Pressure-Independent Control Valves: Selection and Application Guide

nexoradesign.net
Jul 31
2 min read

Modern chilled-water and hot-water HVAC systems increasingly use variable pumping energy and improve part-load performance. However, variable flow creates an important control challenge: as control valves throughout the system open and close, the differential pressure available at individual coils continuously changes.

A conventional two-way control valve is pressure-dependent. If its opening position remains unchanged while the differential pressure across the valve increases, the water flow also increases. This can cause overflow through nearby coils, unstable temperature control, actuator hunting, poor hydronic balance and, in some systems, reduced chilled-water ΔT.

A Pressure-Independent Control Valve (PICV) addresses this problem by combining flow control, automatic differential-pressure regulation and flow limitation within a single valve assembly. (Pressure-Independent Control Valves: Selection and Application Guide)

ASHRAE describes PICVs as control valves incorporating internal differential-pressure regulation so that flow variations caused by changing system differential pressure are substantially eliminated. In practical applications, a PICV can replace both a conventional control valve and a separate balancing device. de explains how PICVs work, how to calculate the required design flow, how to select the correct valve, how minimum differential pressure affects pump selection, and how PICVs should be applied and commissioned in chilled-water and heating systems.