What Is a Vapour Absorption Chiller

What Is a Vapour Absorption Chiller? (Complete HVAC Guide)

That’s where a Vapour Absorption Chiller (VAC) comes in.

In this fully guide, you will learn:

• What a vapour absorption chiller is

• How it works

• Main components

• Working cycle explained step-by-step

• Types of absorption chillers

• Lithium bromide vs ammonia systems

• Advantages and disadvantages

• Applications in HVAC and industry

• Efficiency comparison with vapour compression chillers

• When to choose absorption technology

Let’s start with the basics.

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What Is a Vapour Absorption Chiller?

A vapour absorption chiller (VAC) is a cooling machine that uses heat energy instead of mechanical energy (compressor) to produce chilled water.

Unlike conventional chillers that use electric compressors, absorption chillers use:

• Steam

• Hot water

• Waste heat

• Gas burners

The system operates using a refrigerant–absorbent combination, most commonly:

• Water + Lithium Bromide (LiBr)

• Ammonia + Water

In simple terms:

A vapour absorption chiller converts waste heat into cooling.

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Vapour Absorption vs Vapour Compression Chiller

Absorption chillers are ideal when waste heat is available.

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Main Components of a Vapour Absorption Chiller

A vapour absorption system consists of:

1.  Generator
2.  Condenser
3.  Evaporator
4.  Absorber
5.  Pump
6.  Expansion Valve

Let’s understand each.

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1. Generator

• Heat source applied here.

• Refrigerant separates from absorbent.

Example: Steam heats lithium bromide solution.

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2. Condenser

• Refrigerant vapour condenses into liquid.

• Heat rejected to cooling water.

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3. Evaporator

• Liquid refrigerant absorbs heat from chilled water.

• Produces cooling effect.

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4. Absorber

• Refrigerant vapour absorbed back into solution.

• Heat released and removed via cooling water.

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5. Solution Pump

• Circulates absorbent solution.

• Uses very low electricity.

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Working Principle of Vapour Absorption Chiller (Step-by-Step)

Let’s break it down simply:

Step 1: Heat Input

Steam or hot water heats the generator.

Step 2: Refrigerant Separation

Refrigerant vapour separates from absorbent solution.

Step 3: Condensation

Vapour moves to condenser and becomes liquid.

Step 4: Evaporation

Liquid refrigerant evaporates in evaporator, absorbing heat and producing chilled water.

Step 5: Absorption

Refrigerant vapour absorbed into absorbent.

Step 6: Cycle Repeats

Solution pumped back to generator.

This continuous cycle produces chilled water.

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Types of Vapour Absorption Chillers

1. Single-Effect Absorption Chiller

•  Uses one generator
• Lower efficiency
•  Suitable for low-pressure steam

COP: 0.6 – 0.8

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2. Double-Effect Absorption Chiller

•  Two generators
•  Higher efficiency
•  Requires high-temperature heat source

COP: 1.0 – 1.2

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3. Direct-Fired Absorption Chiller

•  Uses gas burner
•  No external steam needed
•  Higher operating cost

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Lithium Bromide vs Ammonia Absorption Systems

Lithium Bromide (LiBr + Water)

•  Most common
•  Used in HVAC comfort cooling
•  Operates under vacuum
•  Water acts as refrigerant

Limitation: Cannot operate below 0°C

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Ammonia + Water System

•  Used in industrial refrigeration
•  Can operate below 0°C
•  More complex
•  Ammonia is toxic

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Applications of Vapour Absorption Chillers

Absorption chillers are widely used in:

• Power plants

• Refineries

• Chemical plants

• Hospitals

• Large hotels

• District cooling systems

• Cogeneration (CHP) plants

They are especially useful where waste heat is available.

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Advantages of Vapour Absorption Chillers

•  Low electricity consumption
•  Uses waste heat
•  Environmentally friendly
•  Quiet operation
•  Low vibration
•  Suitable for large capacities

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Disadvantages of Vapour Absorption Chillers

•  High initial cost
•  Large size
•  Lower COP than compression chillers
•  Complex maintenance
•  Requires cooling tower

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Energy Efficiency (COP Comparison)

• Vapour Compression COP: 3 – 6

• Single Effect Absorption COP: 0.6 – 0.8

• Double Effect Absorption COP: 1.0 – 1.2

Although absorption COP is lower, overall energy savings occur if waste heat is used.

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When Should You Choose Vapour Absorption Chiller?

Choose VAC if:

1.  Waste steam available
2. Power plant or CHP system present
3.  Electricity cost is high
4. Large industrial facility
5.  Environmental sustainability is priority

Avoid VAC if:

1.  No heat source available
2.  Small commercial building
3.  Limited installation space

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Cost of Vapour Absorption Chiller (India)

Cost depends on type and brand.

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Maintenance Requirements

•  Regular vacuum check
•  Lithium bromide concentration monitoring
•  Cooling tower maintenance
•  Heat exchanger cleaning
•  Leak inspection

Proper maintenance extends lifespan to 20–25 years.

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Environmental Benefits

Absorption chillers:

• Reduce electrical grid load

• Lower carbon emissions

• Utilize waste energy

• Use environmentally friendly refrigerants

Ideal for green building projects.

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Frequently Asked Questions (FAQ)

What is a vapour absorption chiller?

A cooling machine that uses heat instead of electricity to produce chilled water.

Where is vapour absorption chiller used?

In power plants, industrial facilities, hospitals, and large commercial buildings.

What refrigerant is used in absorption chiller?

Commonly water (with lithium bromide) or ammonia.

Is absorption chiller more efficient?

COP is lower than compression chillers, but energy savings occur if waste heat is used.

What is the lifespan of absorption chiller?

Typically 20–25 years with proper maintenance.

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Final Summary

A vapour absorption chiller is a heat-driven cooling system that uses:

• Steam

• Hot water

• Waste heat

• Gas

Instead of mechanical compressors.

It is ideal for:

• Industrial plants

• Cogeneration systems

• Large commercial projects

Although initial cost is high, long-term operational savings make it valuable in the right application.

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Conclusion

Vapour absorption chillers play a crucial role in modern energy-efficient HVAC systems.

By converting waste heat into useful cooling, they reduce electricity consumption and improve sustainability.

If your project includes:

1. Waste heat availability
2. Large cooling load
3. Long-term operational planning

Then vapour absorption technology could be the ideal solution.

Always consult an experienced HVAC engineer before selecting a chiller type.

Stay efficient. Stay sustainable.