Optimising AHU Design for Active Chilled Beam Systems

Humidity Control and Dew Point Management

The required ventilation rate is determined by national regulations, client specifications and application type. To maintain humidity within design parameters, the primary ait must be supplied at a flow rate and dew point that offsets the latent gains in the occupant zone.

Typical room setpoints are as follows:

• 24°C dry bulb / 50% RH → Dew point ≈ 12.9°C
• 25°C dry bulb / 50% RH → Dew point ≈ 14°C

To prevent condensation on chilled beam coils, chilled water is supplied 1°C above the dew point, typically at 14°C, with a return temperature of 17°C. This results in a mean water temperature of 15.5°C, optimising thermal performance.

Condensation Prevention with BMS Controls

To avoid condensation risks, the following Building Management System (BMS) strategies are recommended:

• Monitor internal relative humidity to ensure chilled water temperature remains above dew point
• Use condensation sensors to shut off chilled water supply when condensation is detected, this is important in spaces with openable windows.

However, these strategies result in reduced chilled beam cooling capacity when the external conditions are higher than the design temperatures and humidity – an increasing situation because of climate change.

Challenges with External Humidity

External humidity often exceeds design conditions. For example, a typical design condition in London is 32°C / 50% relative humidity (RH) but actual humidity is often higher. On hot days, this results in an increase in the chilled beam water temperature, reducing cooling capacity when it is needed most.

This can be clearly illustrated in the above reported weather graph for London, which shows that relative humidity remains consistently above 50% for most of the year. Here the graph tracks temperature and humidity from January 2024 to January 2025, highlighting the seasonal changes. Even during those peak summer temperatures, humidity levels often exceed design expectations. This reinforces the need for well delivered dehumidification strategies within AHU design.

Energy Efficiency Advantages of Chilled Beam Systems

Despite these challenges that are posed by high external humidity, chilled beams systems offer notable energy efficiency benefits over traditional fan coil units. One key advantage lies in the higher operating temperatures of the chilled beam system. A chiller running at 14/17°C is significantly more efficient than one operating at 6/12°C [1] resulting in:

• Lower energy consumption
• Reduced CO2 emissions
• Improved overall system efficiency

The benefits of the more efficient chiller are ideally matched to FläktGroup’s iQ STAR chilled beam range, which is designed for ventilation, cooling and heating. With its flow pattern control and adjustable induction, it supports in providing comfort and flexibility in those high demanding indoor environments.

This efficiency gain proves particularly valuable in modern buildings aiming to meet sustainability targets and with our full range of chilled beams being EPD certified you’re sure to meet those targets.

Additionally, when paired with one of our AHUs that manage humidity and temperature, our chilled beam systems can outperform even the most advanced VAV fan coil setups.