Advancing A3 refrigerant leak detection: Sensor technologies, challenges, and research outlook

Refrigerant leakage poses significant safety and environmental challenges in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems, particularly with the increasing use of highly flammable hydrocarbon (A3) refrigerants such as propane (R-290), ethane (R-170), butane (R-600), and isobutane (R-600a). Existing sensor technologies developed for traditional halogenated refrigerants are often unsuitable for accurately detecting low concentrations of hydrocarbons due to differences in chemical properties and flammability risks. This paper presents a comprehensive review of gas-sensing technologies applicable to A3 refrigerants, emphasizing both established and emerging technologies that could be adapted from other industries for use in HVAC&R applications. The sensor categories evaluated include metal–oxide semiconductor (MOS), catalytic, optical (photoacoustic spectroscopy—PAS, quartz-enhanced PAS, non-dispersive infrared—NDIR, fiber optic), acoustic (surface acoustic wave—SAW, quartz crystal microbalance—QCM), electrochemical, capacitive, and emerging nanomaterial-based sensors (C2N, sulfur-doped silicon carbide nanotube, surface plasmon resonance). Each technology was assessed based on critical parameters such as sensitivity, selectivity, response time, power consumption, and practicality for integration into HVAC&R systems. Although MOS, PAS/quartz-enhanced photoacoustic spectroscopy, and NDIR sensors demonstrate potential, limitations related to elevated operating temperatures, vibration sensitivity, and cross-selectivity remain significant concerns. Emerging technologies, including SAW, QCM, and novel nanostructured materials, exhibit promising performance characteristics such as room temperature operation, rapid response, high sensitivity, and compact size; however, they require further development and validation for reliability, long-term stability, and commercialization. This paper also identifies key gaps, challenges, and research opportunities, emphasizing the importance of developing robust calibration protocols and clearly defining operational conditions within HVAC&R systems to optimize sensor selection, safety, and system efficiency.