Understanding Ammonia Refrigeration Systems

As far back as we can remember man has used ammonia for one reason or another. It is in fact the oldest known refrigerant. It is successfully utilized in many industries including food, petrochemical and pharmaceutical. So why is it so misunderstood?

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In this article, we will attempt to clear up and demystify anhydrous ammonia, which is a formulation void of water, as it relates to refrigeration. We will discuss the benefits and drawbacks of this ammonia refrigerant as well as review leak detection and safe handling procedures.

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Why do we use anhydrous ammonia instead of halocarbons in industrial applications? Ammonia is cheap and extremely efficient. Ammonia is the most commonly used refrigerant worldwide for large commercial applications. The main use of ammonia is agricultural (fertilizer). More than 80 percent of the ammonia produced is utilized in this fashion due to its high nitrogen content. Since ammonia is plentiful, the cost is low. The cost for refrigerant-grade anhydrous ammonia typically is less than 50 cents a pound, compared to about $7 a pound for R4O4A and $15 a pound for R-502.

There are two primary grades of ammonia commonly available in the marketplace. There is an agricultural or commercial-grade ammonia that must contain a minimum water content of at least 2,000 ppm water (0.2 percent) with a maximum water content of 5,000 ppm (0.5 percent). The minimum water content prevents stress corrosion cracking of the metals used in equipment for the agricultural industry.

Industrial-grade anhydrous ammonia, commonly called metallurgical or refrigeration grade, has very little water contamination. Metallurgical-grade has a maximum of about 33 ppm water (0. percent) and refrigeration-grade has a maximum of about 150 ppm water (0.015 percent). For optimum efficiency and effectiveness in your industrial refrigeration system, the ammonia supplied to you for your system should meet or exceed these specifications.

In addition to the price the most compelling reason to utilize anhydrous ammonia is the fact that it has such a high latent capability per pound. Its latent capability at 5° F evaporator temperature is 565 Btu per pound. When compared with R-22, which is approximately 69 Btu per pound at the same temperature, its obvious that it takes less ammonia to do the work because it is more efficient. This means less kwh used and lower operating costs.

Because the smell of ammonia is readily perceptible, you will know it if there's even a tiny leak. With halocarbons a technician’s chances of smelling a leak are low, unless it contains a lot of oil and you are near the source.

Ammonia vapor is lighter than air and in a confined area il displaces oxygen from the ceiling downward. Halocarbons are heavier than air and will displace the oxygen from the floor upward. Either situation can be fatal.

Ammonia is flammable and has a lower explosive limit (LEL) of 15 percent (150,000 ppm) and an upper explosive limit (UEL) of 28 percent (280,000 ppm). When the ammonia vapor is mixed with a mistable oil, the LEL can be as low as 8 percent (80,000 ppm).

Ammonia also will undergo what is called hazardous decomposition at temperatures above 850° F. This means it will break down into nitrogen and hydrogen gases. Hydrogen gas has a flammability range of 4 to 75 percent.

Ammonia systems generally are built around an understanding of the characteristics of anhydrous ammonia and its dangers and benefits. As with any system, the first line
of defense is the safety engineering designed into it.

Industry safety standards continue to be the main reason ammonia systems are much safer than most people are aware. Each system must meet strict safety codes, which include materials of construction as well as appropriate relief valves, ventilation, safety switches and other safety engineering concerns.

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As in any other industry, the training of operators and technicians is important. Fully trained operators and technicians are much less likely to cause a situation resulting in death or injury.

Both OSHA and U.S. EPA address training for larger ammonia refrigeration systems. If the ammonia refrigeration system has a charge of 10,000 pounds or more, you must implement or take operational and maintenance training. Many companies follow this regardless of the charge level.

Training must include standard operating procedures for every task that will be performed, as well as safe work practices, including proper line-break procedures. Line-break procedures are what a technician does each time the ammonia refrigeration system is opened for maintenance. Additionally, operating personnel must receive refresher training at least every three years.

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Artificial cooling systems such as ammonia refrigeration keep industries and businesses running. This is your complete guide to ammonia refrigeration systems: how they work, why they are used, and the potential risks involved. 

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How does ammonia refrigeration work?

The basic physics behind a refrigeration system is to move the heat energy out of one area and into another, thereby leaving the first area cooler than before. The most common type of refrigerating system is a vapor-compression refrigerator, in which a refrigerant in the form of a vapour is compressed to become a liquid, before being expanded and vaporised once more. This process repeats on a cycle so that each time the refrigerant vaporises, it absorbs the heart energy from its surroundings, and then releases that heat to a new location when condensing. 

Historically, the refrigerants used in this type of system have been chlorofluorocarbons (CFCs), such as Freon-12, that have a destructive impact on the environment. Ammonia, on the other hand, does not and has therefore become a very popular refrigerant used in vapor-compression systems. 

Why is ammonia used for refrigeration?

There are three major reasons why ammonia is the suitable refrigerant:

1. It has physical properties that make it extremely effective and efficient for large refrigeration systems. The International Institute of Ammonia Refrigeration states ammonia is between 3 and 10% more thermodynamically efficient than competitive refrigerants. A more efficient refrigerant uses less power and therefore has lower operational costs.

2. It breaks down quickly in the environment, which minimises its harmful environmental impact. As ammonia is lighter than air, it quickly rises and dissipates in no more than 7 days. Unlike synthetic refrigerants such as CFCs, it does not contribute to the destruction of the ozone layer and global warming effect. 

3. Accidental leaks or spillages can be quickly identified due to its strong odour. This pungent smell can be recognised when it’s approximately 20 parts per million in the air. This means that even if the tiniest amount manages to leak, it will be obvious while not able to cause any immediate health damage to people nearby. 

The risks of an ammonia refrigeration system

The key risk of using ammonia-based refrigeration systems is that ammonia is poisonous in high concentrations. Due to ammonia’s properties being best suited to large systems, it is likely there will be a high concentration of ammonia in use to ensure the system is operating efficiently. This presents a serious risk if an accident were to occur, and a significant amount were to be released. However, accidents on this scale can be prevented with necessary risk assessments and compliance with official health and safety regulations set out by the governmental bodies. 

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IRS are the UK’s leading independent refrigeration business, specialising in designing, installing, servicing, and maintaining heavy and industrial commercial refrigeration systems. We use ammonia refrigerants, alongside HFC, HC, HFO, CO2, and more. Our range of services are completed to the highest standards by our expert team, who can adapt to different styles and systems. 

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