If you associate high-performance daylighting techniques with new construction and expensive lighting controls, think again. While a facility’s footprint, glazing and daylight aper- tures may be fixed, FMs have low-cost strategies available
to them for retrofits that save money and energy on lighting and
A successful plan balances natural light with heat gain and
integrates architectural features with artificial lighting and controls. When adequate daylight is available, lighting levels are
reduced by either dimming lamps or switching them off (entire
luminaires or individual lamps within a luminaire). Natural light
may be introduced through toplighting (skylights, clerestories) or
sidelighting (windows). Toplighting tends to provide better performance than sidelighting but will likely have fewer applications
in multistory buildings.
1) The Reflectance Factor
A starting point is improving interior reflectance values.
Office Daylighting Potential, a study for the California Energy
Commission, found that improving interior reflectance was one
of the most consistent variables providing energy savings.
The study is based on the California Commercial End-Use
Survey (CEUS) dataset of 536 existing office buildings in the
state. The investigators found that improving reflectance val-
ues for ceiling tiles, walls and carpet had a double-digit sav-
ings effect. Specifically, replacing off-white acoustic tiles (70%
reflectance) with brighter white tiles (85%), changing wall color
from 50% to 60% reflectance, and carpet from 20% to 30% can
reduce square-foot energy use by 15%
for lighting and HVAC. Ceiling and floor
reflectance each have a greater impact
than floor reflectance. These results
assume two-level switching control for
the artificial lighting.
The savings is an average across all
daylit zones, which included primary
zones (those within 8 feet of an exterior
wall with windows), secondary ( 8-16 feet
from windows) and tertiary ( 16-24 feet).
These zones correspond to a typical 8-foot by 10-foot luminaire
grid. Most daylighting tactics have their greatest impact on primary zones.
2) Managing Furniture Heights and Layouts
Although lower partition heights may have a negative effect on
acoustics, they help direct daylight to the interior. The California
study found that reducing partition heights from 60 inches to 45
inches decreases square-foot energy an average 20% on a baseline wall/window ratio. Reducing heights from 60 inches to 30
inches yields an average 24% savings.
The layout of open-office workstation partitions can be optimized to maximize daylight without creating occupant discomfort.
The Daylighting Guide for the Commercial Office recommends that
workstation partitions be kept at 42 inches or lower and parallel
to the window wall. Higher partitions for privacy ( 48 inches and
greater) should have an orientation perpendicular to the wall
3 Daylighting Strategies for Existing Buildings
Don’t let costs and complexity deter a retrofit
THE BENEFITS OF
NATURAL LIGHT include
not only reduced lighting
and HVAC loads but also
higher productivity for