How to Size Chilled-Water Pipes Using Velocity and Friction Limits

nexoradesign.net
Jul 30
2 min read

Chilled-water pipe sizing may appear straightforward: calculate the required water flow and select a pipe large enough to carry it. In practice, however, a good hydronic design must balance several competing requirements.

A pipe that is too small can create excessive velocity, high friction loss, noise, greater pump head, and unnecessary pumping energy. A pipe that is unnecessarily large reduces pressure loss but increases pipe, insulation, fittings, valves, supports, and installation costs.

For this reason, chilled-water pipes should generally be selected by checking both water velocity and friction loss, rather than using either criterion independently.

ASHRAE describes a general hydronic pipe-friction design range of approximately 100 to 400 Pa/m, with about 250 Pa/m representing a typical mean design value. ASHRAE also notes that velocity, pressure drop, noise, erosion, installation cost, and operating cost all influence final pipe selection. (How to Size Chilled-Water Pipes Using Velocity and Friction Limits)

This article explains a practical method for sizing chilled-water piping using these principles.