Saturday, October 23, 2021

Chalk and Talk 

Several years ago a fellow HVAC instructor told me he had been strongly encouraged by his immediate supervisor to do more lecturing. To the academically trained supervisor, working with students in the lab didn’t look like teaching, it looked like training. In the supervisor’s mind, training was a lower level pursuit – akin to monkey see monkey do. The school had just transitioned from a Technical School to a Technical Collage and they wanted to look like a college. 

The instructor was asking for any help I could offer, especially along the lines of “chalk and talk”, his description of what he felt was being asked of him. I think that phrase perfectly embodies why so many students really don’t get a lot out of lectures – they are just observers, not participants. The instructor is writing stuff on the board and talking while the students are just passive observers.  In the days of chalk boards, the instructor was not even facing the class when they were writing. It sometimes seemed like the teacher was engrossed in their own thoughts while they stare at the board and talk to no one in particular. 

We have advanced a bit since then. At least with Powerpoint presentations we are usually facing the class, even if we are staring at our computer monitor most of the time. However, it is possible to lecture and still rise above the mind-numbing norm of a monologue delivered to a captive audience of passive observers.  

Begin by facing your audience and making eye contact with people long enough so they feel you are speaking to them personally. If you are using a Powerpoint presentation, be familiar enough with the presentation and the material that you don’t have to read the notes while looking at the screen. It is OK to look at the screen occasionally, but if your discussion is just straight out reading the notes it will be boring no matter how good the presentation is.

Use voice inflection and hand motion to convey personal interest in your subject matter. How do you expect your class to maintain interest if YOU think the talk is boring.

Stop and take a breath. One dead give away of a nervous speaker is someone who has rehearsed their speech so much that all the words come out in a rapid-fire regurgitation that indicates they are just repeating memorized phrases, not really thinking about they are saying.

Whenever possible, involve your audience. People learn more if they do more. Ways to involve the class could include group questions, prompts for input, or even direct questions to individual students if you know them well enough. Be careful with the last suggestion, the goal is to include the students, not intimidate or embarrass them.

Use visual aids. This is pretty easy to do today. Just be careful not to overdo the videos and pictures you share. You should not be handing your class over to professor YouTube, just showing snippets that enhance and reinforce your talk.

When using online material, make sure and watch it yourself first. Even though you are not the person in the video, if you show it to your class you are in effect endorsing it. There are some things online that you don’t want to be associated with. 

Finally, this is an HVACR class. It is perfectly OK to have gauges, meters, gas valves, compressors, or any other tools or parts you want as visual aids. If you are talking about meters, every student should have one in their hands. You can even do some small exercises during the lesson. Remember, people learn by doing, so have the students do something. No, this is not your typical college class – it is a hell of a lot more interesting.

Friday, October 15, 2021

 Diesel Effect Compressor Explosions

There have been a few rare but potentially fatal accidents involving exploding compressors due to an effect known as diesel effect. If the gas mixture being compressed contains enough air, the heat of compression can ignite the refrigeration oil in the cylinder, much the same way diesel oil is ignited in a diesel engine. The heat of compression plus the heat of combustion from the refrigeration oil then ignites the refrigerant in the cylinder, creating a dramatic increase in pressure which blows the compressor apart. Note that this is not just a phenomenon limited to flammable refrigerants, but can happen with A1 rated refrigerants such as 134a or 410A. How? 

Refrigerants are rated for flammability according to ASTM E681 at a temperature of 60°C. Many refrigerants that will not burn under ASTM E681 conditions will burn at higher pressures and temperatures, including R-22, R-134a and R-410A. It is worth noting that in tests where they were trying to create diesel explosions, the University of Tokyo found no significant difference between the behavior of A1 refrigerants (R-22, R-410A) compared to A2L refrigerants (R1234yf, R32). They also found that compressing refrigerant and air mixtures without refrigeration oil did not create a diesel explosion. The refrigeration oil had to be present. 

So how can we avoid compressor diesel effect explosions? Simply put: keep the air out. With no oxygen you cannot have an explosion. Air is never good for any refrigeration system anyway. It should not be news to anyone who has studied refrigeration at all that air does not belong in a refrigeration system. However, you may not realize that leaving air in the system not only hurts system performance and reduces the equipment life, it can create a real hazard to service technicians. Here are a few precautions you can take to avoid the specter of a diesel effect explosion in your refrigeration system. 

Check new installations for leaks using nitrogen and repair any leaks in the system.

Never use compressed air or oxygen for leak testing refrigeration systems. 

Thoroughly evacuate the lines and coil of new split system installations AFTER verifying they don’t leak.

Never pump a system down into a vacuum. Reducing the low side pressure to a vacuum can suck in air through leaks or incorrectly positioned service valves.

Never jump out safety controls such a low-pressure switches. Forcing a system to run when it is low on refrigerant creates the possibility of sucking in air through leaks on the low side.

Don’t simply add charge to systems that are low on refrigerant. This is especially true for systems that are significantly low. You should find and repair the leaks.

You can read more about the research into compressor diesel effect explosions here.

Friday, October 8, 2021

Human Search Engine

 Instructors worry about not knowing all the answers. I know that I do. Let me put you at ease. You don’t have to know all the answers to be an effective instructor. In fact, I feel that anyone who knows all the answers hasn’t asked enough questions. Our job as instructors is not to be a human search engine, but to teach students how to search for answers on their own. In short, to help students become more proficient at the learning process, specifically applied to our field of HVACR. To be clear, I am not suggesting that instructors do not need to be competent in HVACR. Nor am I saying you shouldn’t want to know as many answers as possible. Just that knowing every answer a student might ask is not necessary. Discomfort with areas where you don’t know the answers can sometimes cause instructors to cling to the specific areas of information they already know and refuse to broaden their scope. This is particularly true when it comes to new technology and industry developments. I believe this is an unconscious effort to “know everything” by limiting the scope of knowledge you expose yourself and your students to. Venturing into areas of new development can be uncomfortable because you don’t have as many answers at the ready. However, it is perfectly OK to tell a student that you don’t know the answer to a question they ask. Help them by directing them to resources where they might find answers. They are going to need research skills when they enter the field. Teaching students to learn on their own is probably the most important thing you can possibly teach them. On those many occasions when you DO know the answer, it can be more helpful to guide them through a search process than to simply hand them the answer. People tend to remember things they discover on their own more than things that people tell them. It takes discipline to do this. Providing the answer immediately basically concludes the interaction with the student. Asking leading questions or discussing relevant informative resources makes the interaction more of a dialogue and requires more student participation. It definitely takes a little longer, but provides a better long-term result. Remember, students learn more by what THEY DO, than by what you do.  

Friday, September 10, 2021

Gigabit vs Dialup


When lecturing, you should be more interested in ensuring the students understand what you are saying than covering a specific amount of material. Even if you manage to vocalize every important piece of information about a particular subject, it is largely a wasted effort if the students are not receiving the information. Your job is not to state all relevant facts, but to communicate them to the students. It is easy for us to transmit data faster than the students can absorb it. Remember, you have seen all this information before, probably said it all before, many times. You are not having to mentally connect the facts into a logical framework because you have already done that. However, the students who are hearing it for the first time have to comprehend each statement and then tie the different statements together in some logical manner in order to really understand what they are hearing. Help them comprehend the information by including analogies, similes, and connecting statements. One of the most powerful teaching techniques is to introduce new concepts and ideas using things people already know and understand. For example, “the refrigeration system moves heat from one place to another, much like a sponge can absorb water in one place and then release it in another when you squeeze it.” Like all analogies, it is imperfect, but it starts the process of thinking about absorbing heat in one place and releasing it somewhere else. Once you get that point across you can start talking about what the refrigerant does to absorb heat. Maybe boil some water in a flask. Learning is not just collecting data, it is making mental connections between the data points to develop new concepts. This takes time. If you are talking at gigabit speed while your students are listening on dial-up, most of the information will be lost. I have been guilty of this. I can recall asking students questions at the end of a one hour lecture only to discover that they did not really understand something that I said 15 minutes into my lecture. So although I discharged my duty to cover everything, really, I just wasted everyone’s time – including mine! So when lecturing, take some time along the way to ask a few questions and engage in some dialogue with the students to make sure your message is being received. Remember, the idea is not to demonstrate your knowledge, but to help the students increase theirs.

Wednesday, August 25, 2021

Teach the Process

A common problem that many students have across all levels of education is a failure to gain a thorough understanding of the subject matter being taught. I believe that the primary culprit is our over reliance on standardized, multiple-choice tests.  Information is presented as a disjointed collection of individual facts to memorize so they can be recalled on a test. Think of these facts as data points. People make poor data storage devices. Computers do a much better job. Now that everyone carries a computer in their pocket that is connected via the internet to supercomputers all over the world, there is very little reason for people to spend much time practicing personal data storage by memorizing and recalling facts. Instead, we should focus on what we are better at: understanding. By studying relationships and processes in addition to data, we gain an understanding of subject matter that is far deeper and more consequential. This level of learning exceeds what is possible by simply storing “facts” in our imperfect personal data storage units. 

It takes very little to make our collection of facts useless. A few years ago I was asked to write some technical literature for schools teaching HVAC in Georgia. I readily agreed, after all, I live in Georgia. After agreeing I found out the literature was to be for the Republic of Georgia, the one next to Russia! They don’t measure things in BTUs, CFM, tons of cooling, pounds, Fahrenheit, or any of the other thousand factoids I have rattling around in my head. Things like “400 CFM per ton” instantly became useless. Memorized snippets of code nearly as useless – I had to look up their laws and codes. Most every “fact” that I thought I knew became irrelevant. 

Fortunately, the principles that make the refrigeration cycle work are still the same. Although pressure is measured in kilopascals, temperature in Celsius, heating and cooling capacity in kilowatts, the processes and relationships are the same no matter which Georgia you are working in. While most of us will not have to worry about working in the “other” Georgia, we will have to adapt to technical advancements and changes which can make our set of “facts” just as useless. Take “400 CFM per ton”. Most new equipment does not come set for 400 CFM per ton out of the box anymore. New refrigerants are going to bring a whole new set of PT charts, so those saturated pressures at 45° and 100° are going to change. It is far easier to adapt to tomorrow’s technology if you truly understand today’s technology. Teach the processes, not an assortment of facts. 

Friday, September 13, 2019

Leaking Money

Done regularly, system inspections, leak checks, and system repairs save money. Yes, they cost money up front, but you save money in the long run. Finding and repairing leaks as soon as possible avoids wasting refrigerant and energy. A system operating undercharged loses capacity and efficiency – which ultimately costs the building owner in the form of higher utility bills. Neglecting system repairs can also shorten the equipment life. The problem is that these avoided costs feel a bit hypothetical: this is what could happen if.... 

So, the EPA has come up with a more tangible cost as an extra incentive: fines. If saving on the cost of refrigerant, energy, and system repairs is not enough incentive, consider the recent case of Southeastern Grocers. They recently agreed to a $300,000 civil penalty and to spend to $4.2 million over the next three years to reduce refrigerant leaks and improve company-wide compliance of EPA regulations. But Southeastern Grocers is certainly not alone. Safeway agreed to a $600,000 civil penalty and $4.1 million in system remediation costs, COSTCO agreed to $335,000 civil penalty and $2 million in system remediation costs, and Trader Joe’s agreed to $500,000 civil penalty and $2 million in system remediation costs. So I thought now might be a good time to review some of the basics in terms of what is expected.

As of January, 2019
Leaks in industrial process refrigeration (IPR), commercial refrigeration, and comfort cooling appliances containing 50 pounds or more of refrigerant must be repaired within 30 days if they exceed the EPA established leak rate. The trigger rates are 30% for IPR, 20% for commercial refrigeration, and 10% for comfort cooling. Note that this is a leak rate – you don’t get to wait until 30% of your refrigerant has leaked out. The leak rate must be calculated every time refrigerant is added to a system.

Verification Tests
After repairing the leak, you are required to perform an initial and follow up test to verify that the leaks have in fact been fixed and the system is operating below the established leak rate. The initial verification is done before adding refrigerant and the follow-up is done after the system has been in service.  The verification tests must demonstrate that leaks were successfully repaired. You may conduct as many additional repairs and verification tests as needed within the 30 day repair period. Note- you don’t get another 30 days every time you figure out it still leaks. The process must be completed within 30 days.

Leak Inspections
You are required to perform regular leak inspections on systems that have exceeded the applicable leak rate until the calculated leak rates found during the inspection indicate the leak rate is below the EPA trigger rate. Commercial Refrigeration and Industrial Process Refrigeration equipment that holds more than 500 lbs of refrigerant must be checked every three months.  Commercial Refrigeration and Industrial Process Refrigeration equipment holding between 50 and 500 pounds of refrigerant must be checked annually. Comfort cooling equipment must also be checked annually.

For more details, check out the EPA fact sheet here

Wednesday, July 31, 2019

What is Vacuum Hose Conductance?

You may have heard or read the term “conductance” in reference to vacuum hoses and fittings. According to VAC AERO, conductance is volumetric flow rate divided by pressure drop, expressed as liters per second. Simplified, the conductance of a vacuum hose means its ability to allow gas to flow through it. The really important point is that no matter how big your vacuum pump is, it cannot move gas through a hose any faster than that hose’s conductance. Vac Aero

Hose conductance is not fixed, but varies with the type of gas, pressure, temperature, geometry of the passageway, hose diameter, and hose length. Duniway Stockroom Corp offers this formula: Conductance = 75 x Diameter3/Length. Note this formula calculates the conductance through a smooth tube in liters per second for dry air at 75°F and very low vacuums (under 50 microns). It won’t really calculate the conductance of a hose removing water vapor or refrigerant at atmospheric pressure. However, we can use it to get some general idea of the effect of diameter and length on hose conductance. Duniway

For example, the conductance of a ¼” diameter, 60” hose would be 75 x 0.253 /60 = 75 x .015625/60 = 0.0195 liters per second. Turning that into cubic feet per minute (CFM) we get 0.0414 CFM. Suppose we shorten the hose to 36 inches. Now the conductance is 75 x 0.15625/36 = 0.03255 liters per second. That translates to 0.069 CFM. More than a 50% increase just by switching from a 60” hose to a 36” hose. What about changing the diameter? Using a 3/8” hose that is 60 inches long, the conductance becomes 75 x 0.3753/60 = 75 x 0.0527/60 = 0.066 liters per second. Translated into CFM, that is 0.14 CFM. We get over three times the conductance by increasing the diameter to 3/8”. Using similar calculations for ½” and ¾” we get 0.33 CFM and 1.12 CFM respectfully. So comparing different diameter hoses using this formula we see that a 3/8” hose has over three times the conductance of a ¼” hose, a ½” hose has more than twice the conductance of a 3/8” hose, and a ¾” hose has more than three times the conductance of a ½” hose. All together, a ¾” hose has 27 times the conductance of a ¼” hose. Large diameter hoses really do make a difference in the time it takes t pull a vacuum. However, there are other restrictions that must be addressed before the hose size matters: the Schrader valve cores. We’ll talk about them next time.