Everything you need to know about Commercial Refrigeration Systems and its Types

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Commercial Refrigeration Systems: An Overview

 

This module provides an introduction to commercial refrigeration systems, covering their applications, types, the fundamental refrigeration cycle they employ, and the key parameters to consider when selecting such a system.

 

Introduction to Commercial Refrigeration Systems

 

Commercial refrigeration systems are vital for various businesses and are found in locations like supermarkets, hotels, malls, and pharmaceutical facilities. These systems are designed to handle larger cooling loads and operate for extended periods. A malfunction in a commercial refrigeration system can pose a significant risk to the entire business operation.

Businesses that typically require commercial refrigeration include:

• Food and beverage companies
• Supermarkets
• Convenience stores
• Restaurants

Commercial refrigeration systems are available in diverse shapes and sizes, tailored to specific needs. Some common types include:

• Rack refrigerators
• Walk-in coolers
• Ice plants

These specific systems will be explored in detail in upcoming modules.

All commercial refrigeration systems operate on the fundamental basic refrigeration cycle, which consists of four main components:

• Compressor
• Condenser
• Metering device
• Evaporator

(A video illustrating the basic refrigeration cycle is typically used to recall this process.) These components are connected in series to achieve the desired cooling effect.

 

How to Choose a Commercial Refrigeration System

 

When selecting a commercial refrigeration system, several parameters are considered:

1. Space Needs: It’s crucial to measure the available space. Commercial refrigeration systems come in all sizes, and maximizing storage capacity within the available footprint is key.
2. Storage Type: The type of business dictates the preferred refrigeration system. For instance, a retail shop might need display units, while a restaurant would likely require high-capacity refrigerators and freezers for bulk storage.
3. Cost: Two primary cost considerations are:
   • Initial Cost: The capital required to purchase and install the new system.
   • Operating Cost: Ongoing expenses directly related to the system’s usage, primarily energy consumption.

Commercial refrigeration systems are characterized by their ability to handle large loads and operate for extended durations.

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Rack Refrigeration Systems

 

This module focuses on rack refrigeration systems, detailing their introduction and components.

 

Introduction to Rack Refrigeration Systems

 

In environments like supermarkets and malls, the effective display of food items is paramount, as shopping decisions are often made instinctively. Thus, food must be presented appealingly and be easily accessible to customers.

A refrigeration system in such settings must provide sufficient cooling even when its doors are frequently opened. This necessitates high cooling capacity and a large refrigerant flow.

Rack refrigeration systems are designed to meet these demands. They feature multiple compressors that share a common refrigerant source and work together to produce a cooling effect. These systems are capable of maintaining different temperatures in various refrigerated cases, making them more efficient than traditional systems for cooling multiple display units.

The core benefit of rack refrigeration systems lies in their use of multiple compressors and condenser fans, which allows for more efficient cooling and flexible operation.

 

Components of a Rack Refrigeration System

 

The main components of a rack refrigeration system are:

1. Compressors:
   • A compressor’s primary function is to increase refrigerant pressure. Unlike residential HVAC systems where a single compressor cycles on and off for smaller loads, this approach is energy-inefficient for larger commercial loads.
   • Instead, multiple compressors are used in compressor racks, which may or may not operate simultaneously. This parallel arrangement (all suction lines connected to a single inlet, all discharge lines to a single outlet) allows for faster and larger refrigerant delivery, akin to multiple bike riders delivering parcels instead of one large truck.
   • Using multiple compressors in a rack is highly beneficial as they operate based on the cooling demand, offering more flexibility than a single on/off compressor. For example, during low-customer periods like overnight, fewer compressors can run, reducing energy consumption.
   • Compressors are typically located in a mechanical room, which can be on the floor, roof, basement, or in a storage area of the supermarket.
2. Condensers:
   • The main job of a condenser is to cool down refrigerant. In rack refrigeration systems, condensers are usually placed on the roof or outside the building.
   • Air-cooled type condensers are generally used in these systems.
3. Metering Devices:
   • Metering devices reduce refrigerant pressure. In rack refrigeration systems, electronic expansion valves (EEVs or EXVs) are used.
   • EEVs can quickly adjust refrigerant flow according to cooling demand. Rack systems have multiple EEVs, with each evaporator coil in a refrigerated case having one to control its refrigerant flow.
4. Evaporators:
   • Evaporators absorb heat from a space to cool it. In rack refrigeration systems, evaporator coils are positioned inside the refrigerated cases where food is displayed. Refrigerant circulates through these coils to provide cooling.
   • Plate type evaporators are commonly used, consisting of two joined plates through which liquid refrigerant flows in a tube. The evaporator cools food items inside the refrigerated cases through the evaporation process.

In summary, a rack refrigeration system utilizes multiple compressors in a parallel configuration, connected to multiple refrigerated cases.

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Walk-in Refrigerators

 

This module provides an introduction to walk-in refrigerators, detailing their components and characteristics.

 

Introduction to Walk-in Refrigerators

 

Walk-in refrigerators are large, insulated, enclosed, box-type structures with access doors substantial enough for a person to enter. They are essentially scaled-up versions of residential refrigerators.

They are used to store a wide range of materials, including:

• Food (fresh, frozen, raw, prepared)
• Beverages
• Meat, fruits, vegetables
• Chemicals
• Pharmaceutical drugs

Walk-in refrigerators offer substantial storage space, enabling the storage of large quantities of food at safe holding temperatures to prevent rapid spoilage. They are manufactured in standard sizes but can also be customized or integrated into kitchen designs or supermarkets. They can be installed either inside or outside a building and constructed with or without floors.

Most walk-in refrigerators are built using insulated panels, typically comprising polyurethane insulation sandwiched between stainless steel. Polyurethane foam, also known as spray foam, is a common insulating material found in various applications.

 

Identification of Walk-in Refrigerators

 

Walk-in refrigerators are identified by:

1. Size: Based on their outside dimensions of length, width, and height (e.g., a $\text{12 x 10 x 8}$ foot walk-in refrigerator).
2. Temperature Application: Divided into two main types:
   • Walk-in Coolers: Operate above $\text{0°C}$ (32°F) and at or below $\text{13°C}$ (55°F). They are used for consumable products that will be used within a few days, such as fresh food, hospital medical supplies, or human remains prior to funeral services. Ideal temperatures are typically below $\text{40°F}$ to prevent spoilage, but not below $\text{34°F}$ to avoid freezing delicate items like dairy products, which can ruin texture and quality.
   • Walk-in Freezers: Operate at or below $\text{0°C}$ (32°F). Temperatures are typically set between $\text{0°F}$ and $\text{-10°F}$ for most frozen items. They are used for consumable products intended for storage over months or even years.

 

Components of a Walk-in Refrigerator

 

A walk-in refrigerator operates on the basic refrigeration cycle. Its main components are:

• Compressor and Condenser: These are typically housed separately in a condensing unit, similar to a residential split system. The compressor increases refrigerant pressure, and the condenser cools it down.
• Metering Device and Evaporator: These are located inside the walk-in refrigerator, usually near the ceiling. The metering device decreases refrigerant pressure, and the evaporator absorbs heat to cool the space.

A fan draws warm air from inside the walk-in refrigerator over the evaporator coils. The evaporator coils cool this air, which is then circulated throughout the unit to maintain the desired temperature.

Humidity Control in Walk-in Refrigerators:

• In comfort cooling (e.g., residential AC), the temperature difference between return air ($\approx \text{75°F}$) and evaporator coil ($\approx \text{40°F}$) is about $\text{35°F}$. This helps maintain comfortable humidity by condensing moisture.
• In a walk-in refrigerator, the temperature difference between return air ($\approx \text{35°F}$) and evaporator coils ($\approx \text{25°F}$) is much smaller, about $\text{10°F}$. This helps maintain humidity at approximately $\text{85%}$. High humidity is beneficial for foods like meat, as it prevents drying out and reduces water evaporation from the food.

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Ice Plants

 

This module provides an introduction to ice plants, including their components and operational principles.

 

Introduction to Ice Plants

 

Since ancient times, humans have used ice to cool foods, beverages, and other products. While natural ice was initially used, artificial ice production has become a vital part of the HVAC industry.

Ice, which is water in a solid state, is still in high demand, particularly in large blocks. Ice blocks are preferred due to their size and small surface area, which slows down melting, simplifying storage, handling, and transport. They can also be processed into different forms of ice as required.

Industries that frequently use ice blocks include:

• Healthcare (e.g., for medical equipment and drug preservation)
• Hotels
• Restaurants
• Convenience stores

Ice blocks are also used for cooling drinks and foods, and even for creating ice sculptures.

Ice plants, also known as ice machines or ice generators, are facilities designed for the large-scale production of ice.

 

Components of an Ice Plant

 

Ice plants operate based on the basic refrigeration cycle. Their main components are:

1. Compressor: Increases refrigerant pressure.
   • Reciprocating Compressors: Driven by a motor, similar to an automobile engine. Less popular now due to noise, efficiency, and maintenance concerns, but still used in smaller capacity ice plants.
   • Screw Compressors: Feature one or two rotating, screw-shaped shafts that compress refrigerant. Commonly used in large capacity ice plants.
2. Condenser: Cools down refrigerant.
   • Fin and Tube Condensers: Similar to residential AC condensers, with aluminum fins and copper tubes. Hot refrigerant flows through the tubes, and fins facilitate heat dissipation to the outside air.
   • Microchannel Condensers: Made of thin, zig-zag aluminum fins. More efficient than fin and tube condensers.
   • Shell and Tube Condensers: Consist of copper tubes inside a larger shell. Water flows through the tubes, cooling the hot refrigerant in the shell. A cooling tower typically supplies water to these condensers.
   • Cooling Towers: Large structures designed to remove heat from water by spraying it down through the tower.
3. Metering Device: Decreases refrigerant pressure.
   • Thermal Expansion Valves (TEV/TXV): Used in residential HVAC and ice plants. They control refrigerant flow into the evaporator based on the evaporator’s outlet temperature.
   • Electronic Expansion Valves (EEV/EXV): More advanced TEVs, offering superior performance due to electrical operation and precise refrigerant flow control into the evaporator.
4. Evaporator: Absorbs heat to provide cooling.
   • Bare Tube Evaporators: Simplest type, consisting mainly of refrigerant tubes. Placed inside a brine tank where ice is produced.
     • Copper Bare Tube Evaporators: Used for small evaporators with refrigerants other than ammonia (e.g., residential applications). Ammonia is not compatible with copper due to rapid reaction and leak formation.
     • Steel Bare Tube Evaporators: Used for large ice plants where ammonia is the refrigerant, as ammonia is compatible with steel piping.
   • Shell and Tube Evaporators: Used in large capacity ice plants. Consist of a bundle of copper tubes within a large metal shell. In ice plants, these evaporator coils are filled with refrigerant, and brine flows over them (instead of air) to cool the brine.

 

Brine Cycle in Ice Plants

 

Brine is a solution formed by mixing a soluble substance (e.g., table salt, calcium chloride, or glycol) in water. Mixing these substances lowers the freezing point of water, allowing the solution to remain liquid below $\text{0°C}$. Brine acts as a medium to transfer cold from the refrigerant to the water-filled ice cans.

Brine tanks are typically made of mild steel sheets with welded tie rods, well-insulated on all four sides and the bottom. The brine temperature in these tanks is maintained between $\text{-10°C}$ and $\text{-110°C}$.

Ice cans, made of galvanized steel with a chromium layer for corrosion prevention, are filled with fresh water and submerged in the brine tank. The refrigerant cools the brine, which in turn cools the water in the cans, leading to ice formation.

Historically, ice has been used to cool various products. Producing ice in large blocks simplifies storage, handling, and transport. The core function of an ice plant is to produce ice in large quantities, utilizing the basic refrigeration cycle and often involving a brine system to facilitate heat transfer for ice formation.