How Chilled Water Systems Work: Basics and Operation

A chilled water system is a central air conditioning system that cools and circulates water to provide cooling to buildings, industrial facilities, and various other applications. Chilled water systems are commonly used in large and medium-sized commercial and industrial settings due to their efficiency and capacity for cooling large areas. Here's a basic overview of how a chilled water system works:

1. Chiller Unit:

• The heart of a chilled water system is the chiller unit. This unit contains a refrigeration cycle similar to what you find in a household air conditioner or refrigerator but on a larger scale. The chiller's primary components include a compressor, evaporator, condenser, and expansion valve.

2. Cooling the Water:

• The chiller's evaporator is responsible for cooling the water. It works by absorbing heat from the water as it circulates through the evaporator coils. The water temperature is lowered to the desired setpoint, typically around 45 degrees Fahrenheit (7 degrees Celsius).

3. Refrigeration Cycle:

• The chiller's refrigeration cycle uses a refrigerant (often a type of hydrofluorocarbon or HFC) to transfer heat. The cycle begins with the compressor compressing low-pressure, low-temperature gas refrigerant, causing it to become a high-pressure, high-temperature gas.

4. Heat Rejection:

• The high-temperature, high-pressure gas refrigerant is then passed through the chiller's condenser coils, where it releases heat to the outside environment. The refrigerant changes from a gas to a liquid in this process.

5. Expansion Valve:

• After heat rejection, the high-pressure liquid refrigerant passes through an expansion valve or metering device, which reduces its pressure. As a result, the refrigerant's temperature drops significantly.

6. Evaporator Coil:

• The low-pressure, low-temperature liquid refrigerant enters the chiller's evaporator coil, where it absorbs heat from the water circulating through the coils. This heat exchange causes the refrigerant to evaporate and return to the compressor, and the cycle continues.

7. Chilled Water Distribution:

• The chilled water that exits the chiller is then distributed through a network of pipes to various air handling units (AHUs) or fan coil units (FCUs) located in different parts of the building or facility.

8. Air Cooling:

• Air-handling units (AHUs) or fan coil units (FCUs) draw warm air from the indoor spaces and pass it over chilled water coils. The cold water within the coils absorbs heat from the air, cooling it. The cooled air is then distributed back into the spaces to provide the desired cooling effect.

9. Heat Rejection:

• The heat extracted from the air in the indoor spaces is returned to the chiller, where it is released to the outside environment through the condenser coils, and the cycle repeats.

Chilled water systems are energy-efficient and offer a cost-effective solution for cooling large buildings and facilities. They also allow for centralized control and the ability to adjust the cooling capacity to meet changing demands. The system's efficiency can be further improved by using variable-speed compressors, efficient heat exchange equipment, and optimized control systems.