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The Issue of Incorrect Control Valve Sizing

Research suggests that well over 50% of control valves within hydronic systems are wrongly sized because of incorrectly fixed Kvs (valve coefficient) values. This is due to a number of reasons, for example, in some cases control valves are pre-mounted onto the cover of the fan coil unit during production, which means the control valve is sized in respect of the fan coil unit rather than the system design. Incorrect sizing can also occur if pressure drops are unknown at the time of specification or if plant modifications are made during or after installation, which render the set kvs values obsolete.

The Consequences

The consequences of this can be far reaching; valves that are not properly sized lead to poor control performance and inefficiency within the system, with oversized valves increasing investment and energy costs due to unnecessarily larger dimensions and control hunting, and undersized valves leading to greater energy consumption as they cause the pump head to increase.