Refrigerant Leak Detection: Low-Power NDIR for R32 / R290

Why refrigerants now need leak detection

Three forces together turn leak detection from optional to mandatory. First, environment: high-GWP refrigerants (R134a GWP≈1430, R410A≈2090) are greenhouse emissions when leaked, and the Kigali Amendment to the Montreal Protocol plus the EU F-Gas Regulation (517/2014) keep lowering the usable GWP ceiling, forcing a shift to low-GWP refrigerants. Second, safety: most low-GWP replacements are flammable — R32 is A2L, R290 is A3 — and a leak in an enclosed plant room or indoors can build to a combustible concentration. Third, efficiency: leaks cut cooling capacity, overload the compressor and raise energy use; early detection prevents silent equipment degradation.

Refrigerant flammability classes: A1 / A2L / A3

ASHRAE 34 / ISO 817 class refrigerants on two axes: toxicity and flammability. On the flammability axis, A1 is non-flammable (R134a, R410A), A2 is flammable and A3 is highly flammable (R290 propane, R600a isobutane); A2L, added after 2010, is the 'lower flammability' tier — low burning velocity (≤10 cm/s) and higher ignition energy — represented by R32 and R454B. Rule of thumb: the larger the number after A, the more flammable; the L means a low-burning-velocity buffer tier.

• R32 has an LEL around 14.4% vol and a low burn velocity, safer than R290, making it the most likely R410A replacement for residential/commercial AC — but as an A2L it is still mandated to have leak detection by standards such as UL 60335-2-40 (2022 edition).
• R290 is simply propane: A3, LEL about 2.1% vol, heavier than air (MW 44), so it pools low in plant rooms — detectors must sit low. Mostly used in fridges, small commercial refrigeration and heat pumps.

Why low-power NDIR leads leak detection

Refrigerant leak detection faces picky applications: split-AC indoor units want battery or very-low-power nodes running long-term; plant rooms need 24/7 continuous monitoring; automotive AC is tighter, with heavy vibration and wide temperature/humidity swings. What they share is a demand for low power, good selectivity for the refrigerant, resistance to temperature/humidity interference, and long maintenance-free life.

NDIR (Non-Dispersive Infrared) uses a dual-wavelength optical path to measure the refrigerant's absorption at its specific infrared band — sensitive to the refrigerant, selective against background gases, and with no chemical reaction involved, it cannot be poisoned, barely drifts and is essentially calibration-free. By contrast, semiconductor (MOS) sensors suffer temperature/humidity and cross-gas interference, have short lives and need frequent calibration; catalytic beads respond weakly to refrigerants and most refrigerants do not support combustion-based measurement. Low-power NDIR is therefore the mainstream for split-AC wireless nodes and plant-room online monitoring.

Standards and thresholds: how far detection must go

ASHRAE 15 (Safety Standard for Refrigeration Systems) requires machinery-room refrigerant detectors that interlock mechanical ventilation and alarms at trigger concentrations; detectors go low in the room (most refrigerants are heavier than air — R32, R290, R134a), with buoyant refrigerants placed by actual density. UL 60335-2-40 (2022 edition) tightens safety for household/similar AC with A2L refrigerants, mandating leak detection and ventilation/shutdown interlock for indoor units in certain occupancy scenarios. The IEC 60335 series is the base product-safety standard.

On the regulatory side, the EU F-Gas Regulation (517/2014) cuts the available volume of high-GWP refrigerants through annual quotas, indirectly pushing OEMs to R32/R290 and amplifying leak-detection demand; fluorinated-gas leaks also trigger leak-rate reporting and recovery obligations. China's ozone-depleting-substance regulations and HFC controls are tightening in parallel. For export equipment, design detection and interlock logic to the strictest target-market tier.

• Threshold logic: a low alarm acts before the 'reachable concentration limit' (e.g. ASHRAE 15 machinery-room limit) to start ventilation; a high alarm near the dangerous concentration triggers evacuation or shutdown. Don't wait until it is flammable.
• Interlock matters more than a single point alarm: the value of leak detection is the 'sense – vent/shut down – alert' loop. Whether fixed or portable, confirm the output reaches the PLC/BMS (4–20 mA / Modbus / UART).

Deployment and selection notes

Placement: most refrigerants are heavier than air (R32 MW 52, R290 MW 44, R134a MW 102), so a leak pools low in the plant room or equipment base — mount detectors 0.3–0.6 m above the floor or at the equipment-base return/collection zone; only raise them if the refrigerant is confirmed lighter than air. Split-AC indoor units can be covered near the return-air inlet, which sees the most likely leak path.

Range and power: leak-detection range is usually tiered to the refrigerant's LEL or machinery-room limit (e.g. 0–XX% LFL or 0–XXXX ppm); for wireless/battery nodes confirm average current and power, favouring low-power NDIR (mA-level, mW-level) to extend battery life and cut maintenance. The Xingpu XPSN40A series is split by refrigerant, φ20×16.6 mm, ≤10 g, 5-year designed life — for portables, wireless nodes and plant-room monitoring.

Frequently asked questions