1 – What is Industrial Refrigeration?

Industrial refrigeration is an engineering application aiming to reduce body or fluid temperature. This reduction happens using a contact fluid, usually air or water, which comes into contact with the body/fluid to cool. But for this, the contact fluid must be at a lower temperature than the body/fluid. The necessary temperature reduction happens using a fluid called refrigerant. The refrigerant is forced to perform evaporation and indirectly exchange heat with the contact fluid.

Sounds complicated, but it’s pretty simple. To make this a little clearer, we need to understand how a basic refrigeration cycle works, and that’s what I’ll introduce you to in the next section.

1.1 – Refrigeration Basic Cycle:

The following image shows how a basic refrigeration cycle works.

It consists of four stages: Compression, Condensation, Expansion, and Evaporation. Despite being a cycle, to understand the system, I will consider it to start at the compressor input represented in Figure 1 as 1. I will also assume some more common states for these points. It is worth mentioning that the fluid’s properties will need to be changed according to the project needs and equipment capabilities.

1.1.1 – Refrigeration Basic Cycle Processes

Compression (1->2): In this step, the refrigerant fluid is compressed by a compressor. This compressor turns out to be like a heart for the system. In addition, it is responsible for initiating fluid displacement in the system.

In a basic refrigeration cycle, the Compression’s purpose is to supply the condenser with a fluid in a vapor state of high temperature and pressure.

Condensation (2->3): In the condenser, heat is lost from the fluid to the environment, which causes a decrease in the temperature of the vaporized fluid, causing it to condense. Thus, the low-temperature high-pressure fluid is transferred to the expansion device.

Expansion (3-> 4): Expansion devices cause a loss of pressure in the fluid (expand it) and dose the flow that will pass through the evaporator. This pressure loss is a consequence of a significant temperature decrease. These changes in properties cause the fluid to exit the expansion device in a liquid + vapor mixture. Finally, this liquid + vapor mixture is transferred to the evaporator.

Evaporation (4->1): In the evaporator, this refrigerant fluid circulates and gains heat from its present environment. As a result, there is an increase in temperature. Thus, this fluid is transferred back to the compressor, and the cycle restarts.

1.2 -The Opportunity

But how exactly can we take advantage of this cycle in our systems?
Remember that at the beginning of the post, I mentioned that the main objective of refrigeration is to cool bodies and/or fluids!?

During which process of a basic refrigeration cycle does this “cooling of the body and/or fluid” happens?

Yea! Exactly what you are thinking! On Evaporation!

Focus on the evaporator in Figure 1. QL represents the heat absorbed from the air by the refrigerator coil, represented by the line inside the evaporator. The air is heated using the forced convection generated when in contact with the cooling coil.

Now, you may be wondering: Isn’t this example similar to what happens in an air conditioning system? Yes, it is. But air conditioning systems are different from industrial refrigeration systems in several ways. In section 2, I will present some of these differences. But before we get to that topic, I will bring one more question: What about the heat the refrigerant loses during Condensation? The loss indicates that the environment in which the condenser is located has gained heat. The most common thing to see is the use of external air to carry out this work. But would be possible to take advantage of this heated air? Yes, it is possible. But that’s a topic for another time. For readers who want to read about it now, reference [3] covers harnessing heat in air conditioning and refrigeration systems.

2- What are the significant differences between Industrial Refrigeration and Air Conditioning?

Despite the similarities in fundamental components, such as compressors, heat exchangers, fans, pumps, pipes, and ducts, air conditioning and refrigeration must be treated differently, since the problems at low temperatures (refrigeration) are not the same as in air conditioning. Furthermore, considering the units installed in an industrial environment and engineers specialized in the area, air conditioning surpasses industrial refrigeration. It happens because refrigeration systems have more complexity than air conditioning ones and a smaller number of applications. In addition, the costs associated with refrigeration are generally higher. It is also worth mentioning that refrigeration, in general, requires greater precision in temperature control. But what stands out the most and, in my opinion, is the best way to differentiate these two systems is the operating temperature range.

2.1 – What operating temperature ranges would you expect to find in an industrial refrigeration system?

In a refrigeration system, the lower limit temperature is -76°F or even -94°F, and the upper limit is 59°F.
The applications working at temperatures below the lower limit would be cryogenic, such as the production and utilization of liquefied natural gas, liquid oxygen, and liquid nitrogen.
The applications working at temperatures above the upper limit would be air conditioning.
Of course, there are situations where you want to use air conditioning systems to reach temperatures below 59°F, but they are specific cases for certain applications.
We generally design air conditioning to achieve thermal comfort and/or humidity control. Applications of this nature are at temperatures above 59°F.

With this wide application range, the applications become varied, but I would like to focus on those related to the food and beverage area in this post.

3 – How does industrial refrigeration is presented in the area of ​​food and beverages?

In the food and beverage industry, industrial refrigeration is presented as a way to increase food exposure time. In Figure 1, there is the exposure time estimate of various foods as a function of temperature stored in a controlled atmosphere of carbon dioxide.

According to the temperature reduction, the storage time increases considerably. But it is also worth noting that many foods do not require freezing conditions to preserve their characteristics, which leads to thinking about optimal storage conditions.

Another point to mention is that reaching the water freezing point is not necessarily equivalent to saying that the product will be freezing since products are not made only of water.

So, it is possible to store various products at temperatures below the water freezing point without ice formation. In Table 1, there are recommended storage temperatures, without freezing, of several foods.

It is worth mentioning that, frequently during harvesting, fruits and vegetables are slightly heated, and to avoid premature deterioration, cooling them quickly in rapid cooling chambers becomes a prudent task.

3.1 – Rapid Freezing Techniques

Rapid cooling technologies were essential to the advancement of the frozen food industry, as they made it possible to reduce the freezing time from days to hours. In addition, these technologies prevent the formation of ice microcrystals in the material structure.

There is a wide variety of rapid cooling techniques, but I would like to highlight the most common ones:

• Cooling by freezing tunnels using high-speed air (air blast);
• Contact cooling/freezing, where food, packaged or not, is arranged between refrigerated plates;
• Freezing by immersing the food in brine at a low temperature;
• Cryogenic freezing: Liquid cryogenic fluid (N₂ or CO₂) is sprayed inside a freezing chamber.

Since industrial refrigeration systems are highly complex applications that often require a greater degree of security, the people involved with the system must be aware of abnormalities. Intending to reinforce the knowledge, in the following section, I present some of the most common problems reported in refrigeration systems.

4 – Main Problems

The main problems presented in industrial refrigeration systems are:

• Compressor’s room overheating;
• The compressor’s suction pressure is high;
• The compressor’s suction pressure is low;
• The compressor’s discharge pressure is high;
• Abnormal noises during operation;
• The compressor’s low oil pressure;
• The compressor’s excessive overload;
• Moiustre in te system;
• Compressor’s suction freezing;
• Air in the system.

As a reference for solutions to the presented problems, I recommend the article published by Refconhvac [4].

5 – Refrigeration Tendency

Finally, I would like to mention what I see as a trend in the refrigeration market, and which, in my opinion, applies to several other areas of engineering.

Based on the advancement of computational modeling technologies, including machine learning algorithms and artificial intelligence, and the growing need to optimize systems for sustainability reasons and to reduce operating costs, I believe that the existence of computational models to optimize systems will be more and more frequent.
In fact, this year IIAR offers a webinar in partnership with a company that works with optimization and exposes the optimization of the thermodynamic behavior of ammonia reasoning systems using real-time machine learning models [5].

A quick search on Science Direct [6], Elsevier’s article portal, using terms such as “artificial intelligence”, “machine learning”, and “optimization” associated with the words “refrigeration system” and “refrigeration systems”, presents 1059/1530 research articles that were published in 2022 and for 2023. It is possible to see a graph indicating the growth in research in the area since 2010.

References:

[1] WILBERT F. STOECKER; JOSÉ M. SAIZ JABARDO. Refrigeração Industrial, 3. ed., p.530, São Paulo: Blucher, 2018 ( Main Reference – Applied to all post).

[2] CLAUS BORGNAKKE; RICHARD EDWIN SONNTAG. Fundamentos da Termodinâmica, 8. ed., p. 730 São Paulo: Blucher, 2018.

[3] JAMES M. CALM. Heat Recovery in Air Conditioning and Refrigeration, Proceedings of the International Symposium, Kuwait, 6–8 February 1983, Pages 159-169,1984.

[4] REFCONHVAC. Refrigeration system: problems, causes, and solutions, 2018. Site: https://refconhvac.com/refrigeration-system-problems-causes-and-solutions/. Access on 04/12/22.

[5] IIAR; CARLOS FERNANDEZ-ABALLI. Real-time Machine Learning Optimization of the Thermodynamic Behavior of Ammonia Refrigeration Systems, 2022. Recorded on 06/22/22. Site: https://www.iiar.org/IIAR/Education/IIAR_Webinars/IIAR/Videos/Webinars/IIAR_Member_Webinars.aspx?hkey=79ac416b-5a14-4fb2-bdb9-7882d4abf2e0. Access on 04/12/22.

[6] Science Direct. Science Direct. Site: https://www.sciencedirect.com/.