PNNL

Refrigerant leaks in heating, ventilating, air-conditioning, and refrigeration (HVAC&R) systems can potentially lead to a range of problems for consumers, including increased fire risk and exposure to toxic gases. 

To help address these risks, researchers at the Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a new, sensitive leak sensor for HVAC&R systems. The work is also guided by an external technical advisory committee that includes industry partners, convened to identify barriers in using next-generation HVAC refrigerants. 

The new sensor uses low‑cost components and showed fast, selective detection in laboratory tests. Initial tests with difluoromethane (also known as R32), an increasingly popular refrigerant gas, showed positive leak-detection results. The sensor worked even in relatively high humidity conditions, which pose a challenge for many sensor technologies.  

“Refrigerant leaks typically result from bad refrigerant piping installation practices or from aging or defective heating and cooling system components,” said Daniel Deng, PNNL laboratory fellow and principal investigator for the development. “Today’s existing detection tools may meet basic needs, but new sensors that are fast, selective, and cost-effective are needed to mitigate flammability risks associated with next-generation refrigerants.” 

Refrigerants are fluids used in appliances and systems used to cool or heat spaces, like refrigerators and air conditioners. They play a crucial role in absorbing and transferring heat, thanks to their unique physical properties. Refrigerants are designed to boil—or turn from liquid to a gas—at very low temperatures, allowing them to efficiently absorb heat from their surroundings during the boiling process. For instance, water boils at 212°F (100°C), whereas R32 boils at −61°F (−51.7°C). This low boiling point makes refrigerants well suited for pulling heat out of spaces, like the inside of a home, and releasing it elsewhere, such as outside. 

Recently, HVAC manufacturers have been transitioning to a new generation of refrigerants, such as R32, that can operate in a wider range of temperatures and transport heat more efficiently. However, these newer refrigerants are also mildly flammable, which poses new safety concerns, Deng said.  

So Deng and his colleagues set out to develop a new sensor that can more quickly and accurately detect refrigerant leaks. 

A highly sensitive sensor 

The PNNL team started with a commonly used sensor called a quartz crystal microbalance (QCM) sensor that can detect tiny changes in mass. QCM sensors are used in a wide range of fields, such as food science and drug development, because of their ability to measure interactions between molecules and various surfaces. The team paired the QCM sensor with a metal-organic framework (MOF), a sponge-like material with micropores that can trap gas in very small quantities. By combining the two, the team created a sensor that rapidly triggers an alert when it detects an extremely small amount of gas, like a refrigerant. 

In initial lab testing, the team coated the QCM sensor with a thin layer of a laboratory-synthesized MOF. As R32 gas was released, the MOF adsorbed the refrigerant’s molecules, increasing the sensor’s weight—which signaled detection of R32. The detection process occurred over a period of seven seconds, which meets established standards, Deng said. The researchers also noted that their MOF worked even in humid conditions, which can be challenging for other types of sensors.  

After the initial testing, the team built a prototype sensor, which delivered reliable and fast measurements of R32 in the lab, Deng said.  

The team has filed for a patent for the new sensor and will soon be looking for industry partners to continue to develop the technology. Looking ahead, the researchers will also build similar sensors for other kinds of refrigerants. They’ve already developed a prototype sensor for detecting propane and are working on optimizing the technology. 

“Putting aside the comfort impacts, a refrigerant leak in heating and cooling systems can reduce efficiency, increase energy bills, and eventually lead to system failure and costly repairs, not to mention create safety concerns,” said Christian Valoria, the project manager at PNNL who oversees this project funded by the Building Technologies Office under the Department of Energy. “There’s a growing need for more sensitive and low-cost sensors that detect refrigerant gas leaks faster and reduce economic and safety impacts on American homeowners and businesses.” 

In addition to Deng and Valoria, the team includes Habilou Ouro-Koura, Wenwen Ye, Jian Liu, Jun Lu, Abhishek Kumar, and Huidong Li.