Challenges & Solutions in Implementing EC Fan Retrofits in HVAC Systems

Published on 11 Sep, 2023read time 6 mins

A fully functioning air handling and Heating, Ventilation and Air Conditioning (HVAC) system is essential for more than just comfort. Many organisations rely on these systems to maintain optimal conditions in their buildings. When your Air Handling Unit (AHU) breaks down, it's crucial to find a quick solution. The prospect of replacing an entire AHU can be daunting and expensive, leading many facility owners to put off critical repairs or replacements. However, it's important to recognize that neglecting AHU maintenance can have severe consequences.

Replacing an AHU as a complete project takes significantly longer than retrofitting. By choosing retrofitting as an alternative solution, facility owners can handle issues with failing, aging, or already failed EC fan arrays efficiently and effectively.

When replacing conventional AHU fans with Electronically Commutated (EC) fans, several considerations must be taken into account to ensure the maintenance of requisite pressure regimes. This article discusses the challenges typically encountered during EC fan retrofits, their impact on system performance, and provides solutions to overcome these challenges. Let’s look at some of the key aspects.

HVAC EC fan retrofit infographic

Key Considerations for EC Fan Retrofits

1. System Design Parameters

Reviewing the design specifications of the existing AHU system is crucial. This includes assessing the required airflows, external static pressure (ESP) requirements, and pressure regimes across different sections of the system. By establishing these baseline parameters, the performance of the new EC fans can be effectively evaluated.

2. Fan Curves

Obtaining fan curves for both the existing AHU fans and the proposed EC fans is essential. Fan curves provide information on airflow rate, static pressure, and power consumption. Comparing the fan curves of both fan types ensures that the EC fans can deliver the required airflow and static pressure at various operating conditions.

3. System Resistance

Assessing system resistance characteristics, such as those offered by filters, coils, dampers, and diffusers, is vital. Accurately calculating the total system resistance, considering existing components and any changes made during the replacement process, helps determine if the EC fans can overcome the system resistance and maintain the required pressure regimes.

4. Fan Control

Evaluating the control strategy for the EC fans is crucial. EC fans often offer variable speed control, enabling precise adjustment of airflow and pressure. The control strategy should effectively modulate the fan speed in response to varying system demands, such as temperature changes or occupancy fluctuations. This ensures the maintenance of the requisite pressure regimes under different operating conditions.

5. Energy Efficiency

Comparing the energy efficiency of conventional AHU fans and EC fans is essential. EC fans are known for their high efficiency and potential energy savings compared to traditional AC or DC fans. Evaluating the power consumption and efficiency characteristics of the EC fans ensures that the replacement not only meets pressure requirements but also results in energy-efficient operation.

6. Computational Fluid Dynamics (CFD) Analysis

Considering conducting a CFD analysis or consulting with an experienced HVAC engineer can help simulate airflow patterns and pressure distribution within the AHU system. CFD analysis assists in identifying potential issues, such as areas of high turbulence or inadequate pressure levels, and optimizing the design accordingly.

Typical Challenges and Solutions in EC Fan Retrofits

1. Inadequate Fan Sizing

Challenge: Selecting the right size of EC fans for retrofitting can be a problem. Sometimes, the replacement fans are not appropriately sized to match the airflow and pressure requirements of the existing system. Undersized fans may struggle to deliver the necessary airflow and maintain the required pressure regimes, while oversized fans can lead to excessive energy consumption and inefficient operation.

Solution: Thoroughly assess the airflow and pressure requirements of the existing system to ensure appropriate sizing of the EC fans. Consulting with HVAC professionals or specialists experienced in EC fan technology can help determine the optimal fan size.

2. Insufficient Static Pressure

Challenge: EC fans may have different pressure capabilities compared to the conventional fans they replace. If the static pressure generated by the EC fans is lower than what is required by the system, it can lead to poor air distribution, decreased airflow, and compromised comfort levels in different zones or rooms.Insufficient static pressure can also cause issues with equipment performance, such as reduced heat transfer in coils or inadequate air filtration.

Solution: Carefully evaluate the static pressure requirements of the system and ensure that the selected EC fans can generate the necessary static pressure. If required, additional modifications to the system may be necessary to address any deficiencies in static pressure.

3. Incompatibility with Control Systems

Challenge: Retrofitting EC fans into existing HVAC systems may result in compatibility issues with the control systems, and the control systems may not be able to effectively communicate with or regulate the operation of the EC fans. This can lead to improper fan control, inefficient operation, or limited ability to modulate fan speed based on system demands.

Solution: Thoroughly assess the compatibility between the existing control systems and the EC fans during the design phase. Consult with experts to ensure seamless integration and effective communication between the control systems and the EC fans.

4. Noise and Vibration

Challenge: Improper installation or balancing of EC fans can introduce noise and vibration into the system. This can be particularly problematic if the retrofit involves replacing multiple fans or if the system operates at higher speeds. Excessive noise or vibrations can affect occupant comfort, potentially leading to complaints and the need for additional noise control measures.

Solution: Follow proper installation practices and conduct thorough testing to ensure proper fan balance. Additionally, consider implementing noise control measures such as vibration isolators or sound-absorbing materials to minimize noise and vibration.

5. Lack of Training and Expertise

Challenge: Implementing EC fan retrofits requires specialized knowledge and expertise in EC fan technology, system design, and control integration. Insufficient training or expertise among the installation and maintenance personnel can result in improper installation, incorrect fan control settings, or inadequate maintenance practices, leading to suboptimal performance and potential issues down the line.

Solution: Engage experienced HVAC professionals or specialists with expertise in EC fan technology. Ensure that installation and maintenance personnel receive adequate training to perform proper installation, control configuration, and ongoing maintenance practices.


EC fan retrofits offer numerous advantages in terms of energy efficiency and performance improvement. However, it is crucial to address the challenges associated with these retrofits to ensure successful implementation. By carefully considering system design parameters, fan curves, system resistance, fan control strategies, energy efficiency, and conducting CFD analysis, HVAC professionals can overcome these challenges and achieve optimal performance when replacing conventional AHU fans with EC fans.