Sustainable cooling without halocarbons, or how to help billions of people adapt to the coming heat

The COP28 presidency put the spotlight on sustainable cooling as a crucial issue. According to the United Nations Environment Programme (UNEP), a sustainable approach to cooling is critically important to addressing climate change, both for greenhouse gas reduction and climate adaptation.

Global warming and extreme temperatures will increase the need for cooling. UNEP estimates that meeting future cooling needs can be done sustainably: reducing greenhouse gas emissions in 2050 by at least 60 percent, taking pressure off energy grids, helping over one billion people adapt to climate change, and creating electricity savings for end users of $1 trillion in 2050.

In particular, these are the key COP28 recommendations on sustainable cooling:

• Develop systems with natural refrigerants that are competitive in efficiency and cost compared to halocarbon-based systems.
• Support restrictions on the use of halocarbon-based fluids with global warming potential over 150 and bans on fluids falling under the perfluoroalkyl and polyfluoroalkyl substances (PFAS) definition.
• Support the development of standards allowing higher taxes on systems using halocarbons.
• Place emphasis on the search for solutions for heat pumps and cooling systems with natural fluids that can replace the use of fossil fuels for residential heating.
• Prioritize the development of high temperature heat pumps using natural fluids to contribute to the decarbonization of industrial needs.

The ozone layer and climate change

Chlorofluorocarbons (CFCs) were used in products like aerosol sprays, refrigerators, and air conditioners until the Montreal Protocol, which entered into force in January 1989, banned their use due to their ozone depleting properties.

CFCs were replaced by other halocarbon-based fluids, the hydrofluorocarbons (HFCs), which, while not ozone depleting, are potent greenhouse gases. We solved one problem but created a new one.

The Kigali Amendment to the Montreal Protocol, in force since January 2019, aims to gradually reduce HFCs consumption. Transitioning to ozone and climate friendly alternatives can help avoid more than a half degree Celsius temperature increase by the end of the century.

However, some proposed low global warming halocarbon alternatives to HFCs, falling under PFAS definition, can accumulate in nature, posing potential health risks.

Moreover, cooling is energy intensive, and sustainability is affected by the energy source. Using renewable energy for cooling is environmentally friendly, but in areas reliant on fossil fuels for power generation, electric cooling can lead to significant indirect emissions. Therefore, it is critical for all systems to maximize energy efficiency.

The new natural fluids

There is already extensive research on sustainable cooling focusing on fluids naturally occurring in the biosphere. For example, refrigerants like carbon dioxide (CO2), ammonia (NH3), hydrocarbons (HCs), and water (H2O).

Using these fluids provides a long term, climate secure solution. Many countries, especially low income ones, can directly transition from HFCs to sustainable alternatives without having to turn to substances that could be phased out soon.

In addition to replacing potent greenhouse gases, CO2 as a coolant can also contribute to energy savings. For supermarkets, integrating cooling, freezing, heating, and air conditioning needs into the same CO2-based system has demonstrated around a 35 percent reduction in power consumption. It is estimated that over 35,000 such systems have been installed globally, mainly in Europe. In Northern Europe, most supermarkets have started using CO2 as a coolant.

Systems using other natural fluids, such as ammonia, hydrocarbons or water, have proven to be highly energy efficient, although challenges for NH3 and HCs include the toxicity and flammability of these fluids. Proper use and adaptation of standards for safe operation and installation will be crucial.