Project Information
Fluid & material
CHW · 7 °C · waterForward sizing — what size pipe?
load + ΔP/m + Vmax → DNResult
Pipe Sizing Summary
Design Conditions
| System | — |
|---|---|
| Fluid | — |
| Material | — |
| Design ΔT (Supply ↔ Return) | — |
| Vmax allowance | — |
| ΔP/m allowance | — |
| Fittings allowance | — |
Calculation Basis
| Mode | — |
|---|---|
| Solver | Darcy-Weisbach friction · Colebrook-White friction factor |
| Cooling/Heating Load | — |
| Run Length | — |
| Elevation Change ∆h | — |
Calculation Results
| Recommended Pipe | — |
|---|---|
| Internal Diameter | — |
| Flow Rate | — |
| Velocity | — |
| Friction ΔP/m | — |
| Total Run ΔP | — |
| Limits Check | — |
Notes & References
What you need to know to read your sizing results.
Fundamentals + how the four modes work + what each output is telling you. Engineer-to-engineer. No fluff. No theory you don't need.
What this tool does
CW Pipe Sizer Lite answers four questions about a single pipe segment using Darcy-Weisbach friction with Colebrook-White friction factors. Same canonical engine as Pro. The four modes change which variable you're solving for — pick the unknown, enter the knowns, read the result.
Five things you need to read the output
The minimum theory to understand what Lite is calculating, what the limits mean, and which numbers matter for your decision. If you already know this, skip to section 3.
For a given flow, smaller pipe means higher velocity and more friction. Bigger pipe means lower velocity and less friction.
That's continuity (v = Q/A) and Darcy-Weisbach friction (ΔP/L ∝ v²/D) competing. Sizing finds the sweet spot — small enough for capex, big enough to stay below noise + erosion limits + within your pressure budget.
Velocity isn't only hydraulics. Above ~2.4 m/s in chilled water, you start to hear the pipe — turbulence noise, valve singing, flow-induced vibration.
Above ~3.5 m/s, erosion of pipe walls becomes a real concern over 20+ years. Lite's defaults bake in typical ASHRAE / CIBSE / AS·NZS practice. Override per project type.
The pressure-loss budget per metre of pipe. Default 400 Pa/m for chilled water — about 4 ftH₂O per 100 ft, the standard HVAC sizing target.
Higher = smaller pipe + more pump energy. Lower = bigger pipe + less pump energy. Tighten for energy-conscious projects, loosen for capex-constrained ones.
What the pump has to overcome:
- Friction — what the engine calculates from pipe + flow + fluid
- Static head — ρ·g·Δh when pipe rises against gravity
- Component ΔP — coil, FCU, or control valve in the loop
Combined head = friction + static + component. That's what you take to the pump vendor.
Re = ρvD/μ. Tells you the flow regime:
- Re < 2,300 — Laminar (rare in HVAC; smooth, predictable, low friction)
- 2,300 – 4,000 — Transitional (avoid — friction is unpredictable)
- Re > 4,000 — Turbulent (where HVAC lives; friction depends on pipe roughness)
Concept-stage HVAC is always turbulent. The Reynolds strip in the Sizer shows you where you sit; if it lights up anything other than turbulent, something's unusual about your scenario.
What each part of the result is telling you
When you compute, the Sizer produces a result card and a sweep card — six distinct elements, each with one job. Here's what to look at and why.
Mode 1 returns DN. Mode 2 returns ΔP. Mode 3 returns flow rate. Mode 4 returns max length. The headline is the single number you came for.
Source → supply pipe → component → return. Pipe length, friction ΔP, elevation rise (when present), and component ΔP all annotated on the diagram. Below the SVG: combined head, flow rate, and pump duty.
Inner bore, outer diameter, velocity, ΔP/m, flow rate, total ΔP, friction factor, Reynolds number. The grid is your sanity check — read each value against your fundamentals.
Three coloured bands (laminar / transitional / turbulent) on a log scale. Marker shows current Re. For HVAC concept-stage work it should land deep in turbulent. If it doesn't, expect the result.
Cyan line = velocity (left axis). Yellow line = ΔP/m (right axis). Three background bands behind the velocity line: green silent, yellow acceptable, red noisy. Engineer pick (♦) should land in green or yellow.
Parametric sketch — system curve through your design point, generic pump curve passing through the same point. Take Q* and H* to your vendor. Add 10–15% margin for fouling and tolerance. The pump curve is illustrative, not a real product.
What Lite is for · and what it isn't
Lite is concept-stage. Single-pipe what-if sizing. Quick answers, sensible defaults, no project authority. Engineer-of-record verifies. That's how concept-stage tools work — and it's why Lite stays useful as a thinking tool while Pro handles project deliverables.
Lite gives you confidence in the decision in seconds. When you need more — multi-pipe schedules, QA gates, sign-off, BIM/CAD export, project-graded reports — that's a different tool, on purpose.