Here’s a detailed explanation of the Types of Vapour Absorption Refrigeration Systems (VARS) — an important topic in refrigeration and HVAC engineering.
Types of Vapour Absorption Refrigeration Systems (VARS)
A Vapour Absorption Refrigeration System (VARS) uses thermal energy (heat) instead of mechanical energy (as in Vapour Compression Systems) to provide cooling. Based on design complexity, energy sources, and components, VARS can be classified into several types.
Table of Contents
🔹 1. Simple Vapour Absorption System
This is the most basic form of VARS and forms the foundation of more advanced systems.
✅ Main Components:
- Evaporator
- Absorber
- Pump
- Generator
- Condenser
- Expansion valve
🧪 Common Refrigerant–Absorbent Pairs:
- Ammonia–Water: Ammonia = refrigerant, Water = absorbent
- Water–Lithium Bromide: Water = refrigerant, LiBr = absorbent
🔧 Working Principle:
- The refrigerant evaporates and absorbs heat.
- The absorber absorbs the refrigerant vapour.
- A solution pump transfers it to the generator.
- Heat input separates the refrigerant vapour.
- The refrigerant is condensed and expanded back into the evaporator.
🔹 2. Electrolux or 3-Fluid Absorption System
Also called the Electrolux refrigeration system, it is a pump-less VARS.
✅ Working Fluids:
- Ammonia (Refrigerant)
- Water (Absorbent)
- Hydrogen (Inert gas to reduce partial pressure in evaporator)
⚙️ Features:
- No moving parts (uses gravity and thermosiphon effect)
- Silent operation
- Heat source: gas flame, electric heater, or solar panel
🔧 Application:
- Caravans, hotel minibars, gas refrigerators
🔹 3. Water–Lithium Bromide Absorption System
This is a specialized VARS where water acts as the refrigerant, and lithium bromide as the absorbent.
✅ Suitable for:
- Air conditioning in large buildings
- Chilled water systems
- Industrial cooling
⚠️ Limitation:
- Only suitable for temperatures above 0°C (since water freezes below that)
🔧 Working:
- LiBr has a high affinity for water vapour.
- Heat is supplied to regenerate water refrigerant.
- Operates under vacuum.
🔹 4. Single-Effect and Double-Effect VARS
These are performance-based classifications of VARS that use multiple generators or heat recovery systems to improve efficiency.
▶️ Single-Effect VARS
- Uses one generator stage
- Lower efficiency (COP ~ 0.6 to 0.8)
- Common in small to medium-scale applications
▶️ Double-Effect VARS
- Has two generators (high-temp and low-temp)
- Utilizes waste heat from the first generator to power the second
- Higher COP (~1.2 or more)
- More complex and costly
- Suitable for industrial HVAC systems
🔹 5. Triple-Effect VARS (Advanced)
- Uses three generator stages
- Achieves even higher COP (~1.4–1.6)
- Maximizes energy recovery
- Used in high-efficiency plants or where high-temperature waste heat is available
📊 Comparison Table of VARS Types
| Type | Refrigerant–Absorbent | COP | Complexity | Heat Source | Application |
|---|---|---|---|---|---|
| Simple VARS | Ammonia–Water / H₂O–LiBr | 0.6–0.8 | Low | Gas, Steam | General cooling |
| Electrolux System | Ammonia–Water–Hydrogen | ~0.5 | Low | Gas/Electric | Minibars, RVs |
| Water–LiBr VARS | Water–LiBr | 0.7–0.85 | Medium | Steam/Solar | Central air conditioning |
| Double-Effect VARS | Water–LiBr or Ammonia–Water | 1.2 | High | High-temp waste heat | Industrial HVAC |
| Triple-Effect VARS | Water–LiBr or Ammonia–Water | 1.4–1.6 | Very High | Steam/Flue gas | Power plants, large facilities |
FAQ: Types of VARS
Q1: Which VARS type is best for off-grid or silent cooling?
Electrolux system is ideal due to its pump-less, noiseless operation.
Q2: Can VARS be powered by solar energy?
Yes, especially Water–LiBr systems and Electrolux systems can use solar thermal collectors as the heat source.
Q3: Why use LiBr–Water system for air conditioning?
Because it is efficient for chilled water generation and works best at temperatures above 0°C, which is ideal for comfort cooling.
Conclusion
Understanding the different types of Vapour Absorption Refrigeration Systems (VARS) helps engineers and designers choose the right system for efficiency, application, and available heat source. Whether you’re designing an industrial chiller, off-grid refrigerator, or HVAC system for a building — selecting the appropriate VARS type is crucial.
