Despite how helpful air conditioners and refrigerators are, the chemicals they consume as refrigerants tend to leak into the environment and play a significant role in climate change. Thankfully, Harvard engineers have figured out how to stay cool without contributing to global warming. Recently, the team presented a new cooling device prototype that uses a solid-state material as a functional refrigerant.
How Refrigerants Work
A material’s cycles of phase transitions provide the cooling power for appliances like refrigerators and air conditioners. Refrigerant chemicals, often hydrofluorocarbons (HFCs), will absorb heat from their surroundings in their gaseous state, cooling an open space or inside a fridge or freezer. The stored heat is released as this gas passes through a compressor, which turns it back into a liquid. Once the pressure is released, the liquid can re-expand into gas to restart the heat cycle. The process is called the “barocaloric effect.”
It’s an efficient procedure that has served us well for years, but these HFCs can seep out of the equipment during use if it’s broken or when being transported or disposed of. When HFCs leak into the environment, they contribute to 1 percent of total global greenhouse gas emissions.
Finding solutions to minimize these emissions is a crucial part of environmental action programs. Once HFCs are in the atmosphere, they are thousands of times more potent than CO2 as a driver of climate change.
Solid-State Refrigerants
The issue could be resolved using solid refrigerants that can undergo the barocaloric effect. The latest study has discovered a promising substance from a group of minerals known as metal-halide perovskites, which are already thriving as a new generation of solar cell materials. In this case, the barocaloric material could be used to cool, similar to traditional gas-liquid cooling systems, except that it stays solid throughout both stages.
Their atomic structure is the key to these efficient barocaloric solids. They usually consist of long, flexible chains of disorganized molecules, but under pressure, they straighten into a more ordered form, which releases heat. They can absorb heat from their environment once more if the pressure is released. Although both phases are solid, the transition is compared by the team to wax that has partially melted.
The team used a prototype device to demonstrate the proof of concept. The solid refrigerant and an inert liquid, such as water or oil, were packed into a metal tube. A hydraulic piston puts the fluid under pressure, transferring that pressure to the refrigerant. The liquid also aids in removing heat from the system.
Why We Need New Cooling Technology
Speaking of current air conditioning units, Adam Slavney, Ph.D., who is presenting this work, said: “Just installing an air conditioner or throwing one away is a huge driver of global warming.”
Fewer than one out of every three households worldwide have an air conditioning unit, yet the technology accounts for approximately 11% of global greenhouse gas emissions.
By 2050, the number of people using air conditioning is expected to increase fourfold to 4.5 billion.
The Future of Cooling
Researchers believe solid-state refrigerant technology may be an ideal solution to replace current air conditioning systems and other existing cooling technologies.
The team claims there are still a few issues to work out, but the technology shows potential. One problem is that, while the pressures required can be achieved using hydraulics, they are a bit too high for consumer electronics — roughly 2,900 psi, as opposed to the 150 psi that a typical air conditioner can withstand. In addition, different kinds of materials might conduct heat more effectively.
This novel class of solid materials can potentially contribute to developing environmentally friendly cooling equipment.
On that note, some companies have developed eco-friendly fridges by making them solar-powered or modifying them to assist the user in reducing food waste.
The research was presented at the American Chemical Society’s autumn meeting. Watch the team’s presentation in the video below.
