Daylight,
Views, and Natural Cooling
Floor
plan depth is the most important single consideration
that affects the potential for daylighting, exterior views
and natural ventilation. Floor plans with relatively narrow
wings, such as I-, H-, U-, or T-shaped plans, ensure that
most interior spaces have good access to natural light
and winds. Courtyards and atria can also be used to bring
light and air to surrounding narrow spaces.
The
area of interior space that can be daylit using windows
depends on both building depth and floor-to-ceiling height.
(Single-story buildings and the top floors of multi-storey
buildings can be toplit using skylights, roof monitors
or light wells
- Since
useful daylight from typical windows can only reach
15 to 25 ft. into spaces with 8 or 9 ft. floor-to-ceiling
heights, floor plans deeper than ~ 56 ft. (two rooms
flanking a double-loaded corridor) will require constant
electric lighting.
- Redirecting
daylight with light shelves, prismatic glazing and other
reflective systems can extend naturally lit interior
space to 30 to 35 ft. deep.
An
occupant’s view of the exterior depends on the distance
from the window, the visible transmissivity of the glazing,
and obstructions to light. To ensure good views for most
occupants:
- Limit
the maximum distance of workstations from the building
exterior to 20 to 25 ft.
- Use
atria and outdoor courtyards to increase the variety
and number of views.
A
well-designed natural cooling strategy can be as effective
as mechanical air-conditioning, but its potential is also
greatly influenced by floor plan depth.
Narrow
floor plans increase the potential for effective cross-ventilation:
bringing outdoor air into one side of a space and exhausting
it on an adjacent or opposite side. Cross-ventilation
can move air effectively over deep floor plans, but air
temperature increases and air quality drops as it moves
across the room. The practical limit for the length of
the airflow path is five times the ceiling height (~50
ft. for a ten ft. ceiling).
Single-sided
ventilation, where only one exterior wall has operable
windows or vents, is also possible but less effective,
since air speed (with its cooling effect) is typically
lower than in cross-ventilation situations.
With
a single operable window or vent, natural ventilation
relies on wind turbulence and buoyancy, instead of the
higher pressures available from wind. In single-sided
ventilation, air flows in the bottom, is heated within
the space, and flows out at the top of the same opening.
The larger the height between the top and bottom, and
the higher the temperature change, the greater the airflow.
Single-sided,
single-opening natural ventilation is
effective to
a depth of approximately two times the ceiling height.
This implies a maximum room depth of approximately 18
to 20 ft., for 9 to 10 foot ceiling height with a window
approximately five foot high.
Where
separate high and low openings are used, warm air leaves
through the upper vent, inducing inflow through the lower
vent. In this situation, if the vertical separation between
the openings is approximately 5 ft., ventilation is effective
for up to 2.5 times the ceiling height. This gives a maximum
room depth of 23 to 25 ft.
Cautions
- Energy
savings from daylighting depend on skylights and windows
and electric lighting controls that must be properly
commissioned.
- Energy
savings from natural cooling require that supplementary
air-conditioning systems are turned off when windows
are open.
- Unacceptable
noise and indoor air pollution are possible when openings
are close to major traffic routes. Traffic noise and
pollution diminish significantly above the third floor.
