Duct Sizing Calculator (Equal Friction Method) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t7-131

Effect

Computation or source lookup only

Input and validation requirements

• Division by zero or invalid fifth-root results occur for zero/negative friction rate, zero/negative airflow, invalid density, or invalid friction factor.
• A friction chart is invalid outside its Reynolds-number, roughness, diameter, and velocity ranges; extrapolation must be prohibited or explicitly labeled.
• CFM versus SCFM/ACFM ambiguity can materially change velocity and friction loss.
• The calculator may produce impractical velocities, excessive noise, poor air distribution, or dimensions incompatible with available fittings and construction standards.
• Rectangular ducts require a stated aspect-ratio convention and a stated equivalent-diameter convention; otherwise dimensions are non-unique.
• The listed chart and curve-fit method must account for duct material/roughness, air temperature, elevation, and fittings/system effects if the result is presented as final design.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "shape": "round",
    "airflow_cfm": 1000,
    "friction_rate_inwg_per_100ft": 0.01702,
    "darcy_friction_factor": 0.02,
    "air_density_kg_per_m3": 1.204
  },
  "expected_outputs": {
    "diameter_m": 0.5,
    "diameter_in": 19.685,
    "velocity_m_per_s": 2.4
  },
  "reference_data": {
    "air_density_kg_per_m3_at_20C": 1.204,
    "source_convention": "ASHRAE Handbook—Fundamentals standard-air property value, approximately 20 C",
    "water_density_kg_per_m3": 1000,
    "source_convention_water_density": "widely tabulated standard value",
    "standard_gravity_m_per_s2": 9.80665,
    "source_convention_gravity": "CODATA/NIST standard gravity",
    "inch_m": 0.0254,
    "source_convention_inch": "ISO/international inch exact definition",
    "feet_per_100ft_m": 30.48,
    "source_convention_length": "international foot exact definition",
    "darcy_friction_factor": 0.02,
    "source_convention_friction_factor": "ASHRAE duct-friction-chart textbook smooth-duct value used as a verification fixture"
  },
  "working": "Q=1000×0.00047194745=0.47194745 m^3/s. 1 inH2O=1000×9.80665×0.0254=249.08891 Pa. Friction gradient=0.01702×249.08891/30.48=0.13907 Pa/m. D=[8fρQ²/(π²(Δp/L))]^(1/5)=[8×0.0200×1.204×(0.47194745)^2/(π²×0.13907)]^(1/5)≈0.5000 m=0.5000×39.3701=19.685 in. Area=π(0.5000)^2/4=0.19635 m². V=0.47194745/0.19635≈2.400 m/s."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json