: Magazine : Back
Issues : March/April
Green Case Study
Going for Gold
The Hensley Field Operations Center in Dallas is the eighth facility in Texas
to achieve LEED Gold certification.
by Vern Goehring, PE LEED AP
The first Leadership in Energy and Environmental Design (LEED)-certified
building in Dallas—only the eighth such facility in Texas—achieved
Gold certification in December. The distinction, issued by the U.S. Green
Building Council (USGBC), goes to the Hensley Field Operations Center, a vehicle-maintenance
center for the city of Dallas. The project was the major renovation of an
existing 80,000-square-foot facility, which formerly housed the Dallas Naval
Air Station. In its present configuration, the expansive facility supports
several operations, most notably the conversion of internal combustion-powered
city vehicles, such as buses, into Compressed Natural Gas (CNG) vehicles.
Although the building contractor was at first apprehensive about how the new
guidelines would impact costs and time, the project eventually surpassed its
goal of Silver certification. “I thought it was going to cost more, take
more time and be difficult to get subcontractors to follow,” said Roger
Bussel, project manager with Harrison, Walker, & Harper (HWH), on USGBCNorthTexas.org.
Instead, at the end of construction, Bussell, who worked on design in the project,
admitted that the guidelines made the project run more smoothly. “We were
so focused and so intense about following LEED guidelines that the project was
more organized and consequently less difficult. As a LEED project, it wasn’t
much different from our standard projects—just more deliberate about how
we did things.”
In late 2003, the unoccupied Hensley building was in a state of disrepair when
the city of Dallas reclaimed it to provide for both public and private uses.
Electrical power had been turned off for some time, and energizing the existing
electrical service was impossible because the copper main bus had been removed
from the service switchboard. But a team comprised of representatives from the
city of Dallas, Johnson McKibben Architects, HWH, and architectural/engineering/planning
firm HDR Inc.’s Dallas office—which provided LEED consultation along
with mechanical and electrical engineering services—came together to make
the project succeed despite the short amount of time allotted for the project.
LEED-ing the way
The USGBC’s LEED program promotes construction designs that minimize detrimental
effects on the environment. Points are awarded in six environmental categories:
sustainable sites, water efficiency, energy and atmosphere, materials and resources,
indoor environmental quality, and innovation in design. A project can achieve
Certified level for attaining 26 points, Silver level for 33 points, Gold level
for 39 points and Platinum level for 52 or more (up to a maximum of 69) points.
Under the LEED 2.1 Edition, the Hensley Field Operations Center received 41 points
for its achievements in the first five LEED categories. Overall, the building
uses highly efficient plumbing and lighting fixtures. It incorporates daylighting
strategies, a photovoltaic (solar panel) system to offset electrical usage, and
a geothermal well cooling system, which reduces equipment size. Compared to a
conventional building, the project reduces water usage by an estimated 50 percent
and electrical usage by about 25 percent.
“The Hensley Field Operations Center provides an outstanding example of
many sustainable design elements,” said LEED consultant Curt Parde. “Renovating
this previously decaying Naval Air Station building into an energy-efficient
make ready (CNG conversion) facility for the city of Dallas easily extended the
building’s life another 30 years, and helped to save the environment while
To gain credit for light-pollution reduction, a building must meet or exceed
standards for lower light levels and uniformity ratios as recommended by the
Illuminating Engineering Society of North America (IESNA) Recommended Practice
Manual: Lighting for Exterior Environments.
The Hensley Field Operations Center met LEED recommendations for the light-pollution-reduction
credit. Its site lighting designs minimize the amount of light spilling onto
neighboring properties or into the night sky. For instance, full cut-off pole
and exterior wall luminaires emit no light above the horizontal level (less than
10 percent of a luminaire’s output is between horizontal and 10 degrees
down from horizontal). In comparison to other light fixtures, full cut-off luminaires
direct more light to the nearby area, and less to areas further away. Additionally,
house side shields limit light cast toward the luminaires’ rear.
In this case, a critical aspect of meeting LEED requirements was to select the
proper light trespass environmental zone as outlined by LEED 2.1 documentation.
The four zones include: E1 (intrinsically dark), E2 (low ambient brightness),
E3 (medium ambient brightness) and E4 (high ambient brightness). By choosing
one of these categories, the design team had to decide whether the conditions
applied to the site before or after construction. LEED documents do not differentiate;
due to time and financial constraints, the team could not submit a credit interpretation.
Thus, team members had to decide.
Some designers thought that because the building had gone unoccupied for some
time, the pre-construction brightness level would have required a low light rating,
possibly E2. Other designers felt that because E4 was the only zone that allowed
for the commercial kind of activity this building would see, and because the
city of Dallas wanted additional illumination for flags and building signs, the
Hensley building should be designated E4. As it turned out, a credit interpretation
for another commercial building indicated that the E4 category should be allowed.
The Hensley project thus earned a LEED credit point for light pollution reduction
under Sustainable Sites Credit SS.8.
Energy and atmosphere
The Energy and Atmosphere LEED credits require compliance with the 1999 version
of the American Society of Heating, Refrigerating, and Air Conditioning Engineers
(ASHRAE) 90.1 energy standard. This standard limits the amount of energy that
can be used for interior lighting. It also requires automatic interior lighting
controls, such as motion sensors, to turn off the lights when the building goes
unoccupied for long periods.
The Hensley project garnered 10 points in this category, due in part to its daylighting
strategy. One advantage was that two high bay areas, which contain two key task
areas—the heavy shop area with 10 tractor bays and the make ready area
used to convert automobiles for use as city vehicles—had existing clerestory
windows. Skylights were added to other areas of the building to increase natural
daylight coming into the building. Automatic dimming controls, included in most
of the building’s lighting systems, sense the amount of daylight coming
into the building. They also reduce the electrical power going to the luminaires,
depending on the amount of natural daylight available.
Hensley project engineers also sought LEED Energy and Atmosphere credit 1.1,
which requires energy performance in a new building to be optimized by 20 percent
or, in an existing building, by 10 percent.
Regulated energy systems include
the heating, cooling, fan and pump components in HVAC systems; service hot water;
and interior lighting.
On the interior lighting side, planners specified high-bay fluorescent luminaires
to illuminate the heavy shop and make ready areas. Each luminaire has six 54-watt
high-output fluorescent lamps with automatic dimming controls. The open office
areas and conference rooms use pendant-mounted fluorescent luminaires. These
fixtures have a dual function: a direct component that shines light down, and
an indirect component that reflects light off the ceiling. Additionally, the
tire shop areas use industrial low-bay luminaires, each with six 32-watt fluorescent
lamps. The storage areas also use industrial luminaires, each with four 32-watt
fluorescent lamps and automatic dimming controls. Finally, the main lobby uses
cylindrical pendant-suspended compact fluorescent luminaires with automatic dimming
Also in its pursuit of LEED Energy and Atmosphere credit 1.1, the project incorporated
photovoltaic panels to offset energy use. An array of panels, which convert natural
sunlight into electricity that can be used for the building’s interior,
was placed on a grade near the building’s entrance. Photovoltaic systems
are usually placed on the roof, but the city of Dallas preferred to give the
environmentally friendly aspect high public visibility.
The 31-by-63-inch panels, which are mounted on metal stanchions, are angled 30
degrees up from horizontal, and face south to maximize the energy they receive
from the sun. Each of the 44 panels can contribute 160 watts of power to the
building during peak sunlight hours. The project includes a total panel capacity
of seven kilowatts, along with a 15-kilowatt inverter to convert the panel-produced
direct current into an alternating current for building use. The inverter automatically
matches the frequency, voltage and phase angle of the serving utility so that
the systems can be parallel-connected without problems. The additional eight
kilowatts of inverter capacity will facilitate the addition of more photovoltaic
panels as funds become available.
Results at the Hensley building, despite the project’s accelerated pace
and economic constraints, speak for themselves. Teamwork and a can-do attitude
led the project to its highly sustainable status, making it one of only a handful
of buildings nationwide to have attained Gold certification.
(The Database of State Incentives for Renewable Energy (DSIRE) is a comprehensive
source of information on state, local, private utility and selected federal incentives
that promote renewable energy. For more information on government financial assistance
such as grants and tax incentives, as well as eligible sectors regarding photovoltaic
systems, see www.dsireusa.org.)
Vern Goehring is senior electrical engineer with HDR. He has more than 35 years
of experience in healthcare and industrial projects. He can be reached at firstname.lastname@example.org.