Chiller Plant – 3 Important Cycles Explained

 Chiller Plant – 3 Important Cycles Explained

A typical water-cooled chiller plant has three main operating cycles that work together to remove heat from a building and reject it to the atmosphere.

1. Chilled Water Cycle — Building Cooling

Chiller Evaporator → CHW Pump → AHU/FCU → Building → Chiller

• The chiller produces chilled water, typically 6–7°C.
• CHW pumps circulate it to AHU/FCU cooling coils.
• The chilled water absorbs heat from the building air.
• The warmer return water, typically 11–12°C, returns to the chiller.
• The chiller removes this heat and cools the water again.

Typical ΔT = 5–6°C

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2. Refrigerant Cycle — Heat Transfer Inside the Chiller

Compressor → Condenser → Expansion Valve → Evaporator → Compressor

Component	Function
Compressor	Raises refrigerant pressure and temperature
Condenser	Transfers refrigerant heat to condenser water
Expansion Valve	Reduces refrigerant pressure and temperature
Evaporator	Absorbs heat from chilled water

This is the core refrigeration cycle that allows the chiller to produce chilled water.

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3. Condenser Water Cycle — Heat Rejection

Chiller Condenser → Condenser Water Pump → Cooling Tower → Chiller

• Condenser water absorbs heat from the refrigerant.
• The condenser water pump sends the hot water to the cooling tower.
• The cooling tower rejects heat to the atmosphere through evaporation.
• Cooled condenser water returns to the chiller.

Typical design conditions might be approximately:

32°C → Cooling Tower → 27°C → Chiller

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🔄 How the 3 Cycles Work Together

                 BUILDING
                    │
             Heat from Rooms
                    ↓
              ┌──────────┐
              │ AHU / FCU│
              └────┬─────┘
                   │
             Warm CHW
              11–12°C
                   ↓
        ┌──────────────────┐
        │      CHILLER     │
        │                  │
        │   EVAPORATOR     │◄── Refrigerant Cycle
        │        ↓         │
        │   CONDENSER      │
        └───────┬──────────┘
                │
          Hot Condenser
              Water
                ↓
        ┌────────────────┐
        │ COOLING TOWER  │
        └───────┬────────┘
                │
        Heat Rejected
        to Atmosphere

In One Line

Building heat → Chilled Water → Refrigerant → Condenser Water → Cooling Tower → Atmosphere

These three cycles are the fundamental operating principle of a water-cooled chiller plant.