CALCULATORS / PUMPS, FANS AND VENTILATION

Fan and duct operating point calculator

Quadratic fan/system pressure intersection; supplied curve coefficients.

pumps-fan-operating-point.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	flowm^3/s	pressurePa
	0.1	200
	0.0894427	160

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

airflow target0.10 m^3/s✓ passes

BASELINE INPUTS

shutoff300 PafanCoefficient10000 Pa*s^2/m^6systemCoefficient20000 Pa*s^2/m^6

CALCULATED

flow0.1 m^3/s

pressure200 Pa

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Fan and duct operating point
# Scope: Quadratic fan/system pressure intersection; supplied curve coefficients.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

shutoff = 300 Pa
fanCoefficient = 10000 Pa*s^2/m^6
systemCoefficient = 20000 Pa*s^2/m^6

flow := sqrt(shutoff/(fanCoefficient+systemCoefficient)) [m^3/s]
pressure := systemCoefficient*flow^2 [Pa]

check airflow target: flow >= 0.08 m^3/s

scenario alternative: shutoff = 240 Pa

Calculated from your source · not saved

Baseline · Baseline

airflow target0.10 m^3/s ✓ passes

alternative · alternative

airflow target0.09 m^3/s ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

flow: flow = sqrt(shutoff/(fanCoefficient+systemCoefficient)) [m^3/s]
pressure: pressure = systemCoefficient*flow^2 [Pa]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

shutoff: 300 Pa
fan coefficient: 10000 Pa*s^2/m^6
system coefficient: 20000 Pa*s^2/m^6

Calculated

flow: 0.1 m^3/s
pressure: 200 Pa

Assumptions and limits

Quadratic fan/system pressure intersection; supplied curve coefficients.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Fan and duct operating point. Inputs: fan curve; duct resistance. Outputs: airflow; static-pressure operating point. Model scope: Measured or manufacturer curves and declared fluid conditions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: fan curve, duct resistance
Outputs: airflow, static-pressure operating point
Modes: calculate, compare, sweep
Drawing: System and equipment curves

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS