chiller working

Introduction​
Chillers play a vital role in maintaining optimal temperatures in a wide range of settings, from large – scale industrial facilities and commercial buildings to data centers and hospitals. They work by removing heat from a fluid, typically water or air, and transferring it to another medium, thus cooling the targeted environment or process. There are several types of chillers, each with its own unique working principles and operational characteristics. Understanding how chillers work is essential for facility managers, engineers, and anyone involved in the design, operation, and maintenance of cooling systems.​

Vapor – Compression Chillers: The Most Common Type​
Working Principle​
The vapor – compression chiller operates based on the vapor – compression cycle, which consists of four main processes: compression, condensation, expansion, and evaporation. These processes work in a continuous loop to remove heat from the environment or substance that needs to be cooled.​
Compression: The cycle starts with the compressor, which is the heart of the vapor – compression chiller. The compressor takes in low – pressure, low – temperature refrigerant vapor and compresses it. During compression, the pressure and temperature of the refrigerant increase significantly. This is an adiabatic process, meaning that no heat is exchanged with the surroundings during the compression. The work done by the compressor on the refrigerant increases its internal energy, raising its temperature and pressure. For example, a reciprocating compressor uses a piston to compress the refrigerant within a cylinder, while a centrifugal compressor uses the centrifugal force generated by high – speed rotating impellers to compress the refrigerant.​
Condensation: The high – pressure, high – temperature refrigerant vapor then enters the condenser. In the condenser, the refrigerant releases heat to the surrounding environment or a secondary cooling medium, such as air or water. As the refrigerant loses heat, it condenses from a vapor state back into a liquid state. This is an isobaric process, as the pressure of the refrigerant remains relatively constant during condensation. For air – cooled condensers, fans are used to blow air over the condenser coils, facilitating heat transfer. In water – cooled condensers, a continuous flow of water is passed through the condenser tubes to absorb the heat from the refrigerant. For instance, in a large commercial building, a water – cooled condenser might use a cooling tower to dissipate the heat absorbed from the refrigerant into the atmosphere.​
Expansion: After condensation, the high – pressure liquid refrigerant passes through an expansion valve or device. The expansion valve reduces the pressure of the refrigerant abruptly. As the pressure drops, the refrigerant expands and its temperature decreases significantly. This is a throttling process, which is also adiabatic. The expansion valve controls the flow rate of the refrigerant, ensuring a proper supply to the evaporator. Some common types of expansion valves include thermostatic expansion valves, which adjust the flow rate based on the superheat of the refrigerant leaving the evaporator, and capillary tubes, which are simple and commonly used in smaller systems.​
Evaporation: The low – pressure, low – temperature liquid refrigerant then enters the evaporator. In the evaporator, the refrigerant absorbs heat from the fluid or space that needs to be cooled, such as chilled water in a building’s air – conditioning system or the interior of a cold storage room. As the refrigerant absorbs heat, it evaporates back into a vapor state. This is an isothermal process, as the temperature of the refrigerant remains constant during evaporation. The heat absorbed by the refrigerant in the evaporator is what effectively cools the surrounding medium. For example, in a refrigerated truck, the evaporator coils are placed inside the cargo area, and as the refrigerant evaporates, it absorbs heat from the air inside the truck, maintaining the desired low temperature for transporting perishable goods.​
Key Components and Their Functions​
Compressor: As mentioned, the compressor is responsible for increasing the pressure and temperature of the refrigerant. It consumes electrical energy to perform this work and is typically powered by an electric motor. The efficiency of the compressor has a significant impact on the overall performance of the chiller. Different types of compressors, such as reciprocating, scroll, screw, and centrifugal compressors, are used depending on the size, capacity, and application requirements of the chiller. For example, scroll compressors are often used in smaller – scale commercial air – conditioning chillers due to their compact size, quiet operation, and relatively high efficiency at part – load conditions.​
Condenser: The condenser’s main function is to transfer the heat absorbed by the refrigerant during the cooling process to the external environment or a secondary cooling medium. Its design, including the type of heat – transfer surface (e.g., finned tubes) and the choice of cooling medium (air or water), affects the rate of heat transfer and the overall efficiency of the chiller. Proper maintenance of the condenser, such as cleaning the coils regularly to remove dirt and debris, is essential to ensure optimal heat – transfer performance.​

Expansion Valve: The expansion valve regulates the flow of the refrigerant from the high – pressure side of the system (condenser) to the low – pressure side (evaporator). It also plays a role in reducing the pressure and temperature of the refrigerant. The accurate adjustment of the expansion valve is crucial for maintaining the proper balance between the refrigerant flow and the cooling demand, which in turn affects the chiller’s efficiency and performance.​
Evaporator: The evaporator is where the actual cooling process occurs. It absorbs heat from the medium being cooled and transfers it to the refrigerant. The design of the evaporator, such as its size, shape, and the type of heat – transfer surface, is optimized to maximize heat – transfer efficiency. For example, in a chilled – water system for a building, the evaporator cools the water, which is then circulated through the building’s air – handling units to cool the indoor air.​
Absorption Chillers: An Alternative Working Mechanism​
Working Principle​
Absorption chillers operate on a different principle compared to vapor – compression chillers. Instead of using mechanical compression to raise the pressure of the refrigerant, absorption chillers use a heat – driven process that involves the use of an absorbent and a refrigerant. The most common combination is water as the refrigerant and lithium bromide as the absorbent.​
Absorption: In the absorber, the low – pressure refrigerant vapor (water vapor in the case of water – lithium bromide systems) is absorbed by the absorbent (lithium bromide solution). This absorption process is exothermic, meaning it releases heat. The heat released during absorption is removed by a cooling medium, typically water, which is circulated through the absorber. As the refrigerant vapor is absorbed, a strong solution of refrigerant in the absorbent is formed.​
Regeneration (Desorption): The strong solution of refrigerant in the absorbent is then pumped to a generator. In the generator, heat is applied, usually from a source such as steam, hot water, or natural gas combustion. The heat causes the refrigerant to vaporize from the solution, a process known as desorption. This results in the separation of the refrigerant vapor from the absorbent, with the refrigerant vapor being at a higher pressure. The absorbent, now in a weaker state, is returned to the absorber for reuse.​
Condensation: Similar to vapor – compression chillers, the high – pressure refrigerant vapor from the generator enters the condenser. In the condenser, the refrigerant releases heat to the surrounding environment or a secondary cooling medium and condenses back into a liquid state.​
Expansion and Evaporation: The high – pressure liquid refrigerant then passes through an expansion valve, where its pressure and temperature are reduced. After expansion, the refrigerant enters the evaporator, where it absorbs heat from the fluid or space to be cooled, evaporating back into a vapor state. The low – pressure refrigerant vapor then returns to the absorber to complete the cycle.​
Advantages and Applications​
Absorption chillers have several advantages. They can be powered by heat sources, making them suitable for applications where there is an available waste – heat source, such as in industrial plants or combined heat and power (CHP) systems. This can lead to significant energy savings and increased overall system efficiency. Additionally, absorption chillers are generally quieter and have fewer moving parts compared to vapor – compression chillers, which reduces maintenance requirements. They are often used in large commercial buildings, hospitals, and industrial facilities where there is a need for cooling and a suitable heat source is available. For example, in a hospital that has a boiler system for heating, the waste heat from the boiler can be used to power an absorption chiller, providing an energy – efficient cooling solution.​
Other Types of Chillers and Their Working Features​
Magnetic Bearing Chillers​
Magnetic bearing chillers are a type of advanced vapor – compression chiller that use magnetic bearings instead of traditional mechanical bearings. In these chillers, the compressor’s shaft is levitated using magnetic fields, eliminating physical contact between the moving parts. This reduces friction and wear, resulting in higher efficiency, lower maintenance requirements, and quieter operation. The magnetic bearings are controlled by sophisticated electronic systems that continuously adjust the magnetic fields to maintain the proper position of the shaft. Magnetic bearing chillers are often used in large – scale commercial and industrial applications where high efficiency, reliability, and low – noise operation are critical, such as in data centers and high – rise office buildings.​

Scroll Chillers​
Scroll chillers use scroll compressors, which consist of two interleaved scrolls, one fixed and one orbiting. As the orbiting scroll moves, it creates a series of crescent – shaped chambers that gradually decrease in volume. The refrigerant vapor is drawn into these chambers, compressed as the volume decreases, and then discharged at a higher pressure. Scroll chillers are known for their compact size, quiet operation, and relatively high efficiency, especially at part – load conditions. They are commonly used in small – to medium – sized commercial air – conditioning systems, such as in restaurants, retail stores, and small office buildings.​
Adapting to Different Cooling Demands​
Chillers are designed to adapt to varying cooling demands in different applications. In commercial buildings, the cooling load can change significantly throughout the day depending on factors such as occupancy, weather conditions, and the use of internal equipment. To handle these variable loads, many chillers are equipped with control systems that can adjust the chiller’s capacity. For example, variable – speed drives can be used to control the speed of the compressor in a vapor – compression chiller, allowing it to operate at a lower capacity during periods of lower cooling demand, reducing energy consumption. In addition, some chillers can be operated in parallel, with multiple chillers working together to meet the total cooling load. The control system can then adjust the operation of each chiller based on the current demand, optimizing overall efficiency.​
In industrial applications, the cooling requirements may be more complex and specific. For example, in the manufacturing of semiconductors, precise temperature control is essential, and the cooling system needs to be able to respond quickly to changes in the process. Specialized chillers are designed with advanced control features and high – performance components to meet these demanding requirements. Some industrial chillers may also be designed to handle corrosive or high – purity fluids, depending on the nature of the industrial process.​
Conclusion​
Chillers are integral to modern cooling systems, and understanding how they work is fundamental to their effective use. Whether it’s the widely used vapor – compression chiller with its four – stage cycle, the heat – driven absorption chiller, or the more specialized types like magnetic bearing and scroll chillers, each has its own unique working principles and characteristics. By knowing how these chillers operate, from the role of key components to their ability to adapt to different cooling demands, facility managers, engineers, and operators can make informed decisions regarding chiller selection, operation, and maintenance. This knowledge ultimately leads to more efficient, reliable, and cost – effective cooling systems in a variety of applications.