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Daylight Autonomy 101
Specifying useful daylight deeper into the interior
Sponsored by Lutron Electronics Co., Inc. | By Jeanette Fitzgerald Pitts
T
The Vista Center was designed to achieve daylight autonomy and is able
to illuminate a significant portion of the interior space exclusively with
daylight during working hours.
Photo courtesy of Coscia Moos Architecture
hroughout history, daylight has been considered in the
design of the built environment, although the philosophy
of its use and the objective of its presence have changed
dramatically over the years. Before electric light was invented, in the
late 19th century, daylight was the primary light source available
to illuminate the interior of buildings, schools, and residences.
The houses of Ancient Rome were commonly found to have been
planned around a courtyard, with surrounding rooms positioned
so that the available daylight could penetrate deeper in the
interior space. A guiding principle of the design of Michelangelo’s
iconic Laurentian Library, built around 1550, was to maximize
the presence of daylight from both the northern and southern
exposures in the reading room. In the mid-1800s, the one-room
schoolhouses that dotted the United States from New England
through the prairie and into the western frontier relied on large
windows to provide the teacher and students with enough light for
their lessons.
Almost 100 years after the invention of electric light, and,
subsequently, after fluorescent lighting became more widely
used, the philosophy of daylight’s role in the interior changed
quite dramatically. Instead of relying on large windows and
daylight as the primary source of light, the mid-1960s and
1970s saw schools that were designed with few and no windows,
citing significant energy losses from windows. The views to the
outdoors were even considered a distraction for the students,
indicating that a windowless room may be thought to actually
improve student performance.
Today, the attitudes toward daylight seem to have come full
circle. Study after study has quantified the benefit of daylight
exposure to employees and students alike. Daylight exposure
has been linked to improved employee productivity, student
performance, and even the regulation of a person’s circadian
rhythm, which drives the all-important wake/sleep cycle. Daylight
exposure is considered such a benefit to building occupants that the
preeminent green building rating system in the United States, the
Leadership in Energy and Environmental Design (LEED®) green
building rating system contains credits that are specifically awarded
for the project’s incorporation of daylight and outdoor views.
Beyond improving the human experience, effectively
incorporating daylight in the interior, or daylighting, can
dramatically improve the operational performance of the building
and create energy savings. In 1997, the Illuminating Engineering
Society of North America (IESNA) published a guide entitled
Daylighting Design: Smart and Simple in which it posited that a
building with a 25 percent window-to-wall ratio could realize a
lighting energy savings of roughly 30 percent by reducing electric
light levels when sufficient daylight levels were available.
Both daylighting know-how and technology have dramatically
improved over the past decade, advancing the role and the potential
benefits that daylight can now deliver to the built environment.
Daylight harvesting, the practice of reducing electric light levels
when daylight is present, is becoming more and more commonplace
and is now, in fact, required by ANSI/ASHRAE/IESNA Standard
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Photo © Bruce Damonte, courtesy of Lutron Electronics
CONTINUING EDUCATION
90.1 – 2010 and the California Building Efficiency
Standards. Some designers are now interested in
taking daylight availability to the next level and
using it, when possible, as the exclusive light source
for a space, in much the same way it was used in
the one-room schoolhouses of the past. The phrase
for this new design objective: daylight autonomy.
INTRODUCING DAYLIGHT AUTONOMY
Today, designing a space to meet specific
daylight-related objectives is a common practice.
The usual daylighting goals include achieving
some predefined daylight illuminance level on
the workplane or at the floor, incorporating
some measure of glare control, or delivering a
daylight zone of a certain size. Achieving daylight
autonomy essentially requires a project to achieve
all of the above and more.
The 10th edition of The Lighting Handbook,
published by the IES (Illuminating Engineering
Society of North America, formerly IESNA),
defines daylight autonomy as “the percentage of
the operating period (or number of hours) that a
particular daylight level is exceeded throughout
the year.” It is a dramatically different way to
think about and measure the presence of daylight
in a building. “One advantage of using daylight
autonomy to quantify daylight availability
in a building, is that the daylight autonomy
calculations take climate into account, an aspect
that previous metrics for quantifying daylight had
not included,” explained Jack Bailey, Partner at
One Lux Studio in New York City. “This metric
could benefit architects and owners significantly.
Architects can use daylight autonomy analysis to
evaluate different design alternatives to determine
which concept provides more usable daylight in
the interior, and owners will know, definitively,
that their building is making good use of daylight.
It also provides a consistent metric for comparing
the performance of different buildings for building
codes and green building initiatives.”
It should be noted that at this moment
achieving daylight autonomy in a building is not
required by any international, federal, state or local
building code. “It was included in the first public
draft of the International Green Construction
Code (IgCC), but was removed in favor of a
simpler metric,” explains Bailey, who served on the
committee that wrote the IgCC. “Nor is daylight
autonomy analysis required for a project wishing
to achieve LEED or any other type of green
building certification,” he continues, “however,
daylight autonomy is recognized as an option for
achieving the daylighting credit in LEED v4.”
Metrics for Measuring Daylight Autonomy
The measurement of daylight autonomy (DA) is
the percentage of working hours that a particular
daylight level is exceeded throughout the year. The
DA value represents the percentage of the workday
that a space could be exclusively illuminated with
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A 2003 study conducted by Heschong Mahone Group linked daylight exposure in the
workplace to improved employee productivity and satisfaction.
daylight. There are a few other metrics that can
be considered along with the DA value to paint a
more complete picture of the presence of daylight
in a building throughout the day. Continuous
Daylight Autonomy (cDA) gives partial credit
to hours where daylight is present, but cannot
completely achieve the target illuminance level.
Spatial Daylight Autonomy (sDA) refers to the
percentage of floor area where 30 footcandles (fc)
is achieved for at least 50 percent of the workday.
There is a key term used in the definition of
daylight autonomy, and some of the supporting
daylight autonomy metrics, that warrants
additional attention to ensure that the full concept
of daylight autonomy is truly understood.
Defining Useful Daylight
Where daylight autonomy is the goal, it is critical
to understand that not all daylight is created equal.
As the definition of daylight autonomy implies,
there is useful daylight and daylight that is not
usable or practical for the interior environment.
Useful daylight describes the daylight in the
interior space that does not cause glare or
discomfort to building occupants.
In an office setting, the range of useful daylight
illuminance is generally considered to be between
10 fc and 200 fc at the workplane. This aligns
with recommendations developed by the IES that
define the optimal light levels for various visual
tasks. The IES recommends that office buildings
maintain 30 fc at the workplane in private offices,
open office spaces, and conference rooms. Lower
light levels are recommended for circulation areas
and higher levels are recommended in areas where
reading and studying will be the primary task.
There is even a metric, entitled Useful Daylight
Illuminance (UDI), which refers to the percentage
of work hours where the illuminance from
daylight is between 10 fc and 200 fc.
People can experience visual discomfort when
direct or overly bright sunlight is present in a
workspace due to the intensity and contrast it
creates. Two metrics that have been developed
to help designers identify and protect a space
against this potentially destructive and glarecreating daylight are referred to as Max Daylight
Autonomy (maxDA) and Annual Sunlight
Exposure (aSE). The metric maxDA measures
the percentage of work hours where daylight
levels provide 10 times the necessary levels of
design illuminance. The metric aSE measures
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Learning Objectives
After reading this article, you should be able to:
1. Describe daylight autonomy and how it
improves well-being of building occupants
and energy efficiency of the electric
lighting system.
2. E
xplain the importance of daylight
management in attaining daylight autonomy.
3. C
ompare the ability of manual shade and
automated shade systems to deliver energy
savings and usable daylight.
4. M
aximize the potential daylight autonomy
and energy savings that a space can
achieve.
To receive AIA/CES credit, you are required
to read the entire article and pass the test. Go
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DAYLIGHT AUTONOMY 101
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Photo courtesy of Lutron Electronics
Daylight autonomy can create significant energy savings and
improve the quality and comfort of the available views.
the number of hours per year where the space
receives direct sunlight. This direct or bright,
potentially glare-causing sunlight may be
considered unusable daylight, whereas the
diffuse daylight that fills the sky on a cloudy day
is generally considered usable.
The Benefits of Daylight Autonomy
In many instances, energy savings is achieved
by sacrificing something else that is deemed
valuable, such as occupant comfort. One of
the reasons that daylight autonomy is such an
attractive design objective is that it manages
to deliver significant energy savings, without
negatively impacting occupant comfort or
the functionality of the space. In fact, it may
improve occupant comfort by improving access
to outdoor views and ensuring that occupants are
exposed to optimal amounts of usable daylight
throughout the day, which improves productivity
and satisfaction, while protecting the space
from direct or overly bright light that can cause
glare and discomfort. Daylight autonomy
creates energy savings by being smarter about
the inclusion and management of daylight and
by eliminating excess lighting energy that is
essentially unnecessary.
The Obstacles to Achieving
Daylight Autonomy
If there is a down-side to daylight autonomy, it
may be that, especially as a relatively new design
objective, daylight autonomy can be challenging
to achieve. It requires the ongoing, optimal
management of a very dynamic light source
and, as such, achieving daylight autonomy is
very dependent upon selecting the right daylight
management technology for the project. Setting
a project up to achieve daylight autonomy may
also require designers to retool their traditional
approaches to a new project as it relates to the
planning of the building envelope and interior.
At this stage, achieving daylight autonomy
requires that the design team include a person
who has a specialized knowledge of the complex
software used to determine the DA factor of a
conceptual building.
The dynamic nature of daylight. At the
center of the daylight autonomy challenge is
the dynamic and powerful nature of daylight.
Daylight levels can range from a few footcandles
on an overcast day to over 8,000 footcandles on
a clear, sunny day. It can arrive at the window in
many forms: streaming directly from the sun,
gently diffused through the clouds, or harshly
reflected off of a surrounding structure. And
it arrives, in some form or another, every day,
although its angle and position will vary as the
earth orbits the sun.
The potential intensity and daily presence of
daylight require that, if daylight is allowed into a
building, it must be effectively managed or it can
wreak havoc on the visual environment. Some
problems commonly experienced as a result of
mismanaged or uncontrolled daylight include:
glare, hot spots, and thermal heat gain. These
problems can cause larger issues of occupant
discomfort, loss in productivity, loss of usable
interior space, and energy waste.
Selecting the right technology. It is often
prudent practice to design a building to be
functional in the worst-case scenario. As it relates
to the lighting system, the worst-case scenario
would be something like blackout or midnight
conditions, where zero daylight is available and
all of the illumination must be provided by the
electric lighting system. In terms of a daylight
management system, the worst-case scenario
would be that the building was subjected to
intense, direct, glare-creating, and unusable
daylight all day long, so the daylight management
Illustration courtesy of Lutron Electronics
The angle of the sun changes constantly throughout the day, affecting daylight inside a space.
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DAYLIGHT AUTONOMY 101
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Photo courtesy of Coscia Moos Architecture
DESIGNING TO ACHIEVE
DAYLIGHT AUTONOMY
The daylight autonomy a building can achieve
is affected by so many variables, it is critically
important that the goal of daylight autonomy be
identified and actively considered as early in the
project as possible. Decisions about the shape
and position of the building, interior layout,
furnishings, and type of daylight management
The massing, siting, and orientation
of a building all affect the amount and
penetration of usable daylight that will be
available in a building throughout a year.
that daylight will have to the interior space.
For example, the deeper the floorplate of the
building, the more challenging it becomes to
achieve target levels of daylight illumination in
the more central spaces. In terms of orientation,
in the northern hemisphere, it is generally
accepted that northern exposures offer the best
access to glare-free, ambient light throughout
the day, whereas eastern exposures are often
subjected to intense and glare-causing daylight as
the sun rises, and western exposures experience
direct sunlight exposure as the sun sets.
Interior Layout and Furnishings
“Interior space planning is another opportunity
to optimize daylight autonomy, especially in
office space,” explains Bailey. “Designing private
offices with solid walls around the perimeter of
the building used to be common practice, but
that approach blocked daylight from penetrating
deeper into the building. To improve the daylight
autonomy of an office building, private offices
are strategically placed in more central locations
and equipped with glass office fronts, to provide
occupants with access to daylight and views,” he
adds. Designing a circulation space around the
perimeter of an open office area is another way
to improve the potential daylight autonomy of
the space, by creating a buffer zone to help limit
the potential of glare on the workplane. Lighter
colors and lower cubicle walls are two examples
of interior furnishings that are often specified to
help daylight reach deeper into the space.
system specified are all critical components in the
amount and penetration of usable daylight that is
ultimately found in a building throughout a year.
Building Envelope
Many designers begin creating the conceptual
design for a building by considering the general
shape and mass the building will have, also
known as massing, selecting the location on the
site that the building will occupy, referred to as
siting, and determining how the building will be
oriented on the site in relation to the sun.
The initial decisions made with regard to the
massing, siting, and orientation of the building
all dramatically impact the type of daylight that
is available to the project and the potential access
The Need for Daylight Management
Achieving daylight autonomy requires more than
filling a space with daylight, it must be filled
with “usable daylight.” As a reminder, usable
daylight is defined as daylight within the range
of 10 fc and 200 fc that will not disrupt the visual
environment or cause glare or hot spots in a
space. This range of usable daylight represents a
pretty select segment of the daylight that could be
available at the window of a building throughout
the year, especially considering that daylight can
range from a few footcandles on a cloudy day to
over 8,000 footcandles on a bright, sunny day.
Intense daylight exposure can trim away the
usable space in a building by making areas too
bright, too glaring, or too hot to use for parts of
the day. Avoid the potential pitfalls of daylight
exposure by equipping a building to manage the
daylight as it enters the space and protect the
interior from the bright, direct daylight that can
destroy the visual environment and undermine
the daylight autonomy of the space.
Continues at ce.architecturalrecord.com
Lutron Electronics, headquartered in Coopersburg, Pennsylvania, designs and manufactures energy-saving light controls, automated
window treatments, and appliance modules for both residential and commercial applications. Its innovative, intuitive products can be
used to control everything from a single light, to every light and shade in a home or commercial building. www.lutron.com
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CONTINUING EDUCATION
system would need to be deployed to either block
or diffuse the daylight all day long. Fortunately,
the conditions of an actual day rarely mirror those
defined in a worst-case scenario.
It is the technology of the daylight
management system that enables or limits the
building’s ability to adjust to realize some of the
efficiencies available when the actual daylight
situation is more favorable than the worst-case
scenario. In fact, selecting the right technology
to manage the daylight in a building is one of the
most essential tasks that must be completed to
achieve daylight autonomy.
A new approach to design. The daylight
autonomy of a building is affected by variables
of the building envelope as well as the interior
layout and furnishings. “One of the challenges
in achieving daylight autonomy is that it
requires the design team to consider how the
massing, siting, and orientation of the building
impact the availability of daylight in the interior
floorplate,” explains Bailey. It also requires that
many of the elements of the interior space be
reconsidered in terms of how it affects daylight
penetration and daylight management. This
includes the layout of the interior space, the
placement and selection of cubicle walls, and
even the interior color and finish.
Complex software analysis is required.
Perhaps one of the greatest challenges for early
adopters trying to achieve daylight autonomy
is the complexity of the software programs
currently available to help designers evaluate
the daylight autonomy values of their various
concepts. “The complex software often requires
that a lighting designer with a specialized
knowledge of these programs be included in
the design team. The need for this specialized
expertise is one of the factors currently limiting
the inclusion of daylight autonomy in many of
the building codes or wider adoption of this
metric in green building programs, because
it does not seem reasonable to mandate that a
professional with this capability be required on
every project, regardless of scale,” says Bailey.
“I’m confident that a more out-of-the-box
software solution will be available soon, but it’s
just not there yet.”
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Here’s an example of how a space may be negatively affected if it does
not have a way to manage the daylight streaming in through the windows.
Consider a section of an open office bay, positioned on the perimeter of the
building where one wall is completely exposed to direct daylight.
On a sunny day, the daylight level may reach up to, or over, 8,000
footcandles at its most intense. Today, glass used in Class A office space
may have a visual transmittance value (or Tv) of 0.65, which indicates
that 35 percent of the available footcandles are reflected back out into the
atmosphere and 65 percent of the visible energy is transmitted through the
glass and into the building. In this case, 5,200 fc of the 8,000 fc of daylight
would enter the open office space, well outside the range of usable daylight.
This scenario was simulated to evaluate the percentage of working hours
where the presence of daylight exceeded the usable range of 200 fc on a
sunny day. The simulated open office space is 30 feet by 30 feet, the windows
are 8 feet tall and the working hours were defined as 8 a.m to 6 p.m. The
simulation used real NYC climate data and assumes that no immediate
surrounding buildings are present that would cast shadows onto the facade.
The DA plots illustrate the percentage of time, during those predefined
working hours, that the anticipated daylight level will exceed 200 fc.
Images courtesy of Lutron Electronics
Eastern Exposure
Southern Exposure
Western Exposure
Northern Exposure
The simulation of useful daylight illuminance resulted in much of the office
space being potentially uncomfortable for much of the work day.
The results were shocking. Without any way to manage the available
daylight beyond the glass, portions of the office space were too bright to
occupy comfortably throughout the entire workday, shown here in red. Even
more surprising was that in the examples with eastern, southern and western
exposures, over half of the office space was uncomfortably bright for over
50 percent of the workday. In the open office area with northern exposure,
nearly a third of the office space would be potentially uncomfortable for half
of the working hours. That is a significant amount of usable square footage to
lose on a sunny day.
Selecting the Right Daylight Management System
Luckily, designers have many options for managing the daylight that penetrates
into a building’s interior. There are permanent exterior and interior shading
devices, like fixed overhangs and high-performance glazing, which provide
constant glare control, but are limited in their ability to offer any variety in
the amount of daylight protection they provide. As a result, these systems
treat daylight on an overcast day and daylight on a sunny day as if it had equal
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opportunity to create glare, which it does not. In an attempt to protect the
interior from damaging daylight, designers may, inadvertently, minimize the
amount of usable daylight that is allowed into the work space, reducing the
level of daylight autonomy that the building could achieve.
A shading system is a great example of a daylight management solution that
offers enough flexibility to mitigate glare and heat gain when the outside daylight
is intense and unusable, but maximize the penetration of usable daylight, when
it is available. This variable level of daylight control makes a shading system a
great tool to help a building reach its goal of daylight autonomy, without risking
daylight exposures that would make the spaces unusable or uncomfortable.
When selecting the right shading system for a project, the fabric is the key to
mitigating glare and unusable daylight and the controllability is the key to
achieving daylight autonomy and greater energy savings.
Images courtesy of Lutron Electronics
Charcoal (Tv 0.04)
Oyster Pewter (Tv 0.12)
Stone (Tv 0.20)
It is important to specify shade fabric with the Tv value necessary to
manage the daylight in the space appropriately.
Specifying fabric. It is a common practice to select the fabric for a
shading system based on its color, instead of based on how the shade will
need to perform in terms of daylight management. While color can impact
the view provided to the outside when the shades are deployed, for example,
darker fabrics can provide a crisper view than lighter alternatives, selecting
a shade based exclusively on its color compromises the ability of the shading
system to prevent glare and maintain an optimal visual environment in the
building. It can also negatively impact the aesthetic appeal that the shade
color was intended to have in the first place. If the window is too bright to
comfortably look at, no one will be able to appreciate the carefully selected
color of the shade.
A shade manages solar energy in three ways: reflect it, absorb it or
transmit it into the interior. The key to glare mitigation is limiting the
visible transmittance of the daylight through the shade and into the visual
environment, so that it stays within an acceptable brightness. In terms of
achieving daylight autonomy, the daylight passing into a space should not
exceed 200 fc in intensity.
In order to specify a shade fabric that will function as needed, it is
important to understand that the shade does not work alone. Both the window
glass and shade fabric impact the total visual transmittance of daylight
together and must be considered in tandem to create a glass/fabric system that
appropriately manages the available daylight throughout the year.
The glass used in most buildings today has a visual transmittance of
65 percent, allowing 65 percent of the light to pass through the glass and
into the building. Fabric shades are most commonly available in visual
transmittances ranging from 3 percent to 30 percent. If a building has
standard, double-paned windows with a 65 percent transmittance, then on
a sunny day where 3,000 fc of daylight is available, 1,950 fc will pass through
the glass. If a shade fabric with a 10 percent visual transmittance is specified
on these windows, then only 195 fc, of the 1,950 fc that were transmitted
through the glass, will be ultimately transmitted into the interior space.
A daylight level of 195 fc supports the design goals of achieving daylight
autonomy and maintaining a comfortable visual environment. The shade
fabric keeps the space comfortable and usable, even on a sunny day.
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Typically, windows with higher visual transmittance values should
be paired with fabrics that have lower transmittance values. Spaces that
receive direct sunlight, such as the direct early morning light that an eastern
exposure receives, should keep the combined transmittance of the glass
and fabric to less than 10 percent. Areas without the threat of direct sun
exposure can benefit from shades with higher transmittances to maximize
the potential level of daylight autonomy it could achieve.
SPECIFYING CONTROLLABILITY: MANUAL VS. AUTOMATED
SHADING SYSTEMS
Specifying the way that the shading system is controlled can have a powerful
impact on the level of daylight autonomy that a building is able to achieve.
The controllability of shading systems can be divided into two categories:
manual and automated. While the shades in either system can be made
from identical fabrics and similarly positioned at any height, a person must
physically deploy or retract the shade fabric of each shade in a manual system.
Automated shades are programmed to move into their different positions
throughout the day in response to a pre-determined schedule or in response
to sensors that measure the intensity of the daylight at the window. No
manual manipulation is necessary to ensure that glare conditions are being
prevented and usable daylight is allowed in.
Manual Shading System and Daylight Autonomy
The primary challenge that a building equipped with a manual shading
system will face, when attempting to achieve daylight autonomy, is
reliably letting in diffuse, ambient daylight, when available. People are
relatively proficient in closing the shades to relieve a space from glaring or
uncomfortable conditions, however, they are not as diligent at opening the
shades back up, when the daylight transforms from direct to diffuse. It is
quite normal for a shade to be pulled down to block harsh, direct light and
then left down for days, months or longer. A window with a manual shade
deployed over it, day after day, protects the space from glare, but it limits the
usable daylight allowed into the interior and significantly reduces the space’s
ability to exclusively illuminate the space with daylight.
Automated Shading Systems and Daylight Autonomy
An automated shading system is a powerful tool for a building trying to
achieve daylight autonomy. These systems are dedicated to managing the
dynamic and ever-changing nature of daylight, every day, all day long. The
automated shading systems use the solar path of the sun as it arcs over the
building to determine the optimal position of the shade and continuously
adjust the position to accommodate the changing solar angles. The
adjustments reliably block direct sunlight, while allowing usable daylight into
the building. These systems also have sensors placed near the windows that
can detect the level of daylight in the space and adjust accordingly, keeping
shades deployed on overly bright days and retracting shades on overcast days
to allow the soft, diffuse daylight into the building.
Here is an example of how an automated shading system in a glass-clad
building may function throughout the day. As the sun rises, the shades on
the eastern exposure may deploy to a position halfway down the window to
block early morning light, while the shades on the northern southern and
western exposures may be entirely retracted, to let in the gentle morning
light. As the morning progresses, the shades on the eastern exposure
may lower to a full closed position, while the shades on the northern and
southern exposure deploy to one-fourth of the way down the window, and
the shades on the western façade remain fully open. As it approaches noon,
the shades on the eastern exposure retract to halfway position, while the
shades on the southern exposure are deployed to the halfway position and
the western exposure shades lower to cover the top fourth of the window. In
early afternoon, the shades on the eastern exposure are retracted completely,
letting in the available afternoon light and the shades on the southern and
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Photo courtesy of Lutron Electronics
Automated shading systems move shades to precise, aligned levels
along a window wall.
western sides deploy further to block the direct light as the day progresses.
At sunset, all of the shades are fully open, allowing occupants to enjoy the
soft light of early evening. Automated shades move silently and automatically
through all of these position changes, without requiring any manual
manipulation. It should also be mentioned that automated shading systems
move shades to precise, aligned levels along a façade, maintaining the curb
appeal of the building, while maximizing the daylight autonomy of the
interior.
“Our firm was recently hired to compare the daylight autonomy that
could be achieved with manual shades and automated shades on a large,
corporate campus,” Bailey said. “Our analysis concluded that automated
shades significantly increased the DA factor of the building and provided
additional energy savings. The owner also installed daylight responsive
controls throughout the project which reduced the building’s overall
dependence on electric energy.”
When deciding which shading system to specify, the most common
challenge to selecting an automated system is the cost, however, the attitude
is changing as the benefits of daylight exposure and daylight autonomy
become more widely accepted and valued. As Jack Bailey experienced on a
recent project, “The owner of this particular project knew how much they
were spending to install glass curtain walls around the buildings. The added
cost of an automated shading system was not significant when compared to
the cost of the windows. From the owner’s perspective, this automated system
allowed the building to make better use of the windows and provided access
to improved daylight and views for a small up-charge. It made a lot of sense
to them.”
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Compare and Contrast the Performance of Manual and
Automated Shading Systems
These shading systems can deliver significantly different results in terms of
the amount of interior space that can be exclusively lit throughout the work
day by daylight and the energy savings that can be generated.
Compare useful daylight zones. The useful daylight zone refers to the
area of a building that achieves its useful daylight illuminance level at least
90 percent of the working day. It identifies the square footage of a space that
could be almost extensively illuminated by daylight throughout the work day.
For example, Coscia Moos Architecture worked with an outside team
to complete the analysis that compared the different useful daylight
zones created by manual and automated shading systems. The proposed
700,000-square-foot Vista Center would have 25 floors, each measuring
28,500 square feet. For the analysis, 9-foot-tall windows with visual
transmittance values of 0.65 were paired with shades that offered a 10 percent
transmittance value.
The DA simulation of the 14th floor identified that dramatically different
useful daylight zones were created by manual and automated shading
systems. The manual shading system generated a useful daylight zone that
was 12 feet deep around the perimeter of the building. The automated
shading system created a useful daylight zone that was twice as large,
measuring 24 feet deep around the entire perimeter of the building.
Compare energy savings. With daylight harvesting products now
being required in skylit or daylit areas, the increased presence of daylight
in a space can immediately generate energy savings. As automated
shades are able to more reliably allow greater amounts of usable daylight into
a space, the systems can also deliver greater energy savings when compared to
manual shades.
Images by Coscia Moos Architecture, courtesy of Lutron Electronics
A Useful daylight zone (manual shades) = 12 ft.
Expanded useful daylight zone (automated shading) = additional 12 ft.
The simulations run on the Vista Center floorplan concluded that
automated shades would create a significantly larger useful daylight
zone than manual shades.
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recent study, completed in collaboration with Lutron Electronics and Purdue
University, compared the energy savings that could result from both shading
systems. An energy simulation of a perimeter private office with a lighting
power density of 0.9W/square feet, standard, clear, double-pane glass, and a
shade fabric with 5 percent transmittance was conducted. The study averaged
the results of spaces with 20 percent, 40 percent and 60 percent window-towall ratios. Manual shades were defined as closed shades for the study. The
team concluded that an automated shading system was able to reduce the
electric light use in the private office by 83 percent, when compared to the
amount of electric light used if the windows were fitted with manual shades.
In projects of any scale or application type, the effective incorporation of
daylight is steadily becoming a more and more common design goal. Armed
with more advanced technology and daylighting design know-how, designers
today are able to adequately illuminate a space using daylight exclusively.
Achieving daylight autonomy saves energy and creates a more satisfying and
productive atmosphere for building occupants, which are just two examples
of how a daylit workspace works harder. And with automated shading
systems, no one has to lift a finger.
QUIZ—FOR REFERENCE ONLY
1.
Daylight harvesting, reducing electric light levels when daylight is
present, is now required by ANSI/ASHRAE/IESNA Standard 90.1-2010 and
others.
a.
True
b.
False
2.
Which of the following correctly explains if/how daylight
autonomy is currently incorporated into building codes and green building
initiatives?
a.
Achieving daylight autonomy is not required by any federal, state or
local building code.
b.
It was included in the first public draft of the IGCC, but was
removed for a simpler metric.
c.
Daylight autonomy is recognized as an option for achieving the
daylighting credit in LEED v4.
d.
All of the above
3.
Daylight Autonomy (DA) is defined as:
a.
the hours where daylight is present, but cannot completely achieve
the target illuminance level.
b.
the percentage of an operating period (or number of hours) that a
particular daylight level is exceeded throughout the year.
c.
the percentage of the floor area where 30 footcandles is achieved for
at least 50 percent of the workday.
d.
the percentage of work hours where daylight levels provide 10 times
the necessary levels of design illuminance.
4.
What is the accepted range of daylight used to calculate the Useful
Daylight Illuminance (UDI) of a space?
a.
10-200 footcandles
b.
30-3,000 footcandles
c.
0-10,000 footcandles
d.
All levels of daylight are considered useful.
5.
Which of the following is an obstacle to achieving daylight
autonomy?
a.
The dynamic and changing nature of daylight
b.
Requires design teams to consider how massing and orientation
impact daylight on the floorplate
ONLINE PORTION
c.
Achieving daylight autonomy requires use and analysis of complex
software programs
d.
All of the above
6.
How many footcandles will be transmitted into the interior of a
building on a day where the daylight intensity is 8,000 footcandles, the glass
has a transmittance value (Tv) of 0.70, and there is no shading system?
a.
210 footcandles
b.
560 footcandles
c.
5,600 footcandles
d.
8,000 footcandles
7.
Which of the following characteristics of a shading system is key to
mitigating glare and unusable daylight?
a.
The color of the shade
b.
The visible transmittance value of the shade
c.
The controllability of the shading system
d.
Shading systems do not help mitigate glare
8.
Why is achieving daylight autonomy more difficult with a manual
shading system?
a.
The shades can be deployed to different heights, reducing curb
appeal.
b.
Shades are often closed to block intense daylight and then left
down, instead of being reopened to allow ambient daylight into the space.
c.
Manual shades cannot manage glare.
d.
It is not more difficult to achieve daylight autonomy with manual
shades.
9.
Why are automated shades a powerful tool in helping to achieve
daylight autonomy.
a.
The systems use the solar path of the sun to determine the optimal
position of the shade.
b.
The automated system continuously adjusts the shade position
throughout the day, reliably blocking direct sunlight, while allowing usable
daylight into the building.
c.
The automated system can keep shades deployed on overly bright
days and retract the shades on overcast days.
d.
All of the above.
10. In the Vista Center example, how did the useful daylight zone
modeled for automated shades compare with the zone modeled for manual
shades?
a.
They were the same size.
b.
The useful daylight zone created by manual shades was twice as
large as the useful daylight zone created by automated shades.
c.
The useful daylight zone created by automated shades was twice as
large as the useful daylight zone created by manual shades.
d.
Neither system generated a useful daylight zone in the building.
Answer Key
1.
A
2.
D
3.
B
4.
A
5.
D
6.
C
7.
B
8.
B
9.
D
10. C