pressure the system held the moment before you connected. This example might incentivize some to make the switch to probes, and ditch the hoses! Another example of the Observer Effect is checking electrical current on an indoor blower motor with the cabinet door removed.

One last point to make…accuracy and precision ≠ resolution. The resolution simply specifies to what decimal point the measurement is going to display. The resolution does not provide any direct information about accuracy, or precision. So next time you are comparing tools to see which is the best quality for the price, you may find a more accurate tool at a lower relative resolution. It is important to note, however, that precision and resolution are related. The higher the precision, the higher the resolution necessary to interpret the readings. It’s all about what you need the measurement to do for the application in which you use it.

 

Here are some links, in case you want to gain more insight into sensors, the Observer Effect, and the Heisenberg Uncertainty Principle:

https://podcasts.apple.com/us/podcast/going-deep-on-iaq-sensors-and-instruments/id1155660740?i=1000481776701 

https://www.sciencedaily.com/releases/1998/02/980227055013.htm

https://www.khanacademy.org/science/physics/quantum-physics/quantum-numbers-and-orbitals/v/heisenberg-uncertainty-principle

This is the second article in a three-part series, where Advanced Psychrometrics are explored. The source material for each of the articles in this series is ACCA Manual P Sections 3, 4, and 5. This article is based on information found in Section 4.

If you followed the previous Advanced Psychrometrics article, you now know how to use a Psych Chart to plot a Room Sensible Heat Ratio (RSHR) Line, and how to calculate Design Room CFM. However, if you followed that exercise, you will note the absence of real-world variables, such as ventilation and bypass factors. Equipment Sensible Heat Ratios are almost never an exact match to the RSHR. This exercise will account for these variables, and walk you through how to plot these properties on a Psychrometric Chart. 

It is worth reminding you that this is an exercise to help illustrate the complexities of psychrometry in the real world. This may not always be a practical method utilized in the design process. 

When outdoor ventilation air is mixed with return air before the equipment coil, the equipment is exposed to latent and sensible loads beyond that of just the conditioned space. This characteristic causes the Coil Sensible Heat Ratio (CSHR) to alter from the RSHR. Remember, the Room Design Conditions will be met only when the supply air properties fall on the RSHR Line. With two different SHRs, we no longer have the luxury of choosing any supply condition we wish. The supply air must be able to cool and dehumidify the space. It also must now compensate for the additional load introduced by the ventilation air. Therefore, the only supply condition that will satisfy the Room Design Condition is the point at which both the RSHR Line and CSHR Line meet on the Psych Chart.

To plot the RSHR Line should be a breeze at this point. For a review on that process, and the first part of this article series, CLICK HERE.

The construction of the CSHR Line, however, is a bit more involved. There is a little trial and error in the construction of the CSHR Line. It’s not impossible, of course, and with practice, you get pretty good at nailing it on the first try. Here’s why a trial and error process is required in order to plot the CSHR Line:

  • The location of the CSHR Line is determined by the Mixed Air Condition (MAT) and CSHR
  • The CSHR and the MAT can’t be plotted without knowing the percentage of Outdoor Air (OA)
  • The percentage of OA can be calculated only when the supply CFM is known.
  • The supply CFM can be calculated only when the ΔT between the room return and supply is known, which is determined by the intersection of the CSHR and RSHR Lines
  • The CSHR Line is the line we are solving for; therefore, it is unavailable.

This is why a trial and error process is required. Simply put, we’re going to use an estimated guess as to what we think our supply air condition will be, then follow the process until we can determine if our selection actually results in the intersection of the CSHR and RSHR Lines. To help aid in the accuracy of your guess, keep in mind that, on average, a Direct Exchange Fan Coil can provide supply air temperatures which may fall between 14-25 degrees below the space temperature at typical relative humidities between 80% and 95%.

To begin this exercise, let’s start with some basic information, which will ALWAYS be available to you from a quality load calculation. This information can be plotted on the Psych Chart with complete certainty:

Room Sensible Heat: 21,700 BTUh

Room Latent Heat: 2,300 BTUh

Room Total Heat: 24,000 BTUh

RSHR: 0.90

Room Design Condition: 75℉ db / 50% RH

Outdoor Design Condition: 95℉ db / 75℉ wb

Ventilation Required: 245 CFM

In this scenario, a Room-to-Room load calculation has been done on a home. The RSHRs have all been averaged together for a mean room sensible heat ratio. We can go ahead and plot what we can on the chart:

Let’s select a 57℉ supply temperature at about 90% RH. Now we can determine the Supply CFM. Since the RSHR is the average of the entire home, the Supply CFM will equal the total system CFM.

CFM = Room Sensible Load ÷ (1.08 x ΔT)

21,700 ÷ (1.08 x 18) = 1,116 CFM

Now that we know the Supply CFM, we can calculate the percentage of ventilation air.

Ventilation =  245 CFM ÷ 1,116 CFM 

Ventilation = 22%

We have a good bit of information here now, but the math starts to get a little confusing without explanation. We now know that 22% of Outdoor Air (at 95℉ db / 75℉ wb) will be mixing with the remaining 78% Return Air (at 75℉ db / 50% RH). To calculate the Mixed Air Condition, complete the following equation:

MAT = (0.22 x 95℉) + (0.78 x 75℉)

MAT = 20.9℉ + 58.5℉

MAT = 79.4℉

We can now plot the Mixed Air Condition on the Psych Chart.

At this point, we have everything we need to construct the Coil Sensible Heat Ratio Line. If you notice on the Psych Chart, there is a list of helpful formulas to the left of the page. We need to solve for Total Coil Heat Load (Qt) if we are to determine Coil Sensible Heat Load (Qs) and CSHR. To do that, we need to figure out the change in enthalpy (ΔH). Enthalpy is heat energy in BTUs per pound of dry air.

ΔH = 30.6 – 23.4

ΔH = 7.2

Now let’s plug our ΔH into the Total Coil Heat Load calculation. (4.5 here is Air Density x Run Time in minutes. 0.075 x 60 = 4.5)

Qt = 4.5 x CFM x ΔH

Qt = 4.5 x 1,116 x 7.2

Qt = 36,158 BTUh

Solve for Coil Sensible Heat Load. To do this, make sure you are using the entering air condition the equipment will actually see: MAT.

Qs = 1.08 x CFM x ΔT

Qs = 1.08 x 1,116 x 22.5

Qs = 27,119 BTUh

We can finally solve for Coil Sensible Heat Ratio at this point:

CSHR = Coil Sensible Load ÷ Total Coil Load

CSHR = 27,119 BTUh ÷ 36,158 BTUh

CSHR = 0.75

We can now plot the CSHR Line on the Psych Chart.

If you look closely, you may be thinking, “Wait a second, the CSHR Line does not intersect with the RSHR Line.” You would be absolutely correct. This is why the trial and error solution is necessary. However, if you notice, the CSHR Line is extremely close to our selected supply temperature. The CSHR Line is just slightly above the RSHR Line.

What does this mean?

We can still use the design CFM and supply condition, and the equipment will satisfy the sensible load, but will maintain a slightly higher humidity level in the space than what was designed. Take a look at the actual grains of moisture for the Mixed Air Condition in comparison to the Supply Air off the coil at 57℉.

The equipment will be able to dehumidify from 73 grains of moisture/lb of dry air down to 63 grains of moisture, rather than the ideal 62 grains. We’re talking about a difference of 1 grain of moisture. This can be acceptable, and the difference likely unnoticeable. In cases where a coil selection will not match the latent load requirements of a space, a viable option would be to add supplemental dehumidification to deal with the remaining latent load. Ultra-Aire Ventilating Dehumidifiers are an excellent option, and will also help lessen the additional latent load from the ventilation air.

Lastly, let’s talk about Bypass Factor. Remember, the ideal supply temperature would be the apparatus (equipment) dew point. However, there is a small percentage of air that will bypass the coil and not transfer its heat to the coil. This can be calculated using the known apparatus dew point. The Bypass Factor formula is as follows:

 Bypass Factor = (Supply Air Temperature – Apparatus Dew Point) ÷ (Mixed Air Temperature – Apparatus Dew Point)

Bypass Factor = (57 – 53.5) ÷  (79.4 – 53.5)

Bypass Factor = 3.5 ÷ 25.9

Bypass Factor = 0.14

At this point, you would need to look up a manufacturer’s extended performance data for their equipment to ensure that the coil you select will meet a sensible capacity of 27,119 BTUh and a total capacity of 36,158 BTUh at 1,116 CFM, with an entering condition of 79.4℉ db / 65.6℉ wb and an outdoor condition of 95℉ db / 75℉ wb. Let me translate that to something you might actually see on a Performance Table:

Entering Air Condition: 80℉ db / 67℉ wb

Outdoor Air Conditions: 95℉ / 75℉ wb

Total Capacity: 36,000 BTUh

Sensible Capacity: 27,000 BTUh

Airflow: 1,100 CFM

If you can select a coil that will match these criteria, you will be able to maintain an indoor air condition that is nominally close to your design.

To see how this chart would look in another scenario (without going through the step-by-step process), here is a psych chart based on my house and ASHRAE Design Conditions:

Room Sensible Heat: 16,800 BTUh

Room Latent Heat: 7,200 BTUh

Room Total Heat: 24,000 BTUh

RSHR: 0.70

Room Design Conditions: 75℉ db / 50% RH

Outdoor Design Conditions: 90℉ db / 80℉ wb

Ventilation Requirement: 46 CFM

In this case, my selected supply air condition happened to fall perfectly at the intersection of the CSHR and RSHR Lines. The tricky part, however, is finding a coil that will meet the sensible and latent heat requirements under the design conditions. I would need to look for a coil with 18,000 BTUh sensible capacity and 29,000 BTUh total capacity. I’d have to settle for a 2.5 ton (30,000 BTUh) coil with a close CSHR under design conditions, and potentially add supplemental dehumidification. (A Carrier FB4C–030 would actually fit the bill quite nicely.) Remember, the equipment selection performance table will have actual capacities that differ from the nominal rating; thus, care must be taken when using manufacturer performance tables to select equipment.

If you’ve made it to the end of this exercise, congratulations: you are as nerdy as they come! I hope this helps illustrate the complexities of psychrometrics. If nothing else, the take away should be a new-found respect for psychrometrics, and its integration into a technician’s daily diagnostic toolbag.

Stay tuned for Part 3, where we will dive into ACCA Manual P, Section 5. There we will learn how to account for duct gains, and how reheat dehumidification looks on a Psych Chart.

 

–Kaleb Saleeby

This is the first of a three-part series of articles, which will dive deep into Advanced Psychrometrics. The source material for each of these articles may be found in ACCA Manual P Sections 3, 4, and 5. This article is based on information found in Section 3. 

Psychrometrics is the study of the physical and thermodynamic properties of gas-vapor mixtures. In HVAC/R, we are specifically interested in air-moisture mixtures, and how varying properties affect human comfort and equipment performance. The Psychrometric Chart is a tool used to describe all the possible combinations of gas-vapor mixtures, and can be used to calculate the sensible and latent loads associated with HVAC/R equipment.

Using a Psychrometric Chart can be a bit confusing at first, but with practice and familiarity of the formulas, a Psych Chart can be easily used for a wide variety of purposes. Basic Psychrometric education can be found in the Refrigeration and Air Conditioning Technologies Manual (RACT) and in the first two sections of ACCA Manual P. In this article, however, I’m going to show you how you can apply psychrometrics to calculating Design Room CFM and illustrate how psychrometry can be used to help a technician understand supply air properties. All of the information discussed here can be found in Section 3 of ACCA Manual P.

When selecting equipment for a home or building, it is recommended a Room-to-Room Heat Load Calculation be done as opposed to a Block Load Calculation (Wrightsoft is an excellent software for load calculations, just saying). Room-to-Room calculations result in a more accurate representation of the heat gains and losses per zone (room), and can greatly improve the accuracy and performance of system sizing and design. Assuming a Room-to-Room Load Calculation has been done on a building, the next step in utilizing the Psychrometric Chart would be to plot out the Room Sensible Heat Ratio Lines for each zone. Room Sensible Heat Ratio (RSHR) is the ratio of sensible heat to total heat (including latent) for a room (or zone). If, for example, a room had a total heat load of 2,500 BTUh and 1,800 BTUh sensible heat, the RSHR would be 0.72.

RSHR = Room Sensible Load ÷  Room Total Load

RSHR = 1,800 BTUh ÷ 2,500 BTUh

RSHR = 0.72

Now that we know the RSHR, it’s time to plot the RSHR Line on the Psych Chart. To do this, we need to find a “reference dot”.

80℉ db at 50% RH is considered the standard reference dot. Locate and mark the reference dot and then run a line through the reference dot using a straight edge that is lined up with the RSHR (0.72), which can be found on the far right-hand side of the chart. 

Now, locate the design conditions for the zone in question. Let’s say the design conditions (on a design day of 90℉) is 75℉ db at 50% RH. Plot that dot on the chart. Now, run a line straight through that dot heading to the left of the chart, making sure it is parallel to the reference line. This line is your RSHR Line. This line may now be used to select a supply air condition that will maintain the design room condition on a design day. However, the supply air condition must fall somewhere between the design room condition and dew point (which in this example is about 51.5℉). Theoretically, the lowest possible supply air condition would involve the evaporator coil in cool mode to be 51.5℉ (dew point), and the supply air leaving the register to be the same. However, this theory is in no way practical when you consider duct gains, air leakage, and bypass factors (let alone the fact no one wants a sweaty supply register). Practically, a supply condition falling somewhere between 80%-95% RH will result in good dehumidification, lower airflow, and low fan power consumption. 

Select a supply temperature condition. For this example, let’s choose 55℉ at 90% RH. The next step is to calculate the Design Room CFM. The equation for CFM is as follows:

CFM = Room Sensible Load ÷ (1.08 x ΔT)

Remember, the Sensible Load for this zone is 1,800 BTUh. The difference between the Room Condition and the Supply Air Condition is 20℉. 

CFM = 1,800 BTUh ÷ (1.08 x 20℉)

CFM = 83

The required volume of air given an hour of the runtime is 83 CFM for this room to maintain the design room air condition under design load.

 

But what if my ΔT is lower?

The required volume of air increases. The new supply air condition is 63℉ at 72% RH, giving us a ΔT of 12℉.

CFM = 1,800BTUh ÷ (1.08 x 12℉)

CFM = 139

Both of the different supply air selections will maintain the design room condition on a design day, because they each fall on the RSHR Line. But as the temperature difference between return and supply air decreases, the required CFM increases

 

What is 1.08 supposed to be?

That is the product of the following equation:

Runtime (minutes) x Isobaric Air Density x Isobaric Specific Heat of Air

60 x 0.075 x 0.24 = 1.08

Some caveats must be addressed regarding this formula, and I credit Alex Meaney with Wrightsoft and Genry Garcia with Comfort Dynamics, Inc. for helping me understand these complexities. Both gentlemen are brilliant-minded experts in their fields, and have contributed (and continue to contribute) to HVAC School.

 First, the runtime is specified in minutes, because we are solving for cubic feet per minute (CFM), but also using British Thermal Units per hour. Converting the hour of runtime to minutes gives us 60 minutes, and makes sure our units of measurement are compatible.

Second, you may notice the term isobaric. This refers to any property at a constant pressure. At sea level, atmospheric pressure is around 14.7 psia. At this presumed fixed pressure, the density of dry air is 0.075 lb/ft3, and the specific heat of dry air is 0.24 BTU/lb/℉.

In reality, atmospheric pressure is not fixed, and outdoor air is not always dry. While you may be able to correct for actual pressure and humidity, it may not always be practical. On the other hand, with the ability to use MeasureQuick (which corrects for air density and pressure in its calculations), the processes discussed in these articles may become more practical. It is important to note that manufacturers use isobaric air density and specific heat in their capacity ratings and airflow calculations. Therefore, the argument could also be made that even with this caveat, the end result will (on average) still land you nominally close to the actual air condition requirements. (Please note the wording used here) 😉

So how does this all circle back to practical application? It must be understood that a coil can operate in only one sensible heat ratio at a time, and it may not equate to any of the RSHRs calculated for any particular zone. In the case of a home with multiple zones, you may choose one of the following options when selecting a cooling coil to match the load conditions:

  1. If humidity control is critical to a specific zone, use the RSHR for that room to select a coil. All other rooms will vary in humidity, but the critical zone will be maintained.
  2. Average all the RSHRs together for a mean RSHR that can be used to select a coil. Each room will vary slightly from its individual RSHR, but it will be minimal and likely unnoticeable. 

And that, in a nutshell, is how you may use a Psychrometric Chart and data from a Load Calculation to determine Room Design CFM. This exercise, however, merely scratches the surface of the many factors that must be considered in an HVAC system. This exercise works only for a system that does not suffer from duct leakage, bypass factor, and has no ventilation whatsoever for the home/building. This exercise would fall short of providing any real-world insight into psychrometric properties involving an HVAC system. However, the skills learned here translate into the next phase of advanced psychrometrics! In the next two articles, I will detail how these variables can be accounted for (even solved for). In the end, I hope you will understand a little more about Psychrometrics in general, and how to add that knowledge to your ability to efficiently diagnose a system as a whole (including the envelope and people).

I’ll end this article with a quote from Alex Meaney, and I think it is important to keep this idea in mind throughout the rest of this series of articles:

“I’m of the opinion that local humidity is usually a[n] infiltration/ventilation/return problem, not a supply problem.”

–Alex Meaney

For access to the Testo Psych Chart I used for this article, click here.

 

— Kaleb

Many installers and service technicians know how to read and use a manufacturer fan table, but this is a quick review with a few extra tips for newer techs. It’s also a good reminder to senior technicians how this easy-to-use practice can also be easily abused.

At installation, it is imperative to the performance and longevity of the appliance to set up airflow properly. A practical way to do this is utilizing the manufacturer-supplied fan tables found in every installation manual. Here’s a review on how to set up airflow on a new system:

  1. Determine your target airflow (The national average is 400cfm/ton. However, in a dry climate, design airflow may be 450-500cfm/ton, and in a humid climate, airflow is typically designed at 350-300cfm/ton.)
  2. Set your fan speed (choose the speed tap, or set the dip switches)
  3. Verify the equipment and duct work is clean, and all packing materials are removed from inside the appliance (yes, this gets missed sometimes)
  4. Run the system in order to achieve the test conditions in which the Fan Table was created (Fan Table airflow readings are only valid if the field conditions match as closely to the lab conditions as possible; i.e. wet coil, dry coil, with or without heat strip kits, etc.)
  5. Measure Total External Static Pressure (see how to measure TESP below)
  6. On the fan table, find the model matching the equipment you have, and locate the speed tap being used
  7. Match the real-time static pressure with the fan table
  8. The point at which both the TESP column and Speed Tap row meet is the corresponding estimated airflow.
  9. Make any adjustments to ductwork or fan speed in order to achieve the target airflow (This is made easy if ductwork is slightly oversized and installed with manual dampers on the supply.)

TruTechTools.com

For servicing, techs may use the fan table method as a quick and dirty way of verifying airflow without extensive and time-consuming testing. This can be acceptable, but only if the following conditions are met:

  1. The equipment and ductwork are clean (This includes making sure the filter has been replaced)
  2. The equipment has been benchmarked once before (Without a reference, the fan table cannot be relied upon as an accurate representation of estimated airflow.)
  3. The equipment is running as closely to the documented lab conditions as possible. (But even then, how wet is “wet”?)

Static pressure readings stand alone as a valuable measurement during a service call, and TESP can inform a technician whether more extensive testing is required. But if the equipment has never been worked on by you, or your company did not install the equipment, the fan tables will not be useful until a full-system commissioning has been completed. 

Carrier FB4CNF Installation Manual

Another important tip is to always keep the return static pressure below 0.4” w.c. According to many manufacturers’ literature, a return static pressure of 0.4’ w.c. or higher can potentially result in water from the primary drain pan being picked up and thrown around inside the cabinet area, and sometimes into the ductwork. 

It is important to understand static pressure measurement is NOT a measurement of airflow. This is where many technicians abuse this method. Static pressure is just that: a measurement of pressure in reference to the space outside the ductwork. Based on lab testing conditions, a manufacturer is able to determine the airflow of a system under a known resistance. Static pressure is used as a proxy to estimate airflow, but this method is only as good as the conditions in which it is applied. Static pressure readings are air density dependent, so zeroing a manometer in a cold, dry attic, then inserting the probes into a humidified, warm duct system will adversely affect the accuracy of your measurements. This method is also heavily dependent on how detailed the manufacturer fan table is. An example of a good fan table would be one that lists the equipment model, if the unit was tested under wet or dry conditions, if heat strips were installed during testing, and any corresponding wattage/rpm determinations under given conditions. 

Carrier FB4CNF Installation Manual

The difficulty with using Fan Tables as a way to measure airflow is realizing the resistance across the equipment is dynamic, and will likely change many times over the course of a test (the coil may get wetter as it is loaded with latent heat, the coil will become dirty over time, etc.) Measuring actual airflow is difficult to do, but static pressure measurements are still very valuable, and are a good way to determine if a problem exists and on which side of the ductwork it exists (supply or return). 

A great product for measuring airflow in the field is the TrueFlow Grid by The Energy Conservatory. For more information on Airflow and Airflow Measurements, TruTechTools has an entire section of literature and webinars on the topic. Here is a video we recorded for them in 2017 regarding Static Pressure and Fan Tables:

— Kaleb

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