Size a hydronic pipe network

Pipe Sizing sizes one pipe network on a circuit, segment by segment. What it's mostly for is the index circuit's total, the head the pump is sized on, and the network's water volume, which the expansion tank needs.

• –A segment's flow is the flow of the terminals it ends at plus everything that branches off below it, so a trunk carries the sum of its branches. A fixed flow on the segment overrides that sum, for a constant-flow bypass or a minimum-flow line, and the branches below it are still sized on their own flows.
• –The return length mirrors the supply length unless you enter one.
• –The size is the smallest in the dimensions table at which both the velocity and the pressure gradient sit inside the criteria band for that size. The Rule column states the band each segment was judged by.
• –Friction is Darcy–Weisbach with the Colebrook–White friction factor, over the supply and return lengths, with the circuit fluid's density and viscosity. Each fitting adds its resistance from its library row, as K times the velocity pressure.
• –A segment reads Within criteria when its size meets the band. A size you picked is kept whatever it gives, and reads Within, as fixed or Outside, as fixed.

The index circuit is the supply-and-return path from the plant to the terminal with the highest total, with that terminal's own pressure drop from Circuits included. Its segments are marked on the ledger. Index circuit total is the head Pumps takes as its network pressure drop, and Network water volume is the pipework volume Expansion & Volume takes.

Balancing totals every terminal's path the same way and shows its Surplus to absorb: the index total less the path's own, which a balancing valve on that branch must throttle away for the terminal to take its design flow. The index terminal has none.

• –When no size in the table meets the criteria, Kelvin shows the largest and the segment reads No size meets it. It never invents a size the table doesn't list.
• –The network doesn't hold together yet means a segment branches off one that's no longer in the network, or segments loop back on themselves. Give the segment a new parent, or make it a source segment.
• –A terminal no segment ends at is named in a notice: its flow never enters the network, so the segments above it are sized low.
• –A terminal is served twice when more than one segment names it, so its flow is counted twice in the trunks.
• –Every segment needs a length. A blank length holds the whole network back: Kelvin never takes it as nil.
• –A terminal with no pressure drop entered on Circuits is totalled with none, so the pump head may be understated and its surplus reads high.
• –Flow between laminar and turbulent carries a warning: the gradient is taken on the turbulent, conservative side, and a size that clears that range is worth considering.
• –The network also waits for the circuit's fluid properties, and for every library table it uses. A fitting whose row gives no K for the size chosen counts as a missing table. See missing reference tables.

The dimensions, roughness, criteria and fittings are always chosen from Kelvin's reference library, never typed. Where the library has none of a kind, the cell says so. Saving a network makes the circuit's pumps and vessel stale, because both are sized on figures from it.