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Guide to Refurbishing AHUs


Refurbishing Air Handling Units (AHUs) is a cost-effective way to extend the life of HVAC systems, improve energy efficiency, and ensure occupant comfort. Whether upgrading individual components, replacing worn-out parts, or integrating advanced controls, this guide outlines the critical steps to ensure a successful refurbishment.

 

1. Perform a Full Survey of Existing AHUs

 

A comprehensive survey is the foundation of a successful AHU refurbishment.

 

Why this is important:

  • Assess the condition of fans, coils, filters, dampers, and casing for signs of degradation.
  • Ensure the existing ductwork and fan setup provide the required airflow and pressure.
  • Focus investment on upgrading or replacing parts that significantly impact performance.

 

Key Actions:

  • Inspect fan motors, belts, and bearings for wear and efficiency.
  • Check for leaks, corrosion, or damage in the AHU casing and access panels.
  • Measure pressure drops across coils, filters, and dampers.
  • Test airflow rates to confirm they meet design requirements.

 

2. Provide a Detailed Specification

 

A clear and detailed specification guides the refurbishment process and ensures all stakeholders understand the project requirements.

 

Why this is important:

  • Defines the performance requirements and ensures compatibility between new and existing components.
  • Specify upgrades such as high-efficiency motors, EC fans, and advanced controls.
  • Incorporate regulatory standards for ventilation, air quality, and energy efficiency.

 

Key Actions:

  • Specify energy-efficient fans (e.g., EC fans) and motors compliant with current efficiency standards.
  • Define replacement coil materials (e.g., copper or aluminum) and fin configurations to improve heat exchange.
  • Include high-efficiency filters and ensure compatibility with existing pressure drop tolerances.
  • Detail control requirements, such as modulating dampers, fan speed control, and integration with BEMS.

 

3. Upgrade and Replace Critical Components

 

Targeted upgrades to AHU components deliver improved performance and efficiency without the need for full replacement.

 

Key Upgrades:

 

Fans and Motors:

  • Replace belt-driven fans with direct-drive or EC fans for improved efficiency and reduced maintenance.
  • Install variable speed drives (VSDs) to modulate fan speeds based on demand.


Heating and Cooling Coils:

  • Replace damaged or scaled coils with new, higher-efficiency units.
  • Ensure coils are correctly sized for the system’s current load demands.​

 

Filters:

  • Upgrade to high-efficiency particulate air (HEPA) or F9 filters to improve air quality.
  • Install filter monitoring sensors to alert when replacement is needed.


Dampers and Actuators:

  • Replace corroded or non-functional dampers with low-leakage models.
  • Use modulating actuators to improve control over airflow and mixing.

 

Key Actions:

  • Verify that all replacement components are compatible with the existing AHU structure.
  • Test new components for correct installation and performance before commissioning.

 

4. Address Ductwork and Air Distribution

 

Ductwork and airflow distribution are often overlooked during AHU refurbishments but play a critical role in system performance.

 

Common Issues:

  • Air leakage in ductwork reduces system efficiency and increases operational costs.
  • Poor balancing results in uneven heating, cooling, or ventilation across zones.
  • Lack of proper insulation leads to energy loss and reduced comfort.

 

Key Actions:

  • Inspect ductwork for leaks and repair as necessary.
  • Clean ductwork to remove debris and contaminants.
  • Rebalance the system to ensure even air distribution across all zones.
  • Reinsulate ductwork to minimize thermal losses.

 

5. Integrate and Optimize BEMS Controls

 

Modernizing the control strategy of an AHU is one of the most impactful steps in a refurbishment project.

 

Why this is important:

  • Advanced controls can optimize heating, cooling, and ventilation based on real-time data.
  • Integrated alarms and trend logs help identify and resolve issues before they escalate.
  • Dynamic control of airflow, temperature, and humidity ensures optimal indoor conditions.

 

Key Actions:

  • Integrate the AHU with the building’s BEMS to enable real-time monitoring and control.
  • Define control strategies, such as:
  • Demand-based ventilation using CO₂ sensors.
  • Optimum start/stop sequences to align with occupancy schedules.
  • Heat recovery operation based on outdoor air temperature and energy demand.
  • Install sensors for temperature, humidity, pressure, and air quality, and calibrate them during commissioning.

 

6. Commission the Refurbished AHU Thoroughly

 

Proper commissioning ensures the refurbished AHU performs as intended and meets design goals.

 

Key Steps:

  • Test all mechanical components, including fans, dampers, coils, and filters, for correct operation.
  • Validate control sequences and setpoints in the BEMS, ensuring they align with design specifications.
  • Balance airflow rates across all zones and confirm pressure levels.
  • Document commissioning results and provide an updated Operation and Maintenance (O&M) manual.

 

7. Plan for Long-Term Maintenance

 

A refurbished AHU requires regular maintenance to sustain its performance and efficiency over time.

 

Key Actions:

  • Schedule regular inspections for components such as filters, fans, dampers, and coils.
  • Monitor performance via the BEMS, including energy consumption, pressure drops, and alarm logs.
  • Update the O&M manual as new components are installed or control strategies are adjusted.

 

Conclusion

 

Refurbishing an AHU is a cost-effective alternative to full replacement, offering significant improvements in efficiency, reliability, and indoor air quality. Start with a thorough survey of the existing system, provide a clear specification, and focus on upgrading critical components such as fans, coils, and controls.
 

By integrating modern BEMS controls and ensuring proper commissioning, a refurbished AHU can deliver long-term benefits, reducing operational costs and enhancing occupant comfort.

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