Industrial Refrigeration System Basics: A Focus on Ammonia Refrigerant
This guide explores the fundamentals of industrial refrigeration systems, with a particular emphasis on ammonia refrigeration. We’ll cover basic concepts and progress to typical system configurations, including single-stage, two-stage, and cascade systems, to help you grasp the essentials of industrial refrigeration.
For a more in-depth visual learning experience, you can watch the YouTube tutorial at the end of this article. Additionally, if you’re interested in a free course on industrial refrigeration, you can start your free Ammonia eLessons today by clicking here. Danfoss Learning offers an online training platform with hundreds of free eLessons accessible from your computer, smartphone, or tablet, helping you discover how ammonia can enhance the efficiency and environmental friendliness of industrial refrigeration applications.
Where Are Industrial Refrigeration Systems Found?
Industrial refrigeration applications are typically found in large-scale cooling systems in places such as:
- Cold food storage facilities
- Dairy processing plants
- Beverage production facilities
- Ice rinks
- Heavy industry settings
Why Use Ammonia as a Refrigerant?
Ammonia is a highly beneficial refrigerant for several reasons:
- Natural Occurrence and Abundance: It occurs naturally in the environment and is available in abundant quantities.
- Environmental Impact: It has an ozone depletion rating of zero and a global warming potential (GWP) of less than 1. This is significantly lower compared to other common refrigerants like R134a (GWP of 1,430) and R404A (GWP of 3,922).
- Cost-Effectiveness and Efficiency: Ammonia is inexpensive to produce and energy-efficient to use.
- High Heat Absorption: It possesses the capability to absorb large amounts of heat as it evaporates, which is a crucial characteristic for an effective refrigerant. This also allows for thinner and smaller pipes and components in the system.
- Leak Detection: Unlike most refrigerants which are odorless, ammonia has a very sour smell, making leaks easily noticeable.
- Environmental Reaction: If ammonia leaks, it reacts with carbon and water in the air to form ammonium bicarbonate, which is a harmless, washable compound.
However, it’s important to note that ammonia is toxic and can be flammable at certain concentrations.
Single-Stage Ammonia Industrial Refrigeration System
The single-stage system is the simplest type of ammonia industrial refrigeration system, aside from a direct expansion type.
- Compressor: This is the “heart” of the system, pumping ammonia refrigerant. It pulls in low-pressure vapor refrigerant that has absorbed unwanted heat from the evaporator, then compresses it into a much smaller volume, making it very hot and high-pressure.
- Condenser: The high-pressure refrigerant vapor flows from the compressor to the condenser. Here, unwanted heat is removed from the refrigerant and discharged into the ambient outside air. This is typically done by passing the hot refrigerant through tubes while a fan forces cooler ambient air across them. Often, a pump also sprays water over the pipes, with some evaporating to carry away more heat. The refrigerant remains sealed within the pipes, never mixing with the air or water; only its heat transfers. As heat is removed, the refrigerant condenses into a high-pressure liquid.
- Receiver: The high-pressure liquid refrigerant flows to the receiver, which acts as a storage vessel or reservoir for excess liquid refrigerant not currently in use. This helps maintain minimum head pressure and provides a buffer for varying cooling loads. A line often connects the receiver to the condenser inlet for pressure equalization, allowing easy flow of liquid refrigerant.
- Expansion Valve: The refrigerant then flows to an expansion valve, which regulates the pressure and the amount of liquid refrigerant entering the evaporator circuit.
- Liquid Separator and Pumps: From the expansion valve, the refrigerant flows into a liquid separator. The liquid settles at the bottom and is typically drawn in by refrigerant pumps. These pumps ensure the correct circulation rate through the evaporators as the cooling load changes. The refrigerant is then pushed to the expansion valves of the evaporators, which control its flow into the cooling load.
- Evaporator: The cold refrigerant enters the evaporator, flowing inside pipes. A fan blows warm room air across the outside of these tubes. The cold refrigerant absorbs this heat, causing the air to leave much cooler, thus providing cooling to the space. As the warm air passes over the evaporator pipes, the ammonia boils and evaporates into a part-liquid, part-vapor mixture, carrying the heat away. The refrigerant remains sealed inside the pipes, never mixing with the air.
- Return to Separator and Compressor: The refrigerant leaves the evaporator as a liquid/vapor mixture and returns to the liquid separator. The liquid portion falls and repeats the cycle through the evaporator, while the vapor portion rises and is drawn back into the compressor as a low-pressure vapor to restart the entire cycle.
Two-Stage Ammonia Industrial Refrigeration System
This system is an evolution of the single-stage design, suitable for low-temperature refrigeration applications, offering high efficiency and low compressor discharge temperatures. It includes additional components and cycles:
- Intermediate Cooler: A tank called the intermediate cooler is situated between the receiver and the main expansion valve. The primary flow of refrigerant passes through a coil submerged within this tank.
- Subcooling: Another stream of refrigerant branches off the main line and is sprayed into the intermediate cooler tank via an expansion valve. As it sprays and evaporates, it creates a cooling effect, which subcools the main flow of refrigerant inside the submerged coil before it proceeds to the main expansion valve.
- Two Compressors: The vapor refrigerant drawn from the separator still flows to a compressor, but in this system, there are two:
- Low-Stage (Booster) Compressor: The refrigerant first flows to this compressor to increase its pressure.
- Intermediate Cooler Release: From the low-stage compressor, the refrigerant is released into the intermediate cooler, which helps to condense it.
- High-Stage Compressor: The vapor refrigerant is then drawn out of the intermediate cooler and flows to the high-stage compressor. From here, it returns to the condenser to complete the cycle.
Cascade Ammonia Industrial Refrigeration System
The cascade system is the most advanced and can be quite complex. It is ideal for refrigeration systems requiring different temperature ranges for their cooling loads and simplifies compliance with health, safety, and environmental regulations.
- Multiple Circuits: These systems typically consist of two or more separate refrigeration circuits, often utilizing different refrigerants to achieve the cooling effect.
- Cascade Condenser: Connecting the two circuits is a heat exchanger known as a cascade condenser. This component functions as a condenser for the high-temperature circuit and an evaporator for the low-temperature circuit.
- Optimized Refrigerants: The two refrigerants used can be the same, or they can be different and optimized for each specific circuit. For example, ammonia could be used for the high-temperature side, and CO2 for the low-temperature side.
- Benefits: Using different refrigerants (e.g., ammonia and CO2) can mean less ammonia is required in the overall system, and the system can be more efficient compared to a two-stage ammonia-only system.
Watch the YouTube Tutorial
For a visual explanation of these concepts, you can watch the YouTube tutorial here: [suspicious link removed]