By Eamonn Ryan

The following is derived from a Cape Town TechTalk on 10 June by Theo van der Linde, Pr. Tech, Head of Project at SFI Group, on the topic ‘Basics of Airflow Commissioning’. This is Part 10 of a 10-part article.

Thorough documentation and effective training are critical for the long-term success and maintainability of any HVAC system.

Thorough documentation and effective training are critical for the long-term success and maintainability of any HVAC system. Freepik

…continued from Part 9.

Effective data representation and a systematic troubleshooting approach are vital for both immediate problem-solving and long-term system maintenance.

  1. Clear data representation: Commissioning reports must present data clearly and intuitively. A well-structured report allows anyone, from the professional team to the client or a future maintenance technician, to immediately understand the system’s performance without needing to be physically on site. For example, a fan coil unit report should clearly show:
  • Design airflow versus measured airflow
  • Operating voltage and current
  • Other relevant parameters like coil temperatures

Similarly, a schematic layout showing the central pressure point of a system and how individual branch airflows contribute to the total flow provides an invaluable visual aid. This allows for quick cross-referencing and ensures data integrity, making it possible to revisit and understand the data months or years later.

  1. Systematic troubleshooting for low airflow: When encountering low airflow, a systematic approach starting at the source is paramount:
  • Source verification: Always begin by checking the primary air source – the fan or Air Handling Unit. Is it receiving power? Is it running at the correct speed or frequency? Is the fan motor drawing the expected current?
  • Upstream restrictions/blockages: Inspect components upstream of the fan.
  • Filters: Are filters clean and correctly installed? A clogged filter is a very common culprit for low airflow and high pressure drop.
  • Inlet louvres/screens: Are intake louvres or screens obstructed by debris?
  • Ductwork: Are there any physical blockages within the main intake duct? In existing buildings, accumulated debris (even just on an elbow) can significantly alter airflow characteristics.

Faulty components:

  • Fans: Do not rule out a faulty fan, even if it’s new. There have been instances where new fans deliver significantly less than the desired flow rate. If all other variables are correct, the fan itself might be the issue, necessitating a replacement from the supplier.
  • Actuators/dampers: Ensure that all dampers are fully open where intended. A common issue is a faulty or misaligned actuator on a damper (e.g., a chilled water valve actuator indicating 90 degrees open, but the valve itself is 180 degrees off due to incorrect installation). Also, consider the minimum open limit for VAV diffusers; restricting them too much (e.g., below 30% of their full open position) can cause actuator burnout or undesirable airflow patterns.
  • Sensors: Verify that pressure-inducing sensors (like those for VSD control) are working correctly and are calibrated. Incorrect readings from these sensors can lead to the fan’s Variable Speed Drive (VSD) operating at an inappropriate speed, resulting in insufficient airflow.
  • Design discrepancies: Review the original design. Were fan selections appropriate for the calculated system resistance? Were duct sizes adequate? Instances where clients downsize fans or alter duct routes due to space constraints after the initial design can severely impact system performance.
  • Access and continuity: Ensure that access points in the ductwork (e.g., for pressure taps) are visible and properly sealed with plugs for future continuity. This facilitates quick re-checks or troubleshooting down the line.
  1. Collaboration and expert assistance: In complex troubleshooting scenarios, collaboration is key. While it’s natural to try and solve problems independently, don’t hesitate to seek expert assistance. When a specialist is brought in, provide a clear, concise overview of what has already been checked. More importantly, allow them the space and time to assess the situation without constant interruptions, as fresh perspectives often lead to breakthrough solutions.

Final checkpoints for ongoing performance:

  • Installation quality: Poor installation quality, such as unsealed duct joints or damaged flexible connections, is a perennial issue that undermines design performance.
  • Sensor calibration: Ensure all sensors (temperature, pressure) and controls are regularly checked and calibrated, as their accuracy directly impacts system performance. This includes verifying that Building Management System (BMS) inputs align with actual conditions.
  • Fan direction: Confirm the fan’s rotation direction matches the intended airflow. Amazingly, some fans, particularly certain axial designs, can be installed or wired incorrectly to push air in the wrong direction, drastically reducing effective flow. Even if the arrow on the fan indicates direction, verify that the fan’s internal components (impeller body, intake cone) are oriented correctly.

By adhering to these principles of meticulous preparation, systematic measurement, clear documentation, and logical troubleshooting, airflow commissioning transitions from a mere compliance exercise to a powerful tool for ensuring optimal HVAC system performance, energy efficiency, and occupant comfort.

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