Chiller in HVAC Systems – Purpose, Types, and Practical Applications
A chiller is one of the most important components in an HVAC (Heating, Ventilation, and Air Conditioning) system. Its primary purpose is to remove heat from a building or industrial process through vapor compression or absorption refrigeration cycles. Chillers act as heat exchangers, transferring heat from a secondary refrigerant (water/air) to a primary refrigerant (such as ammonia, NH₃), producing chilled water that circulates through the system.
Purpose of a Chiller in HVAC
- Heat Removal: Chillers absorb heat from water or air and reject it to the atmosphere.
- Cooling Medium: The chilled water produced flows into Air Handling Units (AHUs) or Fan Coil Units (FCUs), cooling indoor spaces.
- Continuous Cycle: As the chilled water absorbs heat from the building, it returns to the chiller to be cooled again.
Practical Example: In a large office building, a central chiller plant produces chilled water at around 7°C. This water circulates through AHUs, cooling the air supplied to different floors.
Essential Components of a Chiller
1. Evaporator – Absorbs heat from the secondary refrigerant (water/air).
2. Compressor – Increases the pressure and temperature of the refrigerant vapor.
3. Condenser – Rejects heat from the refrigerant to air or water.
4. Expansion Valve – Reduces refrigerant pressure, allowing it to evaporate again in the cycle.
Types of Chillers Based on Secondary Refrigerant
1. Air-Cooled Chiller
- Working Principle: Uses motorized blowers or fans to blow air across the refrigerant lines.
- Purpose: Maintains ambient temperature by rejecting heat directly to the atmosphere.
- Advantages:
- Easier to install.
- Lower maintenance compared to water-cooled systems.
- Limitations:
- Less efficient in hot climates.
- Requires open space for proper ventilation.
Practical Example: Shopping malls often use air-cooled chillers on rooftops where space is available and water supply is limited.
2. Water-Cooled Chiller
- Working Principle: Transfers heat from refrigerant vapor into condenser water.
- Process:
1. Heat moves from refrigerant vapor into condenser water.
2. Warm condenser water is pumped to a cooling tower, where heat is discharged to the atmosphere.
- Advantages:
- Higher efficiency, especially in large buildings.
- Better performance in hot climates.
- Limitations:
- Requires cooling towers, pumps, and water treatment.
- Higher installation and maintenance costs.
Practical Example: Hospitals and high-rise commercial complexes use water-cooled chillers because they provide reliable cooling for large loads.
Subsystems of an HVAC System (Including Chiller)
A basic HVAC system assembly includes:
- Chiller – Produces chilled water.
- AHU (Air Handling Unit) – Distributes cooled air.
- Cooling Tower (for water-cooled systems) – Rejects heat to the atmosphere.
- Pumps and Piping – Circulate chilled water throughout the building.
Conclusion
Chillers are the backbone of large HVAC systems, ensuring efficient cooling in commercial, industrial, and residential applications. Whether air-cooled or water-cooled, chillers work by removing heat from water or air and maintaining comfortable indoor environments.
