How do I size a control valve Cv for a chilled water coil?

Control valve Cv is calculated using the formula Cv = Q / √(ΔP), where Q is flow in GPM and ΔP is the pressure drop across the valve in PSI. For chilled water coils, a good starting point is to size the valve so it takes 25–50% of the available branch pressure drop at design flow, which typically yields good valve authority (0.25–0.50). Per ASHRAE Handbook, valves should not be oversized — an oversized valve will operate near the seat and exhibit poor control, often hunting between 10–20% stem travel. Belimo's Characterized Control Valve (CCV) line provides equal-percentage characteristics that compensate for coil heat transfer non-linearity when properly sized.