What is an Absorption Chiller? How Does it Work?

In today’s eco-conscious world, where energy efficiency and sustainability are at the forefront of technological advancements, innovative technologies are continuously reshaping various industries. One such technology that has gained considerable attention in recent years is the absorption chiller. Unlike conventional cooling systems that rely on electricity-driven compressors, absorption chillers harness the power of heat to provide efficient and environmentally friendly cooling solutions. This guide delves into the nuances of absorption chillers, explaining their operation, types, applications, benefits, and considerations for selection.

What is an Absorption Chiller?

An absorption chiller is a refrigeration system that relies on a heat source to drive the cooling process, rather than mechanical energy. This type of chiller uses a thermal cycle that involves a refrigerant and an absorbent. It is distinguished from more common vapor-compression chillers by its use of heat energy (from steam, hot water, or combustion) instead of mechanical energy. They consist of four main components: evaporator, absorber, generator, and pump. The system uses a refrigerant-absorbent pair, such as water-lithium bromide or ammonia-water, to transfer heat and generate cooling.

How Do Absorption Chillers Work?

Absorption chillers operate on the principle that certain substances can absorb a large amount of heat when they change their physical state or when they dissolve in another substance. The cycle typically involves four main processes:

  1. Evaporation: The refrigerant, usually water being stored in the absorber, evaporates at low pressure in the evaporator unit, absorbing heat from the surrounding environment. This causes the temperature of the environment to drop, thus producing a cooling effect.
  2. Absorption: The vaporized refrigerant is then absorbed by a liquid absorbent, commonly a solution of lithium bromide or, in some systems, ammonia. This absorption process helps maintain the low pressure necessary for evaporation to continue.
  3. Regeneration: The diluted absorbent solution is then pumped into the generator where it is heated. The heat causes the refrigerant to boil off from the absorbent solution, and the vapor is then sent to the condenser.
  4. Condensation: In the condenser, the refrigerant vapor releases its heat to the outside environment and condenses into a liquid. This liquid refrigerant then flows back to the evaporator, completing the cycle.

This continuous cycle, driven by heat, makes absorption chillers unique in leveraging thermal energy to produce cooling.

Types of Absorption Chillers

Absorption chillers come in various types, each differing primarily in their configuration and the number of stages involved in the absorption refrigeration cycle. The primary types of absorption chillers include single-effect, double-effect, and triple-effect chillers. Let’s explore each type:

  • Single-Effect Absorption Chillers: These chillers are the simplest and most common type of absorption chillers, making them easier to install and maintain. They use a single stage of absorption and have lower efficiency compared to multi-stage chillers. They are typically used in small-scale applications and can be indirect-fired (using steam or hot water) or direct-fired (using gas or oil burners) to provide the necessary heat for refrigerant vaporization.
  • Double-Effect Absorption Chillers: These chillers use two stages of absorption, resulting in higher efficiency and capacity compared to single-effect chillers by utilizing heat more effectively. They are typically used in large-scale applications and can be indirect-fired or direct-fired. However, they have a more complex design with additional components, leading to higher installation and maintenance costs.
  • Triple-Effect Absorption Chillers: These chillers have three generators (high-, medium-, and low-pressure), one absorber, one condenser, and one evaporator. They offer even higher efficiency and capacity among the three types, making them suitable for applications where maximizing energy savings is crucial such as industrial-scale applications. They are less common and are the most complex and expensive type of absorption chillers due to the additional stages and components involved.

Each type of absorption chiller offers distinct advantages and is suitable for different applications based on factors such as efficiency requirements, available heat sources, and budget constraints. Understanding the characteristics and operation of single-effect, double-effect, and triple-effect absorption chillers is essential for selecting the most appropriate solution for specific cooling needs.

Uses of Absorption Chillers

Absorption chillers have diverse applications across various industries and settings. Some of the key applications of absorption chillers include:

  1. Refrigeration: Absorption chillers are commonly used in refrigeration applications in industries such as the oil and petroleum industry, chemical industry, and food processing. They provide efficient cooling solutions without the need for mechanical energy, making them suitable for refrigeration needs in different sectors.
  2. HVAC Systems: Absorption chillers are integral components of heating, ventilation, and air conditioning (HVAC) systems in commercial buildings, industrial plants, hospitals, hotels, and large office buildings. They offer reliable and energy-efficient cooling solutions for space conditioning and air conditioning requirements.
  3. Solar Cooling: Absorption chillers are utilized in solar-driven cooling systems, where they can be powered by solar thermal energy. By harnessing solar energy, absorption chillers provide sustainable and environmentally friendly cooling solutions for various applications, including cold storage warehouses and district energy plants.
  4. Geothermal Applications: Absorption chillers can utilize thermal energy extracted from geothermal sources as a heat source instead of relying on the combustion of fossil fuels. This application demonstrates the versatility of absorption chillers in utilizing renewable energy for cooling purposes, contributing to energy efficiency and sustainability.
  5. Combined Heat and Power (CHP) Systems: Absorption chillers are integrated into CHP systems to provide air conditioning, refrigeration, and process fluid cooling in commercial buildings and industrial plants. They are often exhaust-fired using thermal energy recovered from CHP prime movers, making them an essential component of energy-efficient CHP applications.

These applications highlight the versatility and efficiency of absorption chillers in meeting cooling needs across a wide range of industries and settings, from industrial processes to commercial buildings and renewable energy systems.

Benefits of Absorption Chillers

The primary advantages of absorption chillers include:

  • Energy Efficiency: By using heat as their primary energy source, these chillers can significantly reduce the electrical consumption associated with cooling. In certain applications, waste heat can entirely replace the need for electrical input, leading to exceptional energy savings.
  • Reduced Environmental Impact: They contribute to lower greenhouse gas emissions by optimizing energy use and potentially using renewable energy sources such as solar thermal collectors. This creates a sustainable cooling solution that leverages the power of the sun, minimizing dependence on non-renewable resources.
  • Cost-effectiveness: Particularly in scenarios with ready access to waste heat, the operational costs of absorption chillers can be notably lower than those of traditional systems. This translates to significant financial benefits over the lifespan of the chiller.
  • Lower Maintenance Needs: Absorption chillers typically have fewer moving parts compared to electric chillers. This translates to less wear and tear, leading to lower maintenance requirements and reduced downtime. However, they still require regular maintenance to ensure optimal performance and longevity.
  • Flexibility: Absorption chillers can be powered by various heat sources, including steam, hot water, natural gas, and solar energy. This makes them suitable for diverse cooling needs across industries.
  • Low noise and vibration: Absorption chillers operate at lower noise levels compared to conventional chillers, making them suitable for applications such as hospitals, hotels, and office buildings where noise reduction is essential.

In a nutshell, absorption chillers offer a compelling value proposition beyond just basic energy efficiency. Their ability to harness waste heat, reduce environmental impact, and provide operational advantages makes them a sustainable and cost-effective choice for a wide range of cooling applications. When considering a cooling solution, carefully evaluating the potential benefits of absorption chillers alongside traditional electric chillers can lead to a more sustainable and cost-conscious decision for your specific needs.

Choosing the Right Absorption Chiller

Choosing the right absorption chiller requires careful consideration of several factors. Here are some key points to consider:

  1. Heat Source: Absorption chillers can be powered by various heat sources, such as natural gas, steam, hot water, or waste heat. Identify the available heat source and its temperature, as it will significantly impact the efficiency and performance of the absorption chiller.
  2. Cooling Capacity: Determine the cooling capacity required for your application. Absorption chillers are available in a wide range of cooling capacities.
  3. Energy Efficiency: Absorption chillers have lower energy efficiency compared to vapor compression systems. However, they can be more energy-efficient in applications where waste heat is available, as they can utilize this heat instead of electricity to drive the cooling process.
  4. Space Requirements: Absorption chillers are generally larger and heavier than vapor compression systems. Ensure that you have sufficient space and structural support for the absorption chiller before purchasing.
  5. Maintenance: Absorption chillers have fewer moving parts, which can lead to lower maintenance requirements. However, they still require regular maintenance to ensure optimal performance and longevity.
  6. Noise and Vibration: Absorption chillers produce less noise and vibration due to the lack of a compressor. This can be a critical factor in certain environments.
  7. Refrigerant Type: Absorption chillers use low Global Warming Potential (GWP) refrigerants, which can be an advantage in terms of environmental impact.
  8. Cost: The capital cost of absorption chillers is generally higher than vapor compression systems. However, the operating costs can be lower due to the use of waste heat and lower electricity consumption.
  9. Regulations and Standards: Ensure that the absorption chiller complies with local regulations and standards related to energy efficiency, safety, and environmental impact.

By carefully evaluating these factors, you can choose the right absorption chiller for your specific needs and application. It is also recommended to consult with HVAC experts or manufacturers to ensure that you make an informed decision.


Absorption chillers are a promising cooling technology, offering efficient, sustainable, and flexible solutions for various applications. By understanding the fundamentals of absorption chillers, their working principles, types, uses, benefits, and selection criteria, industry professionals can make informed decisions when selecting and implementing absorption chiller systems. As the demand for energy-efficient and environmentally friendly cooling solutions continues to grow, absorption chillers are poised to play a significant role in the future of cooling technology.