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nstallation of an ammonia detection system is an essential element in preserving the safety of employees and products at any cold storage or processing facility, along with that of residents within close proximity. Ammonia leaks must be spotted quickly and efficiently, which means that sensors must be properly installed and maintained, and possess an adequate detection range that meets the needs of the facility. While detection systems offer a means to monitor and quickly initiate automatic responses, the human nose remains one of the most reliable and sensitive means of detection. Humans can typically detect concentrations of 5 parts per million or less. This is generally recognized as one advantage of ammonia. Not only can people easily detect ammonia, they will naturally avoid it, whereas they might not be aware of other gases and chemicals that can displace air before anyone is aware of an issue. In recognition of this sensitivity, IIAR 2-2014 permits alternatives to fixed detection and alarm equipment in rooms or areas that are continuously occupied, when approved by the authority having jurisdiction (AHJ). Readers should refer to the standard for more detail. Machinery (engine) rooms must either be provided with ammonia detection to activate emergency exhaust fans or must have continuous ventilation. Furthermore, machinery rooms must be equipped with a detection system that will shut off certain machinery and close automatic valves if the room
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reaches 40,000 ppm or the upper limit of the detection system, whichever is higher. But in most facilities, at least one detector is necessary in each room with refrigerating equipment. Considering this, there are six key points that every ammonia refrigeration facility should keep in mind regarding ammonia sensors and detection systems. LOCATION, LOCATION, LOCATION
The industry continues to debate what is the best location to mount sensors. Ammonia vapor leaks will normally rise to the ceiling because the vapor is lighter than air, although a liquid leak will drop to the floor and can result in high concentrations on the floor and low concentrations at the ceiling. Many people believe that for the protection of people, the sensor should be placed five feet off the floor to provide a sample of what they are breathing. Sensors should be installed at spots where they are easily accessible for maintenance. For many years, sensors were mounted on the ceiling to be near the evaporator coils. This was largely because they were capable of detecting an ammonia leak only at 150 parts-per-million. “So you had to be really close to the leak to catch it,” said Brian EuDaly, vice president of engineering at Calibration Technologies, Inc. “But now they can detect a leak at 25 ppm. Sensors mounted on the ceiling aren’t maintained as regularly, and if you ignore a sensor it might not function properly when you really need it to.” In low-charge small package systems, the location of ammonia is concentrated in one
CONDENSER | December 2016 | A Publication of the International Institute of Ammonia Refrigeration
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spot, which makes placement of the sensors more efficient and straightforward. TAKE THE TEMPERATURE
Sensors should be designed to accommodate the environment. “The cold storage and food processing industry has very low temperatures, along with washdown and sanitation concerns,” EuDaly said. “You have to be certain that the equipment can handle the environment.” Sensors placed in coolers and freezers should always be within a heated enclosure so that they will continue to respond properly to the presence of ammonia. “The sensor may not work if the temperature is minus-40 and it doesn’t have a heated enclosure,” EuDaly said. DETERMINE THE SET POINT BEFORE SENSOR RANGE
Selecting the appropriate sensor ranges for your facility is another essential point. But it’s also vital to understand that sensor range and the alarm set point go handin-hand. “We see people install a sensor with a range of 0 to 1,000 ppm with a set point of 25 ppm. But the sensor just won’t be as accurate at that low level as one with a range of 0 to 100 ppm,” EuDaly said. “The first question to be answered when selecting a sensor range is: ‘What is the alarm set point going to be?’” www.iiar.org