A closed-circuit (dry) cooling tower, also known as a fluid cooler or dry cooler with adiabatic assist, is a heat rejection system that keeps the process fluid (water or glycol mixture) isolated from the outside air in a sealed coil, unlike an open cooling tower where water is directly exposed to the atmosphere.
How a Closed-Circuit Cooling Tower Works:
- Process Fluid Circulation – Hot fluid flows through a closed-loop coil (usually finned tubes).
- Airflow Cooling – Ambient air is blown or drawn across the coil, cooling the fluid by sensible heat transfer (no direct water evaporation).
- Adiabatic Pre-Cooling (Optional) – Some models spray water on the coil or use pre-cooling pads to enhance heat transfer in high ambient temperatures.
- Cooled Fluid Return – The cooled fluid is recirculated back to the process.
Key Components:
- Finned-Tube Coil – Sealed loop where process fluid is cooled (no direct air-water contact).
- Fans – Force or induce airflow (axial or centrifugal).
- Spray System (Hybrid Models) – Optional water mist for adiabatic cooling.
- Pump & Piping – Circulates the process fluid.
Advantages:
No Water Contamination – Since the process fluid is sealed, there’s no risk of scaling, fouling, or biological growth.
Lower Water Consumption – Unlike open towers, minimal water is lost (only in hybrid models).
Reduced Legionella Risk – No open water exposure means lower health risks.
Stable Fluid Quality – Ideal for sensitive processes (e.g., chilled water systems, data centres).
Disadvantages:
Less Efficient in High Ambient Temps – Without evaporative cooling, dry towers require more airflow.
Higher Initial Cost – More expensive than open cooling towers.
Larger Footprint – Needs more space for equivalent cooling capacity.
Applications:
- Data centres
- Industrial processes with clean fluid requirements
- HVAC systems (chilled water loops)
- Power plants (where water conservation is critical)
Comparison with Open Cooling Towers:
| Feature | Closed-Circuit (Dry) Tower | Open (Wet) Tower |
| Water Usage | Minimal (only in hybrid mode) | High (evaporation + drift) |
| Maintenance | Low (no scaling, fouling) | High (water treatment needed) |
| Efficiency | Lower in dry mode, improves with adiabatic assist | Higher (evaporative cooling) |
| Legionella Risk | None | Possible if untreated |
| Cost | Higher initial cost | Lower initial cost |
Maintenance Requirements:
- Coil cleaning (dust, debris removal).
- Fan and motor inspection.
Water treatment (only for hybrid systems with spray).