Daylight Design of Building Windows

DAYLIGHT DESIGN OF WINDOWS

Daylighting design of window is the practice of placing windows or other openings and reflective surfaces so that natural day light provides effective internal lighting.

The particular attention is given to daylighting while designing a building. The aim is to maximize visual comfort and to reduce energy use.

Energy savings can be achieved from the reduced use of artificial lighting or from passive solar heating.

The amount of daylight received in an internal space can be analyzed by undertaking a daylight factor calculations.

Windows

• Window is used for allowing light, heat and sound.

• Double layered window is used to reduce noise, heat, cold and other environmental factors.

If window height is increased from floor, light entering the building will be reduced. Further, the ceiling from the floor should be at a height of 2.5 m-3 m for better lighting.

Windows on multiple orientations are combined to produce the right mix of light for the building for different climate and latitude.

Preferred Window - Wall Ratios (WWR)

For view and a positive connection out of doors, a minimum 20 percent to 30 percent ratio of window area in wall area is prefered.

Glazing the wall areas below desk height (0-30 inch above the floor) benefits for day light (Fig.3.8)

High windows

High continuous windows are more effective than individual or vertical windows, to distribute light deeper into the space.

The top of windows should be close to ceiling line (for day lighting). The bottom of windows should not be higher than 48 inches (for view).

The windows must be separated into two horizontal strips. One strip can be placed at eye level for view, and another strip to maximize daylight penetration.

High ceilings

More daylight savings are realized if ceiling heights are 10 feet or higher. Greater daylight harvesting can be achieved by increasing ceiling heights to 11 feet or higher.

Light Shelves

The light shelves (interior or exterior) can be used between daylight window and view window

These are effective for achieving greater uniforming of day lighting. Further, it extends ambient levels of light onto the ceiling and deeper into the space.

Window and office placement

Daylighting is more cost effective if open plan workstations are located on the north and south side of the building. The open plan areas are more continuously occupied and achieve lower savings.

The open configuration also absorbs less light. The inter- reflections provide a more uniform distribution of light deep into the space. (Fig. 3.9)

Interior sun control

Similar to exterior sun control, horizontal blinds on the south windows and vertical blinds on the east and west are most effective. nwode

Vertical blinds that retract fully for the middle of the day are recommended for these conditions. Perforated blinds and translucent shades may cause glare when hit by direct sunlight.