RACA Journal I July 2026 www. refrigerationandaircon. co. za 9
TECH TALK
Measurement lies at the heart of commissioning, and the choice of instrumentation plays a key role. Vane anemometers, hot wire probes, and differential pressure meters are commonly used to determine airflow rates, velocities and pressure relationships. While modern instruments can simplify calculations, they should not replace an understanding of the underlying principles. The fundamental relationship between airflow, area and velocity remains essential knowledge. Without it, the commissioning process risks becoming a series of automated readings rather than an informed assessment of system performance.
This understanding becomes particularly important when interpreting real-world conditions. Manufacturer fan curves, for example, are typically based on laboratory testing under ideal conditions. On site, factors such as air density, turbulence and installation constraints can significantly affect performance. It is therefore prudent to approach these curves with a degree of conservatism, recognising that actual performance may differ from theoretical predictions.
FROM MEASUREMENT TO MAINTENANCE: ENSURING LONG-TERM SYSTEM INTEGRITY Practical challenges are an inevitable part of commissioning. Turbulent airflow, caused by bends, transitions or poorly installed ductwork, can make accurate measurement difficult. Flexible ducts, especially when installed with excessive bends or poor routing, introduce variability that is often overlooked during design. In some cases, measurement itself becomes problematic, particularly with fans that discharge air radially or systems where access is limited. In such situations, commissioning requires not only technical skill but also practical judgement.
These challenges are perhaps best illustrated through real project experience. In one instance, a fresh air system was unable to achieve its required airflow due to a combination of restricted intake geometry and highly turbulent flow conditions. Despite repeated attempts to optimise the system, physical constraints prevented the desired performance from being achieved. The lesson in such cases is that commissioning should not be seen as a corrective process alone, but as an integral part of design thinking.
In controlled environments, such as cleanrooms and laboratories, airflow takes on an even greater level of importance. Here, it is not only the quantity of air that matters, but also its direction and cleanliness. Pressure cascades must be maintained to ensure that air flows from cleaner to less clean areas, preventing contamination. These conditions are verified through differential pressure measurements and particle counting, forming part of a rigorous validation process that is often repeated annually.
When systems fail to perform as expected, troubleshooting must begin at the source. Verifying the performance of the fan or air handling unit provides a baseline from which all downstream measurements can be assessed. Checking main duct airflow before moving to individual diffusers can save significant time and effort, preventing the need to remeasure large portions of the system. Many issues ultimately trace back to relatively simple causes – blocked filters, incorrect damper settings, or even installation errors such as reversed fan orientation or improperly connected ducting.
Indeed, some of the most impactful problems arise from the simplest oversights. A fan installed in the wrong direction can result in a substantial loss of airflow, while incorrectly configured components can reduce system performance by as much as 40 – 50 %. These are not complex engineering failures, but basic errors that highlight the importance of thorough inspection and verification.
The final stage of commissioning, documentation, is often underestimated. A well-prepared commissioning report does more than record measurements; it tells the story of the system. It captures the conditions encountered on site, the tests performed and the corrective actions taken. For those who were not present during commissioning, this documentation provides essential insight into how the system operates and how it should be maintained.
Industry data suggests that a significant proportion of HVAC systems, both new and existing, operate with deficiencies. This is not necessarily due to poor design or installation, but rather to insufficient commissioning. The process is either rushed, simplified or treated as a formality, rather than as a critical phase in project delivery.
Airflow commissioning, when approached correctly, is far more than a technical exercise. It is a discipline that combines engineering knowledge, practical experience and attention to detail. It ensures that systems do not merely operate, but perform efficiently, safely and as intended. In doing so, it underpins the quality and reliability of the built environment and reinforces the value of expertise within the HVAC industry. RACA
The presentation of a technical talk at Cape Town SAIRAC Centre by Theo van der Linde on 14 April 2026. networking associations
RACA Journal I July 2026 www. refrigerationandaircon. co. za 9