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WHAT IS A CHILLER? | MAIN TYPES OF CHILLERS | MAJOR COMPONENTS

WHAT IS A CHILLER?


  • A Chiller is a machine that removes heat from a liquid (usually water or glycol mix) via vapor-compression or absorption refrigeration.
  • The chilled water is circulated through AHUs or FCUs to absorb heat from the building, making it a central part of HVAC systems.

MAIN TYPES OF CHILLERS

1. Based on Heat Rejection:

⭐Air-Cooled Chiller

  •  Heat is rejected to ambient air via condenser fans.
  • No cooling tower needed.
  • Higher power consumption (low efficiency).
  • Used where water availability is limited (like UAE rooftops).

⭐Water-Cooled Chiller

  •  Heat is rejected to condenser water, then to a cooling tower.
  • Higher efficiency and longer lifespan.
  • Requires more maintenance (cooling towers, water treatment).
  • Ideal for large-scale commercial or industrial applications.
2. Based on Refrigeration Cycle: 

→Vapor Compression Chiller

  •  Commonly used.
  • Uses mechanical compressor (screw, scroll, centrifugal).

→Absorption Chiller

  •  Uses heat source (steam, hot water, gas) to generate cooling.
  • Uses lithium bromide-water cycle.
  • No compressor; eco-friendlier but less efficient.


MAJOR COMPONENTS

1. Evaporator

  • Where chilled water is cooled.
  • Heat absorbed from building's water loop.
2. Compressor

  • Pumps refrigerant from evaporator to condenser.

⭐Types of compressor:

  •  Scroll: Small systems. 
  •  Screw: Medium-large systems. 
  •  Centrifugal: Very large capacity, high efficiency.
3. Condenser

  • Rejects heat from refrigerant to air/water. 
  • Water-cooled chillers use cooling tower loop.

4. Expansion Valve (TXV or EXV)

  • Controls refrigerant flow into evaporator.
  • Lowers pressure and temperature of refrigerant.
5. Refrigerant

  • Common types: R134a, R123, R410A, R717 (ammonia), R1234ze (low-GWP).
  • Transfers heat from chilled water to environment.

CHILLER SYSTEM COMPONENTS (HVAC INTEGRATION)

⇒ Primary Chilled Water Loop

  •  Carries chilled water from chiller to AHUs/FCUs and back. 

⇒ Secondary Loop (in decoupled system)

  •  Isolates distribution pumps from chiller pumps.

⇒ Condenser Water Loop (only for water-cooled)

  •  Carries heat from chiller condenser to cooling tower.


⚙ OPERATION SEQUENCE (TYPICAL WATER-COOLED CHILLER)

1. CHW return (from building) → Evaporator → CHW supply. 

2. Heat absorbed → refrigerant evaporates. 

3. Compressor raises refrigerant pressure/temp. 

4. Condenser removes heat via cooling tower water. 

5. Expansion valve lowers pressure → back to evaporator.


⚠ KEY CONSIDERATIONS IN SELECTION

⇒ Capacity (TR or kW) 

⇒ Efficiency: COP, kW/TR, IPLV, NPLV ⇒ Type of compressor 

⇒ Ambient conditions 

⇒ Cooling medium availability (air vs. water) 

⇒ Initial cost vs. life-cycle cost 

⇒ Space availability (rooftop vs. plant room)

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