A Ton of Air

I enjoy playing with numbers to gain insight into things that we often take for granted. There are many ballpark numbers that just about every HVAC tech has memorized, some more accurate than others. One very common ballpark number is airflow of 400 CFM per ton. One problem with this ballpark number is that it does not account for the required specific heat ratio for a particular application. But that is not what I want to talk about today. That airflow rate, 400 CFM per ton, is within the operating parameters of most HVAC equipment, even if it is not the most effective for a particular application.

What I want to show is how much work is involved in moving 400 CFM of air. At the ASHRAE “A” indoor condition of 80°F 50% relative humidity, a pound of air takes up about 13.6 cubic feet. Dividing 400 CFM by 13.6 tells us how many pounds of air the blower is moving each minute: 400/13.6 = 29.4 pounds per minute. Multiplying that times 60 tells us how many pounds of air the blower is moving per hour: 29.4 x 60 = 1764.7 pounds of air per hour. Recalling that a ton of weight is 2000 pounds, an airflow of 400 CFM is nearly a literal ton of air per hour! To get exactly a ton we would need to move 453.3 CFM: 453.3 / 13.6 = 33.3 33.3 x 60 = 2000 pounds per hour. But of course that 400, or 453 is just the airflow per ton of cooling capacity, not the total airflow. So a 2 ton system moving 800 CFM would be moving 3529 pounds per hour. If that same system were moving 906 CFM, it would be moving 4000 pounds of air an hour. That is a lot of weight to push around.

Think of the total external static pressure as the hill up which the blower must move all that weight. It becomes obvious that if the hill is higher, the blower will have to work harder. Think of the external static pressure a blower must operate against as the hill up which it must move all that weight. Forward curved centrifugal blowers lose capacity against higher external static pressures. Just as water pumps move less water if you make them move the water higher, centrifugal blowers move less air against higher static pressure.

In the case of constant airflow ECM motors, the blower motor puts in the work to overcome the loss of blower wheel efficiency to move all that weight up the steeper hill. In the case of constant torque electronic motors, while the motor gives a steady output, the blower wheel still loses efficiency. There is a decrease in the amount of air the blower can move. In the case of PSC motors, not only does the blower wheel lose efficiency, but the motor also loses capacity. The airflow drop can be drastic. So give the poor blower a break. Use air filters with low pressure drop and keep them clean. After all, the blower IS doing a ton of work! Check out my book, Fundamentals of HVACR published by Pearson if you would like to investigate further.

Magic Number 2652 Explained

Testing a capacitor under load means testing it while it is in an operating circuit. To do this you measure the operating capacitor amp draw and voltage and then apply them to the formula

Why does this work and where does the 2652 come from? To answer these questions, we need to understand what a capacitor does in an AC motor circuit.

What Does a Capacitor Do?

A run capacitor’s job is to add enough capacitive reactance to offset the inductive reactance of the winding it is in series with. Current in an inductive (magnetic) load lags the voltage. This means that the current peaks AFTER the voltage. Since the current and voltage are out of phase with each other, they don’t work together, causing inefficiency. Adding a capacitor in series with an inductive (magnetic) load helps correct this because capacitors cause the current to peak BEFORE the voltage. The amount of capacitive reactance needed depends upon the inductive reactance of the motor.

Like resistance, capacitive reactance is measured in ohms. The capacitive reactance produced by a particular capacitor varies with both the frequency of the AC current and the microfarad capacity of the capacitor. Higher frequencies and higher microfarad capacity both decrease capacitive reactance. The formula is

 This means that capacitive reactance is equal to the inverse of the product of 2 x pi x frequency x Farad rating. Through the magic of algebra we know that we can swap the XC (capacitive reactance) and C (capacitance) terms to get our formula for capacitance. That gives us the formula

 This can be rewritten as  

In this formula, 2π is a mathematical expression for a cycle. Recalling that the circumference of a circle is twice the radius times π, the expression 2π represents a complete turn of a circle if we are not concerned with the circle’s radius. Frequency is represented by f, which is always 60 cycles in North America. Together, 1/2πf calculates the effect of frequency on capacitive reactance.

works out to 0.00265258 for 60 cycle power. This would produce an answer in Farads, but we normally work with microfarads. Multiplying this by 1000 to get 2652.58 produces an answer in microfarads. This is usually rounded to 2652.

What about the capacitive reactance, XC? Remember that capacitive reactance is measured in ohms and that ohms can be found by dividing volts by amps. So we can substitute the capacitor voltage divided by the capacitor amps for the capacitive reactance. However, since 1/XC is the inverse of capacitive reactance, the fraction is flipped to perform the multiplication, placing amps on top. Together the two terms become

New Refrigerants Transitional

The American Innovation and Manufacturing Act of 2020, or AIM was passed as part of the 2021 appropriation bill, passed on December 27, 2020. Although you probably would not know it from the title, the AIM Act is about phasing down HFCs. This is a phasedown, not a phase out. This table shows the phasedown schedule. Noite, we started the 60% of baseline period this year.  

AIM Act HFC Phasedown Schedule
Date% of Production Baseline% of Consumption Baseline
2020 – 202390%90%
2024 – 202860%60%
2029 – 203330%30%
2034 – 203520%20%
2036 –15%15%

Allowances

Because this is a phasedown and not a phaseout, some HFCs will still be available for a long time. However, ALL HFCs will not necessarily be available. The phasedown is regulated by assigning allocations for production and/or importing HFCs to producers and distributors. How quickly a company uses up their allocation is calculated by multiplying the quantity of HFC produced or used times its exchange value, which is basically its AR4 GWP. For example, R410A has an exchange value of 2088, R32 has an exchange value of 675, and R454B has an exchange value of 465. This means that a company can make 3 times as much R32 as 410A, or almost 4.5 times as much R454B as 410A.

Still Using HFCs?

One interesting situation is that the “new” refrigerants which will be replacing the current high GWP HFC refrigerants also contain HFCs. R32 is an HFC and it is on the list of refrigerants being phased down. Other alternatives being studied, such as R454B, are blends that contain R32. Phasing down R32 will eventually make both R32 and R454B not practical for equipment manufacturers. They will probably be replaced in ten years or less.

Making the Switch

HFC allowances are currently 60% of the baseline. If manufacturers continue to make exactly the same equipment with the same HFC refrigerants that they have been using, they will run out of their HFC refrigerant allowance before the end of the year. I believe most manufacturers will start producing R32 and R454B equipment this year. Just by switching from R410A to R32 a manufacturer can triple the amount of refrigerant they can use. Doing the math 60% x 3 = 180%. Suppose they used up half of their allowance on R410A before switching, that would be 30% x 3 = 90%. This means they could actually increase their overall production. The math is even better for R454B. 60% x 4.5 = 270%, or 135% if you had already used up half your allocation on R410A.

Down the Road 2029

Things get a bit tighter down the road in 2029 when HFCs are restricted to 30% of baseline. Now the R32 calculation is 30% x 3 = 90%, meaning you are restricted to less than the baseline for your entire production. The manufacturer will either have to use a refrigerant with a lower GWP or figure out a way to reduce the charge of the systems they produce. R454B looks a bit better with 30% x 4.5 = 135%, so you are still in business assuming you have not increased production a great deal and you are not using your HFC allocation for anything else.

Down the Road 2034

By 2034 manufacturers will definitely need to have more answers because the allocation drops to 20% of baseline. Now the R32 calculation is 20% x 3 = 60% and the R454B calculation is 20% x 4.5 = 90%: both fall short, and that is before accounting for any growth or using your HFC allocation for any other purpose.

Crystal Ball

In ten years or less I believe we will see systems using other refrigerants start to take over. At this point, I think the manufacturers are thinking HFOs. They are already widely used in car air conditioning and have very low GWPs. What remains to be seen is whether they will be widely accepted. The European Union is pushing back against fluorochemicals in general. They want “natural” refrigerants such as propane or carbon dioxide. Europe seems more comfortable with R290 in larger systems than we are in the US. I don’t think the added fire risk of R-290 is going to be accepted in larger systems in the US. I don’t believe CO2 is practical in smaller systems the size of residential air conditioners and heat pumps. Whatever the form, I believe in ten years we will be looking at very different equipment.  

A2L Guides, Standards, and Codes

The regulations regarding A2L refrigerant are found in a tapestry of Guides, Standards, and Codes which often refer to each other. Here is a list of the most consequential.

ICC International Mechanical Code 2024, IAPMO Uniform Mechanical Code 2024
These recently revised codes allow the use of A2L refrigerants in traditional HVAC systems. They specify conditions for use of A2L refrigerant and refer to ASHRAE Standard 15/34 2022 and UL 60335-2-40, 2022.

Amendments to ICC International Mechanical Code 2021, IAPMO Uniform Mechanical Code 2021
Some states have passed amendments to their existing 2021 codes to allow the use of A2L refrigerants in traditional HVAC systems and specifies conditions for use of A2L refrigerant. They refer to ASHRAE Standards 15/34 2019 and UL Standard 60335-2-40, 2022.

UL 60335-2-40, 2022
This is the latest standard from UL for HVAC systems. It is similar to the international IEC standard with the same name and number. The provisions in the IEC standard have already been in place in many other places around the world; including, Europe, Japan, and Australia. UL 60335-2-40 spells out in detail how A2L refrigerant may be safely applied. It refers to ASHRAE Standards 15/34 2022.

ASHRAE Standards 15 2022 “Safety Standard for Refrigeration Systems”
This standard describes how refrigeration systems may be safely installed and operated. The 2022 edition includes specific conditions for A2L refrigeration systems.

ASHRAE Standard 15.2 “Safety Standard for Refrigeration Systems in Residential Applications” Standard 15 addresses larger buildings while 15.2 describes how refrigeration systems may be safely installed and operated in residential low-rise applications, including specific conditions for A2L refrigeration systems.

ASHRAE Standard 34 – 2022 “Designation and Classification of Refrigerants” Standard 34 lists refrigerant safety ratings and important safety data for a long list of refrigerants, including several A2L refrigerants. Data listed in Standard 34 is used to determine specific system requirements detailed in Standards 15 and 15.2. Taken together, Standards 15 and 34 provide very clear guidance for application of A2L refrigerant.

EPA Final SNAP Ruling 23
This ruling specifically allows the use of A2L refrigerants R-32, R-452B, R-454A, R-454B, R-454C, and R-457A in new residential and light commercial air conditioners and heat pumps. The rule incorporates UL 60335-2-40 by reference.

EPA AIM Act Final Ruling, Sept 2021
This ruling establishes the HFC allocations for the phasedown of HFC refrigerants under the AIM Act. One unexpected significant component of this ruling is a ban on disposable refrigerant cylinders beginning in 2025.


AHRI Guideline M 2020 “Unique Fittings and Service Ports for Flammable Refrigerant Use”
AHRI Guideline M specifies that service connections for systems with flammable refrigerant. For cylinders holding less than 50 lbs. of A2L refrigerant, it specifies CGA 164 fittings which are 1/4 inch flare with left-hand threads. For equipment using A2L refrigerant it specifies 1/4 inch flare with right-hand threads, exactly the same as those used on systems with A1 refrigerant. Same size and same threads.


CGA Standard V-1 2019 “Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections” The CGA V-1 standard describes the connections on compressed gas cylinders. Standard CGA V-1 2019 introduces the CGA 164 connection specifically for A2L refrigerant cylinders. It describes the CGA 164 connection as a 1/4 inch flare with left hand threads. The latest edition of this standard is now CGA V-1 2021.

What is an HFO Refrigerant?

I have talked to many folks who wondered what exactly is the difference between HFC refrigerants, the refrigerants being phased down, and HFO refrigerants, the low GWP refrigerants that will be replacing HFCs in many applications. The puzzle is that HFOs are also HFCs. That is, they contain hydrogen, fluorine, and carbon. So why the different name?

Alphabet Soup

For many years we have used a sort of short-hand to describe a refrigerant based on the atoms in the molecule. CFC for the older chlorofluorocarbons containing chlorine, fluorine and carbon. HCFC for the Hydrochlorofluorocarbons containing hydrogen, chlorine, fluorine, and carbon. And more recently, HFC for the hydrofluorocarbons containing hydrogen, fluorine, and carbon. So it is natural to think that the O in HFO stands for a single chemical, but it doesn’t. Instead, the O stands for Olefin, which is a description of a hydrocarbon chain containing a double bond between two of the carbons. All our previous hydrocarbon-based refrigerants (CFCs, HCFCs, HFCs) were all built on hydrocarbon chains that used only single bonds. For example R-12 and R22 are methane molecules  while R-32, R-125, and R-134a are ethane molecules. HFOs (Hydrofluoro olefins) are based on carbon chains that contain a double bond between two of the carbons, in other words, an olefin. The most well known HFO R1234yf is based on propene. Notice the “ene” at the end. Hydrocarbons ending in “ane” are single bond molecules while hydrocarbons ending in “ene” have a double bond between two of the carbon atoms.

Why This Matters

So why is this important? The olefin based compounds break down much more rapidly in the air than their single bond cousins, which is how they achieve such low global warming numbers. Their calculated GWP is much lower because of their short atmospheric life. They don’t survive intact for long in the atmosphere. This reduced chemical stability is also why the HFO refrigerants are mildly flammable. So what is the difference between an HFC and an HFO? Basically the way they are put together.

Air Conditioner Can’t Keep Up

Currently, Air Conditioning Technicians are receiving many complaints about air conditioning systems that can’t seem to keep up with the heat. Typically, technicians check refrigerant pressures, superheat, subcooling, temperature splits, and system airflow. But these don’t always identify the problem. What happens when the system is performing as it should but the customer is still unhappy with the results? One way to explain what is happening is to use the analogy of a boat with a bilge pump. Bilge is the nasty water that collects in the lower reaches of boats. Bilge pumps are designed to pump that water out. However, if the water coming into the boat exceeds the capacity of the pump to remove it, the boat will sink. There are two solutions: either get a bigger pump or fix the leaks. The house is like a leaky boat and the air conditioning system is the bilge pump. When we focus all our attention on the air conditioning unit, we are locked into the “get a bigger pump solution” while ignoring the more obvious solution: fix the leaks. If you had a boat with a big hole, would your first thought be “I need a bigger pump”? I would want to fix the leak.

Water leaks in boats are pretty easy to spot, but air leaks in ducts and houses are a bit harder to locate. That is why they are often ignored until the ship is sinking. Most of the time a properly functioning air conditioning system can overcome the added heat load from leaks in the house, leaks in the ductwork, and poorly applied insulation. However, when temperatures rise to the outdoor design point or higher, the system gets swamped with the extra heat load.

So how do we find the leaks? A blower door can be used to determine the amount of house leakage, a duct blaster can be used to identify the amount of duct leakage, and an infra-red camera can identify areas that are improperly insulated. Ideally, you would check these things during and immediately after construction so heat leaks can be addressed. However, many homes have never been checked. It makes sense to locate and correct heat leaks in the homes of customers whose systems are operating correctly but not maintaining temperature.  Doesn’t this cost the customer money? Well, yes it does initially. However, it saves money continuously thereafter. You should of course make sure the air conditioning unit is functioning correctly, but don’t ignore the effect of the leaks.

Stay Safe in the Heat

When you think about the dangers of working on air conditioning equipment, you probably think about working with electricity, refrigerant, and torches. We often overlook a more obvious danger: the weather. The reason we have a job is because it is either hot or cold. It seems like every year there is tragic news involving the death of an HVAC worker found unconscious or dead in an attic due to heat stroke. These tragic deaths are totally preventable and unnecessary.

To avoid becoming a victim of heat stroke you must monitor your body’s reaction to the heat. When you are hot, sweating is good. The evaporation of sweat is your last line of defense against overheating. Sometimes sweating just isn’t enough to counteract the effects of work and hot, humid conditions. If you are sweating profusely and experiencing a rapid pulse, muscle cramps, and dizziness, you are experiencing heat exhaustion. To avoid becoming a victim of heat stroke you need to get out of the heat, hydrate, and cool off. If it is hot and you are NOT sweating, you are past heat exhaustion and entering into heat stroke. This is very dangerous, you can pass out from heat stroke. Symptoms include dry, hot skin (90+); rapid pulse (130+), headache, dizziness, and confusion. If you have these symptoms, you may be the victim of heat stroke – which is life threatening. You should get out of the heat, hydrate, and call 911. Don’t ignore what your body is telling you. If you start feeling bad while working in the heat – get to a cool place and hydrate.

The locations where HVAC techs are exposed to the most extreme heat are attics and commercial rooftops. Jobs in these locations should be scheduled for early morning to avoid the worst heat. Air movement can help in attics. On rooftops you can shield yourself from the sun using canopies or umbrellas. Keeping hydrated is critical. You should have plenty of water and sports drinks available all the time. You should avoid alcohol or caffeinated sodas because they are diuretics and can actually dehydrate you. Sorry, but you cannot keep hydrated by drinking beer.

Tools that can help you stay safe include heat stress meters and wearable health monitoring devices. Heat stress meters can help determine the effective heat index of the work area. They measure the combined effect of temperature, humidity, and mean radiant temperature to determine the effective temperature in an area where you are working. They can include an alarm that warns you if the heat index will exceed a safe level. Wearable devices can measure your body’s reaction to the work environment. While a heat stress meter measures the area, the wearable monitor measures you. One, the CORE, measures your body temperature and heart rate. Using this device you can determine how your body is handling the heat and take action when signs of heat exhaustion are indicated. Here are links for these two devices.

Heat Stress WBGT Meter-HT30 (trutechtools.com)

CORE Body Temperature Sensor

I highly recommend that you do some research to better understand how to stay safe. To that end I am including several links

Heat exhaustion – Symptoms and causes – Mayo Clinic

Heatstroke – Symptoms and causes – Mayo Clinic

Heat Stress Related Illness | NIOSH | CDC

OSHA Guidelines to Prevent Heat Illness | TFT Pneumatic (tft-pneumatic.com)

Beat the Heat: Identifying and Preventing Heat Stress | (3m.com)

A2L Refrigerant Standards and Regulations

The regulations regarding A2L refrigerant are found in a tapestry of Standards, Codes, and Rulings. I like to research using original documentation whenever possible. Not that I don’t trust the folks doing webinars, blogs, and videos, but when answering questions about new technology I want to be able to point to authoritative documents. So, I look for the actual standards, guidelines, and codes. I found it a bit confusing because there are so many agencies publishing many standards and regulations regarding A2L refrigerant. Furthermore, these standards often refer to each other. I have listed below some of the more important documents you should study if you like to do your own research.

ICC International Mechanical Code 2024, IAPMO Uniform Mechanical Code 2024
These completed but yet unpublished codes allow the use of A2L refrigerants in traditional HVAC systems and specify conditions for use of A2L refrigerant. They refer to AHRI Standards 15 and 34 2019 and UL 60335-2-40, 3rd edition.

Amendments to ICC International Mechanical Code 2021, IAPMO Uniform Mechanical Code 2021
Some states have passed amendments to their existing 2021 codes to allow the use of A2L refrigerants in traditional HVAC systems. Typically these amendments accomplish this by referring to AHRI Standards 15/34 2019 and UL Standard 60335-2-40, 3rd edition.

UL 60335-2-40, 3rd edition
This is the latest standard from UL for HVAC systems. It is similar to the international IEC standard with the same name and number. The provisions in it have already been in place in many other places around the world; including, Europe, Japan, and Australia. It spells out in detail how A2L refrigerant may be safely applied. It refers to ASHRAE Standards 15/34 2019.

ASHRAE Standard 15 – 2019 Safety Standard for Refrigeration Systems describes how refrigeration systems may be safely installed and operated. The 2019 edition includes specific conditions for A2L refrigeration systems.

ASHRAE Standard 34 – 2019 Designation and Classification of Refrigerants lists refrigerant safety ratings and important safety data for a long list of refrigerants, including several A2L refrigerants. Data listed in Standard 34 is used to determine specific system requirements detailed in Standard 15. Taken together, Standards 15 and 34 provide very clear guidance for application of A2L refrigerant.

ASHRAE Standard 15.2 – 2022 Safety Standard for Refrigeration Systems in Residential Applications is the low-rise residential companion to ASHRAE Standard 15. Standard 15 has historically primarily been applied to larger commercial buildings, not low-rise residential homes. Standard 15.2 describes in detail what must happen to safely use A2L refrigerant in a residential application.

EPA Final SNAP Ruling 23, April 2021
This ruling specifically allows the use of A2L refrigerants R-32, R-452B, R-454A, R-454B, R-454C, and R-457A in new residential and light commercial air conditioners and heat pumps. The rule incorporates UL 60335-2-40, 3rd edition by reference.

EPA AIM Act Final Ruling, Sept 2021
This ruling establishes the HFC allocations for the phasedown of HFC refrigerants under the AIM Act. One unexpected significant component of this ruling is a ban on disposable refrigerant cylinders beginning in 2025.

AHRI Guideline M 2020, Unique Fittings and Service Ports for Flammable Refrigerant Use specifies that service connections for systems with A2L refrigerant should be exactly the same as those used on systems with A1 refrigerant. The connection on A2L refrigerant cylinders is described as a CGA 164 connection. The CGA 164 connection is described in the CGA Standard V-1 2019 as a 1/4 inch flare with left hand threads.

CGA Standard V-1 2019 Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections introduces the CGA 164 connection. It is designed specifically for A2L refrigerant cylinders. The standard describes the CGA 14 connection as a 1/4 inch flare with left hand threads. While the CGA 164 connection is first introduced in the 2019 edition, the latest edition of the CGA V-1standard is now 2021.

UL Standard 207 Standard for Safety Refrigerant-Containing Components and Accessories, Nonelectrical covers nonelectrical, refrigerant-containing components and accessories in accordance with ASHRAE Standard 15. This standard is specifically referenced by ASHRAE Standard 15.2 when describing fittings, valves, and mechanical joints.

Teach the Process , part 2

In an earlier post entitled “Teach the Process”, I made the observation that many students across all levels of education fail to gain a thorough understanding of the subject matter being taught. I named standardized, multiple-choice tests as the primary culprit. It is not that these assessments don’t have value. It is that they should just be a part of the learning tapestry, not the overarching goal. Nobody’s educational goal should be to pass a multiple choice test. The goal should be to understand the subject matter. Really, this gets back to how we learn. I found a quote by Ruth and Art Winter describing what learning is. According to the Winters, “Learning is the ability to make sense out of something you observe based on your past experience and being able to take that observation and associate it with meaning.” Not just storing away facts, but organizing and associating these facts in our minds so that we can use previous experiences to understand new ones. In our brains, we make new connections between neurons when we learn new things. The more connections you have to any given “fact”, the better the likelihood you will be able to recall it and use it for meaningful association. It is a teacher’s job to help students make these connections. We need to show how the data are related and engage the student’s interest. To achieve good results, teachers need use a variety of techniques beside the standard, and somewhat boring lecture.

Visual aids help catch student attention and can illustrate things that are awkward to describe in words. For example, try writing out the detail for connecting a standard gauge manifold. Each valve on the system needs a name, each valve on the manifold needs a name, you have to describe which way valves are being turned or positioned. It gets complicated and is very confusing to read. Now replace that with a video showing the connections. It is much easier to understand and a whole lot less confusing.

Manipulatives are items that students hold in their hands that help them learn. This is actually a term used for kindergarten classes. I have found that what works with kindergarteners also works with adults. So if you are talking about electric meters, each student should have a meter in their hand during the lecture. Then design the lesson around the fact that the students can actually handle and operate the meters during the lesson.

Analogies are great for helping students understand concepts. Dave Boyd of Appion used to compare pulling a vacuum through a 1/4” charging manifold  to the traffic jams created by merging two lanes of traffic into one. Everyone has experienced that and can relate that experience to the gas slowing down as it travels through the manifold.

Scaffolding is a way to help students reach a higher level of understanding by building information one piece at a time. It can be more successful to describe a complicated procedure in small steps. One way we do this at Athens Tech is to wire a project resembling a packaged air conditioner one circuit at a time. Students often are glassy eyed when they see the whole thing, already done. But each circuit is pretty simple. So doing one at a time gets the job done.

All of these techniques involve exploring relationships. The more ways you can describe something and how it relates to other things, the more brain connections you build. The more connections you build, the better your chance of using that information. I will be speaking at the upcoming National HVACR Education Conference by HVAC Excellence in Las Vegas on Tuesday, March 22. Come see me and we can brainstorm about more ways to make connections.

Decoding HFO Refrigerant Numbers

Undoubtedly you have seen news articles mentioning HFO refrigerants with names like 1234yf, 1234ze(Z), or 1234ze(E). Although these names look like a secret code, there is method in the madness. The good news is that technicians probably don’t need to know exactly how to read this secret code to do their job. However, telling me I don’t need to know what’s behind the curtain just encourages me to pull the curtain back. So here goes.

What is an HFO

First, you need to understand what an HFO is. An HFO is essentially an HFC with a double bond between two carbon atoms. You might remember from high school chemistry that carbon has a valence of 4. Think of the valence as the number of Velcro tabs on the atom. The carbon atoms in a normal hydrocarbon molecule are joined by single bonds, just one set of Velcro tabs joined between each carbon atom in the chain. They are called saturated because they are connected to largest number of atoms possible. Unsaturated hydrocarbon molecules, like HFOs, have a double bond between two of the carbon atoms. They use two sets of Velcro tabs between two of the carbon atoms. The double bond means there is one less atom in the molecule since two bonds are used between a pair of carbon atoms. Thus the designation as unsaturated.

Secret Code

The first four numbers of the secret refrigerant numbering code identify, in order: the number of double bonds, the number of carbon atoms, the number of hydrogen atoms, and the number of fluorine atoms in the molecule. However, there are many ways those atoms can be arranged, and different arrangements of the same components create different refrigerants with different physical properties. The last two or three letters describe how the atoms are arranged in the molecule.

First Number

The first number in the HFO numbering system describes the number of double bonds. At present, I am not aware of any HFO refrigerants that have more than one double bond. Currently all HFO refrigerants start with the number 1.  The 1 at the start of R1234ze(Z) indicates that the molecule has one double bond.  

Second Number

The second number is equal to the number of carbon atoms minus one.  The 2 in R1234ze(Z) indicates that the molecule has three carbon atoms: (#Carbons (3) – 1 = 2).

Third Number

The third number is equal to the number of hydrogen atoms plus one. The 3 in R1234ze(Z) indicates that the molecule has two hydrogen atoms (#Hydrogens (2) + 1 = 3).

Fourth Number

The fourth number is equal to the number of Fluorine atoms. The 4 in R1234ze(Z) indicates that the molecule has four Fluorine atoms.

First Lower Case Letter

HFO refrigerants are based on propylene, which has three carbon atoms. The first lower case letter identifies the atom connected to the middle carbon atom: x for chlorine, y for fluorine, and z for hydrogen. The lower case z in R1234ze(Z) indicates that the atom bonded to the middle carbon is hydrogen.

Second Lower Case Letter

The way the atoms are arranged on the ends of the molecule can vary. The second lower case letter describes the arrangement of the atoms on the end carbon containing the double bond. The letters are defined as 

a: 2 chlorine atoms

b: 1 chlorine atom and 1 fluorine atom

c: 2 fluorine atoms

d: 1 hydrogen atom and 1 chlorine atom

e: 1 hydrogen atom and 1 fluorine atom

f: 2 hydrogen atoms

The lower case e in R1234ze(Z) indicates that the end carbon with the double bond is connected to 1 hydrogen atom and 1 fluorine atom.

The Upper Case Letter in Parenthesis

In some instances, there are two ways to connect the remaining hydrogen atoms. (Z) indicates the hydrogen atoms are on the same side of the double carbon bond. Z stands for zusammen: German for together. (E) indicates the hydrogen atoms are on opposite sides of the double carbon bond. E stands for entgegen: German for opposite. The (Z) on the end of R1234ze(Z) indicates that the two hydrogen atoms are located on the same side of the carbon double bond.

Although R1234yf, R1234ze(E), and R1234ze(Z) are all built out of the exact same type and number of atoms, the difference in how the atoms are arranged makes them three different refrigerants with different physical properties.  

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