Aperture Placement & Area

Aperture

• Refers to any daylight source– Windows– Skylights– Openings– Transparent or translucent surfaces

• Placement and area are important because use of windows and skylights helps achieve thermal and visual comfort passively, saving energy and money

Area

• Side Light – Bigger not necessarily better as it can cause to

much heat lost or gain– Window to wall ration (wwr)– 40% or lower for adequate

insulation in cold climates– Higher R-values raise the ratio

Window to Floor ratio

• Window to floor ratio (wfr)• For side lighting thresholds wfr x tvis– 0.15 < VLT • WFR < 0.18

Area

• Top Light – much brighter than sidelighting, less area is required

• Skylight to roof (SRR) net glazing area divided by gross roof area

• Should be between 3% and 6%, tubular skylights 1-2%

• Area of one skylight = (Floor to Ceiling Height x 1.5)2 • target SRR

• 12' ceiling and 5% skylight to roof ratio the right size skylight would be approximately: (12 x 1.5)^2 x 5% = 16.2sf. Therefore the project should use 4'x4' or 8'x2'

Placement for Daylighting

• Facing the path of the sun receive more direct sunlight than those facing away

• Evenly distributed light is critical for daylighting

• Continuous strip apertures are even better, often best is apertures on multiple sides

• Without careful planning hotspots can occur

Placement for daylighting

• Horizontal bands of windows placed high (avoids glare and bounces light off ceiling) can help as well as evenly spaced vertical windows

Side Light

• Coming from the side light can only reach so far into a building

• One reason for shallow floorplans in multi-story buildings

• At most latitudes the light reaches into the room roughly 2.5x the height of the top of a window

Side Light

• Windows facing away from the sun’s path rather than towards the equator provide the most even illumination, but not the brightest

• East and west facing windows can provide very bright light in the morning or evening but is often insufficient at other times of the day, also prone to glare

• Facing the sun’s path provides the brightest light but can also have a glare, easier to control the glare though

Top Light

• In middle latitudes and those closer to the equator skylights can provided the best illumination

• In latitudes closer to the poles they are less bright and much less seasonal consistency

• Higher apertures are most efficient at bring light deep into a building (glazing on/in roofs)

• Skylights are not the only choice

Top Light

Top Light

• Much brighter than side lights per unit area– Vertical monitor – 2x– Angled monitor – 3x depending on the angle– Horizontal skylight – 5x

• Splayed openings can help spread the light more broadly

Daylight Apertures vs. View Windows

• Good daylighting design considers daylighting apertures separate from view windows

• Daylighting apertures are best located high on the wall so the light reaches deeper into the space

• View windows are at eye level for occupants• Daylighting diffuses light• Often shades and/or light shelves are placed

between the two

• Shades the view while diffusing and redirecting light

Placement for Heating & Cooling

• Can pull in lots of heat but might allow lots of heat loss if located elsewhere

• In many climates east windows can warm spaces early in the day after a cool night

• Warmer climates, west facing windows can be prone to overheating

• Passive solar heating comings solar heat gain with thermal mass inside the building