The heat dissipated at the end of a control loop typically exhibits nonlinear behavior with respect to water flow. This nonlinearity can be mitigated by using a control valve that has inverse characteristics, creating a system (valve + end device) that provides a linear relationship between heat output and valve position, as well as between valve opening and the control signal. However, the valve's performance is based on a constant differential pressure, which may vary with changes in flow, leading to deviations from expected behavior. As a result, the heat output from the terminal device remains nonlinear relative to the valve opening, with the degree of nonlinearity depending on the valve’s characteristics and its authority within the system.
If the nonlinearity is severe, control becomes challenging, especially at medium or light loads, where small flow changes can cause significant fluctuations in heat output. Excessive flow can also lead to poor control, forcing the control valve to operate near the closed position under design load conditions, which causes instability and inaccuracies. Overflow is a major obstacle in achieving effective control, as it not only leads to frequent valve closure but also causes uneven flow distribution across loops, preventing some areas from receiving adequate heating or cooling.
To ensure stable and precise control, balancing valves and proper system balancing are essential for all control loops. Maintaining the flow rate of the heat source within manufacturer-specified limits protects equipment, but does not guarantee optimal performance or energy efficiency. If flow is too low, the system cannot reach its designed capacity, while excessive flow can cause other units to underperform. This often results in unnecessary unit cycling, reducing productivity and increasing energy use.
Installing balancing valves at each unit allows for accurate flow measurement and adjustment, ensuring that both the heat source and distribution system operate within their design parameters. These valves help detect and correct imbalances, maintain proper flow rates, and coordinate the operation of the heat source with the distribution network. They also enable more efficient control, reduce temperature fluctuations, and improve overall comfort.
Balancing the system ensures uniform flow distribution, reduces room-to-room temperature differences, and allows for better control strategies. It also helps lower energy consumption by optimizing average temperatures in heating and cooling zones. Additionally, balanced systems allow centralized controllers to apply consistent control curves across the entire building, improving the effectiveness of zone controllers and thermostatic valves.
In summary, installing balancing valves at key points in the system—such as at each unit, riser, and branch—is crucial for achieving stable, efficient, and comfortable operation. Once installed, these valves provide a reliable tool for diagnosing and resolving issues, ensuring the system performs as intended.
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