Exploring the Different Types of HVAC Chillers in Buildings.

When it comes to maintaining a comfortable indoor environment in buildings, especially in warmer climates or during scorching summers, HVAC (Heating, Ventilation, and Air Conditioning) systems play a pivotal role.

Among the crucial components of HVAC systems, chillers stand out as key players in cooling large commercial and residential spaces efficiently. These units work tirelessly behind the scenes to keep the temperatures pleasant and the atmosphere conducive.

In this article, we delve into the various types of HVAC chillers commonly found in buildings, elucidating their functionalities and applications.

What are HVAC chillers?

HVAC chillers are essential components in heating, ventilation, and air conditioning (HVAC) systems, primarily used for cooling large buildings or spaces. They work by removing heat from a liquid refrigerant to cool air or water, which is then circulated through the building to regulate temperature.

Chillers typically consist of four main components:

Compressor: This component is responsible for compressing the refrigerant gas, raising its temperature and pressure.

Condenser: The hot, high-pressure refrigerant gas flows into the condenser, where it is cooled down and condensed into a liquid. This process releases heat into the surrounding environment.

Expansion Valve: The liquid refrigerant passes through an expansion valve, which reduces its pressure and temperature, causing it to partially vaporise.

Evaporator: In the evaporator, the partially vaporised refrigerant absorbs heat from the surrounding air or water, cooling it down. The refrigerant then returns to the compressor to restart the cycle.

Chillers are crucial for maintaining comfortable indoor temperatures in large buildings like offices, hospitals, hotels, and shopping malls, as well as for industrial processes that require precise temperature control.

Let’s discuss the types of HVAC chillers below!

Air-Cooled Chillers.

An air-cooled chiller is a type of chiller that uses air as the primary method for removing heat from the refrigerant during the cooling process. These chillers are commonly used in situations where water availability or cost is a concern, or where it is impractical to use water-cooled systems.

Here’s how an air-cooled chiller typically operates:

1. Evaporator: The refrigerant enters the evaporator coil as a low-pressure, low-temperature liquid. As it flows through the coil, it absorbs heat from the water or air passing over the coil, causing the refrigerant to evaporate into a gas.
2. Compressor: The low-pressure refrigerant vapor is then drawn into the compressor, which increases its pressure and temperature. This compresses the gas into a high-pressure, high-temperature state.
3. Condenser: The hot, high-pressure refrigerant vapor then flows into the condenser coil, where it releases heat to the surrounding air. Air-cooled chillers use fans to blow ambient air over the condenser coils, transferring heat from the refrigerant to the air. As the refrigerant cools, it condenses back into a liquid state.
4. Expansion Valve: The high-pressure liquid refrigerant then passes through an expansion valve, which reduces its pressure and temperature, preparing it to re-enter the evaporator coil and complete the cooling cycle.

Air-cooled chillers are often used in commercial and industrial applications where a continuous supply of water for cooling is not readily available or where water consumption and disposal are concerns. They are commonly found in office buildings, data centres, manufacturing plants, hospitals, and hotels. Additionally, air-cooled chillers are generally easier to install and maintain compared to water-cooled systems, as they do not require a separate cooling tower or water circulation system.

However, they may be less energy-efficient than water-cooled chillers in certain conditions, particularly in hot climates where ambient air temperatures are high.

Water-Cooled Chillers.

Water-cooled chillers are another type of chiller used in heating, ventilation, and air conditioning (HVAC) systems, as well as in various industrial processes. Unlike air-cooled chillers, which dissipate heat directly to the ambient air, water-cooled chillers use water as the primary medium for removing heat from the refrigerant during the cooling process.

Here’s how a typical water-cooled chiller operates:

1. Evaporator: The process begins with the low-pressure, low-temperature liquid refrigerant entering the evaporator coil. As it flows through the coil, the refrigerant absorbs heat from the water circulating through the evaporator. This causes the refrigerant to evaporate into a low-pressure vapor.
2. Compressor: The low-pressure vapor is then drawn into the compressor, where it is compressed to a high-pressure, high-temperature state. This process increases the energy and temperature of the refrigerant vapor.
3. Condenser: The hot, high-pressure refrigerant vapor then flows into the condenser coil. In water-cooled chillers, the condenser coil is typically cooled by circulating water. The water absorbs the heat from the refrigerant, causing it to condense back into a liquid state. The heated water is then discharged from the chiller and sent to a cooling tower or other heat rejection system, where it releases the absorbed heat to the atmosphere through evaporation or other means.
4. Expansion Valve: After the refrigerant has been condensed back into a liquid, it passes through an expansion valve, which reduces its pressure and temperature. This prepares the refrigerant to re-enter the evaporator coil and repeat the cooling cycle.

Water-cooled chillers are commonly used in large commercial and industrial applications where a continuous supply of water is available for cooling purposes. They are often more energy-efficient than air-cooled chillers, particularly in environments with high ambient temperatures, as water is a more efficient heat transfer medium than air.

However, water-cooled chillers require additional infrastructure for water circulation and cooling, such as cooling towers or other heat rejection systems, which can increase installation and maintenance costs.

Absorption Chillers.

Absorption chillers are a type of chiller that operates on a different principle compared to conventional mechanical compression chillers. Instead of using a mechanical compressor to raise the pressure and temperature of the refrigerant, absorption chillers use a heat source to drive the cooling process.

Here’s how an absorption chiller typically operates:

1. Absorption Process: The absorption process in absorption chillers involves absorbing a refrigerant vapor into a liquid absorbent. This occurs in an absorber where the refrigerant vapor comes into contact with the absorbent. The refrigerant vapor is absorbed into the liquid absorbent, forming a concentrated refrigerant solution.
2. Desorption (or Regeneration) Process: After the refrigerant is absorbed into the absorbent, the concentrated refrigerant solution is then heated, typically by a heat source such as steam or hot water. This heat causes the refrigerant to evaporate from the absorbent, separating it from the absorbent solution. This process is sometimes referred to as desorption or regeneration.
3. Condensation: The refrigerant vapor produced during the desorption process is then condensed back into a liquid state. This is usually achieved by passing the refrigerant vapor through a condenser cooled by water or air.
4. Expansion Valve: The high-pressure liquid refrigerant then passes through an expansion valve, which reduces its pressure and temperature, preparing it for the next cycle of absorption and desorption.

Absorption chillers are particularly advantageous in applications where waste heat or low-grade heat sources are readily available, such as industrial processes, cogeneration systems, or waste heat recovery applications. They can utilise heat from various sources such as natural gas, steam, hot water, or solar energy to drive the cooling process, making them more energy-efficient in certain scenarios compared to traditional mechanical compression chillers.

Additionally, absorption chillers do not require mechanical compressors, resulting in quieter operation and lower maintenance requirements. However, absorption chillers tend to have lower cooling capacities and efficiencies compared to mechanical compression chillers, particularly at higher cooling loads.

They also typically have higher initial costs and larger physical footprints. Nonetheless, their unique operating principle and ability to utilise waste heat make them valuable in specific applications where energy efficiency and sustainability are priorities.

Centrifugal Chillers.

Centrifugal chillers are a type of chiller that uses a centrifugal compressor to compress the refrigerant vapor and achieve cooling. They are commonly used in large commercial and industrial HVAC systems due to their high cooling capacity, efficiency, and reliability.

Here’s how a centrifugal chiller typically operates:

1. Evaporation: The refrigerant enters the evaporator coil as a low-pressure, low-temperature liquid. As it flows through the evaporator, it absorbs heat from the chilled water circulating through the coil. This causes the refrigerant to evaporate into a vapor.
2. Compression: The low-pressure refrigerant vapor is then drawn into the centrifugal compressor. Inside the compressor, the refrigerant vapor is accelerated by a high-speed rotating impeller. As the vapor moves through the compressor, it is compressed to a high-pressure, high-temperature state.
3. Condensation: The hot, high-pressure refrigerant vapor exits the compressor and flows into the condenser coil. In the condenser, the refrigerant releases heat to the surrounding water or air, causing it to condense back into a liquid state.
4. Expansion Valve: After the refrigerant has been condensed, it passes through an expansion valve, which reduces its pressure and temperature. This prepares the refrigerant to re-enter the evaporator coil and repeat the cooling cycle.

Overall, centrifugal chillers are an excellent choice for applications requiring high cooling capacity, efficiency, and reliability, particularly in large commercial and industrial settings.

Scroll Chillers.

Scroll chillers are a type of chiller commonly used for commercial and industrial cooling applications. They operate based on the scroll compressor technology, which is known for its efficiency and reliability. Here’s how scroll chillers work:

1. Scroll Compressor: The heart of a scroll chiller is the scroll compressor. This compressor consists of two interleaving spiral-shaped scrolls—one fixed and one orbiting. As the orbiting scroll moves in a circular motion, it compresses the refrigerant vapor trapped between the scrolls. This compression process raises the pressure and temperature of the refrigerant.
2. Refrigeration Cycle: The high-pressure, high-temperature refrigerant vapor then moves to the condenser. In the condenser, the refrigerant releases heat to the surroundings (either air or water), causing it to condense into a high-pressure liquid.
3. Expansion Valve: The high-pressure liquid refrigerant then passes through an expansion valve, which reduces its pressure and temperature. This prepares the refrigerant for the next stage of the cycle.
4. Evaporator: The low-pressure, low-temperature liquid refrigerant enters the evaporator, where it absorbs heat from the chilled water or air circulating through the system. This absorption of heat causes the refrigerant to evaporate into a low-pressure vapor.
5. Return to Compressor: The low-pressure refrigerant vapor is then drawn back into the scroll compressor to restart the cycle.

Scroll chillers are known for their smooth and quiet operation, thanks to the scroll compressor’s design, which produces minimal vibration. They are also highly efficient, making them suitable for applications where energy savings are important. Additionally, scroll chillers typically require less maintenance compared to other types of chillers, contributing to lower operating costs over time.

Scroll chillers are commonly used in various settings, including office buildings, hotels, hospitals, data centres, and industrial facilities, for air conditioning, process cooling, and other cooling needs. Their compact size, efficiency, and reliability make them a popular choice for many cooling applications.

Final Thoughts.

HVAC chillers are indispensable components of modern buildings, ensuring optimal comfort and climate control year-round. Understanding the different types of HVAC chillers and their respective applications is crucial for architects, engineers, and building owners seeking to design and maintain efficient HVAC systems.

Whether it’s air-cooled, water-cooled, absorption, centrifugal, or scroll chillers, each type offers unique advantages tailored to specific building requirements and environmental considerations, paving the way for sustainable and comfortable indoor spaces.

If you’re looking for a company that offers Heating, Ventilation and Air Conditioning maintenance, design and installation services across the West Midlands, London, and surrounding areas, contact Mid-Tech Services today. Or if you have any questions regarding the types of HVAC chillers, we’d love to hear from you!

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