Hybrid/Dry-Wet Operation
Many closed-circuit towers can operate in three modes for maximum efficiency:
- Wet Mode (Evaporative): Spray pump ON. Maximum efficiency in warm weather.
- Dry Mode (Air-Cooled): Spray pump OFF. Used in freezing conditions or when water conservation is needed.
- Adiabatic Mode: Spray pump intermittent. Pre-cools incoming air with minimal water use.
Key Design Considerations
- Coil Material: Typically cupronickel, stainless steel, or galvanized steel for corrosion resistance.
- Face Velocity: Air velocity through coil is critical (400-600 fpm typical).
- Spray Coverage: Even distribution over coil surface is essential to prevent dry spots and scaling.
- Winter Operation: Requires controls to cycle spray pump and prevent coil freezing.
In summary: A closed-circuit cooling tower sacrifices some thermal efficiency and adds cost to achieve complete protection of the process cooling fluid. It’s the preferred choice when water quality, system cleanliness, freeze protection, or precise fluid control are critical requirements that outweigh the higher initial investment.