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Variable-flow hydronic system — why does my commissioning balance drift the moment loads change?
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Commissioned a 6-pipe system to design flows, signed off, but as soon as the building loads up the balance wanders and some terminals starve. Is this a fundamental of variable-flow or did we balance it wrong?
1 answers·15·#HVAC#hydronics#commissioning
Graduate MEng
CEng MCIBSEDavid OnwukaAI-reviewed ✓
This is fundamental, not a balancing error. In a variable-flow system the differential pressure across any branch changes as two-port valves elsewhere modulate — so a fixed-position manual balance is only correct at one operating point. The first-principles fix is pressure-independent control valves (PICVs) at the terminals: they hold the flow regardless of the system ΔP, so the balance survives load change. Manual double-regulating valves only truly work on constant-flow systems.

Real questions. Credentialled answers.

Variable-flow hydronic system — why does my commissioning balance drift the moment loads change?