What is an Absorption Chiller?

Based on the principles of thermodynamics, an absorption chiller is a type of cooling system that utilizes heat energy instead of electricity to generate cooling. Unlike a conventional chiller that uses a compressor powered by electricity to produce cooling, an absorption chiller harnesses heat energy from various sources, such as solar power, waste heat, burning fuel, or other heat sources to provide cooling.

Two Common Substances of Absorption Chiller

Absorption chillers are used by the combination of two substances in their operations: a refrigerant and an absorbent. The most common solutions are Water/Lithium Bromide and Ammonia/Water. The solution of Water/Lithium Bromide when used at the temperature of 40°F or higher, works well making it suitable for air conditioning systems and the solution of Ammonia/Water is typically used for low-temperature applications like freezing.

Particular Advantages of Absorption Chiller

The absorption chillers hold a special advantage for the places that require constant cooling or have significant cooling demands included but not limited to hospitals, hotels, office buildings, and college campuses. Absorption chillers are also highly effective for industries that need cooling year-round, such as factories, cold storage warehouses, data centers and distinct energy systems.

Types of absorption cycles:

As we know absorption chillers use a closed-loop cycle of evaporation, absorption, generation, and condensation to create chilled water. Now we gonna discuss the cycles of two Common Substances used in the absorption chillers (Ammonia-Water Refrigeration CYCLE

& Lithium Bromide Refrigeration CYCLE)

Ammonia-Water Refrigeration CYCLE

Ammonia-Water Refrigeration CYCLE

In the Ammonia-Water Refrigeration Cycle, the Ammonia is used as a Refrigerant, and Water is used as an Absorbent. The reasons why Ammonia is used as a Refrigerant are as followed:

● Its pressure is very low when evaporated to produce the temperatures required for refrigeration.

● It condenses at pressures that are relatively too low.

● It carries much more heat per pound.

Ammonia is better at Transferring heat as compared to most other refrigerants and why is so because:

● It is non-corrosive to commonly used metals.

● It has a pungent odor that is easily detected by the human nose, so any leaks are easily detected.

● It is a completely naturally occurring chemical.

● It has zero ozone depletion potential and zero global warming potential, making it totally benign to

the environment.

The figure above represents the Ammonia-Water Refrigeration Cycle, where ammonia acts as the refrigerant, and water acts as the absorbent. Here's how it works:

In the absorber, there is a mixture of ammonia and water. This fluid is pumped to the generator where heat is added from an external source, like fire. This heat causes the ammonia to evaporate, while the water becomes concentrated and flows back to the absorber. At this point, the ammonia is at high pressure and high temperature.

Next, the high-pressure ammonia moves to the condenser and at this point, the ammonia releases heat to the surrounding environment. After this process, the ammonia becomes high pressure but the temperature is low.

In the next step, from the condenser, the ammonia passes through an expansion valve. After expansion, the ammonia turns into low-pressure and very low-temperature gas. After getting expanded, the ammonia turns into a gas with low-pressure and low-temperature. This low-temperature ammonia goes to the evaporator. In the evaporator, the ammonia cools it by absorbing heat from the surrounding environment.

Finally, the ammonia returns to the absorber, where it mixes with water again, and the cycle repeats. This entire process forms the Ammonia-Water Refrigeration Cycle, which produces cooling.

Lithium Bromide Refrigeration CYCLE

In Lithium Bromide Refrigeration Cycle Lithium bromide works as an absorbent and water is used as the refrigerant. Lithium bromide being a very strong salt solution has the ability to absorb water vapor easily. During the process, water evaporates at a very low pressure and low temperature. Since water evaporates faster and at a lower temperature compared to lithium bromide, water becomes the refrigerant, and lithium bromide acts as the absorbent. This combination helps the system create a cooling effect.

In the Lithium Bromide Refrigeration Cycle, the lithium bromide solution is mixed with water and sent to the generator where water evaporates .This creates high-pressure, high-temperature water vapor, while the concentrated lithium bromide solution goes back to the absorber.

The high-pressure and high-temperature water vapor then moves to the condenser. Here, cooling water from the cooling tower helps the water vapor release heat. After that, the water vapor flows to the evaporator.

In the evaporator, the water absorbs heat from the surroundings, cooling the environment. Then, the water goes back to the absorber, where it mixes with the lithium bromide solution again. This completes the cycle, and the process repeats.

Types of Absorption Chillers

As we know that the absorption chillers are used to cool spaces using heat instead of electricity. They are categorized based on how they work and the materials they use. Let’s get into the types , uses and other specifications.

It follows as:

1)Single-Effect Absorption Chillers

How They Work: They are used through one main step (stage) to produce cooling. In this step, water turns into vapor and mixes with a salt solution. This process consists of heat that is used to separate them and repeat the process.

Heat Source: Use low-temperature heat like waste heat or hot water.

Efficiency: Not very efficient compared to other types.

Where to Use: Small systems where cheap or low-energy heat sources are available.

2) Double-Effect Absorption Chillers

How They Work: They are used through two steps (generators) to recycle heat better and improve cooling.

Heat Source: Needs higher-temperature heat like steam or direct-fired gas.

Efficiency: Better than single-effect chillers.

Where to Use: Medium to large buildings like hospitals, offices, or factories.

3) Triple-Effect Absorption Chillers

How They Work: They are used through three steps for maximum cooling Efficiency: Each step in this uses heat more effectively and they are the most efficient chillers.

Heat Source: These chillers need very high-temperature heat like gas burners or industrial waste heat.

Where to Use: Big factories or places where saving energy is very important.

4) Water-Lithium Bromide (Li Br) Absorption Chillers

How They Work: They use water as the cooling material and lithium bromide (a salt) to absorb it.

Best For: Moderate temperatures (like air conditioning above 40°F/4°C).

Where to Use: Offices, hotels, hospitals, and large cooling systems.

Note: These chillers are environmentally safe but need careful maintenance because the salt is corrosive.

5) Ammonia-Water Absorption Chillers

How They Work: They use ammonia as the cooling material and water to absorb it.

Best For: Very cold temperatures (below -40°F/-40°C).

Where to Use: Cold storage, industrial freezers, and factories.

Note: These chillers are very effective but ammonia is toxic and needs careful handling.

6) Direct-Fired Absorption Chillers

How They Work: They are used by burning fuel directly (like gas or oil) to provide heat for the cooling process.

Heat Source: Comes directly from burning fuel.

Where to Use: Standalone buildings where electricity is expensive or fuel is easily available.

Note: These chillers are flexible and don't need extra heat equipment.

7) Indirect-Fired Absorption Chillers

How They Work: They use heat from outside sources like steam, hot water, or waste heat.

Heat Source: External heat, such as from a boiler or industrial process.

Where to Use: Power plants, industries, or places with excess heat.

Note: These chillers are the best for using leftover heat, saving energy.

Working of Absorption Chiller

Connection Between Boiler and Generator

Piping from Boiler to Generator:

Pipes carry hot water or steam generated by the boiler. This heat energy is directed to the generator in the absorption chiller.

Function of the Generator:

Inside the generator, there is a lithium bromide (LiBr) solution in a diluted form.

The heat provided by the boiler causes the water (acting as the refrigerant) to evaporate and separate from the lithium bromide solution.

After Separation:

The water vapor continues to the condenser. The remaining concentrated lithium bromide solution flows to the absorber for reuse.

Connection of Condenser to Cooling Tower

High-Pressure Water Flow to Condenser:

The water vapor from the generator (produced by the evaporation process) reaches the condenser.

In the condenser, cooling water supplied by the cooling tower absorbs the heat from the refrigerant .

Condensation Process:

The refrigerant water vapor loses heat to the cooling water.

It condenses back into liquid form, preparing it for the evaporation stage.

Cooling Tower Role:

The heated cooling water is sent back to the cooling tower, where it is cooled and recycled back to the condenser.

Connection to Evaporator

Refrigerant Water from Condenser to Evaporator:

The cooled refrigerant water from the condenser flows to the evaporator.

Inside The Evaporator:

The refrigerant absorbs heat from chilled water coming from the Air Handling Unit (AHU). This causes the refrigerant water temprature increase .

Chilled Water Loop:

• Water from the AHU (used to cool indoor spaces) enters the evaporator.
• The refrigerant absorbs heat from this chilled water, reducing its temperature further.
• The chilled water is then sent back to the AHU for air cooling.

Absorption and Reuse of Lithium Bromide Solution

Flow of Concentrated Lithium Bromide:

• After the refrigerant water evaporates, the concentrated lithium bromide solution returns to the absorber.
• In the absorber, the refrigerant water vapor is reabsorbed into the lithium bromide solution, creating a diluted solution again.
• The diluted solution is pumped again to the generator, completing the cycle.

Applications of Absorption Chillers

Absorption chillers are special machines that use heat instead of electricity to make things cool. They are useful in many places because they save energy and are good for the environment. Here’s where they are commonly applications:

1)Commercial Buildings

Examples: Offices, Hotels, Hospitals, Shopping Malls.

Reason for Use:

● Provides energy-efficient cooling for large spaces.

● Utilizes waste heat from boilers, generators, or solar power.

● Reduces electricity costs compared to conventional chillers.

Benefits: Absorption chillers are quieter than other cooling systems, have lower environmental impact, and integration with district cooling systems.

2)Industrial Facilities

Examples: Factories, Manufacturing Plants, Petrochemical Units.

Reason for Use:

● Utilizes waste heat to drive the chiller, reducing energy waste.

● Maintains stable temperatures for machinery and processes.

Benefits: Cost savings, reduced reliance on grid electricity, and better utilization of industrial byproducts.

3) Data Centers

Reason for Use:

● Keeps servers and IT equipment cool so they work properly and don't overheat.

● Works well in areas with high cooling needs e.g data centers or large computer spaces

Benefits: Runs all the time with less chances of prevention and uses adequate energy for the environment.

4) Cold Storage and Warehousing

Examples: Food Storage, Pharmaceutical Storage, and Distribution Facilities.

Reason for Use:

● Provides low-temperature cooling required for preserving perishable goods.

● Ammonia-water absorption chillers are ideal for such kinds of applications due to their ability to reach very low temperatures.

Benefits: Eco-friendly and energy-efficient cooling for large-scale operations.

5) Power Plants

Reason for Use:

● Recovers waste heat from turbines or exhaust gases to drive the cooling system.

● Maintains optimal working conditions for equipment.

Benefits: Improved efficiency, reduced operational costs, and better utilization of resources.

6) District Cooling Systems

Examples: Urban Residential Areas, University Campuses.

Reason for Use:

● Centralized cooling plants distributing chilled water to multiple buildings.

● Absorption chillers efficiently handle large-scale cooling demands using renewable or waste heat.

Benefits: Energy efficiency, scalability, and reduced environmental footprint.

7) Renewable Energy Integration

Examples: Solar-Powered Cooling Systems.

Reason for Use:

As a fuel, solar thermal energy is used for absorption chillers .

Benefits: Sustainable cooling solutions with minimal carbon emissions.

8) Transportation

Examples: Marine Vessels and Trains.

Reason for Use:

Absorption chillers use the heat produced by engines that would otherwise be wasted.

Benefits: Efficient energy usage and reduced fuel consumption.

9) Specialized Applications

Examples:

● Chemical and pharmaceutical industries for controlled environments.

● Breweries and distilleries for maintaining fermentation temperatures.

Reason for Use: Consistent and efficient cooling for temperature-sensitive processes.

Benefits: Improved product quality and process reliability.

Operation and Maintenance Tips for Absorption Chillers

In support to a comprehensive approach to predictive maintenance in cooling equipment and keeps it operating reliably and efficiently, here are some simple tips to operate and maintain an absorption chiller effectively:

Operation Tips

Check the Heat Source Regularly:

● Ensure that the hot water, steam, or waste heat used to power the chiller is consistent and at the right temperature.

● Excess or deficiency in heat can affect how the chiller works.

Monitor Pressure Levels:

● Keep an eye on the vacuum pressure inside the chiller.

● If the pressure is too high or too low, the chiller may not cool properly.

Control Cooling Water Flow:

● Make sure the water flow from the cooling tower is steady.

● Proper cooling water flow helps remove extra heat and keeps the system efficient.

Keep the Refrigerant Levels Right:

● Ensure there’s enough refrigerant (like water or ammonia) and absorbent (like lithium bromide).

● Low levels can stop the chiller from working properly.

Start and Stop Smoothly:

● Follow the manufacturer's instructions to turn the chiller on and off.

● Avoid sudden starts or stops, as they can damage the system.

Maintenance Tips

Clean the Heat Exchangers:

● Dirt and scaling can build up in the heat exchangers over time.

● Regular cleaning ensures heat is transferred efficiently.

Inspect for Leaks:

● Check pipes, joints, and seals for any signs of leaks, especially in ammonia-based chillers.

● Fixing leaks earlier prevents major issues.

Maintain the Vacuum System:

● The chiller works under a vacuum, so ensure there are no air leaks.

● Air can disrupt the system and reduce cooling performance.

Prevent Corrosion:

● Lithium bromide systems can cause rust if not properly maintained.

● Use anti-corrosion chemicals as recommended by the manufacturer.

Monitor Cooling Tower Water Quality:

● Poor water quality can lead to scaling and fouling.

● Regularly test and treat the cooling tower water to keep the system running smoothly.

Check Pumps and Valves:

● Make sure all pumps and valves are working correctly and not clogged.

● If they are broken or blocked, the system won’t work properly.

Schedule Regular Inspections:

Get a professional to check the system often.

This helps find and fix problems early and makes the chiller last longer.