Modern HVAC Systems' Reliance on Refrigerant
In 2020, nearly 90% of homes used air conditioning systems in the United States. Heating, ventilation and air conditioning (HVAC) systems are used by both homeowners and businesses alike, with their usage only expected to rise as climate change increases global temperatures. Refrigerant, a chemical compound that is capable of transitioning from liquid to gas and back again, has been an important part of indoor cooling systems since modern AC systems were invented in 1902. Its ability to cool as it vaporizes and heat up as it condenses facilitates heating and cooling. As part of both air conditioner and heat pump systems, refrigerant either helps transfer heat and humidity out of one’s home for conditioning or draws heat from outdoor air and brings it inside for heating.
Refrigeration technology has historically relied upon gases like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) to promote cooling in appliances, due to their effectiveness at transferring heat within a refrigeration system. While effective, these gases are hazardous for the environment. HFCs have a global warming potential (GWP) that can be hundreds to thousands of times greater than that of carbon dioxide. Gaseous CFCs have a high ozone depletion potential (ODP), meaning there is less protection from the sun’s rays and greater exposure to UVB radiation, negatively impacting human and ecological health. Instead of relying upon harmful CFCs and HFCs in refrigeration technology, UC Berkeley researchers are on the cusp of developing a new alternative known as “ionocaloric” refrigeration, which utilizes salt water to provide cooling.
How does Ionocaloric Cooling work?
Created in 1987, the Montreal Protocol regulates the production and consumption of nearly 100 human made chemicals classified as ozone depleting substances (ODS). The Montreal Protocol mandated the eventual phase-out of CFCs and HCFCs, instead turning to HFCs as a replacement. Although HFCs do not deplete ozone, they were later found to have a significant GWP, prompting a recent amendment to reduce HFC usage by 80% in the next thirty years. As HFCs are phased out, ionocaloric cooling has been proposed as an alternative for refrigerant.
Ionocaloric cooling relies on the principle that liquids release energy, or heat, when solidified, and solids absorb energy when liquified. In an ionocaloric refrigerant system, a mixture of a liquid and salt is frozen and melted. When a current is added, ions flow and change the material from solid to liquid, which allows them to absorb heat from their surroundings. Similarly, when ions are removed, the material crystallizes into a solid, releasing heat. The mixture is easier to manage as it is never in a gas state and is unable to enter the atmosphere. Additionally, certain solvents like ethylene carbonate, which have been used to test the technology, can be carbon-negative due to their ability to be produced from CO2 supplied by carbon capture. This means that ionocaloric cooling can prevent current emissions with high GWP and ODP, while also removing emitted gases from the atmosphere.
Promise of Ionocaloric Cooling
Ionocaloric cooling has the potential to modify current HVAC systems, which rely upon high GWP gases that act as refrigerants. By using solid and liquid components as opposed to HFCs to function, ionocaloric refrigeration prohibits these harmful gases from ever entering the atmosphere. In addition to its cooling purposes, this technology can also be used for heating. Ionocaloric technology has the potential to compete with or even exceed the efficiency of gaseous refrigerant. Currently, ionocaloric cooling technology is still being developed. If proven successful, this innovative technology could transform the current landscape of HVAC systems.
Hurdles to Overcome
As of now, ionocaloric cooling is not fully developed. Although the material cost for the salt water is cheap, it is unclear the cost of every component needed on a larger scale. The research currently being conducted for ionocaloric cooling experimentation is heavily subsidized. As it is still under R&D, this technology’s viability on a larger-market scale will be continually determined. To facilitate a transition away from gas refrigerants, ionocaloric cooling will likely need government incentives, such as consumer rebates, to make the technology competitive with conventional units.
Dr. Lilley’s Insights into Ionocaloric Cooling
In addition to being environmentally harmful, gas refrigerants have proven to be costly and difficult to dispose of. Dr. Lilley believes that ionocaloric cooling can thus be an advantageous solution in a variety of ways. The end of life management (or disposal) of output components from ionocaloric cooling will be much easier as it relies upon liquid inputs. Additionally, Lilley notes that there is no way to completely seal refrigerants from the atmosphere, so a liquid refrigerant eliminates that problem altogether. As the technology becomes more advanced, Dr. Lilley believes that initial cost concerns will fade with state subsidies and market adoption.
About our guest
Dr. Drew Lilley is the CEO and co-founder of Caliion Technologies. He holds a PhD from UC Berkeley in Mechanical Engineering, where his research is focused on alternatives to current refrigerants. His main research focus is on the R&D process of solid-to-liquid ionocaloric cooling.
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Further Reading
For a transcript, please visit https://climatebreak.org/out-with-classic-refrigerants-and-in-with-ionocaloric-refrigeration-with-dr-drew-lilley/.
