Is You Refrigerant System Constipated?

I am hearing more stories about systems having problems with refrigerant restrictions. Many are from black scale created inside the pipes by brazing without a nitrogen purge. In the old days we often got away with this if we did not take a long time brazing the joints and did not overheat the pipe. Today, however, the POE lubricant and HFC refrigerants scrub off the oxides and carry them around in the system. This is especially problematic with metering devices of all sorts. TEV screens get plugged, orifice metering devices get plugged, and even filter driers get stopped up. The black oxides can also conduct electricity, so if they build up inside the compressor shell they can cause it to ground out. Prevention is the best remedy – not forming the oxides in the first place. You can do this by purging the lines with nitrogen while you braze. Of course you need to let the nitrogen out as you put it in so the system does not pressurize. You can’t braze up a hole under pressure. There are new flow meters that let a trickle through – just enough to keep the air out, which is all you need. No air means no oxygen to form oxides. The primary symptoms of refrigerant restriction are a low suction pressure, a high superheat, and a high subcooling. The head pressure may anywhere from slightly low to kind of high. If someone has tried to fix the problem by adding charge, the high side may be high. Normally, it will be a little low after a few minutes of operation unless the system has been overcharged. If the restriction is anywhere in the liquid line, like the filter drier, there may be a temperature drop at that point due to liquid flashing off.

If your system is constipated with black scale, ex-lax won’t help. You will need to recover the system refrigerant, disassemble it and flush it out using a solvent made specifically for refrigeration systems, such as Qwik Flush by Mainstream Engineering. Using carburetor cleaner will just add to your problems. Re-assemble it with a new filter-drier, pull a good vacuum, and weigh in the manufacturer’s specified charge. You will have to adjust the charge slightly for line length and the amount of refrigerant the filter holds. I recommend using flare filters because they are easier to change, and you won’t have to worry about making any more scale. For more details on this procedure, check out unit 91 Refrigeration System Cleanup in the 2^nd edtion of Fundamentals of HVACR.  

Desired Air Conditioning Temperature Drop

I was recently asked for a formula to determine the temperature drop between the return air and supply air of an air conditioning system. While it is logical to check the temperature drop, determining exactly what it should be is not as simple as plugging in readily available numbers into a formula. Two operating conditions can have a pronounced effect on the results: the relative humidity of the return air and the amount of airflow. Most air conditioning systems condition the air two ways. They cool the air, referred to as sensible cooling; and they take water out of the air, referred to latent cooling. Only sensible cooling creates a temperature drop. Removing water from the air takes system capacity. The more water the system removes from the air, the less capacity is left for reducing the air temperature. Standard airflow is 400 CFM per ton for most systems, but that does not mean your system is actually operating at 400 CFM per ton. If you move less air across the coil, the air will be cooled a little more. To determine the temperature drop you must know the outdoor ambient temperature, the return air dry bulb, the return air wet bulb, the CFM of airflow, and the system’s sensible cooling capacity at that condition.

Take for example, a system that is removing no water out of the air operating at 100% sensible cooling with a standard 400 CFM per ton of airflow and producing 12,000 Btuh per hour. The temperature difference is calculated as TD = 12000/(400 x 1.08) = 28°F TD. If the airflow is reduced, the TD becomes 12000/(350 x 1.08) = 32°F. Increasing the airflow would make the TD 12000/(450 x 1.08) = 25°F. In humid climates, the latent capacity can easily be as much as one third of the total capacity, reducing the sensible cooling capacity to 8,000 Btuh. These same airflows would then give TDs of: 8000/(400 x 1.08)=19°F, 8000/(350 x 1.08)=21°F,8000/(450 x 1.08)=16°. In reality, these TDs would be a little off because the overall system capacity would be a bit less with the decreased airflow and a bit more with increased airflow. The system capacity will also change depending upon the outdoor ambient. The 12.000 Btuh per ton is a nominal figure based on the AHRI rating condition of 95°F outdoor ambient, 80°F indoor dry bulb and 67°F wet bulb.

You can try to account for duct gain by reducing the expected TD by some amount: say 3°F - 5°F. However, it is really difficult to use TD at the registers because the duct gain from one system to another can vary a lot. Ducts in the attic will pick up more heat than ducts in a crawl space. Duct leakage also has a big effect. If 10% of the air entering the coil comes from a 150°F attic, that obviously will affect the delivered air temperature. The rule of thumb people have used for many years is a TD of 15°F to 20°F across the coil, not at the registers. Looking at the above calculations, you can see where this comes from. However, it is also easy to see how little you actually know if you don’t really know all the operating conditions, the system airflow, and the system capacity at those conditions. If all you do is measure the return and supply air temperatures at the registers, you don’t really know much.

Substitute Refrigerant Safety

As R22 prices increase and R22 availability decreases, many technicians have at least thought about using a substitute refrigerant in place of R22. Usually, we are looking for a drop-in which can be used to charge a system instead of R22. My primary consideration is safety. Of course I want any substitute refrigerant to work well and be environmentally friendly, but most of all, I want it to not hurt me or my customers. The refrigerant manufacturer should be able to show that their refrigerant is listed on the EPA SNAP list of acceptable replacement refrigerants. If they can’t, I would not use it. Another source of safety information is the required MSDS sheet. Any chemical sold in the United States must have an MSDS sheet. If the seller cannot provide an MSDS sheet, I would not consider using the refrigerant. The MSDS sheet will list important information such as toxicity and flammability. One replacement refrigerant that is advertised on the internet has enough information on the MSDS sheet to let me know I don’t want any part of it. The proper shipping name is “Petroleum Gasses Liquified.” Other statements include “Vapor may ignite if exposed to static discharge", and "Flammable vapor may form if allowed to mix with air. Accumulation of gas is an ignition hazard. Vapors are heavier than air and may travel to an ignition source." R22 systems are not built to operate safely with a flammable refrigerant. There is no way I would put this in a system designed for R22. Last year technicians were killed while working on refrigerated shipping containers that exploded.(See post about it). They were R22 systems which had been charged with a flammable substitute refrigerant. Although the EPA has recently approved the use of flammable refrigerant in limited charge applications, it is important to note that there are many requirements a system must meet to be safe with flammable refrigerants. R22 systems meet none of these. For more information on flammable refrigerants, take a look at my previous post on Flammable Refrigerants. For more information on R22, take a look at my previous post on R22 Conversion. A couple of simple rules to follow will help keep you safe. Can you buy the refrigerant at your local wholesaler? If you can only get it over the internet or from a guy at a flea market, you don’t want it. Is the refrigerant listed on the EPA SNAP list for the specific application? If not, you don’t want it. Does it seem too good to be true? If so, you probably should avoid it like the plague.

Establishing Your Lifelines

All indications are that the HVACR Industry wants to help more people become involved in the HVACR trade. Their motivation is not founded in philanthropy, but self-interest. Unions cannot prosper without skilled members, contractors cannot prosper without skilled workers, and everyone needs skilled technicians to keep warm in the winter and cool in the summer (unless they live in Australia where keeping warm in the winter is not a problem). Howard Weiss of the ESCO Group recently sent out an message encouraging everyone involved in HVACR to step up to the plate and contribute to the education efforts in our industry. He points out the Bureau of Labor Statistics projects that 65.6% of HVACR service personnel in the industry in the year 2020 will be people not in the industry today. The whole industry has a stake in education. I believe that one problem is that many of the organizations who are already involved and contributing the HVACR education efforts often have a difficult time getting the word out. Teachers are often busy keeping up day to day and don’t always have the time to investigate instructional materials, scholarships, industry sponsored training, or equipment donations already available. I find that sometimes companies and organizations can’t understand why more schools, teachers, or students don’t respond to their offers. What we have here is a failure to communicate.

Anyone wishing to get instructors involved in their activities needs to plan ahead. Early notice is essential to educators. The educational bureaucracy moves at a slothful pace. The first time I went to the AHRI Instructor’s Workshop, the president of my school had to obtain permission from the state for me to go, even though Pearson was paying my way and I would be speaking at the conference. We have to know months in advance to make things happen.

For manufacturers and trade organizations, you need to market your help the way you market your products and services. One or two e-mails or flyers is just not going to get the job done. You need to make pests of yourselves! It is also a good idea to use more than one method to notify us and to make each promotional piece a little different so that it will be noticed. A good example is the National HVACR Educators and Trainers Conference sponsored by the ESCO Group. They put out e-mails and flyers on a weekly basis months away from the date of their conference. The result is that their conference has sold out two years running in a very tight economy. I know that marketing free or low cost products and services might seem counterintuitive. It is really simply a matter of following a successful model. Persistent marketing works.

As instructors, we need to recognize that we must invest time developing a network of support for our programs. If we wait for the resources we need to just show up, we won't have much to work with. I have several local contractors who donate materials and equipment to my program. A local contractor on my advisory board recently gave our program one of the new Trane Communicating touchscreen thermostats that look like an ipad. What does the contractor get out of the deal? He and most of his employees are graduates of Athens Tech. But all donations do not have to be so elegant. A recent graduate now working in the field brought us a 3 ton ICP heat pump that is less than 2 years old. It was involved in a house fire and was being replaced. Students who needed a job cleaning coils cleaned it up and a student who needed a job installing a split system installed it. I am proud to say that the newest addition to our shop runs great! If you have needs, let someone know. Below is a small list of organizations you can use to start your HVACR support network.

Instructor Networking

• Council of Air Conditioning and Refrigeration Instructors  CARE
• Refrigeration Service Engineers Society RSES

Conferences

• RSES National Conference, November 14-17, 2012
• HVACR & Mechanical Conference, March 11-13, 2013
• National HVACR Educators and Trainers Conference, March 17-20, 2013

Equipment Donations

• AHRI has a program connecting equipment manufacturers to programs with equipment needs. AHRI Equipment Donations
• Appion will donate an Appion recovery unit to your school. Also, if you buy their speed kit, they will donate one of their vacuum pumps. Appion Donations
• AMRAD builds the Turbo 200 multi-capacity replacement capacitors. They will give you one for your class. They will also come to your school and do a class on how to use them. AMRAD donations

Scholarships

• AHRI Rees Scholarship literally has more money than they know what to do with because too few students apply. Let’s change that.
• PHCC Scholorship Foundation gives scholarships each year
• Grainger awards many Tools for Tomorrow scholarships throughout the country which include both financial support and a tool kit

Expensive Top Offs

For years, many technicians and customers have been content to “top off” leaky air conditioning units, feeling the time and expense required to find and repair small leaks exceeded the inexpensive price of adding a few pounds. After all, adding refrigerant is pretty easy, does not take long, and most customers were perfectly happy to have their systems gassed up every so often. With the cost of adding refrigerant steadily rising, the era of cheap “top offs” is coming to an end. Newer units also hold considerably more refrigerant than older models, and the refrigerant is quite costly. A bill of $500 for “topping off” a system is quite possible. At $500, I don’t want to call you back next month for a repeat performance. I want the problem fixed. Customers are going to start demanding that we fix the leaks – not just gas up the units.

The temptation to just add refrigerant is strong. Locating and repairing leaks takes time and there is really not a sure-fire leak test that can prove a charged system has no leaks. We detect the refrigerant coming out to prove a leak. However, not finding any leaks does not necessarily mean there are none – it just proves that you did not find them. Like many things, better tools often yield better results. Everyone should have a good electronic leak detector and good quality soap bubbles that will form micro-bubbles. An ultrasonic detector is also a good idea for detecting leaks using nitrogen. You also need to use the tools enough to feel confident and comfortable using them. A fancy electronic leak detector is not much help if you don't trust it or use it .

Some leaks are really not repairable. Take for an example an evaporator coil with multiple pin-hole leaks. Plug a little hole today and a new one springs up tomorrow. The repair is to replace the coil, which is expensive. However, not replacing the coil is also expensive. Not only is the cost of adding refrigerant quite high, so is the cost of electricity. A system with a leak loses capacity and efficiency from the day it is charged. The unit has to run longer and longer to accomplish less and less, until it simply can’t meet the demand. The combined costs of added refrigerant and increased operational cost can add up to the cost of replacing the coil. Topping the charge off is no longer an easy and inexpensive solution. It is now just the lazy and expensive cop out.

A Father's Perspective

I have a tradition of posting to my blog on father’s day. Typically, I write about what I see from the perspective of a son. This year I am looking from the perspective of a father. I have two children. Both are very talented and have an impressive record of achievement. My daughter just graduated from Vanderbilt which a degree in Biomedical Engineering. My son, a rising junior in high school, was recently accepted to the University of Georgia as a dual enrollment student. He will start taking freshman college classes while he finishes high school. They are both wield more academic prowess than their dad who took 20 years to get his bachelor's degree. 

Music is a family tradition and both my kids are excellent musicians. There is nothing more satisfying than performing with your family. After a recent band concert in which both my son and I played, we took a picture of Grandfather, Dad, Son, and Daughter. A love of music passed from each generation to the next. I believe that my children's musical training has helped them immeasurably in their academic success and their poise. They are both natural leaders – inspiring the people around them to excel. Best of all, they are really nice people. I can't tell you how many times other parents who have had the opportunity to spend time with my kids have told me how impressed they were with them. 

Of course I mention these things to brag, but also to point out that these two outstanding young people are my father’s day gift 24-7. Nothing they can buy can compete with the people they have become. I don’t believe anyone can express in words the emotions, pride, and love a father experiences seeing the babies that he held become an engineer, or rip through a Scott Joplin rag on the piano with gleeful abandon. Although I am in no hurry to be a grandfather, I do hope that my children will both raise children one day. The truth is, you can’t really know how much your parents love you until you are a parent yourself. My children have the intellectual, creative, and interpersonal gifts to make the world a better place for the rest of us. Come to think of it, they already do!

Are You Giving Grades or Recording Them?

I have a sort of electronic life-line to several instructors around the country. They send me ideas, links to helpful information, and point out issues in the book or on MyHVACLab that they would like addressed. One of my e-mail buddies, Gary Reecher at Scott Community College, sends me things from time to time that he believes would help other HVACR Instructors so that I can share them with more folks. Recently he sent a link to an article entitled “Why Some Students Need to Fail” by Melissa Nicolas. If you have been teaching any time at all, you have probably experienced a student who is desperately seeking a lifeline to pull them through the course. The compassionate nature of most teachers tugs at us to help solve the student’s problem. Instructors should work with students who are struggling to help them succeed. However, this help should not extend to giving the student a grade they did not earn. An analogy might be the boat that accompanies a swimmer as they try to swim across the English Channel. The people in the boat can help the swimmer navigate the course, they can provide hydration so that the swimmer stays healthy during the event, they can offer encouragement, and they can rescue the swimmer should it become impossible for the swimmer to continue. What they may not do, is put the swimmer in the boat, deliver them to the opposite shore, and then declare that the swimmer successfully swam the English Channel. Giving a student a passing grade when they have failed is like providing a ride in the boat and then declaring they swam the English Channel. 

In her article, Melissa Nicolas suggests a helpful change of verb for the awarding of a grade. Rather than “giving” grades, you are “recording” grades. In fact, recoding is really a better description. Giving suggests that you are reaching into your bag of goodies and pulling out a gift for each student. Students who receive an inferior grade will naturally feel slighted by their less generous gift. “Oh I am sorry Johnny, I am all out of A’s. How about a nice C+!” They may also see grades as an indication of how much the teacher likes them. Receiving an F not only hurts your grade point average, but also hurts your feelings because the F indicates that the teacher does not like you. Students need to know that their grades are an achievement, not a gift or an entitlement. The instructor is not giving grades, just recording the grades the students have earned. When they make their A, they know that nobody gave it to them, they earned it.