South Africa’s interior is warming at roughly twice the global average, according to the CSIR.
Summers now carry more extreme heat days, longer heatwave sequences and higher night-time temperatures. These shifts directly affect how HVAC systems behave. Air handling units (AHUs) built for past climate conditions run closer to their limits, recover more slowly between cycles and struggle to keep indoor temperature and humidity stable. The hotter the outdoor air becomes, the harder each stage of the AHU must work, and the smaller the margin between design assumptions and real operating conditions.
As the temperature difference between outdoor air and indoor setpoints shrinks, heat transfer across the cooling coil drops. Motors operate under higher thermal stress and airflow stability becomes more sensitive to pressure changes. Buildings that rely on older or lightly specified AHUs feel the effects first: rising indoor temperatures, humidity drift, comfort complaints and increased energy use. These problems aren’t faults in the equipment so much as a mismatch between design expectations and a climate that has changed faster than most systems were prepared for. AHUs built for today’s conditions use deeper coils, efficient motors, corrosion-resistant materials and adaptive controls that respond to rapid load fluctuations through the day.
South Africa’s inland regions warm faster because they lack coastal moderation and experience greater day–night temperature swings. Cities such as Johannesburg, Pretoria and Bloemfontein also carry strong urban heat island effects. Higher night-time temperatures reduce cooling recovery periods, so AHUs enter the next day with components that are already warm. As heatwaves become more frequent, sensible heat rises sharply, and latent load becomes harder to predict. Even in historically dry inland areas, hotter air holds more moisture, especially after rainfall or when subtropical air masses move over the interior. This makes humidity control a more complex task for coils that were sized primarily for sensible performance.
Psychrometric behaviour shifts significantly when ambient conditions rise. A higher dew point means the coil must remove more moisture before the air reaches supply conditions. More moisture also means more condensate. If the coil surface is undersized, or if the face velocity is excessive, the coil struggles to stabilise both temperature and humidity. Carry-over becomes a risk when condensate forms faster than it can drain, and this leads to wet downstream components, microbial growth and inconsistent humidity control. Modern AHUs rely on coil geometry, fin spacing and airflow management that support both temperature and moisture stability in hotter, more variable environments.
Different regions of South Africa impose distinct performance requirements. Inland provinces face long spells of dry heat, sharp afternoon peaks and big temperature swings. AHUs in these areas need larger coil surfaces and airflow paths designed to hold performance steady during long afternoon load periods.
Coastal environments place corrosion at the centre of design decisions. Warm, moisture-heavy air carries salt that settles on untreated metals and reduces heat transfer. Coils, casings and fasteners need protective materials or coatings to extend service life. Wider fin spacing reduces clogging and makes cleaning easier in areas exposed to salt, sand and organic debris.
Altitude changes air density. Above roughly 1 300 metres, less dense air reduces mass flow. If fans are not sized for altitude, airflow drops and pressure regimes shift, especially in buildings that rely on stable pressurisation. Matching the AHU to the region prevents premature wear, protects airflow stability and reduces energy waste.
Heat load affects every stage of the AHU. As more heat enters the system, coils must work harder to pull supply air back to its target, and the system relies more heavily on cold-water temperatures or DX performance upstream. If the upstream source is already strained, the AHU shows it through unstable supply conditions.
Humidity becomes more challenging as well. When ambient moisture rises, coils must remove both heat and moisture at once. If the design favoured sensible cooling over latent capacity, the system reaches its limits quickly. Condensate patterns shift, airflow paths change and small oversights in selection become visible during extreme weather.
Mechanical components feel the effect of prolonged high temperatures. Bearings, belts and motors operate in hotter environments for longer periods, which accelerates wear. A climate-ready AHU spreads the load across coil geometry, airflow paths, motor efficiency and thoughtful component placement to maintain stable operation during extended heat cycles.
Coils are central to how well an AHU performs in modern South African conditions. Deeper or multi-row coils give air more contact time with the cooling surface. This stabilises supply air during long periods of high ambient temperature without forcing the chilled-water plant or DX system to compensate unnecessarily. Face velocity influences both heat transfer and moisture control. Lower velocities reduce the risk of moisture carry-over, maintain pressure stability and improve temperature consistency across the coil.
Fin spacing must suit the environment. Inland facilities benefit from tighter spacing that boosts heat transfer. Coastal or dusty areas perform better with wider spacing that resists clogging and simplifies cleaning. Protective coatings like epoxy, hydrophilic or phenolic, extend coil life where corrosion risk is high. Well-matched coil geometry reduces energy penalties, limits fouling and stabilises humidity throughout the hottest periods.
South Africa’s fluctuating power supply influences HVAC reliability as much as heat does. Voltage dips during load-shedding or generator transitions increase current draw and stress motor windings. Efficient motors help counter these effects. IE3 and IE4 motors run cooler, use less energy and tolerate supply variation better than older models. EC motors add further benefits through precise speed control and excellent part-load performance. When paired with suitable VSDs, soft starters and surge protection, the AHU recovers smoothly from interruptions and maintains airflow even when supply conditions shift.
VC 8086 establishes IE3 as the minimum efficiency level for qualifying industrial motors. This provides a solid baseline for AHU performance and ensures equipment can handle both heat and irregular power without rapid degradation. Motor efficiency becomes a resilience feature, not simply an energy-saving measure.
Modern AHUs rely on real-time data from temperature, humidity, pressure and airflow sensors. Controllers adjust fan curves, coil temperatures and water flow in response to live conditions. When outdoor temperatures rise sharply, adaptive logic helps the system stabilise supply air quickly. Advanced controllers identify daily patterns within a building and prepare for afternoon loads before indoor conditions shift.
Reliable data also improves maintenance. Clear trend logs help facility teams detect signs of strain early, such as rising fan power, unusual temperature spreads or unstable humidity. Early intervention reduces downtime and prevents component failure during peak summer periods.
Performance testing ensures an AHU behaves as intended once installed. Factory tests confirm casing strength, thermal bridging, air leakage and acoustic performance under controlled conditions. ISO 5136 measures fan noise in a ducted setup. EN 1886 verifies panel performance, thermal resistance and mechanical reliability.
Commissioning checks confirm that coil temperatures, static pressure, airflow and condensate behaviour match expected values. Early trend data shows whether the AHU performs within its design envelope as the building settles into real operating cycles. Facilities that depend on stable environmental conditions — such as hospitals, laboratories and data-sensitive spaces — rely on this documentation to maintain compliance.
Hotter conditions influence filtration needs. Dust, pollution and particulate levels often spike during heatwaves, increasing filter loading rates and affecting airflow. If filters load too quickly, static pressure rises and the AHU must work harder to maintain stability. Stable pressure is essential for comfort, indoor air quality and specialised spaces that rely on controlled pressurisation.
Climate-ready AHUs use filtration stages that hold performance under varying loads and maintain clean airflow paths. Well-selected filters protect coils, reduce cleaning frequency and help stabilise temperature and humidity in downstream spaces.
Heat load management begins before air reaches the coil. Mixed-air plenums, return-air strategies, duct insulation and outside-air volumes all influence the AHU’s workload. Economiser cycles become less effective in hotter climates because outdoor air rarely falls below indoor temperature. Good return-air design and insulation reduce solar gain and help the AHU maintain stable performance during peak hours.
Bypass factors, coil face area and air distribution patterns also shape how the AHU handles extreme heat. When upstream and downstream systems align with the AHU’s design, the entire HVAC system performs more predictably under strain.
Chilled-water plants and DX systems feeding AHUs also face higher strain when temperatures rise. Condenser performance drops as ambient conditions increase, forcing compressors to work harder. Chilled-water supply temperatures may need tighter control to maintain the AHU’s capacity. Delta-T degradation becomes more common as loads rise, affecting pump performance and energy use. Aligning coil selection with plant capability helps prevent unstable operation throughout the cooling season.
The building envelope plays a major role in how hard the AHU must work. Roofs, walls and glazing exposed to intense solar load raise indoor heat gains. Better insulation, exterior shading and low-solar-gain glazing reduce this burden and help the AHU maintain stable supply conditions during hot afternoons. Duct insulation prevents heat gain in pathways exposed to warm plant rooms or sun-heated shafts.
Climate-ready AHUs need maintenance plans that reflect longer, hotter summers. Coils in coastal areas may require more frequent cleaning. Bearings, belts and motors need temperature checks during peak season. Filters load faster during dusty, hot periods and require closer monitoring. Seasonal commissioning before summer ensures valves, sensors and control sequences respond correctly once loads rise. Trend logs often reveal early signs of performance issues, giving teams time to act before failures occur.
When AHUs are designed for higher ambient conditions, they hold performance more consistently, reduce mechanical stress and maintain airflow stability. Buildings experience steadier temperatures, better humidity control and improved air quality. Facilities pursuing Green Star SA or WELL certification benefit from reliable control of comfort, filtration and environmental quality.
Air Options designs and manufactures AHUs that match South Africa’s rising heat loads, variable humidity and unstable power conditions. Each unit is built around its operating environment, with deeper coils, efficient motors, corrosion-resistant components and adaptive control options. This approach supports dependable cooling, predictable operating costs and long-term performance.
If your project needs an AHU built for current and future climate demands, our team can assist with selection, configuration and technical guidance.
Contact the Air Options team here.
Get the latest updates in your email box automatically.
Your nickname:
Email address:
Subscribe
Request A Quote