ASHRAE Journal - April 2013 - 61

Technology

Tubular
Skylights

Fiber
Optics

Characteristics

• One Roof Penetration Per Device
• Reflective Ducting
• Light Transmitting and Diffusing Prism
•
•
•
•

One Roof Penetration Serves Multiple Devices (and Floors)
2 in. Fiber Optic Bundle
Uses Only Parallel Solar Rays
Active Solar Tracking

• Solar Tracking
Vertical
• Reflective Vertical Ducting
Solar Tracking
• One Roof Penetration Serves Multiple Floors
Light
Shelves

• Exterior Overhanging
• Interior Louvers
• Upper Reflective Surface Paired with Reflective Ceiling

Transom
• Fresnel Lens Light Collecting Panel
Panels
Wall-Mounted • Light Pipes and Diffusers
• Reduces Human Intervention
Automated
• Increases Daylight Penetration During Day
Shading
• Mitigates Glare Issues

Location

Capabilities

Building
Orientation
Dependence

Roof

• Minimal Light Loss <30 ft length;
Loss Increases with Bends
• 10 in. to >29 in. Diameter Roof
Penetrations; >29 in. Serves Large
Complexes

N/A

Roof

• Output ≤4,000 Lux
• Less Loss than Light Tubes

N/A

Roof

• Minimal Light Loss >100 ft
• 1,000 – 2,500 ft2 per Fixture

N/A

Façade • Fixed or Operable
Interior
Walls • Increases Daylight Penetration Depth

Strictly
Dependent

Façade • Suitable for Multistory Buildings

Strictly
Dependent

Façade • Suitable for Multistory Buildings

Strictly
Dependent

Table 1: Technologies for collecting, directing, and transporting daylight.
Both energy savings and the daylighting technologies that can help deliver
them depend on a number of buildingspecific factors (e.g., orientation, exterior
aspect ratio; interior layout; window-towall ratio; occupancy) as well as sitespecific factors (e.g., climate, type of
daylight available, terrain, landscaping).
The New Buildings Institute has reported
that, in a survey of more than 100 buildings in which energy bill savings were
greater than 40%, daylighting was used
in 98% of the projects.7
The renovation of the New York Times
building began in 2003 with daylighting
research in collaboration with Lawrence
Berkeley National Laboratory.8 Guided
by energy efficiency as a goal, analyses
of energy efficient design components in
a test facility led to a final building design
that incorporated three key measures: (1)
interior automated roller shades and a fully
glazed and shaded curtain wall façade; (2)
dimmable lighting with an occupancy, daylight, and set point based control scheme;
and (3) an underfloor air distribution
system. Since 2007, the building has been
occupied, enabling a “post-occupancy”
assessment of the energy savings actually
realized from these design components.
April 2013

The dimmable and controlled
lighting system saves 56%
Demand Charges
of lighting energy relative to
an ASHRAE Standard 90.1Fan Energy
2001 code-compliant building.
Setpoint tuning plus daylight
Heating Energy
dimming provide 72% (8.25
2·year) savings over
kWh/ft
Test Rooms
a code-compliant building.
Cooling Energy
Control Rooms
Scheduling and occupancy
control deliver 55% (6.29
Lighting Energy
kWh/ft2·year) savings over a
code-compliant building. The
0
20
40
60
dimmable lighting fixtures and
Annual Operating Cost (Cents/ft2)
control strategy have a simple
payback of 4.1 years; all three Figure 1: Operating cost savings from daylighting, a
measures have a payback of controlled experiment.
8 years. Overall, the building
saves 24% annually in electricity consump- 20% on operating costs of about $1.13/ft2
tion and 25% on peak electric demand. 9, 10 ($12.16/m2) compared to control rooms outIn addition to the potential for reduced fitted with standard clear-glass windows and
energy consumption and reduced energy ceiling-mounted fluorescent fixtures with no
costs, daylit buildings can allow use of dimming. Operating costs by cost category
smaller chillers via reductions in peak for both test rooms and control rooms are
energy demand.11 In a controlled experi- shown in Figure 1. Half of the total savings
ment conducted by the Energy Center of of $0.24/ft2 came from reduced demand
Wisconsin, it was found that a combination charges. The savings from demand charges
of high-performance windows with reduced assume that a school or office using the same
solar heat gain and direct/indirect electric high performance configuration would use a
lighting with photosensor dimming (“test 25% smaller chiller, with comparable reducrooms”) yielded a savings of more than tion in chiller power draw in operation.11
Energy Cost Category

Energy Savings

ASHRAE Journal

61
ASHRAE Journal - April 2013

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