Working Principle of a Chiller Plant 🔹 A chiller plant is used to remove heat from a building and maintain the required indoor temperature. It operates using two separate water circuits: the chilled water circuit and the condenser water circuit. Main Equipment & Their Functions ▪ Chiller (Evaporator & Condenser) The evaporator absorbs heat from the chilled water, thereby reducing its temperature. The condenser rejects the absorbed heat from the refrigerant to the condenser water. ▪ Chilled Water Pump & Condenser Water Pump The chilled water pump circulates chilled water between the chiller evaporator and the AHUs/FCUs. The condenser water pump circulates condenser water between the chiller condenser and the cooling tower. ▪ Air Handling Unit (AHU) The AHU cools the indoor air by passing it over a chilled water cooling coil. Heat from the air is transferred to the chilled water, causing the water temperature to rise before returning to the chiller. ▪ Cooling Tower The...
Gul Bahar Shah
Gul Bahar Shah
Chilled Water System – Sequence of Operation (Chiller to AHU / FCU)
1. System Enable / Start Command
The chilled water system is enabled by BMS, time schedule, or manual command.
Interlocks such as power availability, system alarms, and safety controls are checked before start-up.
2. Chilled Water Pump Operation
Upon system enable, the chilled water pump starts.
Pump status and differential pressure are monitored by BMS.
Flow is established through the chilled water loop, including piping, valves, and terminal units.
3. Chiller Start-Up
Once minimum chilled water flow is proven (via flow switch or DP sensor), the chiller is permitted to start.
The chiller operates to maintain the chilled water supply temperature setpoint (typically 6–7°C).
Chiller loading/unloading is controlled based on return water temperature and system demand.
4. Chilled Water Distribution
Chilled water is supplied from the chiller evaporator to:
AHUs (large air-handling units)
FCUs (fan coil units)
Distribution is through supply headers, control valves, and branch piping.
5. AHU / FCU Cooling Demand
Room thermostat or BMS senses space temperature.
When cooling demand exists:
The 2-way or 3-way control valve at AHU/FCU modulates.
Chilled water flows through the cooling coil.
6. Heat Exchange at AHU / FCU
Warm return air passes over the chilled water coil.
Heat is transferred from air to chilled water.
Supply air temperature is reduced and delivered to the conditioned space.
7. Chilled Water Return
Chilled water absorbs heat and returns to the chiller at a higher temperature (typically 12–13°C).
Return water temperature reflects building cooling load
8. Capacity Control & Energy Optimization
As load varies:
Control valves modulate.
Variable speed pumps (if provided) adjust flow based on DP setpoint.
Chiller capacity adjusts (compressor staging or VFD control).
System maintains required comfort conditions with optimized energy use.
9. System Shutdown
When cooling demand is satisfied:
AHU/FCU control valves close.
Chilled water pump slows down or stops after a time delay.
Chiller shuts down once no cooling demand is detected.
System returns to standby mode.
10. Safety & Alarms
The system shuts down automatically in case of:
Low chilled water flow
High/low temperature limits
Pump or chiller fault
BMS emergency stop
*** Typical Design Temperatures***
Chilled Water Supply: 6–7°C
Chilled Water Return: 12–13°C
Summary
The chilled water system operates by producing chilled water at the chiller, circulating it via pumps to AHUs and FCUs, removing heat from indoor spaces through cooling coils, and returning the heated water to the chiller for continuous cooling.
The chilled water system is enabled by BMS, time schedule, or manual command.
Interlocks such as power availability, system alarms, and safety controls are checked before start-up.
2. Chilled Water Pump Operation
Upon system enable, the chilled water pump starts.
Pump status and differential pressure are monitored by BMS.
Flow is established through the chilled water loop, including piping, valves, and terminal units.
3. Chiller Start-Up
Once minimum chilled water flow is proven (via flow switch or DP sensor), the chiller is permitted to start.
The chiller operates to maintain the chilled water supply temperature setpoint (typically 6–7°C).
Chiller loading/unloading is controlled based on return water temperature and system demand.
4. Chilled Water Distribution
Chilled water is supplied from the chiller evaporator to:
AHUs (large air-handling units)
FCUs (fan coil units)
Distribution is through supply headers, control valves, and branch piping.
5. AHU / FCU Cooling Demand
Room thermostat or BMS senses space temperature.
When cooling demand exists:
The 2-way or 3-way control valve at AHU/FCU modulates.
Chilled water flows through the cooling coil.
6. Heat Exchange at AHU / FCU
Warm return air passes over the chilled water coil.
Heat is transferred from air to chilled water.
Supply air temperature is reduced and delivered to the conditioned space.
7. Chilled Water Return
Chilled water absorbs heat and returns to the chiller at a higher temperature (typically 12–13°C).
Return water temperature reflects building cooling load
8. Capacity Control & Energy Optimization
As load varies:
Control valves modulate.
Variable speed pumps (if provided) adjust flow based on DP setpoint.
Chiller capacity adjusts (compressor staging or VFD control).
System maintains required comfort conditions with optimized energy use.
9. System Shutdown
When cooling demand is satisfied:
AHU/FCU control valves close.
Chilled water pump slows down or stops after a time delay.
Chiller shuts down once no cooling demand is detected.
System returns to standby mode.
10. Safety & Alarms
The system shuts down automatically in case of:
Low chilled water flow
High/low temperature limits
Pump or chiller fault
BMS emergency stop
*** Typical Design Temperatures***
Chilled Water Supply: 6–7°C
Chilled Water Return: 12–13°C
Summary
The chilled water system operates by producing chilled water at the chiller, circulating it via pumps to AHUs and FCUs, removing heat from indoor spaces through cooling coils, and returning the heated water to the chiller for continuous cooling.
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