Skip to content Skip to footer

How HVAC Chillers Work and their Importance

How HVAC Chillers Work and their Importance

Imagine stepping into a bustling commercial building on a scorching summer day, only to be greeted by a refreshing wave of cool air. Ever wondered how this comfort is maintained? The secret lies in the chiller. Today, we’ll be delving into what they are, how they work, and their proper maintenance. Understanding their main components and operational mechanics will shed light on how chillers keep our environments comfortable and efficient, and perhaps even help you improve the efficiency of the HVAC system in a large commercial or industrial building.

The Purpose of Chillers in HVAC Systems

All buildings generate unwanted heat from various sources, such as solar heat gain, occupants, and equipment. This makes air conditioning essential for maintaining comfort and efficiency. Smaller buildings often use A/C units, but for larger commercial or industrial buildings, centralized systems become more cost-effective and essential. Centralized systems utilize chillers, which are essentially large A/C units that operate differently, are more powerful, and are more complex to install and maintain. Chillers remove heat from a gas or liquid, typically water, and are crucial when it comes to circulating cool air throughout a building to maintain a comfortable environment in the warmer months.


Types of Chillers

One way to categorize chillers is by how they operate. Additionally, understanding the differences between air-cooled and water-cooled chillers helps in selecting the right system for different applications.

Air-Cooled Chillers:

Air-cooled chillers use ambient air to dissipate heat, and they are often employed in rooftop applications. They blow air across a condenser, much like an air conditioning unit, to disperse unwanted heat into the atmosphere. This method of heat dissipation makes them suitable for smaller buildings or locations where water is scarce. However, their efficiency can be lower in extremely hot climates since they rely on air temperature for cooling.

Water-Cooled Chillers

Water-cooled chillers use water from a cooling tower to remove heat. These chillers are typically used in larger buildings and industrial applications due to their high efficiency and ability to handle substantial cooling loads. They utilize cooling towers, which are specialized heat exchangers where water and air interact to lower the temperature of the water. Through the operation of cooling towers, some water evaporates, reducing the temperature of the fluid circulated back through the system. This process is essential in removing heat from a building space, process, or system. In a closed-circuit design, warm water containing heat from the building is pumped through a coil into the cooling tower, where it is cooled before being recirculated. Although water-cooled chillers require a consistent water source and regular cooling tower maintenance, their superior performance and energy efficiency often justify the investment.


Operation of HVAC Chillers

Before we get into their operation, it’s essential to understand the four main components of a chiller: the evaporator, condenser, compressor, and expansion valve. Each of these components plays a vital role in the chiller’s operation. In this section, we will take a look at how these four components interact with each other in the operation of HVAC chillers, and delve into their individual importance. Understanding these components helps in appreciating the complexity of chillers, and how they can efficiently maintain comfortable and controlled environments.

4 Main Components of Chillers

  1. Evaporator: The evaporator is where the cooling process begins. The refrigerant enters the evaporator as a low-pressure, low-temperature liquid. Inside, it absorbs heat from the chilled water loop, causing the refrigerant to evaporate into a gas. This phase change is essential as it allows the refrigerant to carry the absorbed heat away from the water. The evaporator is designed to maximize the surface area in contact with the refrigerant, enhancing the heat absorption efficiency.
  2. Condenser: After absorbing heat in the evaporator, the refrigerant, now a hot gas, moves to the condenser. The condenser’s role is to expel the absorbed heat to another medium, often water or air. This process cools the refrigerant back into a liquid state. The design of the condenser, similar to the evaporator, aims to maximize surface area contact, but in this case, to facilitate heat rejection. Effective heat exchange in the condenser is critical for the overall efficiency of the chiller system.
  3. Compressor: The compressor is the powerhouse of the chiller system. It compresses the refrigerant gas from the evaporator, increasing its pressure and temperature. This step is crucial because it prepares the refrigerant to release the absorbed heat in the condenser. Compressors come in various types, including centrifugal, screw, and reciprocating compressors, each suited for different applications and efficiency requirements.
  4. Expansion Valve: The expansion valve regulates the flow of refrigerant into the evaporator. It reduces the pressure and temperature of the refrigerant before it enters the evaporator, ensuring it can absorb maximum heat. The expansion valve is vital for maintaining the balance in the refrigeration cycle, preventing excess refrigerant from flooding the evaporator, and ensuring efficient operation


Step-by-Step Operation of HVAC Chillers

  1. Refrigeration Circuit Operation 
  • Function: The refrigeration circuit is a closed loop through which the refrigerant circulates. This circuit includes the evaporator, compressor, condenser, and expansion valve. The refrigerant absorbs heat in the evaporator, is compressed in the compressor, releases heat in the condenser, and is then expanded in the expansion valve before returning to the evaporator. This continuous loop allows the chiller to remove heat from the building or process efficiently.
  • Heat Transfer: The primary function of the refrigerant is to transfer heat. In the evaporator, the refrigerant absorbs heat from the chilled water, causing it to evaporate. In the condenser, the refrigerant releases this absorbed heat to another medium, typically water or air. This heat transfer process is what enables the chiller to cool the building or process effectively.


  1. Chilled Water Production in the Evaporator 
  • Process: Chilled water production starts in the evaporator. The refrigerant absorbs heat from the water, cooling it down to the desired temperature. This chilled water is then circulated through the building to provide cooling.
  • Temperature: The target temperature for the chilled water leaving the evaporator is typically around 6 degrees Celsius. This temperature is ideal for absorbing a significant amount of heat from the building while ensuring the efficiency of the refrigeration cycle.
  • Circulation: A centrifugal pump is used to circulate the chilled water through the building. This pump ensures that the chilled water reaches all areas that require cooling, maintaining a consistent and comfortable indoor environment. The design and capacity of the pump are critical for efficient water circulation and overall system performance.


  1. Heat Collection by Air Handling Units (AHUs)
  • Air Handling Units (AHUs): The chilled water is distributed through the building via air handling units (AHUs). These units are responsible for transferring the heat from the indoor air to the chilled water. AHUs contain coils through which the chilled water flows, absorbing heat from the air passing over these coils.
  • Heat Transfer: As the chilled water absorbs heat, its temperature increases. This process effectively removes unwanted heat from the indoor environment, contributing to a comfortable and controlled climate.


  1. Chilled Water Loop Cycle 
  • Heat Transfer: The heated water returns to the chiller carrying the absorbed heat. This return water is typically at around 12 degrees Celsius. The chiller then cools this water back down to 6 degrees Celsius in the evaporator, ready for another cycle of heat absorption.
  • Temperature Change: The temperature change from 12 degrees Celsius to 6 degrees Celsius represents the amount of heat the chilled water has absorbed from the building. This consistent temperature change is crucial for maintaining the efficiency and effectiveness of the chiller system.
  • Cycle: This process of heating and cooling the water repeats continuously, ensuring a constant removal of unwanted heat from the building. The reliability of this cycle is essential for the stable operation of the HVAC system.


  1. Heat Transfer from Evaporator to Condenser
  • Refrigerant Role: In the evaporator, the refrigerant absorbs the heat from the chilled water, evaporating in the process. The refrigerant, now a hot gas, carries this heat to the condenser.
  • Isolation: The refrigeration circuit and chilled water loop are completely isolated from each other. The heat is transferred between these two loops via the refrigerant, ensuring no direct mixing of the fluids and maintaining system efficiency and safety.


  1. Condenser Circuit: The Heat Rejection Process 
  • Heat Pickup: The condenser picks up heat from the refrigerant. This heat is then transferred to another medium, typically water or air, which is circulated through the condenser.
  • Heat Rejection: The heat is then expelled from the condenser, often through a cooling tower. The cooling tower uses air and water to dissipate the heat into the atmosphere.


  1. Cooling Tower: Heat Dissipation
  • Air Flow: A fan inside the cooling tower forces air over the water, enhancing the evaporation process to dissipate the heat into the atmosphere. The cooling tower design maximizes the contact between the water and the air, improving the efficiency of heat rejection.
  • Temperature Change: The water heated by the refrigerant releases its heat in the cooling tower, dropping from about 32 degrees Celsius to 27 degrees Celsius. This cooled water is then ready to return to the condenser to absorb more heat from the refrigerant.


  1. Repeat the Cycle from the Beginning
  • Heat Rejection: The cooled water returns from the cooling tower to the condenser ready to pick up more heat from the chilled water system. This continuous loop ensures a steady and reliable removal of unwanted heat from the building or process.

Cycle: This continuous cycle of absorbing and rejecting heat keeps the system running efficiently, maintaining a consistent and comfortable indoor environment. Proper maintenance and monitoring of this cycle are crucial for the longevity and efficiency of the chiller system.


The Importance of Chiller Maintenance

Chiller maintenance is crucial for ensuring the longevity and efficiency of HVAC systems. Regular maintenance helps prevent unexpected breakdowns, reduces energy consumption, and ensures optimal performance. Properly maintained chillers also have a longer lifespan, providing reliable cooling for commercial and industrial facilities.

Key Maintenance Tasks for Chillers

  1. Regular Inspections: Routine checks of the chiller components, including the evaporator, condenser, compressor, and expansion valve, to identify any wear and tear.
  2. Cleaning: Regular cleaning of heat exchangers, coils, and water circuits to prevent scaling, fouling, and blockages that can reduce efficiency.
  3. Lubrication: Ensuring all moving parts, such as bearings and motors, are properly lubricated to minimize friction and wear.
  4. Refrigerant Levels: Checking and maintaining the correct refrigerant levels to ensure efficient heat transfer and prevent system strain.
  5. Performance Testing: Conducting performance tests to ensure the chiller is operating within specified parameters and making necessary adjustments. 

Expert Maintenance Services

TRI-AIR SYSTEMS offers comprehensive chiller maintenance services tailored to meet the specific needs of each client. Their HVAC Proactive Maintenance Program includes detailed inspections, cleaning, and performance optimization. With 24/7 customer support and rapid response times, TRI-AIR SYSTEMS ensures minimal downtime and maximum efficiency for your HVAC systems. Their experienced technicians are skilled in handling all aspects of chiller maintenance, providing peace of mind and reliable cooling solutions.



Chillers are fundamental to maintaining comfortable and efficient environments in commercial and industrial buildings. Understanding how they work, their main components and the differences between air-cooled and water-cooled chillers is essential for selecting and managing the right system for your needs. Regular maintenance is critical to ensure optimal performance and longevity of these complex machines. Neglecting maintenance can lead to unexpected breakdowns, increased energy consumption, and shortened equipment life.

For expert chiller maintenance services, look no further than TRI-AIR SYSTEMS. Their comprehensive HVAC Proactive Maintenance Program includes detailed inspections, thorough cleaning, and performance optimization to keep your systems running smoothly. With 24/7 customer support and rapid response times, TRI-AIR SYSTEMS ensures minimal downtime and maximum efficiency for your HVAC systems. To learn more about their specific services and how they can help maintain your chillers, visit their HVAC maintenance page.

Ensure your chillers are in top condition and enjoy a comfortable indoor climate by partnering with TRI-AIR SYSTEMS today.