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Introduction
This article will take an in-depth look at air cooled chillers.
The article will bring more detail on topics such as:
Principle of Air Cooled Chillers
How Air Cooled Chillers Work
Types of Air Cooled Chillers
Applications and Benefits of Air Cooled Chillers
And much more…
Chapter 1: Principle of Air Cooled Chillers
This chapter will discuss what air cooled chillers are, their components, and their working principle.
What are Air Cooled Chillers?
Air cooled chillers are refrigeration systems that cool fluids and work in tandem with the air handler system of a facility. Air cooled industrial chillers are types of industrial chillers that rely on the use of fans to reject heat outside the building rather than relying on cooling towers. The system uses air to cool water and fluids that are circulated through the system to absorb and remove heat to lower the temperature of equipment, processes, and areas.
Air cooled industrial chillers consist of a compressor, an evaporator, a condenser, and an expansion valve. They are used for large industrial operations and various other structures such as indoor malls, industrial complexes, hotels, and hospitals. Air cooled industrial chillers are also used in locations that consist of several buildings, like theme parks and outdoor malls and are workhorses capable of providing cooling power to large and small operations.
The compact design of air cooled industrial chillers makes them portable, inexpensive to maintain, and easy to install. Portable air cooled industrial chillers can be used for large events or emergency situations and have a simpler structure to that of water cooled industrial chillers. Most air cooled industrial chillers use screw compressors or scroll compressors.
Air cooled industrial chillers are also called modular industrial chillers since they can be stacked horizontally to increase their cooling capacity, which ranges from about 10 refrigeration ton (RT) to 550 RT. When scroll compressors are used, a single air cooled industrial chiller can be designed to have a maximum cooling capacity of about 200 RT. On the other hand, with screw compressors, a single air cooled industrial chiller can be designed with a maximum capacity of up to 550 RT.
An air cooled industrial chiller has at least two compressors. If one compressor malfunctions, the remaining one will continue to function, with the total cooling capacity of the chiller reduced to 50%. Air cooled industrial chillers are not very efficient compared to water cooled chillers. The energy efficiency of air cooled chillers is only around 1.00 kW/ton, while the efficiency of water cooled industrial chillers is twice that.
Components of an Air Cooled Industrial Chiller
The components of an air cooled chiller include:
Air Cooled Industrial Chiller Compressor
The compressor provides the driving force that moves the refrigerant through the system. The different types of compressors are screw, reciprocating, scroll, rotary, and centrifugal with centrifugal compressors being the most dynamic and unlike the four other types that use positive displacement as their working principle.
With positive displacement compressors, there is a continuous reduction in a certain amount of gas in terms of volume through the use of screws, pistons, spirals, or rotations that increase vapor pressure. With centrifugal compressors, compression of the gas occurs as a result of being accelerated by an impeller’s rotation followed by the speed reduction in a diffuser to increase the pressure
Centrifugal compressors are well suited for large-capacity applications. Compressors can be categorized into three categories: hermetic compressors, semi-hermetic compressors, and open compressors. In hermetic compressors, the compressor and the electric motor are placed in an enclosed casing that cannot be opened when maintenance needs to be done. This type of compressor is utilized in low-capacity applications as a result. In semi-hermetic compressors, there is a two-piece casing in which the electric motor and the motor are enclosed.
The compressor and the motor are separate and distinct parts of the assembly. These types of compressors are available with mid-range capacity, which is more than a hermetic compressor. In an open compressor, the electric motor is separated from the enclosure of the casing but is connected to it by means of a coupling. These types of compressors are often made with high capacity.
Air Cooled Industrial Chiller Condenser
The condenser is a heat exchanger that transfers heat from the refrigerant to the air and is cooled by air. Air cooled condensers consist of tubes made of copper, running liquid refrigerant, and aluminum fins that serve in the transfer of heat with the passing air. The condensers in air cooled industrial chillers are air cooled, evaporative condensers, or water cooled condensers. In air cooled condensers, the function of the air is to serve as a cooling agent that distills the refrigerant.
On the other hand, water is used for the cooling of the refrigerant in a water cooled compressor. Evaporative condensers are capable of using both air and water. Although evaporative condensers increase the temperature of the passing air to some extent, the distillation of the refrigerant is done by the evaporation of water sprayed on the condenser. The air serves in the promotion of evaporation by removing the vapor that results. Air cooled chillers often make use of condensers of the first type mentioned.
Air Cooled Industrial Chiller Condenser Fans
These fans are what differentiate air cooled industrial chillers from water cooled industrial chillers. Their purpose is to move air across the condenser. As they move air across the condenser, unwanted heat is removed from the system, and the cycle starts all over again.
Air Cooled Industrial Chiller Expansion Valves
The expansion valve controls the flow of refrigerant from the condenser and varies the flow based on cooling load changes. It receives the refrigerant in a filtered liquid state and reduces the pressure on the refrigerant before it is sprayed into the evaporator. The restriction caused by the expansion valve makes the refrigerant backup and expand into a low pressure liquid and vapor mix. As the pressure builds, the liquid refrigerant transforms into a hot gas and then a cold gas.
There are seven types of expansion valves that include thermal, low pressure, high pressure, electronic, and automatic. Each of the various types have the job of controlling the flow of refrigerant to the evaporator and maintaining the pressure difference between the condenser and the evaporator. They remove pressure from the liquid refrigerant to allow it to change from a liquid to a vapor that takes place in the evaporator.
Air Cooled Industrial Chiller Evaporator or Heat Exchanger
In the evaporator, heat is extracted from the refrigerant before it enters the condenser. The evaporator is a heat exchanger that transfers heat from refrigerant to water or coolant . The various forms of evaporators are coil, shell and tube, and plate. The efficiency of the heat transfer is an essential function of an air cooled industrial chiller, with high efficiency being measured by an evaporators ability to transfer more energy using less heat exchanger area.
The purpose of this component is to cool down the refrigerant. It achieves this by transforming it into gas. The purpose of the cooldown of the refrigerant is for the collection of heat from the water that comes from the fan coil to the evaporator, or air handling units to the evaporator.
The evaporators are classified into three categories based on their structure:
Shell and Tube: These are often made from copper or steel tubes. This type of coil is utilized in the cooling down of liquids.
Finned Evaporators: In these types of evaporators, there are secondary heat transfer surfaces, which are the fins placed over the tubes. This increases the transfer of heat from the tube to the air. In addition, the external surface area is increased, thus improving the efficiency of air cooling. The surface of the evaporator can be insulated to prevent thermal dissipation.
Plate Evaporators: These types of evaporators integrate two metal plates containing grooves that distribute the refrigerant. There is also another type of plate evaporator that consists of a tube placed between two metal plates welded together at the ends of the metal plates. In these evaporators, an eutectic solution is used to fill the space that is between the two plates.
This improves the contact between the tube running the refrigerant and the plates.
Air Cooled Industrial Chiller Filter Drier
The purpose of this component is to protect the chiller by the removal of unwanted contaminants and moisture from the system. They need to be replaced regularly as they get clogged after repeated use.
Chapter 2: How Air Cooled Industrial Chillers Work
The working principle of air cooled industrial chillers is based on the absorption of heat from processed water. Once the air handler system uses up the water, it becomes warm and is returned to the chiller. The chiller’s evaporator is utilized to transfer heat away from the water. A low-pressure gas is created by the evaporation of liquid refrigerant over the evaporator tube. Next, the refrigerant that has been evaporated travels to the compressor. At the compressor, low-pressure gas is compressed into high-pressure gas.
The gas will then leave and travel to the air cooled condensers. While inside the condenser, heat is removed from the chiller by blowing out the heat to the outside through the fans located on the side of the condenser. It is ideal if the chiller is placed outdoors or in a large indoor location. This is so because the heat is blown outside the chiller, and the excess heat effect is reduced.
The refrigerant turns into a high-pressure liquid soon after the gas leaves the condenser. The high-pressure liquid then flows to the evaporator via the expansion valve. As this process takes place, the refrigerant changes from a high-pressure liquid to a low-pressure liquid. Since an industrial air cooled chiller’s working principle is also based on a continuous cycle, this low-pressure liquid will then be transferred back to the evaporator. At the evaporator, the whole cycle repeats itself.
Air Cooled Industrial Chillers vs. Water Cooled Industrial Chillers
Air cooled and water cooled industrial chillers have several factors in common. They are from the vapor compression chilling family and use electronically driven mechanical compressors to force refrigerant through the system. The difference between air cooled and water cooled is how they remove heat from the system.
In water cooled industrial chillers, water is pumped via a sealed condenser and dispersed through a cooling tower. On the other hand, air cooled industrial chillers make use of fans that force air through the condenser. The tower of a water cooled industrial chiller, as well as its pump, uses up more space than air cooled chillers’ fans. This main component difference makes air cooled industrial chillers have a more compact footprint. Water cooled industrial chillers are more expensive due to their cooling towers, which are expensive to maintain. On the other hand, air cooled industrial chillers are cheaper since their maintenance cost is lower and the upfront cost of air cooled industrial chillers is lower.
Factors to Consider When Choosing an Air Cooled Chiller
Some considerations when choosing an air cooled chiller include:
Minimum Industrial Chiller Capacity
When opting for an air cooled industrial chiller, the environmental characteristics and the device's capacity must be considered. When there is a cold environment and a large temperature difference between day and night, air cooled chillers are preferred. However, in those cases, the capacity of the device, whether minimum or not, must be considered. When the appliances are of low capacity, it is ideal to use air cooled industrial chillers.
Effect of Industrial Chiller Height
The height of the surroundings is an important factor that must also be considered. Always pay attention to the height factor when purchasing an air-cooled chiller because the air cooled chiller capacity decreases as the altitude increases.
Industrial Chiller Control Type
When choosing an air cooled chiller, operators must consider how the chiller will be controlled. This is so because devices that can be easily controlled are more likely to promise more efficient work as well as performance.
Industrial Chiller and Refrigerant Pressure
Any type of industrial chiller must be protected against high pressure as much as possible, whether the water is cold or the air is cool. For this purpose, the quantity of air that flows in the condenser must be high. At the same time, medium and low-pressure refrigerants should be preferred.
Resistance to Air Temperature
In air cooled devices, the device’s remaining capacity is reduced by 1% for every 1°C. This is an important factor that will largely affect the choice when opting for an air cooled industrial chiller. This change also greatly affects the compressor and increases the amount of power that is used by the compressor by 1%.
Evaporator Pressure Drop Value
In air cooled industrial chillers, the pressure drop value of the evaporator must not exceed 60 kPa by a large amount. This must not occur in the air cooled industrial chillers that prefer the lowest pressure drop.
Physical Size of an Industrial Chiller
The size of the chiller is an important factor to consider. In the space of the building in which the chiller is going to be used, a small chiller must be chosen according to the available space. Usually, most air cooled chillers use little space.
The Amount of Noise Produced by the Device
The issue of the noise produced by the device during operation must also be considered. In places where noise is an important factor, categories of air cooled chillers with sound pressure less than 75dBA at a distance of 16.4ft (5 m) in an open space must be selected. There should be a preference for categories with low noise levels.
Number of Compressors
The number of compressors that an air cooled chiller contains is important. These are written in the specifications of the device.
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Chapter 3: Types of Air Cooled Industrial Chillers
Air cooled industrial chillers are grouped by their types of compressors, which are screw, reciprocating, scroll, rotary, and centrifugal.
Portable Air Cooled Industrial Chiller
The label “portable air cooled industrial chiller” refers to the system's basic configuration, not its mobility. Most portable industrial chiller units can never be moved once they are installed. The term portable air cooled industrial chiller refers to any chiller system that contains all the ideal components such as the refrigeration circuit, the pump or pumps, and the reservoir.
These are all contained within a single footprint. The controls of an air cooled industrial chiller unit include motor starters with a single-point electrical connection. Industrial chillers provide notifications for maintenance milestones, fault codes, technical alarms, and alerts to nearly eliminate downtime. Portable chillers can be found ranging from 2 to 100 tons in capacity.
Portable Air Cooled Industrial Chiller Standard Flow
The standard flow chiller system is fitted with an integrated tank. This chiller system is used in a closed-loop cooling application. In this application, all the water pumped from the chiller returns to the main unit under pressure generated by the pump.
Portable Air Cooled Industrial Chiller Reversal Flow
The reverse flow air cooled industrial chiller is not fitted with a tank but has an open-loop cooling system where an external tank or trough is put to use. Water in the tank or trough is supplied to the chiller pump by gravity and moves through the chiller and filter and back to the tank or trough.
Portable Air Cooled Industrial Chiller Continuous Flow
Continuous feed portable industrial chiller units work by cooling a fluid source on a single pass. They are equipped with a pump, a tank, and a secondary heat exchanger followed by a filter.
Industrial Stationary Air Cooled Chillers
A “stationary air cooled industrial chiller” refers to any chiller that does not have a pump or a tank. The main component in a stationary air cooled industrial chiller is a stand-alone chiller unit connected by piping to a pump and a separate reservoir to function properly. This system has separate controls for the chiller and the pump or pumps.
Each of these components has an electrical connection. The electrical controls should be wired together properly to prevent the chiller system from cooling until the circulating pump starts operating. The stationary air cooled chillers can be found in sizes ranging from 2 tons to 200 tons.
Reciprocating Industrial Chiller
The gas contained in a reciprocating industrial chiller is compressed by pistons, whose applied pressure heats the gas. Adjustable intake and exhaust valves open to allow the piston to idle. Leaving the piston when there is a demand for chilled water helps manage capacity. Reciprocating industrial chiller systems are flexible and can cope with the specific demands of load on the system. They can also manage the capacity to match the demand with a hot gas bypass. This process is not considered to be as efficient as possible. Some chiller systems utilize both capacity control systems to unload pistons. The same chiller systems can also utilize the hot gas bypass to match demand.
Each of these components has an electrical connection. The electrical controls should be wired together properly to prevent the chiller system from cooling until the circulating pump starts operating. Stationary air cooled industrial chillers come in sizes that range from 2 tons to 200 tons.
Rotary Screw Industrial Chillers
The screw compressor is also referred to as a helical compressor. Inside its stationary housing, it contains helically grooved rotors. When the helical rotors are in rotation, direct volume is reduced.
The capacity of a rotary screw compressor ranges between 20 tons up to 450 tons. The rotary screw compressor is controlled by a sliding inlet valve or variable speed drive.
Centrifugal Compression Industrial Chillers
One of the main features of the centrifugal compression industrial chiller is its ability to provide a high cooling capacity in a compact design. The centrifugal compression industrial chiller operates via an impeller, which is much like a water pump and compresses the refrigerant. Centrifugal compression chillers can have variable speed drives and inlet vanes.
The variable speed drives and inlet vanes regulate the control of the chilled water capacity. Centrifugal compression industrial chillers are high capacity and can handle 150 tons and up.
Frictionless Centrifugal Industrial Chillers
The design of frictionless centrifugal industrial chillers is much like a regular centrifugal design. They function using the same principles but have magnetic bearings, which eliminate the need for lubricants.
Frictionless centrifugal industrial chillers also feature variable-speed DC motors that are direct-drive and attached to the chiller. They have a capacity ranging from 60 tons to 300 tons.
Absorption Industrial Chillers
Unlike other industrial chillers that utilize a mechanical compressor, the absorption industrial chillers use a heat source as the driving force behind the refrigeration cycle and use two liquids with one to cool and one to absorb. The absorbent liquid is usually lithium bromide or ammonia, while the coolant is usually water. The absorbent and coolant are separated and recombined during the absorption cycle. The water changes phase easily due to the low-pressure conditions in the chiller. Water and the absorption liquid also function efficiently in industrial chillers because of their natural affinitive properties.
The refrigeration cycle begins with the heating of the combined liquids, which boils the water out of the absorption liquid at high pressure. In the next stage, refrigerant water vapor is passed to a condenser coil, where the heat is rejected, and the water vapor is phased into a high-pressure liquid. After which, the high-pressure liquid is passed along to the lower-pressure evaporator, where adiabatic flash evaporation returns the water to a gas. This process leads to the heat being absorbed from the water that needs to be chilled. In the final stage, the concentrated absorption liquid is directed back to be recombined with the lower pressure water vapors coming from the evaporator.
Chapter 4: Applications and Benefits of Air Cooled Industrial Chillers
This chapter will discuss the applications and benefits of air cooled chillers.
Applications of Air Cooled Industrial Chillers
For industrial operations, air cooled chillers are used to create heat through the use of friction, high-powered equipment, and furnaces or ovens. They are able to increase the lifespan of heavy-duty equipment by circulating cooled liquid through equipment to maintain their efficiency and productivity. Due to the fact that the food industry has strict regulations regarding the storage temperatures of ingredients and products, air cooled industrial chillers are used as a traditional cooling system for food. In the pharmaceutical field, medicines require using chilled water in the manufacturing process and precise temperature control. Industrial chiller systems have the accuracy and precision for the chilling process and can be central process chillers or compact process chillers.
The common types of pharmaceutical chillers are reciprocating, centrifugal, and absorption. In power generation, power plants generate a great amount of heat so as to produce electrical power. Due to this case, chillers are used to cool components and processes by absorbing the heat they generate. Medical instruments require precision temperature control. CT scanners, MRI scanners, and LINAC machines produce heat that has to be removed and controlled. Air cooled chillers are used to provide a constant source of cool temperatures. This is done in order to ensure the efficient operation of critical equipment.
Benefits of Air Cooled Industrial Chillers
Air cooled chillers can be brought quickly into installed systems,saving time and money. Installation teams require less time to install this type of chiller system, which can lead to significant upfront cost savings. Another benefit of air cooled chillers is that they have fewer assemblies to maintain as compared to water cooled systems. Without a condenser pump, a cooling tower, and other parts, these chillers require less maintenance than other systems with a more complex component structure. The air cooled chillers are ideal in an area prone to drought or that has a limited water supply as they provide a water-saving alternative to traditional water cooled systems. An air cooled chiller is able to eliminate the water requirement by cooling the process with ambient air instead of water, creating room for optimal performance. Air cooling systems do not modify the ambient humidity or temperature as compared to other chiller systems.
Drawbacks of Air Cooled Industrial Chillers
Air cooled chilled may encounter a shortened lifespan. This is because air cooled chillers reside outdoors, so they are exposed to environmental elements that could shorten their lifespan such as ice, rain, snow, wind, and hail. Finally, air cooled chillers have a high level of noise output as a result of the cooling fans.
Conclusion
Air cooled industrial chillers are refrigeration systems that cool fluids and work in tandem with the air handler system of a facility.
Air cooled industrial chillers are types of industrial chillers that rely on the use of fans to reject heat outside the building rather than relying on cooling towers and have four major parts, which are a compressor, an evaporator, a condenser, and an expansion valve.
Air cooled industrial chillers can be found in various types, which include portable air cooled chillers and industrial stationary air cooled chillers.
The working principle of air cooled industrial chillers is based on the absorption of heat from processed water. Once the air handler system uses up the water, it becomes warm and is returned to the chiller. The chiller’s evaporator is utilized to transfer heat away from the water.
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