Crossdraft

Airflow sketchpad. Indicative 2D, not CFD.

Thickness 0.25 m

Speedt = 0.0 s

+3 K

Draw walls freehand. Hover to read the air at any point.

Wind

W 270°

blows toward E

Light breeze

Typical windsDirection the wind comes from270°Speed3.0 m/s

Drag the dial or use the sliders. The wind blows across the whole domain.

Typical values for teaching, not site data. Real wind changes with street, height and year.

Rooms

--/ 100no closed room

Stale air flushed-

Dead-zone area-

Draft comfort-

Mean air age-

Room	m²	m/s	Dead	Fresh	+K	T90

Walls must form a closed loop. Cut doors and windows with the Opening tool, since openings count as part of the wall.

score = 50 x flushed + 30 x (1 - dead zone) + 20 x comfort. Comfort is 100% up to 0.3 m/s and falls to 0 at 1.5 m/s. T90 is the time for a room to reach 90% fresh air.

Wind-direction sweep

Tests this layout against wind from every direction at the current wind speed, then ranks the directions. It runs in the background and takes about a minute.

DirectionsLength per direction

Compare layouts (A/B)

Runs a fresh test from stale air at the current wind and stores the result. Change the design, test again into B.

Test length

Layouts

Example

GridCell size

What to notice: Windows face each other across the room, so air runs straight through. This is the benchmark to compare against.

Domain 30.0 x 20.0 m. Plan: all four edges are open to the outside.

Physics

Turbulent mixing0.030 m²/sSwirl boost0.50Fan speed3.0 m/sHeater excess+15 KRoom heat gain (Plan)25 W/m²Ceiling height2.7 m

Incompressible Stam solver on a grid. Walls are one cell thick and leak-tight. Room heat gain stands for people, appliances and sun, and it warms every enclosed room in Plan view. Temperatures are rises above outdoor air. Real rooms have 3D turbulence, furniture and pressure fluctuations that this does not model, so use it to compare layouts, not to certify them.

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