How does a refrigerator work? Anyone who is interested or interested in how air conditioning works in the home must have heard of “vapor compression” systems.
Our existing devices produce cold by circulating liquid in pipes. When the liquid turns into a gas in the “evaporator”, it absorbs the heat present in the air – this allows it to cool. The gas must then be condensed (or compressed) to return it to a liquid state so the process can begin again. This step, in turn, produces heat – which is released behind the refrigerator or outside the home in the case of an air conditioner.
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Refrigerators and air conditioners heat the atmosphere three times!
This process of vapor compression not only contributes directly to global warming by emitting heat—especially through the mass air conditioning of buildings in large cities during a heat wave—it also participates in two indirect ways.
On the one hand, after the device is disposed of in a landfill and destroyed, the gases it contains – mainly hydrofluorocarbons (HFCs), substitutes for the more harmful traditional chlorofluorocarbons (CFCs) – are released into the atmosphere and intensify the greenhouse effect. It is several thousand times more powerful than carbon dioxide (CO2).
On the other hand, this classic process requires a lot of energy: more than half of the energy consumed in homes is for cooling or heating. However, electricity generation from grid-supplying sources (fossil fuels, etc.) against renewable and nuclear), global warming.
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A solid-liquid shift, not a liquid-gas?
But how can we cool our home or food without going through this process that is harmful to our planet? Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab, California) have developed a new method called “ionocaloric cooling”, which they present in an article published in the journal. Science (12/2022).
The principle, they explain in a press release, is the same as when you sprinkle salt on roads to prevent water from freezing. Therefore, it is always a matter of playing with the transition between the two states of matter, but this time not liquid and gaseous, but alternating liquid and solid states – thus preventing harmful gases ending up in the atmosphere.
Melting of the material absorbs heat from the environment, and solidification releases it. This “ionocaloric cycle” is based on the flow of ions – electrically charged atoms or molecules – from the salt. When an electric current is applied to it, ions enter and turn the solid material into a liquid, while also absorbing heat from the air. When the process is reversed and the ions are released, the material crystallizes and releases heat.
In their experiments, the scientists used a salt consisting of iodine and sodium, as well as ethylene carbonate – a very common solvent, especially in lithium batteries. With such a device, they achieved a temperature change of 25°C using less than a volt of current.
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“The field of refrigerants is an unsolved problem: no one (so far) has been able to develop an alternative solution that cools things, works efficiently, is safe and doesn’t harm the environment.“, Berkeley Lab research assistant and first author of the study, Drew Lilley, is quoted in the press release.We believe that the ionocaloric cycle has the potential to achieve all of these goals if properly implemented..”
Ionocaloric cooling has the advantage of switching from a solid state to a liquid state, while other similar methods are currently under development – particularly using magnetic or electric fields, pressure or traction forces. A situation where the material can circulate in the system under the influence of the pump, emphasize the authors.
Otherwise,”the use of a material such as ethylene carbonate can achieve carbon neutrality, since it is produced on the basis of carbon dioxide. This may represent a way to use CO2 carbon sequestration (in the air)”, the researcher believes.
The stakes of this research are high: The Kigali agreement, adopted in October 2022 by 145 parties, including the United States, commits signatories to reducing the production and consumption of hydrofluorocarbons by at least 80% over the next 25 years. But in order to achieve this goal, the team will need to continue working to expand their technique by increasing the range of temperature changes the system can tolerate.
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Meanwhile, everyone can act on their own scale by preferring the alternatives already available; such as natural air conditioning to cool an unconditioned room or a pantry to keep perishable foods cool. And by getting your appliances repaired – the government’s repair bonus also applies to fridges – and buying appliances that use less energy.
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