Windows and Doors

Windows and doors are openings in the building envelope that affect both transmission heat transfer and solar heat gain.

You work with windows on the Windows tab, and doors on the Doors tab, in Building Model → Envelope. Both are placed on wall segments.

Adding Windows

1. On the Windows tab, click Create Windows
2. Enter the window Width and Height, or turn on Assign as percentage of wall area and set the Wall Area Percent
3. Choose a Window Type
4. Optionally turn on External Shading or Internal Shading and enter its values. External shading needs a Top Overhang Depth or a Side Overhang Depth. Internal shading needs IAC₀, IAC₆₀, and IAC_D
5. Click Create Windows in the dialog
6. Place the windows on the canvas
7. Click Done when finished

Windows go only on walls that have a wall type assigned. How you place them depends on the entry mode:

• Width and Height - Each click on a wall places one window at the point you click.
• Wall Area Percent - Click a wall, or drag a box across several walls, to add one window centered on each wall. The window’s width and height are each the wall length and the space’s Slab-to-Slab Height scaled by the square root of the percentage, so the window area equals that percentage of the wall area. Walls that already have windows are skipped.

Window Properties

Select a window from the Windows list, or click it on the canvas, to open the Window Data panel.

Window Type

Links to the window type definition, which supplies the U-value, SHGC, and infiltration rates used in the calculations.

Dimensions

• Width - Horizontal dimension
• Height - Vertical dimension

Advanced Settings

Expand Advanced Settings for shading and placement:

• External Shading and Internal Shading - Reduce the window’s solar heat gain. See Solar Heat Gain.
• Sill Height - Under Placement, the distance from the floor to the bottom of the window. Leave it empty to center the window on the wall.

External shading models a top overhang and side fins:

• Top Overhang Depth - How far the overhang projects from the wall
• Top Overhang Offset - Gap between the window head and the overhang
• Top Overhang Width - Total width of the overhang, centered on the window. Leave it empty to match the window width. The overhang shadow slides sideways as the sun moves off the wall, so a narrow overhang shades less and a wide one keeps the window shaded later in the day. For a continuous soffit or balcony, enter a width that runs well past both jambs
• Side Overhang Depth - How far the side fins project from the wall
• Side Overhang Offset - Gap between the window jamb and each fin

Solar Heat Gain

Windows are the primary source of solar heat gain. The calculation considers:

SHGC (Solar Heat Gain Coefficient)

The fraction of solar radiation that enters through the window:

• Values range from 0.2 to 0.8
• Lower SHGC means less solar gain
• Affects cooling loads significantly

Orientation

Solar gain varies by wall orientation:

• South - Highest gain in winter, moderate in summer
• West - High afternoon gain in summer
• East - Morning gain
• North - Lowest direct solar gain

Shading

Enable External Shading on a window to model an overhang above and beside the glass. You set Top Overhang Depth and Side Overhang Depth (how far each overhang projects) and Top Overhang Offset and Side Overhang Offset, how far it sits from the window edges. Internal Shading models an interior shade with a radiant/convective split and incident-angle coefficients. Both reduce the window’s solar heat gain, and both live under Advanced Settings in the Window Data panel. You can also turn them on in the Create Windows dialog.

Adding Doors

Door Entry

1. On the Doors tab, click Create Doors
2. Enter the door Width and Height and choose a Door Type
3. Click Create Doors in the dialog
4. Click walls on the canvas to place the doors. Each click places one door at the point you click. Doors go only on walls that have a wall type assigned
5. Click Done when finished

Door Properties

Select a door from the Doors list, or click it on the canvas, to open the Door Data panel:

• Door Type - Links to the door type definition, which determines the U-value, surface absorptance, open fraction, and whether the door has seals
• Width and Height - The door’s dimensions

Glazed Doors

Door types do not model solar heat gain through glazing. For doors with significant glazing, add the glazed portion as a window at floor level so its SHGC is included in the solar calculations.

Skylights

Skylights are windows in the roof:

• See Roof for skylight configuration
• Higher solar gain due to sun angle
• Significant impact on top-floor loads

Best Practices

1. Verify areas - Check that window areas match specifications
2. Use accurate SHGC - This significantly affects cooling loads
3. Consider shading - Account for overhangs and external shading
4. Don’t forget doors - Include exterior doors in the envelope
5. Check orientations - Solar calculations depend on correct orientation