ASHRAE Journal - April 2013 - 60

emerging technologies

Harvesting Daylight
By Mildred Hastbacka; Tracy Beeson; Alissa Cooperman; John Dieckmann, Member ASHRAE; Antonio Bouza,
Associate Member ASHRAE

E

daylight deeper into the building in addition

lectric lighting accounts for 20% of the total primary energy con- to reducing glare by increasing surface
luminances. Another daylighting strategy

sumed by commercial buildings in the U.S.1 Over the entire U.S. involves reconfiguring the interior spaces
building sector, lighting accounts for more than 14% of the total primary so the more highly occupied open plan
energy consumed.2 Consequently, reducing lighting energy consumption
presents a potential for considerable energy consumption reduction
across the building sector. One effective approach to reduce the use
of electric lighting is daylight harvesting.

A successful daylight harvesting system
requires two things: the controlled introduction of direct and reflected sunlight
into a building and the reduction of the
electric lighting load in response to the
available daylight. In daylit spaces, the primary source of interior illumination during
parts of the day is daylight, which has the
potential of lowering building electricity
consumption and reducing peak energy
demand when paired with a lighting control system. Incorporation of daylighting
technologies in both new buildings and
renovations continues to increase, driven
by energy standards, code requirements,
and building energy rating metrics.
Investing in daylighting controls for
the electrical lighting adds value only
if enough daylight enters the space to
reduce the demand for electrical lighting.
Fenestration can be chosen to optimize
the transmittance of light (visible transmittance, or VT), e.g., tinted glazing can
be replaced with glazing of a higher VT.
Once the daylight entering the space has
been optimized, a system needs to be put in
place to reduce the electric lighting load.3
The electrical lighting system may
need to be modified to incorporate dimming capabilities, but any heating or
cooling offset claimed by implementing
60

ASHRAE Journal

a daylighting harvesting system will not
be realized until the electrical lights are
set up to function in response to daylight
availability. When daylight admitted to
an interior space is used and the electric
lights are turned off or dimmed, the heat
gain from the lighting system can be
reduced significantly, resulting in a reduction to the cooling load. Consequently,
daylight harvesting saves not only lighting energy but also energy from reduced
air-conditioning loads.
If daylight harvesting is considered
when a building is being built, some of
the most influential variables for a successful design should be considered early,
in the design stage.4 Siting, orientation,
and the building footprint all play a large
role in the availability of useful daylight.
Many daylighting techniques are sitespecific, so the amount of fenestration,
window to wall ratios (by orientation),
skylights or roof monitors, and fixed
shading devices can all be adjusted to
optimize the use of available daylight.
Even if daylight harvesting was not
considered from the beginning, there are
daylighting techniques that can be applied
to any building to help maximize the usefulness of the available daylight. Increasing the
surface reflectances in the space helps bring
ashrae.org

spaces are located around the perimeter of
the building and small spaces with opaque
walls are located in the middle of the floor
plan. The savings associated with these
sorts of space planning techniques will fully
be realized once the responsiveness of the
electric lighting system is in place.
Advances in window technology have
been essential to harnessing the benefits
of daylight. Recent development efforts
in advanced window technologies include
attempts to separate the transmission of
the infrared and visible portions of the
daylight spectrum, allowing better control of the indoor environment.5 Active
electrochromic fenestration products that
control light transmission (the visible
portion of the spectrum) in addition to
solar heat gain are already commercially
available. These types of products that
can be tuned to meet the needs of a specific building based on siting, orientation,
and climate result in energy consumption
reduction while helping to manage glare
and preserve views.
Other commercial daylighting technologies collect, direct, and transport
daylight. These daylight management devices (Table 1) are typically mounted on
the roof, on interior or exterior walls, or
on windows. Automated shades or blinds,
in particular, are an active daylighting
control option that can be used to mitigate
glare and, when integrated with windowbased daylight sensors, can also detect
and respond to cloud cover or shadows.
Combined with electrical lighting control
systems, shade automation contributes to
energy savings while providing desired
levels of interior illumination.6
April 2013



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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