Refrigerants: What Are They?
May 15, 2023

Refrigerants: What Are They?

At Recoolit, our mission is to reduce climate impact by collecting and destroying waste refrigerants. This mission is often unclear to people who aren't familiar with the refrigeration industry. We often hear questions like, "What are refrigerants?" or "Why are refrigerants a problem?" We've skipped over such questions on our explainer page because they're quite technical, and we don't want to overwhelm our customers.

This post is for those special nerdy few who want to know all the gory details!

Heat pumps: how do they work?

Refrigerators and air conditioners are both “heat pumps” -- a kind of device that moves heat from one location to another. Because of conservation of energy, the only way to cool down your apartment, or the inside of your fridge, is to move that heat somewhere else. Heat pumps do this by using refrigerants - a substance that is pumped through a closed loop, alternating between gas and liquid.

(Usually the term “heat pump” means specifically a device that can operate either as an AC or a heater. They work on the same principles, and they’re also a super important climate solution. Read more about them here. We'll call these "two-way" heat pumps to avoid confusion.)

First, refrigerant in liquid form is pumped through a special device called an “expansion valve”. This causes the liquid to evaporate into a gas, which also cools it down. Next, it’s pumped into a “heat exchanger”, where the cold gas pulls heat out of its surroundings. The gas heats up, while the air around the heat exchanger cools down. In an AC or fridge, or a two-way heat pump on "cooling" mode, the heat exchanger is located in the place you want to make colder: the refrigerator, freezer, or too-warm room or building.

The vapor compression cycle. (Diagram by Daniel Overbey.)

Next, the cold low-pressure gas is pumped into a compressor, which increases the pressure and temperature of the refrigerant. The hot gas is pumped through a condenser, which is another type of heat exchanger, where the gas cools down and gives off heat into the surrounding air. In an AC or fridge, this heat exchanger is on the outside of the system, which is why your fridge pumps out hot air. In a two-way heat pump on "warming" mode, this heat exchanger is located inside a building or room, and this warming is the desired effect. Finally, fluid is then pumped back to the expansion valve, and the cycle begins again.

Mechanically, all heat pumps rely on just these few components – a compressor, an expansion valve, heat exchangers – plus the refrigerant that cycles between them as a liquid and gas. Physically, this process relies on just a few basic principles of nature -- the ideal gas law, plus the laws of thermodynamics.

What are refrigerants?

Refrigerants are the fluid used inside heat pumps to move heat from one place to another. There are many considerations when picking a substance to use as a refrigerant. For instance, a common early refrigerant was ammonia (R-717).  (Refrigerants have chemical names, but they also have industry-standard names starting with “R-”. These names are assigned in a systematic way based on the chemical structure of the molecule.) Ammonia boils at a low temperature, which makes it easy to turn into a gas. It does not freeze until a very low temperature, so there's no risk of it freezing inside the heat pump during the expansion phase. And it has a fairly high specific heat, which means that it can absorb and release a lot of heat.

Typical (but not recommended!) refrigerant storage in Indonesia.

Unfortunately, ammonia is highly toxic and corrosive. Other early refrigerants, such as sulfur dioxide (R-764) and methyl chloride (R-40), were also toxic. To avoid the safety issues associated with early refrigerants, scientists began experimenting with other substances. In 1928, Thomas Midgley, Jr. invented the first chlorofluorocarbon (CFC) refrigerant, which was marketed by DuPont as Freon-12 (R-12). R-12 was cheap to produce, non-toxic, non-flammable, non-corrosive, and it had a low boiling point and a high specific heat. These properties led to R-12 becoming the most popular refrigerant in the world, with production peaking at over 1 billion tons per year in the 1980s.

The Montreal Protocol

When searching for safer replacements to early refrigerants, scientists looked for substances which were highly stable, since stable substances pose less of a health risk to humans. This made R-12 an attractive choice, since it was highly stable and non-toxic. However, this stability also proved to be a problem. In the 1970s, scientists studying the ultimate fate of CFCs like R-12 discovered that these gases could make their way up to the stratosphere. There, they could be broken down by ultraviolet radiation, releasing chlorine atoms (the first C in CFC and HCFC). The chlorine would then react with, and destroy, atmospheric ozone, in a chain reaction.

Launch of NASA's Aura satellite, which provided direct evidence of the healing ozone layer.

In response to these findings, in 1987 the international community adopted the Montreal Protocol on Substances that Deplete the Ozone Layer. The agreement was initially signed by 46 countries, and has since been ratified by 198 parties, including all member states of the United Nations. It sets out a schedule for the phase-out of the production and consumption of ozone-depleting substances (ODSs), including CFCs like R-12 and HCFCs like R-22.

The phase-out schedule differed for different substances and in different places. For instance, R-12 was phased out in developed countries in 1996, and in developing countries in 2010. Meanwhile, R-22, an HCFC common in home and commercial heat pumps, was phased out in developed countries in 2010, but it continues to be in-use in developing countries until 2030.

GWP and the Kigali Amendment

If you recall, one of the properties of a good refrigerant is its ability to absorb and release heat. Refrigerants continue to play this role even after they've been released into the atmosphere. In particular, they absorb and release heat in the form of infrared radiation, which is the same type of radiation that is absorbed and released by greenhouse gases like carbon dioxide and methane.

The heat-trapping ability of a greenhouse gas is measured by its global warming potential (GWP). The standard basis of comparison is the most common greenhouse gas, carbon dioxide (CO2), which has a GWP of 1. The GWP of Freon, or R-12, is 10,900. This means that, released into the atmosphere, R-12 traps 10,900 times as much heat as an equivalent mass of CO2, calculated over a 100-year time period.

CFCs and HCFCs phased out under the Montreal Protocol were often replaced by hydrofluorocarbons (HFCs), which have many of the desirable properties of a refrigerant, but without the ozone-destroying chlorine. For example, an HFC called R-134a is a common replacement for R-12 in automotive air conditioners. However, R-134a has a GWP of 1,430: much less than R-12, but still substantially heat-trapping.

When the Montreal protocol was adopted in 1987, the focus was on the ozone-depleting properties of CFCs and HCFCs. However, as the world began to phase-out these substances, it became clear that their global warming potential was also a problem. In response, in 2016 the international community adopted the Kigali Amendment to the Montreal Protocol. The Kigali Amendment is meant to prevent additional global warming from refrigeration by also phasing-out the production and consumption of HFCs. The amendment has, so far, been ratified by 148 parties

Like the Montreal Protocol, the Kigali Amendment sets out a schedule for the phase-out of HFCs, but this schedule differs from place to place. In the developed world, the phase-out began in 2019, and is scheduled to complete by 2036. In the developing world, however, the phase-out is not scheduled to end until 2045, with some countries receiving additional extensions to 2047 or later.

The world has a lot of air conditioning.

How Recoolit Fits In

Refrigerant pollution is a major global problem, and the world is working hard to solve it. However, as you can see, even the phase-out of ozone-depleting substances like R-22 will not be complete until 2030. With high-GWP HFCs like R-134a, the process has barely begun, and will last for decades. What do we do in the meantime?

This is where Recoolit comes in. While the world works to phase out harmful refrigerants, we can work to reduce the amount of refrigerant pollution that is released into the atmosphere.

Some of this release is accidental or the result of equipment malfunction. However, a significant portion of refrigerant pollution is the result of intentional venting. This is because, without Recoolit, technicians simply have no other way to dispose of refrigerant properly. Even well-intentioned technicians, who are concerned about pollution and environmental impacts, have no other choice when a system must be depressurized for maintenance or repair. We've seen technicians vent refrigerant through a hose inserted into a bucket of water, in the (mistaken) belief that this will somehow "scrub" the refrigerant.

Additionally, the process of recovering refrigerant is time-consuming and expensive. The international protocols do not provide any funding for the transition to cleaner refrigerants, or to mitigate the damage from refrigerant pollution. We sell carbon credits and use the proceeds to help technicians keep refrigerant out of the atmosphere. This is where you come in.

Now that you know about the problem, you can help us solve it. Fund our work by buying our carbon credits. Tell your friends and colleagues about the problem, and about our solution.

(post by Igor Serebryany)