Velocity-Based Pipe Sizing

Velocity-based pipe sizing is an engineering approach that selects pipe diameters to maintain flow velocity within a specified range. Unlike table-based methods that prescribe sizes from code tables, velocity-based sizing calculates the theoretical minimum diameter from the flow rate and velocity limits, then selects the nearest available pipe size.

The velocity-based method in Plumbing Booster: 1. **Determine design flow rate** — From WSFU conversion or manual entry. 2. **Set velocity limits** — User-configurable minimum (default 0.5 m/s) and maximum (default 2.5 m/s). 3. **Calculate theoretical diameter** — Using Q = V x A, solve for inner diameter: d = sqrt(4Q / pi*V). 4. **Select nearest pipe size** — Map the theoretical inner diameter to the closest available pipe. 5. **Calculate actual velocity** — Recompute velocity with the selected pipe's actual inner diameter. 6. **Check friction loss** — Use the Hazen-Williams equation with material-specific C-factor. 7. **Compliance check** — Verify actual velocity is within limits.

While not directly from a code table, velocity-based sizing aligns with: - **IPC Section 604.5** — Water velocity guidelines (recommended <= 8 ft/s) - **ASHRAE Applications Handbook** — Service water heating velocity recommendations - **Hazen-Williams equation** — Standard fluid mechanics formula for water flow in pipes

Given: 14 GPM (0.88 L/s) design flow, max velocity 2.0 m/s, PPR PN10 SDR 11 pipe. Theoretical inner diameter: d = sqrt(4 x 0.00088 / (pi x 2.0)) = 0.0237 m = 23.7 mm Nearest PPR PN10 SDR 11 pipe with ID >= 23.7 mm: - 25mm OD -> ID = 20.5 mm (too small) - 32mm OD -> ID = 26.2 mm (selected) Actual velocity with 32mm PPR (ID = 29.1mm): V = 4 x 0.00088 / (pi x 0.0291^2) = 1.33 m/s (within 0.5-2.5 m/s). Friction loss (C=150 for PPR, L=10m): hf = 10.67 x 10 x 0.00088^1.852 / (150^1.852 x 0.0291^4.87) = 0.012 m head per 10 m.

In System Structure Configuration, select "Velocity-Based" as the pipe sizing method. Set your min/max velocity limits. The software: - Calculates separate cold and hot water pipe sizes for each branch and riser. - Uses material-specific inner diameters (PPR, PEX, Copper, CPVC, UPVC). - Applies Hazen-Williams with material-specific C-factors. - Shows compliance status and velocity warnings in the System Summary. - Suggests alternative materials when velocity limits cannot be met.