Design settings
Detailed method
One node per fitting along the index run, from the fan to the last terminal. Tap a picture to see the fitting. Tees, wyes and transitions: the row is the outlet or branch (W2, H2, Q2); the inlet W1, H1, Q1 comes from the previous node unless you type it.
Quick method
Each column is one section of the index run, starting at the fan. Enter flow, length and size, then how many of each fitting are in that section. Elbows use the project elbow setting.
Accessories & terminals
Enter each item's own size and flow. The suggested pressure drop scales from a typical catalogue point; type the manufacturer's value in Override when you have it.
Design basis
Methods behind every number on this page. The same text is printed in the PDF report.
Duct friction
Velocity from the actual duct area (W × H, or π·Ø²/4). Velocity pressure Pv = ρ·V²/2.
Darcy-Weisbach ΔP/L = (f/Dh)·Pv, hydraulic diameter Dh = 2WH/(W+H), Re = 66.4·Dh·V, Altshul-Tsal friction factor f' = 0.11(ε/Dh + 68/Re)^0.25; f = f' if f' ≥ 0.018, else 0.85f' + 0.0028 (ASHRAE Fundamentals, Duct Design).
Fittings
ΔP = C·Pv with C worked out for each fitting's own size and flow.
Elbows: smooth radius rectangular elbows from the ASHRAE CR3-1 table by r/W and H/W (W = side in the plane of the bend), round elbows by r/D (ASHRAE CD3-1), × ASHRAE angle factor K. Choose the radius for each elbow in the Elbow column. Mitred elbows with or without turning vanes use typical values.
Junctions use r = V/Vupstream: straight-through C = 0.4(1−r)²/r²; angled branch C = A'(1 + r² − 2r·cos α)/r² (Idelchik); 90° conical tap C = (1 + 0.6r²)/r², fitted to ASHRAE data.
Transitions: expansion φ(1 − A1/A2)² on upstream Pv; contraction k(1 − A2/A1) on downstream Pv, by included angle.
Accessories and totals
Accessories: ΔP = ΔPref·(V/Vref)² from typical manufacturer catalogue points (mid-to-upper range). Use the manufacturer's selection value (Override) for final design.
Total ESP = (duct + fittings + accessories) × (1 + safety factor), rounded up to the selection step. ESP excludes losses inside the fan unit (coils, internal filters, casing).
Junction relations are for supply (diverging) flow. For return and exhaust systems the same relations are applied and the report says so.