Ammonia Refrigeration

Ammonia Refrigeration: How it Works, Types & Use Cases

Ammonia refrigeration is one of the most effective and widely used methods for industrial cooling. Known for its efficiency and cost-effectiveness, ammonia refrigeration has been the backbone of many industries, especially in food processing, cold storage, and chemical manufacturing. If you’re wondering whether this cooling system is efficient for your company, let’s break it down to how it works, drawbacks, and the safety measures involved.

Using Ammonia as a Refrigerant

The use of ammonia as a refrigerant dates back to the mid-19th century. When it was first observed that chlorine, when released into the atmosphere, contributes to ozone depletion and global warming. Chlorine and fluorine containing refrigerants were replaced with ammonia as it stands out among alternative refrigerants due to its chemical properties.

It has a much higher latent heat of vaporization than many other refrigerants, which means that it can absorb large amounts of heat during evaporation, acting as an effective coolant in multiple industries.
This allows ammonia systems to be highly efficient and economical to operate. Another key reason ammonia is widely used is that it has zero ozone depletion potential and very low global warming potential, which makes it an environmentally friendly option compared to synthetic refrigerants.

How Ammonia Refrigeration Works

Before understanding how ammonia refrigeration works, it’s crucial to gain an overview of the working components present in the system.

• Compressor: The heart of the system, the compressor pressurizes the ammonia gas, raising its temperature to facilitate heat release.
• Condenser: Here, the heat is removed from the gas, converting it back into a liquid state.
• Evaporator: This component allows the ammonia to absorb heat, cooling the surrounding environment or substance.
• Expansion Valve: This valve controls the flow of ammonia and its pressure, ensuring smooth movement back into the evaporator.

These parts work in harmony to produce consistent cooling and maintain efficiency.

Types Of Ammonia Refrigerators

Ammonia refrigeration systems utilize the thermodynamic properties of ammonia (NH3) to achieve a cooling effect. There are three main classifications based on the method of refrigerant feed and control:

Thermal Expansion Valve (TXV) Systems:

These, also referred to as dry expansion systems, precisely control the amount of liquid ammonia entering the evaporator using a thermal expansion valve (TXV). This ensures all liquid is vaporized before reaching the compressor, preventing damage. TXV systems are generally less complex but have slightly lower efficiency due to the need for larger evaporators to guarantee complete vaporization.

Flooded Liquid Recirculation Systems:

In flooded systems, a pump or pressurized gas circulates a large quantity of liquid ammonia through the evaporator, often exceeding the amount that can be vaporized. This ensures a constant liquid level in the evaporator coil, maximizing heat transfer efficiency. However, flooded systems require additional equipment like pumps and separators, increasing complexity.

Liquid Overfeed Systems:

Similar to flooded systems, liquid overfeed systems circulate a large amount of liquid ammonia. However, the driving force is the pressure difference between the high-pressure receiver and the evaporator, eliminating the need for a separate pump. This simplifies the design but requires careful management of pressure differentials to prevent excessive liquid carryover to the compressor.

The most suitable type of ammonia refrigeration system for a specific application depends on various factors, including:

• Desired cooling capacity: Flooded and overfeed systems are generally better suited for larger capacity applications.
• Temperature control requirements: TXV systems offer precise temperature control, making them ideal for situations requiring tight tolerances.
• System complexity and maintenance needs: TXV systems are simpler but may require more precise control measures. Flooded and overfeed systems offer higher efficiency but involve additional equipment and maintenance considerations.

Consulting with qualified engineers is crucial to determine the optimal type of ammonia refrigeration system for your specific needs

Ammonia Refrigeration System Diagram

An ammonia refrigeration system diagram typically shows the flow of ammonia through each major component involved in the cooling cycle. Key components generally included in the diagram are:

Evaporator: Where liquid ammonia absorbs heat and changes to gas.
Compressor: Compresses ammonia gas, increasing its pressure and temperature.
Condenser: Releases heat to the surroundings, converting gas back to liquid ammonia.
Expansion Valve: Controls the pressure drop as ammonia moves from the condenser back to the evaporator.

Benefits of Ammonia Refrigeration

This refrigeration system offers several unique benefits, making it a preferred choice for large-scale industrial applications. Here are some key advantages:

High Energy Efficiency: Ammonia has a high latent heat of vaporization, which allows it to absorb more heat with less energy consumption, reducing overall operational costs.

Eco-Friendliness: Ammonia is a natural refrigerant with zero ozone depletion potential and very low global warming potential, making it an environmentally responsible choice.

Cost-Effective: Due to its high efficiency, ammonia refrigeration systems are often more economical to operate over the long term compared to systems using synthetic refrigerants.

Detectability: Ammonia has a strong, distinctive odor, making leaks easier to detect, which adds a layer of safety through early detection.

Drawbacks of Ammonia Refrigeration

Ammonia refrigeration systems, while efficient, present a significant risk due to ammonia’s hazardous properties, making it a potential life-threatening hazard for workers and the environment. Here’s a detailed overview on the disadvantages of using ammonia as a refrigerant:

Toxicity: Ammonia is highly poisonous and can result in severe injury, including skin burns or permanent eye damage, when exposed to. In substantial concentration, it can irritate the eyes, lungs, and skin.

Corrosiveness: In gaseous state, ammonia is highly reactive with certain materials like copper, which limits its use to refrigeration systems with copper pipes.

Flammability: Due to its highly flammable properties, ammonia can readily react with air leading to explosions, especially when combined with lubricating oil.

Environmental Concerns: Ammonia was initially utilized due to its low global warming potential, however, its progressive use can lead to nitrous oxide emissions and nitrogen oxide, which can further enhance atmospheric complexity.

Safety Hazards: Being a highly corrosive and toxic gas, ammonia spills pose safety hazards to workers working in close quarters with ammonia refrigeration systems.

To mitigate these threats, the International Institute of All-Natural Refrigeration (IIAR) released a set of guidelines to promote safe use of ammonia in refrigeration systems to ensure safe practices.

Ammonia Leak Detection Methods

Prompt detection of leaks is critical for ensuring the safety and environmental compliance of ammonia refrigeration systems. Various methods are employed to identify and locate ammonia leaks, each with its own advantages and limitations.

• Direct Detection:
  • The most basic method involves physically observing the system for signs of leakage, including visual inspection of piping, flanges, and joints for frost formation or liquid ammonia accumulation. However, this method can be unreliable for small leaks or those obscured by insulation.
• Ammonia Detectors:
  • These electronic devices continuously monitor the atmosphere for ammonia gas. They typically employ electrochemical sensors or infrared absorption spectroscopy to detect ammonia concentration exceeding a preset threshold. Upon detection, alarms are triggered, alerting personnel and initiating appropriate response protocols.
• Leak Detection Solutions:
  • Certain solutions, often applied with a spray bottle, change color when exposed to ammonia. These solutions are relatively inexpensive and easy to use for qualitative leak detection, but may not be suitable for continuous monitoring.
• Ultrasonic Leak Detection:
  • Ultrasonic detectors can identify leaks by pinpointing areas emitting high-frequency sound waves generated by escaping ammonia gas. This method is particularly useful for detecting small leaks that may not be readily apparent by other methods.
• Infrared Cameras (IR Cameras):
  • IR cameras can visualize temperature variations. Since escaping ammonia gas causes a localized cooling effect, IR cameras can be used to identify potential leaks by detecting areas with lower than expected temperatures.

IIAR Safety Guidelines For Using Ammonia As A Refrigerant

The International Institute of Ammonia Refrigeration (IIAR) is an organization that educates and informs about best practices for safely using ammonia for refrigeration.

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.

Safety and Handling Precautions

While ammonia is efficient, it must be handled carefully. Ammonia is toxic in high concentrations and can be hazardous if not managed properly. Here are some essential safety practices:

• Leak Detection: Ammonia’s strong odor serves as a natural detection mechanism. However, facilities often install sensors to quickly identify leaks, especially in high-risk areas.
• Personal Protective Equipment (PPE): Workers need to wear appropriate protective gear, such as gloves, goggles, and respirators, when working with ammonia systems.
• Ventilation: Ensuring proper ventilation is crucial to prevent ammonia buildup in case of a leak.
  Emergency Protocols: Staff should be trained on how to handle ammonia leaks or spills safely, including evacuation procedures if necessary.
• Ammonia Pipe Labeling Requirements: The IIAR released a set of guidelines to label piping systems with ammonia present to ensure workplace safety. This approach was implemented to provide visual information to emergency responders during a crisis.

By adhering to these precautions, industries can harness the benefits of ammonia refrigeration while prioritizing worker and environmental safety.

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.

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.

Final Thoughts

Ammonia refrigeration has been a tried-and-true method for large-scale cooling needs. Its efficiency, affordability, and eco-friendliness make it a valuable choice for many industries. While handling ammonia requires stringent safety measures, the advantages it brings to refrigeration continue to make it a top choice in industrial applications. Understanding these basics can be helpful for anyone involved in industries reliant on large-scale cooling, especially as sustainability and cost-efficiency remain high priorities.