Posted by Charley Cormany, EFCA Executive Director
No Free Lunch: The Global Warming Potential (GWP) of Refrigerants in Heat Pumps
We have all heard about how burning fossil fuels releases CO2, which contributes to global warming by trapping heat in the atmosphere. People may not be aware that there are dozens of other greenhouse gasses (GHGs), all of which contribute to global warming. Many gasses used as refrigerants are of particular concern. This is a problem, as heat pumps, one of the most important technologies for reducing fossil fuel use, require refrigerants.
Currently, there is no single alternative to these refrigerants that doesn’t have its own problems. But if we are going to make progress on combating climate change, we need to weigh different options and realize that there is no free lunch when it comes to saving the planet.
The Global Warming Potential (GWP) of Different Greenhouse Gasses
Scientists use a metric called Global Warming Potential (GWP) to measure the heat-trapping strength of these different gasses. The GWP scale is a way to identify GHGs and how effective they are at trapping heat in the earth’s atmosphere. Because CO2 is the most common greenhouse gas, it serves as the baseline, with a GWP of 1, while other gasses are measured in comparison to it.
Methane is probably the second largest contributor to global warming. Methane is the primary component of natural gas before it is burned. Methane also leeches from landfills and is the primary emission from cattle (use your imagination – yes, you are right). According to the Environmental Protection Agency (EPA), methane has a GWP of 27 – 30. This means methane has a GWP 20-30 times that of CO2. This is why leaking natural gas infrastructure is such a concern.
Some greenhouse gases are thousands of times more impactful than CO2, though they are generally emitted in much smaller quantities. In addition, some gases have long-term impacts, persisting in the atmosphere for centuries, while others are broken down more quickly and dissipate within years or decades. All these factors are considered when assessing their climate effects.
When it Comes to Protecting the Climate, There Are No Perfect Solutions
There will always be compromises as we transition from fossil fuels and adopt a clean energy future. For example, we recently had an internal discussion regarding using spray foam to air-seal buildings. Air-sealing a building saves a ton of energy, which helps reduce greenhouse gas emissions.
The issue is that many people use spray foams [LP1] with a high GWP propellant for sealing. The energy saved by doing this likely offsets the impact of using the propellant, but there’s no question it has an impact. Is there a better way? Some folks use special tapes and caulking versus gun foam, but the downside is that the labor increases significantly, reducing the impact.
The Effort to Electrify is Counting on Heat Pumps
We have larger-scale concerns as we push toward an all-electric future. Heat pumps are all the rage these days, and we at Efficiency First support their adoption. However, the refrigerants used in heat pumps are a concern.
Heat pump appliances move energy from one place to another by using refrigerants. Refrigerators move heat from inside the box to outside, which cools down the inside of the fridge. The extra heat is discharged behind or under the refrigerator. That’s right, your fridge does not make cold air; it removes hot air with refrigerants.
An air conditioner works much like a fridge. It moves the hot air from inside your home and discharges it outside, which in turn cools down the building. Image now that you reverse the process. With a heat pump system, you can reverse the refrigerant flow to transfer the warm air outside the building and heat the interior of the building.
Heat Pumps Can be Used to Heat or Cool
We can use heat pumps to heat and cool buildings, hot water, food, or electric cars. But as cool as refrigerants are (that’s a pun), there is a dark side.
Most refrigerants used in heat pumps are extremely powerful greenhouse gases. Refrigeration systems can leak, making refrigerant leaks from heat pumps a serious concern. How powerful are these refrigerants? I have created a chart below that shows the GWP of several commonly used refrigerants. The last four, in grey, are common and have significant GWP impacts.
| Refrigerant | Common use | GWP | Notes |
| H20 – Water | Commercial Chillers | 0 | R718 |
| CO2 | Some new Heat Pumps | 1 | R744 |
| Ammonia | The original refrigerant | 0 | R717 |
| Propane | Just like your BBQ | 3 | R290 |
| R-22 (Freon) | HVAC, Phased out | 1,810 | HFC |
| R-404A | R22 replacement | 3,922 | HFC |
| R-410A | HVAC, Standard today | 2,088 | HFC |
| R-134 | Automotive, Refrigerators | 1,430 | HFC |
For a more comprehensive list, check out this chart at CARB. *HFC stands for hydrofluorocarbons, which are man-made chemical refrigerants.
Looking at the chart above, you might see that some of these refrigerants have very low GWPs and wonder why we are not using these versus HFCs. The problem is that each of these refrigerants has its own issues that limit mass adoption.
Which gets back to the point about no free lunch.
Refrigerants Can be Deadly
Willis Carrier invented modern air conditioning systems. The story goes that he was waiting for a train in the fog and made the connection that the fog made it colder. He then applied this change of state (water vapor phase changing) and used his knowledge to create the first air conditioner. The refrigerant he used was ammonia, which worked well. The only drawback is that if you breathe ammonia, it can burn your respiratory tract and lungs, which can lead to death. Ammonia has a GWP of 0, but if you happen to breathe some in, it may kill you. I think most would agree that this is not an ideal solution.
Propane and other fossil gasses like butane are making a comeback as refrigerants. They have low GWPs and can be effective refrigerants. You might have guessed their limitations. They are highly flammable. If they blow up, my guess is they might kill you, too! Even with their high flammability, these types of refrigerants are showing promise as an alternative to HFCs.
CO2 has promise, but so far, the equipment developed to use CO2 as a refrigerant is expensive, which limits its adoption. I know one brand of heat pump water heaters that relies on CO2. They use a split system, which allows the outdoor unit to be charged and sealed at the factory. The heat is moved to a storage tank by heated water. They have been in the market for several years and have proven the technology. Perhaps mass adoption will reduce the costs, as this seems to be a viable solution.
The Biggest Issue is Hydrofluorocarbons
In the 1970s and 80s, scientists realized that chlorofluorocarbons (CFCs), a class of chemicals used to make refrigerants and other products, were destroying the ozone layer. In 1987, the international community came together to ban CFCs. The industry created hydrofluorocarbons (HFCs) as an ozone-friendly replacement. However, while HFCs do not damage the ozone layer, their global warming impacts are not sustainable.
Regulations have been passed to limit refrigerants’ GWP. Some set a goal of less than 150 GWP. The air resources boards are the primary oversight entity regarding GHGs, and they constantly release new information about the progress made with low-GWP refrigerants.
The American Innovation and Manufacturing Act (AIM) has tasked the Environmental Protection Agency (EPA) with phasing down the use of HFCs. As part of this process, the EPA created a new class of refrigerants known as A2L refrigerants. A2L designation is based on a system that identifies various features or refrigerants: A = Non-toxic, 2 = Flammable, and L = Low burning velocity. Manufacturers are working feverishly to develop new refrigerants that meet A2L requirements.
To be certified as an A2L, refrigerants must meet several criteria, including having a GWP of less than 750. Starting in January 2025, the Environmental Protection Agency will require that all new equipment meet the A2L requirements, which includes a GWP of less than 750.
A2L is not a new idea. A2L refrigerants have been used in other countries for several years. Eighty percent of new vehicles sold in the US use A2L refrigerants. Other countries have figured out that HFCs are an issue and are finding solutions. Phasing out HFCs is now underway in the United States and will reshape the heating and cooling industry forever.
Science and New Technologies May be the Answer
Some other new ideas are starting to bubble up as alternatives to refrigerants. Phase-change materials (PCMs) are making significant headway and may someday replace refrigerants altogether. A phase-change material can absorb heat and change phase, perhaps from a liquid to a gel or from a gel to a solid. The energy used can be stored for some time and released later. Imagine an air-conditioner that uses a barrel full of phase-change materials, often inexpensive salt formulas, instead of an outdoor unit with compressors and refrigerants.
The principle of thermal storage is simple, and has been used for generations. Put a few barrels painted black out in the sun and then use the captured thermal energy to heat the building when the sun goes down. On a smaller scale, how about drywall that absorbs the sun’s energy during the day and radiates heat in the evening? We are just starting to see the real-world applications of phase change materials.
Our ancestors realized the value of storing thermal energy. Adobe buildings are a great example. They store the sun’s energy in their thick brick walls (3 ft thick) and release it at night. The next day, the interior stays cool throughout the day, as the thick walls limit the radiant energy from the sun outside.
PCMs might seem like science fiction, but they are real and being developed as we speak. I attended a conference presentation on using phase-change materials in large commercial heating and cooling applications. The PCMs are being used in line with refrigerants. As the hot or cold refrigerant travels through the PCMs, they absorb thermal energy. The thermal energy can be stored and utilized to make the refrigeration cycle more efficient.
The Lesser of Two Evils?
As bad as refrigerants can be you still need to ask which is worse. Carbon dioxide might have a much lower GWP than HFCs, but by burning fossil fuels, we produce a lot more of it.
It will take time to phase out fossil fuels, likely decades. In the meantime, there is a ton of effort now focused on low GWP refrigerants, and the chemists are making progress every day. I have confidence we can use science to overcome the problem of high-GWP refrigerants, way before we are done with fossil fuels. Fossil fuels will be an ongoing problem as long as we continue to rely on them.
We Can’t Look back
The naysayers often point to the problems of refrigerants as a reason not to electrify. While they have a point and the GWP of many refrigerants is a concern, I don’t think it is a strong enough argument to abandon adopting heat pumps, which are powered by electricity generated from clean renewable sources.
We are making progress on developing less impactful refrigerants, and some exciting new technologies might make them obsolete. On the other hand, I don’t think we will ever be able to provide safe fossil fuels. The time has come to embrace a clean energy future without fossil fuels, as there really is no other alternative.
