Every segment is auto-sized on the basis chosen under Pipe sizing, and judged against Velocity bands and ΔK limits. Both are on the sheet below the ledger.
- 1
Under Pipe sizing, choose Velocity target, Max ΔK or Both in Auto-size driven by.
- 2
For Max ΔK or Both, enter a Max ΔK total for each line type in Velocity bands and ΔK limits. A line type left blank stays on the velocity target.
- 3
Check each line type's velocity Min and Max. The Source column says whether a figure is the page default, as saved with the layout, or entered on this page.
- 4
Read the result in the Segment ledger. Under each size it says how it was reached: on the velocity target or the ΔK budget, raised to the largest branch it feeds, or entered on this page.
The three bases
- Velocity target picks the smallest tube whose velocity is at or below the line's target.
- Max ΔK shares each path's saturation-drop budget along it, per equivalent metre, from the plant out. Trunks take their share, and the last run on each path takes what's left.
- Both starts from the velocity sizes and raises a size only where a path needs it to stay inside its budget, the cheapest raises first.
A path is every segment carrying an evaporator's flow back to the plant, tee-offs included. Kelvin sums the pressure drop along it and reads it as a drop in saturation temperature at the line's own pressure: on the dew line for suction, the bubble line for liquid.
The velocity bands
- The page starts at suction 4–12 m/s (target 8), discharge 10–18 m/s (target 15) and liquid 0.5–1.5 m/s (target 1.0). The Source column cites the ASHRAE Handbook—Refrigeration Ch.1 velocity practice, and says where the page's own suction edges and liquid maximum differ from it.
- A segment above its band is flagged critical, and one below it a warning.
- A condenser drain to the receiver is judged against a maximum only, because a drain should run slow.
- Reset to defaults puts all the sizing settings back to the page's own, the tube series and standstill temperatures included.
Sizes you choose
- Pick a size in a row's Size cell to fix it. The ΔK bases never change a size you entered, and it counts against every path through it. Choose Auto to hand the segment back.
- A trunk is raised to at least the largest branch it feeds, but a size you entered is never raised.
- If a path can't be held inside its budget, because of sizes you entered or because the largest tube isn't enough, it's left over and flagged Path over ΔK limit.
Note
A line type with no Max ΔK total is never judged on ΔK. With one set, each segment is judged on its own saturation drop and on its path's.