Fluids & HVAC Quick Pack

Three fast checks: (1) Reynolds, friction factor, and pressure loss for water, (2) duct diameter from velocity method, (3) ACH to flow conversion. For concept sizing; use standards for detailed design.

1) Water Reynolds, f, and Pressure Drop (Darcy-Weisbach)

Flow Q [m³/h]Diameter D [mm]Pipe length L [m]Roughness ε [mm]Typical steel ~0.05 mm

Re106,103

f (Darcy)0.0227

Velocity v2.65 m/s

Δp (along L)99.81 kPa

Assumptions: water at 20°C (ρ=1000 kg/m³, μ=1 cP). Δp = f·(L/D)·ρv²/2. Minor losses, fittings, and temperature effects are excluded.

2) Duct Velocity Method (equivalent diameter)

Flow Q [m³/h]Target velocity v [m/s]

Area A833.33 dm²

Equivalent D326 mm

Dynamic pressure q22 Pa

Typical velocities: offices 4–6 m/s, industrial 6–10 m/s. Check manufacturer catalogs for noise and loss; elbows/dampers add extra losses.

3) Air Changes per Hour (ACH) ↔ Flow

Volume V [m³]ACH [1/h]

Flow1,200 m³/h

Flow (m³/s)0.333 m³/s

Typical ACH: offices 4–8, classrooms 6–10, labs 8–15. Check building codes and indoor air quality standards.

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Formula

Δp = f·(L/D)·ρ·v^2/2 | Re = ρ·v·D/μ | Q = A·v

Assumptions

Water at 20°C with ?=1000 kg/m³ and µ=1 cP assumed.
Minor losses and fittings are not included.

References

Crane TP-410 (Flow of Fluids)
ASHRAE Fundamentals

Standard Documentation

Fluids & HVAC

Scope: What does this tool calculate?

Fluids & HVAC performs the core engineering calculation for this tool type and presents results in a traceable format.

Assumptions and Units

SI units are the baseline; input unit consistency must be verified by the user.
The calculation path is deterministic (same inputs = same outputs).
If default material/environment values are used, replace them with project-specific values.

Limits / Boundaries

This tool is intended for preliminary sizing and technical checks, not final design approval.
When inputs are outside expected ranges, validate input quality before interpreting outputs.

Reference Standard