Durable electrochemical cells for detecting ammonia (NH3)

Ammonia (NH3) is in wide use as primary refrigerant for large and very large compression cooling systems. Ammonia has the lowest indirect greenhouse effect index, because the energy required for a given cooling effect is the lowest among all low-GWP refrigerants. Ammonia however is toxic and with OEL concentration levels as low as 50 ppm, potential leakage of ammonia can be dangerous. Ammonia can be detected using NDIR gas sensor technology, but it is difficult with NH3 NDIR gas sensors to become a stable zero, which in effect compromises the signal-to-noise ratio. For the detection of NH3, Pewatron recommends the use of electrochemical cells.

As opposed to CO2, the physical and chemical properties of ammonia make the positioning of the sensors in relation to the cooling system difficult. In short, ammonia gas (due to the molecular weight) tend to diffuse upwards, but because of the high solubility of ammonia in water (humidity), a so-called ammonia fog (ammonia leak dissolved in humid air) can diffuse downwards.

Ammonia, even in small concentrations, has a very distinct and unpleasant smell. The smelling of ammonia is sometimes used to detect leaks, but this is in no way a recommended method of detection. Pewatron has a range of ammonia products in the program – from ammonia electrochemical gas sensors (photo) to ammonia transmitters with a standardized output signal. Pewatron offers also gas sensing systems for process control with ammonia detectors integrated into a flow path system together and with optional sensors. The picture below shows an example, where an ammonia transmitter is integrated into a flow box together with oxygen and carbon dioxide sensors. The ammonia is there to detect ammonia leaks from the cooling system and the two other sensors are there to control a fruit storage process.