RACA Journal I March 2026 www. refrigerationandaircon. co. za 43
RETROFITS
THE ADVANTAGES OF COOLING TOWER RETROFITS USING EC FAN ARRAYS
By Eamonn Ryan
Explore how modern EC fan arrays are transforming cooling tower retrofits in this technical white paper from Ziehl-Abegg, featured on HVACInformed. com. Learn how innovative multi-fan installations deliver enhanced energy efficiency, improved safety and operational redundancy, while providing rapid return on investment – all without the need for costly full tower replacements. A detailed case study from Raleigh, North Carolina, illustrates the real-world impact of this cutting-edge technology. technical
Background image by HVACInformed. com
EXECUTIVE SUMMARY Cooling towers are critical infrastructure in large-scale HVAC systems, yet the fans that drive their performance often fail long before the towers themselves. Traditional retrofits involve replacing large single fans, which can be costly, timeintensive and unsafe. A new approach – retrofitting with arrays of electronically commutated( EC) fans – offers significant advantages in energy efficiency, redundancy, safety and costeffectiveness.
BACKGROUND AND CHALLENGES Cooling tower structures are designed for durability, with lifespans of 30 – 50 years if corrosion is controlled. However, fans typically last only 5 – 10 years, creating a recurring point of failure.
Traditionally, replacing a failed large fan requires:
• Long lead times for replacement motors and gearboxes
• Significant safety risks in handling heavy impellers( up to 6m in diameter)
• High labour demands, often requiring large teams and cranes
These challenges are amplified in critical facilities such as government campuses, hospitals and data centres, where downtime is unacceptable.
TECHNOLOGY OVERVIEW: EC FAN ARRAYS Ziehl-Abegg’ s EC fan technology introduces a modular retrofit solution that replaces a single large AC fan with multiple smaller EC-driven axial fans.
Key features of EC fans:
• High efficiency: EC motors supply only the precise energy required for rotation
• Variable speed control: Integrated electronics eliminate the need for external VFDs
• Modular installation: Lightweight fans( about 34kg) can be installed by one or two workers
• Safety and redundancy: Failure of one fan does not halt cooling tower operation
• Scalability: Arrays can be sized to meet airflow and static pressure requirements
This approach, already standardised in air handling units( AHUs) for over a decade, is now gaining traction in cooling towers.
CASE STUDY In April 2025, a central cooling tower fan failed at a 2-hectare government office campus in Raleigh, NC. The site depended on two 300-ton cooling tower cells; the failure immediately cut cooling capacity by 50 % ahead of the peak summer season.
Traditionally, replacing a failed cooling tower fan can present major challenges. In this case, the government facility faced a 10-week lead time to source a replacement motor, while the installation itself carried significant safety risks due to the size and weight of the large fan. To avoid extended downtime, the facility chose an alternative approach – a retrofit with electronically commutated( EC) fans.
Instead of reinstalling a single 75-horsepower AC fan, the solution deployed 21 Ziehl-Abegg ZAplus axial EC fans, each measuring 910mm in diameter. The retrofit was completed in just four weeks, less than half the time of the traditional replacement path. Installation was further streamlined by the use of modular kits, which included pre-engineered wiring harnesses and control panels, reducing complexity and labour requirements.
RESULTS AND BENEFITS The retrofit delivered immediate and measurable advantages across multiple performance areas.
Energy efficiency was one of the most striking outcomes. During peak summer demand, the EC fan array demonstrated a 29 % reduction in energy use compared to the twin cooling tower cell that still operated with a conventional large fan. Even greater savings are expected during moderate spring and autumn conditions, when the variable-speed capability of EC fans allows them to run at lower, more efficient speeds.
RACA Journal I March 2026 www. refrigerationandaircon. co. za 43