RACA Journal I June 2026 www. refrigerationandaircon. co. za 5
TECH TALK
CONSTANT VERSUS VARIABLE FLOW SYSTEMS BALANCE SIMPLICITY AND EFFICIENCY In chilled water system design, choosing between constant volume and variable volume approaches profoundly impacts energy use and performance.
Constant Volume( three‐way valve systems): Constant volume systems maintain a steady water flow through the coil circuit, regardless of cooling demand. A three‐way valve either directs flow through the coil or bypasses it – but the total flow rate remains unchanged.
This design is:
• Simple and reliable.
• Lower cost at installation( no variable speed drives or complex control instrumentation).
• Stable for chiller operation, reducing risk of low‐flow faults.
However, because pumps operate at full capacity even at low load, these systems are inherently less energy efficient, and bypassed water can result in a lower return water temperature( low ΔT syndrome), decreasing chiller efficiency. Variable loads are also more difficult to zone and control precisely in this configuration.
Variable Volume( two‐way valve systems): Variable volume systems regulate water flow to match demand using two‐way valves. As demand falls, the valve partially closes and pumps slow accordingly, reducing energy consumption.
Advantages include:
• Higher energy efficiency.
• Improved comfort and load adaptability.
• Lower mechanical wear from reduced pump speeds.
Drawbacks include increased system complexity, such as pressure differential sensors and variable speed drives, and a need for more sophisticated control strategies to avoid chiller low‐flow conditions.
Van der Vyver emphasised that the choice between constant and variable volume should be driven by the specific operational requirements of each building. The right balance of cost, complexity and efficiency depends on building profile and use patterns.
BELIMO BALL VALVES Traditionally, ball valves were not used for precise modulation because of their rapid flow increase with small openings. Belimo’ s Characterised Control Valve( CCV) changes this paradigm by integrating a characterising disc that shapes the flow curve to match an equal‐percentage control characteristic.
This design means:
• A 50 % control signal produces approximately 50 % cooling capacity, reducing control‘ hunting’.
• Smooth and predictable modulation across the control range.
• Air bubble‐tight shut‐off, minimising leakage and energy waste compared to traditional globe or butterfly valves.
CCV valves are robust and self‐cleaning due to the ball’ s rotary motion, enhancing longevity and reducing maintenance. From this foundation, Belimo developed the Energy Valve, which integrates:
• CCV ball valve.
• Ultrasonic flow measurement.
• Temperature sensing.
• Pressure‐independent control.
• Energy monitoring.
The energy valve can measure flow, temperature and energy transfer across a coil in real time. This enables analytics and diagnostics via a building management system( BMS) or cloud platform, helping operators identify issues such as dirty coils or performance degradation.
A key feature is the Delta‐T( ΔT) manager, which combats low ΔT syndrome by adjusting flow to maintain the desired temperature differential, improving both chiller and pump efficiency.
CCV FOR WATER APPLICATIONS Belimo’ s CCV technology valves deliver precision modulation with features such as:
• Smaller ball designs requiring less actuator torque.
• Equal percentage flow characteristics that ensure proportional system response to control signals.
• Air bubble-tight shut‐off to prevent unwanted flow and conserve energy.
These features improve performance, longevity and maintainability in chilled‐ and hot‐water systems.
PIQCV AND ENERGY VALVES Modern HVAC water circuits increasingly use pressure‐independent control valves( PIQCV) like Belimo’ s, which automatically regulate flow independent of system pressure fluctuations. The PIQCV’ s mechanical design maintains a set flow rate despite differential pressure changes, eliminating the need for manual balancing valves.
The Energy Valve builds on this by adding energy and flow measurement, and cloud connectivity. It uses ultrasonic flow sensing, temperature inputs and built‐in logic to provide real‐time data on performance, enable energy profiling and optimise chilled‐water distribution.
CONCLUSION Belimo’ s actuator and valve technologies represent a comprehensive solution framework for modern HVAC control – supporting precise airflow and hydronic regulation, smart diagnostics, energy optimisation and adaptability for varying building demands. By combining robust mechanical design with digital connectivity and intelligent control strategies, these solutions contribute to efficiency, comfort and operational insight across installations. RACA
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RACA Journal I June 2026 www. refrigerationandaircon. co. za 5