Ammonia refrigeration is one of the older types of refrigeration that is still used today. While the average person doesn't realize it, just about all food and drinks that are purchased have been kept cold using ammonia refrigeration at some point along the way. This is because it is a reliable and efficient refrigerant with years of safe, proven utility.
History of Ammonia Refrigeration
People first started using ammonia as a refrigerant in France starting in the 1850's, and its use was brought to the United States in the 1860's. By the 1900's, ammonia refrigerators were being used in many commercial facilities to create blocks of ice, keep food cold, and produce other chemicals. Starting in the 1920's, it was used in ice rinks, and by the 1930's it was used in air conditioners for both industrial requirements and for keeping homes cool.
While ammonia is not commonly used in air conditioning units anymore, it is still very common for cold storage of food and in many industries that require this type of cooling. Today ammonia is mostly used for larger scale cooling requirements such as college campus dorm room air conditioning, large office buildings, hospitals, airports, hotels, and more.
What is Ammonia Refrigeration
Ammonia refrigeration systems are, as the name implies, a system of refrigeration that uses ammonia. The ammonia is the chemical that is used to absorb the heat from one area, and bring it to another area to dissipate. Concentrated ammonia is much colder than typical room temperature, which makes it an excellent choice for keeping things cool.
Most people are used to using refrigeration systems that use CFCs, or even older systems that use Freon. Due to the environmental impact of these chemicals, and their cost, they are not the ideal choice in industrial environments.
How Does Ammonia Refrigeration Work?
An ammonia refrigeration system, like all vapor-compression refrigeration systems, are made up of a number of components working together. Essentially, the ammonia is the chemical that is contained within the system to remove heat from an area, and then dissipate it in another area. Ammonia is very efficient at this because it has a very low boiling point when liquid (-27F).
Components of an Ammonia Refrigeration System
As with all refrigeration systems, there are a number of components that are needed to keep the system working properly. If any of them are missing or break down, the refrigeration system will stop working almost immediately. The required components are a compressor, condenser, expansion device, and an evaporator.
You can see the basics of how this works in the following image:
In addition to these basic components, many units will have additional parts to help ensure everything works as efficiently as possible. Many refrigerators will have a fan to direct the cool air where it needs to be, and of course there will be an insulated area to help keep heat out so that the refrigeration unit doesn't have to work any harder than necessary.
Ammonia Refrigeration Cycle
An ammonia refrigerator works in the same basic way that most other refrigeration systems operate. The ammonia refrigeration cycle works by bringing warm air into the refrigeration system, stripping the heat out of it, and then sending the cooled air back where it needs to be.
Each step in this cycle is essential in regulating the temperature properly. The following image gives a good introduction to the ammonia refrigeration cycle, which will be explained in more detail after. Part of this is offering advice on how to recognize a hazard in these refrigeration units. Early detection of a leak can allow everyone time to safely evacuate while the leak is repaired.
While the hazards are something that need to be taken seriously, they aren't a common enough issue to make most facilities worry about installing these refrigeration units. When the installation is done properly, and everyone receives the right training, ammonia refrigeration units are a very safe way to keep areas cool.
In the cycle, the ammonia gas is compressed using the compressor, which causes it to heat up as it is pressurized. As it is pressurized, it travels up into the coils, typically located in the back of the refrigeration unit. In the coils, the heat id dissipated, which causes the ammonia to condense and turn into a liquid, which is still at high pressure.
The pressurized ammonia then travels through the expansion valve, which is essentially a small hole that opens up into a lower pressure area. When this occurs, the ammonia quickly begins to boil. It is important to note that liquid ammonia boils at -27F, which means it will be much colder than the surrounding area.
The very cold ammonia cools the air around it, the inside of a refrigerator in many cases. While the ammonia begins to warm, the air gets colder. The ammonia continues to travel through the refrigerated area slowly becoming warmer as it goes. Finally, it will be sucked back into the compressor where it will begin the cycle again.
Hazards of Ammonia
When using ammonia refrigeration, or ammonia for anything in the workplace, there are a variety of OSHA regulations that need to be followed. Having proper safety equipment in place and keeping the refrigeration unit well maintained can help reduce the risk to employees.
Ammonia can be very dangerous. If someone is exposed to as little as 300 parts per million in the air around them, they will experience extreme health issues and potentially even death. Direct contact with ammonia is also corrosive to humans. If ammonia gets on someone's skin or eyes, it must be washed off immediately and treated right away to prevent long-term problems.
OSHA provides guidance for handling ammonia emergencies, as well as first aid recommendations.
Fortunately, ammonia has a very strong odor that people naturally find offensive. This odor is very distinctive and detectable at around 20 parts per million, which is significantly lower than the hazardous levels. When people begin smelling ammonia, they can evacuate the area quickly and have the maintenance teams take care of the problem.
Ammonia is also quite flammable. If there is a 15% or higher concentration in the air, it can ignite when exposed to an ignition source. In ammonia refrigeration, the ammonia is often mixed with lubricating oils, which can cause it to become even more flammable. Having fire suppression systems in place around ammonia refrigeration units is often recommended.
Advantages of Ammonia Refrigeration
When proper precautions are taken, ammonia refrigeration units offer many advantages compared to traditional CFC or HCFC based units. For many large industrial situations, these advantages make this type of refrigeration unit a smart choice:
- Less Expensive - Ammonia refrigerators require narrower piping, which is cheaper to make. This type of refrigeration unit will cost 10-20% less than other models.
- Efficient - Ammonia refrigeration is also 3-10% more efficient to run than units that use CFCs. This translates to lower electric bills and a facility that is more environmentally friendly.
- Ozone Safe - Unlike CFCs, ammonia does not harm the ozone layer. Experts also agree that ammonia use in refrigeration does not contribute to global warming.
- Chemical Cost - Ammonia is significantly cheaper to obtain and use than CFCs, which makes it more affordable to "recharge" a unit.
Piping Requirements
Whenever working with ammonia refrigeration units, it is important to remember that ammonia can be corrosive to certain types of metals. Copper piping, which is commonly used in other types of refrigeration units, cannot be used when working with ammonia.
Labeling the piping in these units to alert those performing maintenance to this requirement can help avoid potential problems. If this precaution is not taken, someone may unintentionally replace a pipe with one made of copper, leaving the facility at risk of a leak.
International Institute of Ammonia Refrigeration (IIAR) Bulletins
The International Institute of Ammonia Refrigeration is an organization that educates and informs about best practices for safely using ammonia for refrigeration. IIAR also provides standards for this purpose.
Additionally, IIAR publishes bulletins that offer guidance to facilities. This guidance provides clarification about safe ammonia use, especially when standards do not explain a particular topic. Below are relevant bulletins:
IIAR Bulletin 108 - Guidelines for: Water Contamination in Ammonia Refrigeration Systems
- Explains how water can contaminate an ammonia refrigeration system, how this can be prevented, and how water can be removed.
IIAR Bulletin 109 - Guidelines for: IIAR Minimum Safety Criteria for a Safe Ammonia Refrigeration System
- Covers the safe design, operation, and inspection of ammonia refrigeration systems. Also includes ammonia refrigeration safety inspection checklists for equipment.
IIAR Bulletin 110 - Guidelines for: Start-Up, Inspections and Maintenance of Ammonia Mechanical Refrigerating Systems
- Covers ammonia hazards as well as equipment maintenance and start-up issues.
IIAR Bulletin 114 - Guidelines for: Identification of Ammonia Refrigeration Piping and System Components
- Provides ammonia labeling guidelines that cover label materials, sizes, colors, etc.
Ammonia Pipe Labeling Requirements
As mentioned above, IIAR Bulletin 114 covers the requirements for ammonia piping labels. These requirements are different from ANSI pipe label guidelines, which apply to most other pipes and are accepted by OSHA in its pipe labeling requirements as well.
IIAR's guidelines explain that ammonia marking labels must meet specific requirements for content and formatting.
Labels have five parts: abbreviations for ammonia system components, physical state (liquid/vapor), marker body ("AMMONIA"), the pressure level (low/high), and an arrow indicating the flow direction.
Ammonia Pipe Abbreviations
IIAR Bulletin 14 includes a list of abbreviations that can appear on an ammonia pipe label such as: CD (Condenser Drain), LT (Liquid Transfer), LTRS (Low Temperature Recirculated Suction, OD (Oil Drain), and RV (Relief Vent). Users can consult IIAR for a full list of accepted abbreviations.
Ammonia Piping Color Code
Recent updates to IIAR Bulletin 114 require that ammonia pipe labels are orange with black text (they were previously yellow). The physical state Liquid should be on a yellow rectangle, and Vapor should be on a blue rectangle. The pressure Low should be on a green rectangle, and High should be on a red rectangle. Consult the diagram above for placement of these label parts.
Those interested can also learn more about these industrial labeling requirements in our Ammonia Pipe Marking Guide, which explains how to create labels according to IIAR pipe marking guidelines.
Ammonia Process Safety Management
Businesses that use ammonia for refrigeration and have systems that contain 10,000+ pounds of ammonia (about 2000 gallons, according to the EPA) should also consult guidelines for process safety management. OSHA's standards can be found here. OSHA's Ammonia Refrigeration eTool also has information about IIAR Process Safety Management Guidelines for Ammonia Refrigeration.
Process safety management deals with how to safely manage processes that use hazardous chemicals, and ammonia falls into this category of very hazardous chemicals.
Resources
- https://www.osha.gov/SLTC/ammoniarefrigeration/index.html
- http://www.goodway.com/hvac-blog/2009/08/ammonia-as-a-refrigerant-pros-and-cons/
- http://www.aboutammoniarefrigeration.com/aaranswers_history.cfm
