Chilled Water Systems: What Are They and How Do They Work?
- Aug 26, 2022
- 7 min read
Updated: Aug 14
The foundation of HVAC (heating, ventilating, and air conditioning) cooling systems are chilled water systems. Chilled water systems are primarily used in industrial settings due to the lower cost of using water for chilling.
Applications that require significant cooling capacity, such hypermarkets, industrial processes, and commercial air conditioning, like offices and factories, frequently use chilled water air conditioning systems.
They operate on the same principles as other air conditioning systems that utilise normal refrigerant. Additionally, running water pipes instead of refrigerant lines over a sizable business space allows for more efficient water distribution to air handler evaporator coils.
Due to its affordability and lack of any safety risks associated with having refrigerant pipes running throughout the entire house, more and more households are employing this system to air condition their entire structure.
However, these systems are complicated and need to be maintained by well-trained personnel despite their cost-saving benefits.
How Do Chilled Water Systems Function?
Cooled water is used in chilled water systems to cool a building by absorbing heat from its interior spaces.
A chiller, the brain of the water-chilled system, uses a refrigeration cycle to extract heat from water. Heat is either transferred to the condenser water or the outside air in the chiller's condenser.
The refrigeration cycle of a chilled water system functions by eliminating heat from chilled water in the chiller's evaporator. The compressor powers the entire operation. In a chilled water system, it also consumes the greatest energy.
A building's chilled water is circulated via a chilled water loop, which comprises pipelines and pumps. The chilled water supply is the cold water that comes out of a chiller, its temperature is typically around 45 °F or 7.2 °C.
The building's air conditioning devices, such as air handling units (“AHU”) and fan coil units (“FCU”), are supplied with chilled water via a pump that travels through the chiller.
The chilled water is sent through a heat-exchanging coil in AHUs and FCUs to lower the coil's temperature and a fan circulates air through the coil to circulate cold air throughout the structure. AHUs and FCUs typically blow out supply air at a temperature of around 55 °F or 12.78 °C.
The chilled water returns to the chiller after leaving the heat-exchanging coil, where it is once more cooled, and the cycle is repeated. A single chiller and a single pump can make up a straightforward chilled water system setup.
More sophisticated or complex chilled water system layout can consist of numerous chillers, multiple pumps, cooling towers, heat exchangers, and various types of valves to reroute flow in accordance with the heat load inside the building.
Types of Chillers
Air Cooled Chiller
Almost often placed outside of a building or structure, air-cooled chillers exhaust heat from the condenser coil directly into the surrounding air. The outside air blows over the condenser coil as warm refrigerant runs through it, removing heat from the refrigerant.
The chilled water is subsequently cooled by the refrigerant as it travels through the evaporator and an expansion valve, where it rapidly cools. Then, the entire procedure is repeated.
Air Cooled Chiller designed by TCW Group
Air-Cooled Chiller in progress at TCW group’s manufacturing plant
Completed Air-Cooled Chiller assembled by TCW group
Water Cooled Chiller
Chillers that use water cooling are typically found inside of buildings. They operate nearly identically to air cooled chillers. The distinction is that they exhaust heat from chilled water to a second, separate water line known as the condenser water line.
Heat is absorbed by the condenser water as it passes through the chiller. The cooling tower then receives the condenser water. The cooling tower, which is typically situated outside of the structure, evaporates some of the condenser water into the atmosphere to remove heat.
Heat is removed from the condenser water as some of it evaporates, and the cool condenser water then flows back to the chiller. Then, the entire procedure is repeated.
Water cooled chillers are particularly energy efficient. However, they are frequently more expensive to install and maintain due to their complexity and numerous parts.
They are therefore typically only found in huge buildings. This is true since the system's installation and maintenance costs are offset or exceeded by the energy savings.
Different Water Cooled Chiller assembled by TCW Group
Types of Compressors
The effectiveness and dependability of a water chiller are often most influenced by the type of compressor that is utilised.
Reciprocating Compressors
For many years, the small chiller market's mainstay was the reciprocating compressor. A single chiller frequently housed many compressors.
Scroll Compressors
As a well-liked substitute for reciprocating compressors, scroll compressors are often offered in hermetic versions for use in water chillers. Like reciprocating compressors, a single chiller would frequently house numerous scroll compressors to accommodate bigger capacities.
Because they have roughly 60% less moving parts than reciprocating compressors, scroll compressors are often 10 to 15% more efficient than reciprocating compressors and have a track record of being very reliable. Smaller water chillers are frequently equipped with reciprocating and scroll compressors.
Helical-rotary (or screw) compressors
Helical-rotary (or screw) compressors have long been employed in low-temperature refrigeration and air compression in medium-sized water chillers. Helical-rotary compressors, like the scroll compressor, are more reliable and more efficient than reciprocating compressors because they have fewer moving parts.
Centrifugal compressors
Larger water chillers have long utilised centrifugal compressors due to its high efficiency, greater reliability, decreased noise levels, and relatively inexpensive price.
How Does a Chilled Water System Work? (Including Condenser Loop)
A complete chilled water system operates using two interconnected loops:
Chilled Water Loop
Cold water (typically around 6–7 °C) is pumped from the chiller to Air Handling Units (AHUs) or Fan Coil Units (FCUs), where it absorbs heat from the building. The now-warmed water (around 12–13 °C) returns to the chiller to be recooled.
Condenser Water Loop (For Water-Cooled Chillers)
The refrigerant inside the chiller transfers the absorbed heat to a separate condenser water loop. This loop carries the heat to a cooling tower, where it is released into the atmosphere. The cooled condenser water then returns to the chiller to repeat the process.
This dual-loop setup is essential for efficient heat transfer and stable indoor cooling.
Key Components of a Chilled Water System
Component | Function |
Chiller | Produces cold water by removing heat through a refrigeration process. |
Chilled Water Pump | Circulates chilled water to AHUs/FCUs and back. |
Condenser Water Pump | Circulates warm water to the cooling tower for heat rejection. |
Cooling Tower | Releases unwanted heat into the atmosphere from the condenser water. |
AHU / FCU | Uses chilled water to cool indoor air by passing it through cooling coils. |
Expansion Tank | Manages pressure fluctuations caused by temperature changes in the loop. |
Pipes & Valves | Direct and regulate water flow across the system. |
Air-Cooled vs Water-Cooled Chillers
Feature | Air-Cooled Chillers | Water-Cooled Chillers |
Cooling Method | Uses ambient air via fans | Uses condenser water and a cooling tower |
Initial Cost | Lower | Higher |
Efficiency | Lower, especially in hot climates | Higher and more stable year-round |
Maintenance | Less complex | Requires water treatment and tower cleaning |
Best For | Small to mid-size buildings | Large commercial or industrial properties |
If water availability and space allow, water-cooled chillers offer long-term energy savings.
Understanding Energy Efficiency: COP and EER
When evaluating chiller performance, two common metrics are:
Coefficient of Performance (COP)
COP is the ratio of cooling output to energy input. A COP of 5 means the system delivers 5 units of cooling for every 1 unit of electricity consumed.
Energy Efficiency Ratio (EER)
EER compares the system’s cooling capacity (in BTU/hr) to its power input (in watts). A higher EER means better energy efficiency.
Systems with a COP of 4.0 and above are considered highly efficient and reduce operational costs significantly.
Importance of Maintenance and Water Treatment
Proper maintenance ensures a longer lifespan and higher performance. Key tasks include:
Water Treatment
Prevents scale, corrosion, and bacteria growth in pipes and cooling towers.
Routine Servicing
Includes pump checks, valve inspections, and verifying temperature differentials.
Cooling Tower Cleaning
Required to remove sludge, scale, and prevent Legionella bacteria, especially in humid environments.
System Design Considerations
Every chilled water system should be customised based on:
Total cooling load (in RT or kW)
Building layout and occupancy
Supply/return temperature settings
Water flow rate and pipe sizing
Redundancy (e.g., N+1 configuration for critical systems)
Accurate design ensures energy efficiency, minimal downtime, and consistent indoor comfort.
FCUs vs AHUs: What’s the Difference?
Feature | Fan Coil Unit (FCU) | Air Handling Unit (AHU) |
Size | Compact, room-sized | Larger, centralised unit |
Cooling Use | For small spaces or zones | For entire floors or buildings |
Fan Location | Built-in | May be external or integrated |
Ducting | Minimal | Extensive ducting system |
Best For | Hotels, offices, individual rooms | Large buildings, commercial spaces |
What Are District Cooling Systems?
District cooling systems supply chilled water from a central plant to multiple buildings through underground pipes.
These centralised systems:
Improve efficiency through scale
Lower equipment costs per building
Simplify maintenance and monitoring
Common in urban developments, hospitals, and university campuses, district cooling offers a sustainable alternative to individual chillers.
Common Problems and Prevention Tips
Problem | Cause | Prevention |
High energy usage | Dirty coils or oversized chiller | Regular cleaning and proper sizing |
Uneven cooling | Air trapped in pipes or faulty valves | Bleed air, inspect valve function |
Scale or corrosion | Poor water treatment | Use anti-scaling and corrosion inhibitors |
Bacterial contamination | Warm stagnant water in cooling tower | Regular biocide dosing and tower cleaning |
Conclusion
Chilled water systems are frequently a reasonable alternative to putting numerous distinct pieces of equipment in various locations since they function as a centralised cooling system providing cooling for a full building or multiple structures.
For example, there is a terrific approach to make it easier to reach the units for maintenance.
A chilled water system can be expensive up front, but the higher energy efficiency and cheaper maintenance costs typically make up for it.
A chiller is only a device that facilitates heat transmission from a building's interior to its outside, and the chilled water system can be set up in a variety of ways.
They can be put indoors or outdoors, and depending on the required cooling capacity and efficiency, they can have a variety of compressors and refrigerants.
In summary, chillers offer excellent customization choices. They may enable the selection of a wide range of choices and accessories that will allow the chiller unit to be completely adjusted to the requirements of a particular application.
Get a quotation from TCW group or contact our friendly experts to learn more about chilled water systems!
Custom built portable water chiller in progress at TCW group’s manufacturing plant