Eco-friendly air conditioners are possible — here’s how future cities can keep cool

Scientists are working on greener solutions as the global demand for cooling grows.

by Saugat Bolakhe and Knowable Magazine
Originally Published: 
Air Conditioning Unit
CSA Images/CSA Images/Getty Images

It was a monumental day for the environmental movement more than 30 years ago when all 198 countries in the world agreed on something for the first and only time ever. They signed on to the Montreal Protocol, making a pact to phase out a roster of chemicals that damage the Earth’s ozone layer. Chief among these were the chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons used by the cooling and refrigeration industry. Alternatives, such as hydrofluorocarbons (HFCs), were quickly found.

But in recent years, scientists have come to realize that the Montreal Protocol of 1987 might have traded an immediate problem for a long-term one. Though HFCs don’t cause the same damage to the ozone layer as CFCs do, the chemicals have warming potentials hundreds to thousands of times higher than that of CO2 — making their growing global use a cause for concern.

The 20th-century industrial revolution saw a major boom in the air-conditioning and refrigeration industry in Europe and North America. Now, as developing nations boost their economies, countries such as China, India, and Nigeria are seeing skyrocketing demand for these appliances.

About 3.6 billion cooling appliances — for cooling buildings and refrigerating food and other items such as medicines — are in use today, according to a 2020 report by the United Nations Environment Program; the number is expected to leap to 9.5 billion by 2050. What’s more, that figure would be a staggering 14 billion if everyone who needed cooling services could acquire them, according to one estimate.

Environmental engineer Shelie Miller


Knowable Magazine spoke with Shelie Miller, an environmental engineer at the School for Environment and Sustainability at the University of Michigan. Miller co-authored an article in the 2021 Annual Review of Environment and Resources that examined the rising global demand for cooling and refrigeration, its effects on greenhouse gas emissions, and potential solutions. This conversation has been edited for length and clarity.

This may sound like an odd topic for a lot of people. Why should we be concerned about the cooling and refrigeration industry?

When people think about environmental impacts that need to be tackled, it’s very rare that people think about cooling services. But it is an incredibly important issue that isn’t really being addressed. “Cooling service” is a very broad category that refers to temperature-controlled environments. And it intersects the building, transportation, and food sectors. It has a tremendous impact when you start looking at overall global energy use and greenhouse gas emissions.

What kind of alternative refrigerants are we talking about? Can you give me some examples?

Some of them can just be things like carbon dioxide, actually, which can be used as an alternative refrigerant by using the thermodynamic properties of gases and methods common to heat pump technologies. CO2-based cooling systems use highly compressed CO2 and then manipulate the pressure of the gas. When the gas expands due to reduced pressure, it absorbs heat. Unlike many common refrigerants that can have greenhouse gas potentials orders of magnitude greater than CO2, any CO2 that leaks from these cooling systems have minimal warming potential.

Are we planning on industrializing the process of using alternative refrigerants? Are there any processes already on the market? Or is it only in the development phase?

I think there’s definitely major interest in some of these new alternative coolants. And they can be very effective. I think there is a challenge, though, in that a lot of our installed equipment has these historic HFCs in them. And so, even if we have alternative refrigerants that go in newly installed equipment, we still have this overall stock of refrigerants in our buildings, air conditioners, and refrigerators that causes a major warming threat, particularly when the devices are at the end of their life.

Why are you so interested in the growth of this industry for developing nations? How much is the refrigeration industry expected to expand in these parts of the world?

One of the big reasons to be concerned about cooling services as an industry is the tremendous expected growth, not just in one but in two major sectors. The first is in building cooling, which includes air conditioning of spaces. The second is product refrigeration — keeping products like meat, vegetables, and vaccines cool and safe throughout their supply chains.

Both of these services are currently experiencing, or are expected to experience, rapid growth in developing countries in the coming decades. If we don’t deal with cooling services as an industry and reduce the overall environmental impacts, then we will see tremendous growth in environmental impact.

When you look at things like household air conditioning, in much of the developing world, they don’t have broad access. But we’re facing an increasingly warming climate, so the demand for cooling services, particularly in buildings, is going to be critical for health and safety.

People are getting wealthier and paying for cooling services. The most efficient kinds of air conditioning are centralized systems that will heat entire buildings and residences. Unfortunately, that is often offered at a price point that is outside of the consumer’s ability to pay and which requires massive retrofits of existing buildings. That’s why we will be seeing a lot of room air-conditioning units being installed in major cities of developing countries.

Apart from the warming impacts, are there other kinds of environmental impacts that we should be worried about?

The big ones do tend to be associated with global warming potential. But anything that requires energy has all of the impacts associated with the electricity sector. If you’re talking about electricity grids that rely largely on coal, you have a lot of localized air quality emissions; you have mining emissions associated with coal mining; and the whole slate of toxins and other air quality issues associated with the burning of coal.

How seriously do you think this problem is? To what extent do the refrigeration and air conditioning sector tend to damage the environment?

It goes back to this idea: Cooling spaces requires a tremendous amount of energy. Even very efficient air conditioners and refrigerators require a lot of energy to operate. If we don’t have a clean energy grid, there are always going to be environmental impacts associated with the expansion of cooling services.

That said, even if you had a perfectly clean electricity grid, you still have the refrigerant emissions associated with cooling. So you don’t ever erase the global warming potential, at least with our current existing stock, but you certainly can reduce it by reducing grid emissions.

What kind of interventions can we apply to this existing system?

I always think of them in two bins. One directly impacts the technology, and one indirectly impacts the technology.

For direct interventions, we can come up with alternative refrigerants to replace high global warming-potential refrigerants. We can also find ways to reduce the overall energy needs by providing cooling services. That can come in the form of making more energy-efficient equipment or changing consumer behaviors, like having a slightly warmer environment in office spaces and residential spaces.

For indirect interventions, we need to think more broadly about the built environment to reduce the need for air conditioning technology. This often takes the form of better building design and reducing urban heat island effects. It can also go with varying air conditioning and refrigeration loads according to time of day and actual need. There are a lot of ways that we can think about making air conditioning and refrigeration smarter, not just in terms of the technologies themselves but also in terms of managing energy use.

Are there systems or industries, or companies that are already using these kinds of innovative techniques? Can you give me examples?

In terms of direct interventions, there are a lot of activities that are incredibly promising. So again, we have the Kigali Amendment to the Montreal Protocol, which is trying to phase out high global warming-potential refrigerants in favor of low global warming potential refrigerants. It’s going to take a while, but we’re going to get those new refrigerants into the marketplace.

The second major thing is energy-efficient appliances. Depending on the specific country, there are manufacturing labels and certifications for room air conditioners or household refrigerators that have energy-efficiency ratings. In the US, it’s Energy Star. In Europe and Asia, they have a variety of certifications and labels to highlight to consumers that these are less energy-consuming devices.

And then the other thing is smart intervention, like using smart thermostats in homes and offices that adjust air conditioning according to the time of day and when people occupy spaces.

Do you see an emphasis from governments or any other sector on this industry? Are these issues being addressed in major climate conferences like the Conference of Parties?

Cooling services as an industry get missed quite a lot. Cooling services span across different sectors, so we have a little blind spot for it. And it often gets lost in the overall conversation. I haven’t seen much focus on this industry at such meetings.

Our group is really trying to highlight the importance of cooling services as an industry.

Hmm... I agree because I realize that when talking about global warming, impacts of transport or manufacturing factories come up pretty much all the time, but I think we find it hard to view the cooling industry as a separate entity. You’ve also mentioned that reducing food waste can reduce demand for refrigeration services. Can you briefly elaborate on that?

Often, when we try to think about reducing the environmental impacts of technology, we tend to focus on the technology itself, but that’s not always the most impactful intervention. Often, we have to step back and think through why we’re using the service in the first place. And that gets to thinking through the sectors that cooling services support.

Food, as a sector, is incredibly environmentally impactful. The cold chain — which is refrigeration throughout a food supply chain — is important in keeping food fresh and safe. But globally, we waste about 40 percent of the food that is produced. In developing countries, much of the food waste happens throughout the supply chain before it reaches the consumer, largely due to a lack of cooling services.

Whenever you reduce food waste, you save energy since there is no longer a need to cool food that will never get eaten. And so, while it’s not an intervention that a lot of people normally would think about, by reducing food waste, we reduce the need for more cooling services. And as you reduce food waste, you reduce all of the environmental impacts of agriculture as well as the services associated with the whole food supply chain.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter.

This article was originally published on

Related Tags