REFRIGERANTS


Finding ammonia


Tom Burniston of Samon discusses how to apply NH3


It typically takes a long time for leaked gas to evenly disperse into the


environment, so clouds of leaked gas can be moved by ventilation. Placing


refrigerant gas detectors in this air fl ow is good practice for eff ective detection.


A NH3 mmonia (NH3 refrigerant leak detection. ) is commonly used in larger, industrial


refrigeration applications, and often when very low temperatures need to be achieved. However, it is


corrosive to the skin, eyes, and lungs and at high levels can be explosive. Standards and regulations vary by country, but typical levels


are as below. concentration in air 25ppm 35-50ppm 70-300ppm 300ppm 5,000ppm 15-28% Eff ects


Long term exposure limit - 8 hours TWA


Short-term exposure limit – 15 minutes, some physical discomfort


Severe irritation of nose, throat, and airways, risk of fl uid accumulation in the lungs


IDLH limit (Immediate Danger to Life & Health)


Rapid respiratory arrest Flammable, explosive Any leakage of ammonia is generally used to trigger an


emergency alarm due to its acute toxicity. Although humans can detect ammonia by smell, typically in ranges from 5ppm – 50ppm, this is not a reliable method because repeated exposure can reduce sensitivity. The use of electronic gas detectors is therefore both recommended and mandated in most applications.


How to apply NH3 NH3


detection? is lighter than air, meaning it will rise to the highest point


in the room in which it leaks. Gas detectors should be installed at a high level, circa 20cm below the ceiling. Consideration should be given to the accessibility of the installation for service and maintenance. Common practice is to install refrigerant leak detectors


above the likely source of a leak, for example valves, fl anges, joints, and pressure reducers. Detectors can also be installed above areas with a high concentration of refrigerant, such as


26 August 2024 • www.acr-news.com


compressors, storage tanks/cylinders, pipes, and conduits. Consideration should be given to air fl ow and ventilation, both natural and mechanical. It typically takes a long time for leaked gas to evenly disperse into the environment, so clouds of leaked gas can be moved by ventilation. Placing refrigerant gas detectors in this air fl ow is good practice for eff ective detection. There is no general rule or standard for establishing the


appropriate number of sensors and their location for each application. Therefore, the guidance given is intended as support for installers, and not as rules in their own right. All local, state, and national regulations should be adhered to.


is typically detected using electrochemical sensors. This technology has a number of benefi ts in refrigeration applications. These include high selectivity, minimal cross- interference, and high stability. The sensors are also highly accurate and can be ranged for the required target measurement concentration. Electrochemical sensors have a limited life span, typically


NH3 NH3


requiring replacement every 2 years. There are, however, some refrigerant gas detectors now on the market with fi eld proven NH3


sensors with a lifetime in excess of fi ve years.


Selecting a refrigerant gas detector with simple maintenance procedures is particularly important due to the periodic requirement for replacing the sensor, and the more frequent requirement (at least every 12 months) to test and calibrate the instrument. Applications for NH3


detection often require detection in


high-pressure vent lines from pressure relief valves. Special mounting accessories should be used in this case, in order to ensure eff ective measurement and to protect the gas detector from damage by over-pressurisation. A suitable NH3


refrigerant leak detector should have the


following characteristics: ■Fast response time ■Appropriate temperature range (e.g. -30°C - +50°C) ■ Suitable IP rating for the installation environment (e.g. IP66 or IP67) outputs for system integration, control & safety alerts (e.g. relays, Modbus, analogue outputs). For any areas zoned as being potentially explosive, a detector with the appropriate EX-certifi cation for that zone should be selected.


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