Maximizing
Daylighting and Views
Window
design is the most important building envelope consideration for energy
conservation. In Santa Monica, their design should maximize daylighting,
views to the exterior and ventilation, while minimizing traffic noise
and solar heat gain during cooling periods. Since these considerations
vary with building orientation and surroundings, window design will
vary from one facade to another. Also, it is important to distinguish
between glazing strategies for cooling-load dominated buildings and
those providing passive solar gains to offset winter heating requirements.
or cooling-load dominated buildings:
- Increase window
area and glazing visible transmissivity on north- and northeast-facing
walls to admit more daylight.
- Limit the amount
of glazing on west and southwest orientations where mid-afternoon
summer sun is difficult to shade effectively with fixed fins or
overhangs.
- The choice
of glazing is critical in ensuring good daylighting. A wide range
of glazings is available offering both good admission of daylight
and low heat gain.
- Avoid heavily
tinted or reflective glasses that reduce solar heat gain but also
reduce daylight and exterior views.
- Specify high-performance
low-emissivity glazing with visible transmissivity greater than
0.6 and solar transmissivity less than 0.4. This can reduce annual
operating energy by 20% compared to a Title 24 compliant building.
A further 20% reduction can be achieved if high-performance glazing
is combined with daylight controls.
Light shelves are
particularly suited to the predominantly clear sky conditions enjoyed
in Santa Monica. Light shelves reflect sunlight and daylight toward
the ceiling, even out light distribution, and shade view windows.
The reflected light can significantly reduce electrical lighting needs
and associated cooling loads within deep plan buildings.
Use a combination
of exterior and interior shelves on southeast, south and southwest
orientations:
- Exterior shelves
sized and shaped to reflect the majority of direct sunlight provide
shade for the view window beneath. The best daylight penetration
typically results from using light-colored, sloped external shelves.
- Interior shelves
sized and shaped to redistribute the light and increase illumination
deeper in the building interior.
- Use interior
shelves on north orientations to improve light distribution in spaces
with high floor-to-ceiling dimensions. Integrate light shelves and
ceiling design:
- Combine light
shelves
with flat, light-colored ceilings free of obstructions for better
light penetration.
- Slope the ceiling
down from the window side to enhance light distribution, and reduce
contrast and glare.
Visual contact
with the outdoors provides occupants with cues about orientation,
time of day and weather, and is important for their sense of well-being.
- Maximize the
“information content” of views. Include skyline, upright
middle objects (trees, buildings) and horizontal foreground objects
(streets, lawns). Tall vertical windows typically provide the best
range of views.
- Select glazing
with visible transmissivity greater than 0.6 to avoid distortion.
Many of the performance
criteria above apply equally to passive-solar heated buildings. The
primary additional requirements for window design are that:
- The glazing
used to admit winter solar gains has high solar transmission (>0.8)
and high thermal resistance (R-value >2.0 sq.ft.hour/Btu).
- The window
area and distribution used to admit winter solar gains are carefully
matched to the thermal mass.
- An effective
solar control strategy is incorporated to minimize excess gains
during cooling periods.
Cautions
- Use computer
energy simulation to evaluate trade-offs between daylight transmission
and solar control.
- Avoid reflecting
coatings or films since they reduce daylighting opportunities, and
may cause glare problems and increased cooling loads for adjacent
buildings. 7'- 6" min.
