Episode Details

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 un