The Energy Design Process for Designing and
Constructing High-Performance Buildings
SHEILA J. HAYTER, P.E., Senior Engineer, National Renewable Energy Laboratory, 1617
Cole Blvd., Golden, Colorado, 80401, USA, phone (303) 384-7519, fax (303) 384-7540,
sheila_hayter@nrel.gov
PAUL A. TORCELLINI, Ph.D., P.E., Senior Engineer, National Renewable Energy
Laboratory, Golden, Colorado, U.S.A.
RICHARD B. HAYTER, Ph.D., P.E., Associate Dean of Engineering, Kansas State
University, Manhattan, Kansas U.S.A.
RON JUDKOFF, Director, Center for Buildings and Thermal Systems, National Renewable
Energy Laboratory, Golden, Colorado, U.S.A.
ABSTRACT
Successfully designing, constructing, and operating high-performance buildings requires
the building owner and all members of the design team to set goals to minimize energy
consumption and environmental impact. The team should establish these goals early in the
design process and maintain them through the building occupation. One method for achieving
high-performance building goals is to follow the energy design process. This process begins
in the predesign phase and continues after the building is commissioned and occupied.
Understanding which strategies are best suited for the building site and function, setting
aggressive energy targets early, and relying on computer simulations to evaluate design
options are essential to the process. The building envelope is designed first to minimize
energy consumption. The mechanical/electrical/control systems are designed after optimizing
the envelope design. Detailed specifications must accurately reflect the design intent. After
construction, the building is commissioned, the owner/operators are instructed on the optimal
operation of the building, and building operation documents are provided for future reference.
This paper focuses on the energy design process. An actual high-performance building
demonstrates how to apply the process. This building incorporates energy-efficient and
renewable energy design features including daylighting, passive heating and cooling,
improved thermal envelope, and photovoltaics.
1. INTRODUCTION
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers
(ASHRAE) President Bill Coad wrote, “There is a new standard of professionalism in
engineering, and that is to practice in our profession with an emphasis upon our responsibility
to protect the long-range interests of the Society we serve, and specifically, to incorporate the
ethics of energy conservation and environmental preservation in everything we do.” Coad
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The Energy Design Process for Designing and Constructing High-Performance Buildings
stressed that “Energy and the environment…must be elevated from ‘design parameters’ to
‘moral standards.’” (Coad 2000)
A new trend in architecture is “sustainable design.” However, this term has many
meanings. The U.S. Green Building Council defines it as “a building’s total economic and
environmental impact and performance, from material extraction and product manufacture to
product transportation, building design and construction, operations and maintenance, and
building reuse or disposal.” (USGBC 2000). The Earth Summit in Rio concluded that
sustainability means providing for the needs of the present without detracting from the ability
to fulfill the needs of the future. (UNCED 1992). As noted by Stum (Stum 2000), “A ‘green’
building is designed, constructed, and used in a way that minimizes negative environmental
consequences from both an economic and life-cycle perspective…” Stum continues to
explain that in addition to being environmentally benign, the buildings “are designed, built,
and operated to be cost-effective under current business conditions.” Although many
definitions are similar, none have exactly the same meaning as another. This variance in
definitions make it extremely difficult for building designers to know how to respond when
requested to create a sustainable building.
There is one area in which sustainable building design definitions are similar. They all
imply that buildings have an environmental impact. This impact is evident in land, material,
and energy use. There is also an affect on humans occupying the building. According to the
U.S. Department of Energy, Energy Information Agency (EIA), the U.S. residential and
commercial building sectors consumed 36x109 GJ (34.17 Quads) in 1999 or 35% of the total
energy consumed in the U.S. (DOE 1999a). EIA also reports that in 1999, the residential and
commercial building sectors accounted for 65% of all the electricity consumed in the United
States (DOE 1999b). With this energy consumption is the environmental impact for
extracting and processing the resources needed to provide the energy to the buildings. The
statistics above show that energy consumption contributes significantly to the environmental
impact from buildings.
The energy design process was developed to reduce building energy consumption. This
process encompasses the entire design. It starts with the predesign phase, continues through
occupancy of the building, and uses energy simulation throughout the process. The energy
design process steps must be completed in the order in which they are presented in this paper
to ensure a successful high-performance building. For the purpose of this paper, a highperformance building is defined as one whose savings significantly exceed applicable energy
codes and standards, such as performing 50% better than these codes and standards
(ASHRAE 1989, USGVMT 1995).
Although more difficult to quantify, it has been documented that high-performance
buildings increase occupant satisfaction, which increases productivity, test scores, sales, and
other functions taking place within the building (Nicholas and Bailey 1995, Heschong et.al.
2000, Okura et. al. 2000b, USGBC 2000).
This paper focuses on how to achieve low-energy goals by applying the energy design
process. This process was used to design the new Zion National Park (ZNP) Visitor Center in
Springdale, Utah, U.S.A. Energy-efficient features include daylighting, natural ventilation,
evaporative cooling, passive solar heating, computerized building controls, and an
uninterrupted power supply (UPS) integrated with a photovoltaic (PV) system. These
“features” form the integrated energy solution that met the project goals. The total expected
energy cost reduction is approximately 80% compared to a building designed to meet the
minimum requirements of the applicable energy code (USGVMT 1995).
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The Energy Design Process for Designing and Constructing High-Performance Buildings
2. THE ENERGY DESIGN PROCESS
In a traditional design process, the architectural team determines the building form and
articulation of the façade, including orientation, color, window area, and window placement.
This architectural design is then handed off to the engineering team, who designs the heating,
ventilating, and air-conditioning (HVAC) system, ensures compliance with applicable energy
codes, and ensures acceptable levels of environmental comfort for building occupants. From
an engineer's point of view, energy efficiency occurs by improving the design of the HVAC
system. It is then the engineer's goal to create an efficient system within the context of the
building envelope that has been previously designed—the architectural decisions have been
finalized and few changes can be made to the envelope design.
For successful realization of low-energy buildings, the building owner, architect, engineer,
and energy consultant must form a design team and establish a cost-effective energy goal.
Once a commitment to energy minimization has been made, the energy-design process can be
used to guide the team towards good decision making and trade-off analysis without
sacrificing the building’s programmatic requirements.
The concept of a cost-effective goal depends on the values of the owner and the owner’s
economic criteria. Traditional methods for evaluating criteria often included first cost, simple
payback, savings-to-investment ratio, life-cycle cost, or net present value of savings. Many
times, with some creativity, this cost-effectiveness can stretch into the ability to market a
building as green or as disaster resistant (e.g., able to function if no grid-power is available).
No matter how cost-effectiveness is defined, the method for determining cost-effectiveness
should be agreed to and understood by all team members.
The design should meet or exceed all the functional and comfort requirements of the
building. Low-energy design does not imply that building occupants endure conditions that
are considered unacceptable in traditional buildings. However, research has shown that some
low-energy design strategies result in occupants being more tolerant of varying indoor
conditions, increasing the opportunities for applications of these strategies (Brager 2000).
The energy-design process is a simulation-based, quantitative, and qualitative method to
help architects and engineers create low-energy buildings. Low-energy design is not intuitive.
The energy use and energy cost of a building depends on the complex interaction of many
parameters and variables. The problem is far too complex for “rules of thumb” or hand
calculations. The interactions are best studied using computerized hourly energy simulation
tools to thoroughly evaluate all the interactions of the building envelope and systems design
features.
Application of the process begins in the predesign phase when the building size, type,
location, and use are known. The process then continues with design, construction, and
commissioning phases according to the following steps. These steps assume a team has been
formed and they are committed to low-energy building design.
Step 1: Pre-design. The design team develops a thorough understanding of the building
site, local weather patterns, and building functional requirements. A qualitative evaluation of
these issues early in the design process often leads to later solutions for minimizing building
energy consumption. Many design strategies are applicable to most buildings in most
climates; however, each building is unique, and thus, will have unique energy minimization
design solutions.
Step 2: Create a Base-Case Building Model. Simulate a base-case model of the building
to identify energy minimization opportunities using an hourly building-energy simulation
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The Energy Design Process for Designing and Constructing High-Performance Buildings
computer tool. In general terms, a base-case building is “solar neutral.” It is rectangular with
windows distributed equally on all of the four cardinal orientations and has simplified zoning.
It has the same floor area and the same footprint area as the proposed building and it complies
with the prescriptive standards of the applicable energy code for that type of building in that
location. The base-case computer model simulates annual loads and peak demands for
heating, cooling, lighting, and plug loads and for HVAC system fans and pumps to determine
the energy-use profile of the base-case building.
Step 3: Parametric Analysis. An “elimination” parametric analysis guides the designer to
understand the sensitivity of the total building energy performance to specific building loads.
A parametric analysis is accomplished by eliminating loads one at a time from the simulation,
such as conduction losses, people, solar gains, and plug loads. For example, if eliminating all
conductive heat transfer through the building envelope has a small effect on energy costs,
there would be little sense in increasing building insulation levels beyond those prescribed by
code. Similarly, the parametric modeling exercise may demonstrate an upper limit to the
amount of insulation before internal loads begin to increase air-conditioning loads. The
design team may find that reducing insulation levels and using the money elsewhere has a
larger impact on the total energy picture. Another example is if eliminating all solar gains has
a large affect on energy costs, then it is worth exploring solar related issues such as window
area, orientation, window solar heat gain coefficient (SHGC), and façade shading geometry
(such as the use of overhangs).
Step 4: Brainstorm Design Solutions. The design team brainstorms possible solutions to
energy problems. At this stage, the emphasis is on solutions relating to building geometry.
For example, daylighting might be a solution if lighting loads and associated cooling loads are
a large percentage of the energy costs. If winter heating loads are an important issue, passive
solar heating may be desirable. These solutions have significant implications for building
geometry, siting, zoning, and orientation, which are aspects of the building that are difficult or
impossible to alter later in the design process.
Step 5: Simulate Performance of Design Solutions. Simulations are performed on
variants of the base-case building relating to the list of possible solutions developed in Step 4.
Issues that will have a profound influence on the architectural aspects of the building are
quantitatively explored prior to the conceptual design phase. The energy impact of each
variant is determined by comparison to the original base-case building and to the other
variants. Computerized design tools bring all the architectural and engineering pieces
together to predict how the building’s components will interact. In other words, daylighting
systems, thermal issues, and building control strategies may be addressed by different
building disciplines, but successful low-energy performance can only be achieved by
examining the interrelation between these components.
Step 6: Conceptual Design. The conceptual design is the most difficult part of the energy
design process. It is essential that the energy features be integrated into the architecture of the
building. The objective is to use the architectural and envelope features to minimize energy
costs for heating, cooling, and lighting. Often, energy features that effect the visual impact of
the building can also serve as the main architectural aesthetic features, thereby saving costs.
If the addition of an energy feature substantially increases the building cost, it is evaluated
with the cost-effectiveness criteria already established.
In Step 6, the architectural team prepares a preliminary set of drawings based on the siting,
orientation, and basic geometry of the building decisions made in Step 5. A computer model
predicts the energy performance of this preliminary design. Variants of the preliminary
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The Energy Design Process for Designing and Constructing High-Performance Buildings
design are simulated to provide information to the architectural team for refinement of the
design. At this stage, solutions will not affect the overall form, but will affect the appearance
of the building. The variables include determination of the ratio of glazed to opaque surface
area on each orientation; the geometry of fixed shading devices and light shelves on each
façade; the optical and heat transfer characteristics of the glazing on each façade; use of
natural ventilation; the resistance and capacitance of walls; and the quantity of internal
thermal mass. It is essential to use validated computer models that properly account for the
physics of these complex interactions (Judkoff and Neymark 1995).
Note that only the building envelope has been considered at this point in the design. The
HVAC design is evaluated after optimizing the building envelope for energy efficiency.
Because slight changes in the envelope design can have significant effects on total building
energy loads, it is best to wait until the envelope design is well developed before considering
the HVAC design. The HVAC design should reflect the needs of the building envelope.
Step 7: Design Development. After the architectural features impacting energy use have
been determined, the computer model simulating the performance of the proposed building is
updated to reflect those decisions. A set of simulations is then performed to guide decisions
regarding the HVAC system and associated controls. These simulations are primarily to
optimize annual energy use, annual energy cost, and the occupant comfort. The simulations
can also be used to help properly size the equipment. Low-energy buildings defy the industry
norms used for equipment sizing. First cost savings in substantially downsized equipment can
often be used to pay for improved envelope energy features. At this point, there will be some
iteration or trade-off between mechanical system decisions and architectural features;
however, it is best to optimize the architectural features first.
Although the energy design process may increase the cost to design the building by
approximately 20%, compared to the traditional design process, the increased design cost is
often offset by reductions in errors and decreased mechanical system cost. Fewer errors occur
because careful attention was paid throughout the design process and more effort is placed on
checking and review. Also, small mechanical systems require less space in the building
(requiring less building to be built), and therefore, lower capital costs.
Step 8: Bid Documents and Specifications. Plans and specifications must be carefully
reviewed to find areas where the design intent is not met and to catch unacceptable component
substitutions. Examples include ensuring that there are no thermal bridges connecting the
conditioned space with the outdoors, window thermal and optical properties are specified,
HVAC equipment is specified for efficiency and performance, control algorithms are
adequately expressed, and insulating values of insulation materials are specified. A final
simulation is based on these plans and specifications to ensure a low-energy building and to
show energy code compliance (e.g., the building should perform more than 50% better than
the code-compliant base-case building in most cases). In the case of high construction bids,
the design may need modification to reduce costs. All modifications should be closely
evaluated to ensure that the original energy savings goals are maintained.
Step 9: Construction. At this phase, most of the simulation work has been completed;
however, occasional simulations will need to be performed as needed in response to
unanticipated circumstances. This might include the need to determine if a substitute
component really meets the energy related specifications or review of a construction detail
that must be modified because of a problem on the construction site. Scheduled plan reviews
and site inspections are crucial to ensure that specified details omitted from the plans do not
compromise the energy design. A clear communication path between the constructor,
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The Energy Design Process for Designing and Constructing High-Performance Buildings
building operator, and the design team will help ensure that components are installed properly.
In many cases, once construction on a particular area is incorrectly completed, it cannot be
reinstalled and the building owner is forced to live with the energy performance
consequences.
Step 10: Commissioning and Post-Occupancy Evaluation. The commissioning process
includes testing all subsystems in the building to ensure that they operate as intended. For
example, poorly calibrated economizer controls can bring in excess air or poorly calibrated
daylight sensors may not turn off the lights. Occasional simulations will be required to help
solve problems that emerge during this final phase and to respond to changes in building use
that may occur once the building is occupied. The key is that the controls function with the
design intent of the building. A good building quickly becomes a “bad” building with
improper control strategies. In addition, it is important to educate the building owner,
occupants and the maintenance staff to properly use the building systems as conceived by the
design team. The building’s energy performance can only be optimized if the people running
the systems understand how the systems interact.
3. CASE STUDY – ZION NATIONAL PARK VISITOR CENTER
Zion National Park (ZNP) encompasses a canyon desert region located in southwest Utah,
U.S.A. In an effort to enhance the visitor experience and reduce the environmental impact on
their natural resource, the Park embarked on a plan to eliminate automobile traffic from the
canyon by implementing a revolutionary transportation system. The Park hosts 3000 visitors
per hour during the peak summer season. Before the new transportation system was
implemented, most of these visitors drove private vehicles on a two-lane road to the top of the
narrow box canyon. On a typical summer day, 3000 cars visited the park, yet there was a
maximum of only 400 parking available spaces. Not only was the visitor experience
hampered by the traffic congestion, the vehicle load had noticeable adverse affects on the
canyon’s flora and fauna. Visitor safety was also a concern.
The Park outgrew its existing Visitor Center as well. Interpretive space was limited for
displays describing the Park’s features. The restrooms were unable to handle the visitor load.
The layout of the building was not conducive to effectively serving the large number of
visitors. The National Park Service (NPS) concluded that a new Visitor Center should be
constructed as part of the overall transportation improvement plan.
A series of design charrettes were held to brainstorm project goals, including
transportation, visitor amenities, and energy issues. The design team, NPS staff, exhibit
designers, and other interested parties participated in the charrettes. Each of these design
charrettes were conducted over several days and were held at the existing ZNP Visitor Center,
giving the participants a unique opportunity to experience natural phenomenon occurring
within the Park.
3.1 Applying the Design Process
During the first of the charrettes, the energy consultant observed natural cooling effects
within the canyon that could easily be adapted to the built environment. These were
important observations for a region whose daily high summer temperatures exceed 38°C
(100°F). Over the past millennium, The Virgin River has cut a deep narrow slot (up to 610-m
(2000-ft) deep) through many layers of rock. This slot canyon opens to the wider canyon that
comprises the most popular destination in the Park. The slot canyon walls shade the canyon
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The Energy Design Process for Designing and Constructing High-Performance Buildings
floor from the hot summer sun. In many parts of the slot canyon, direct sunlight on the lower
walls and canyon floor lasts less than an hour per day. Water seeping through the rocks wet
the canyon wall surfaces. Hot air rising from the wider canyon below passes through the
narrow passage of the slot canyon. This combination of the hot air evaporating water from the
canyon walls and the high-mass walls maintains comfortable temperatures in the canyon.
Solar load avoidance, thermal mass, evaporative cooling, and natural ventilation work
together to create a comfortable, cool environment in an otherwise harsh climate.
The lack of direct solar gain results in predominantly diffuse light available within the slot
canyon. The diffuse light makes the building seem cooler, further improving the summertime
comfort.
An opposite effect was observed in wider areas of the canyon. The evening sun heats the
east canyon wall. This side of the canyon then remains warm into the night, even though
average summer nighttime temperatures drop to 15°C (60°F). The massive stone materials
absorb the heat and slowly releases it during the cooler hours of the evening and night. Even
though nighttime air temperatures drop, comfort is maintained where stored heat is re-radiated
from these rocks.
The canyon vegetation reflects the success of the natural environmental tempering. The
walls of the canyon and the canyon floor are lushly vegetated. On leaving the canyon, almost
no vegetation can exist in the hot, dry desert plains.
Original program requirements for building size were evaluated as well. The summer
climate, when 90% of the total annual visitors are in the Park, is hot and dry. With some
outdoor microclimate interventions, such as providing shading and water features, the design
team determined that many of the Visitor Center exhibits could be moved to permanent
displays located outside of the building. Several advantages resulted from this decision. The
building became smaller, less expensive, and thus required less energy to operate. Building
comfort improved because the visitor concentration could be spread out between inside the
building and the outside displays. Finally, visitors would have access to the educational
displays until dark, long after the Visitor Center closed.
These observations resulted from a clear understanding of the natural environment in
which the building was to be located and a careful analysis of the programmatic needs of the
building. Daylighting, natural ventilation, evaporative cooling, elimination of summer solar
gains with building shape and envelope features, massive building materials to stabilize
indoor temperatures, passive solar heating, and siting with relation to mature trees and newly
constructed outdoor shade structures are part of the integrated building design. A roofmounted PV array further reduces the building’s environmental impact (Figures 1 and 2).
Figure 1. Zion National Park Visitor Center
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The Energy Design Process for Designing and Constructing High-Performance Buildings
Figure 2. Zion National Park Visitor Center Energy-Efficient and Renewable Energy Design Features
Base-case computer simulations of the building were then performed using an hourly,
building energy computer simulation tool, to distinguish building energy loads and calculate
energy performance of a code-compliant building (LBNL 1994, Palmiter 1984). The ZNP
Visitor Center base-case simulations complied with the applicable energy code (USGVMT
1995, ASHRAE 1989). In this project, two base-case simulations were created. One to
reflect the original specified floor area of the building and a second equal to the smaller
footprint after moving permanent displays outdoors.
An elimination parametric analysis was completed using the base-case building simulations
to evaluate the effects of specific elements of the building. For example, the U-value of the
wall, floor, roof, and windows were individually minimized to simulate zero heat transfer
across these components. The resulting building energy requirements from each of these
parameters showed that daylighting, shading, natural ventilation, evaporative cooling, and
passive solar heating reduced total building energy requirements the most. Results from the
parametric analysis are shown and discussed in Section 3.2, Performance Results.
By combining the parametric analysis results with elements used to keep the canyon
comfortable, the design team analyzed strategies to address primary energy loads. Computer
simulations were performed to quantitatively evaluate the effectiveness of these strategies.
Those strategies affecting the building architecture were carefully studied in preparation for
the next design process step.
Following the conceptual design, the team began to finalize the architectural design.
Architectural requirements were merged with energy-efficient strategies. For example, the
original conceptual design ideas for the building envelope included tall elements to tie the
building design in with the towering stone structures of the surrounding canyon walls. To
meet this architectural requirement and the energy goals of the project, the team chose
downdraft cooltowers as the primary cooling system (Figure 3). This system is a chimney in
reverse. Water is pumped onto a honeycomb media at the top of the tower. The evaporatively
cooled air, which is denser than the ambient air, falls through the tower under its own weight
where it then enters the building. No fans are required to cool the building. Windows
strategically placed in the building envelope promotes natural ventilation to move the cool air
to move through the space. This is an example of how architectural features enhance the
energy performance as well as give the building a unique aesthetic style. In the ZNP Visitor
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The Energy Design Process for Designing and Constructing High-Performance Buildings
Center, the building’s overhangs, clerestories, roofline, massive building materials, and other
architectural features all contribute to the building’s energy performance. Hourly computer
simulations helped engineer all components to create a package where the envelope became
most of the HVAC system.
Figure 3. Downdraft Cooltower
A Trombe wall was selected to provide most of the building heating because of strong
winter solar gains. As with the cooling system design, simulations were used to optimize the
envelope for winter performance (Figure 4).
Figure 4. Trombe Wall
After the envelope was designed, the remaining heating, cooling, and lighting loads were
studied. A small amount of heating remained. Because these heating loads were low, the
most cost-effective solution for meeting them was to install overhead, electrically powered
radiant heating panels. Installing electric heat eliminated the need for a central heating system
that would have required a hot-air furnace or boiler and associated ductwork or piping.
Natural gas is not available on site, so a central heating system would either have required
transporting and storing propane or operation using electrical power. The cost of propane for
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The Energy Design Process for Designing and Constructing High-Performance Buildings
this site is equivalent to the cost of electricity. Electric resistant heat was the most costeffective solution.
All cooling loads were met with natural ventilation, the evaporative cooling using the
cooltowers, and careful design of shading devices to minimize the solar gains. The only
mechanical input to the cooling system is a pump to circulate water through the evaporative
media. The cooling system meets all summer ventilation requirements as well.
Winter occupancy loads are very low. Natural infiltration through the building envelope as
well as people entering and exiting the building provides adequate ventilation.
At this point in the process, the design team investigated the potential impact of
incorporating a PV system. The architectural team ensured that the building would be PV
ready, meaning that mounts for a roof-mounted PV system were designed into the southfacing roof structure. Because of poor power reliability at the site, the UPS was included in
the original plan for the building electrical system. By specifying an inverter for this system
that could handle the direct current input from a PV system, the existing UPS was converted
to a PV-powered UPS. It was later determined that a 7.2-kW PV system would be installed
(Figure 5).
Figure 5. Energy Consultants Adjusting the Roof-Mounted, 7.2-kW PV System
After optimizing the architectural and engineering designs, the final set of bid documents
and specifications were created. The design team carefully reviewed all drawings and
documents to ensure that the design intent was clear and to minimize the chance for errors or
misinterpretation of the design during construction. A final design computer simulation was
completed to accurately reflect the requirements described in the drawings and specifications.
The design team carefully observed the building construction and was available to answer
construction crew questions about the drawings and specifications. If the contractor
recommended a change to the design, the design team reran the computer simulations before
authorizing the change to ensure that the change would not adversely affect the overall
building energy performance. The good communication between the contractor and the
design team was enhanced by frequent visits to the site during construction by the
architectural and energy consultant members of the design team.
After construction was completed, the energy consultant monitored the building’s
performance to identify commissioning problems. When a problem was identified, the energy
consultant worked directly with the building operators and maintenance staff to correct the
problem. This close relationship between those operating the building and the design team led
to occupant acceptance of the nontraditional systems within the building. Although the
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systems are not complicated to operate, educating the building operators was required so that
they could learn to identify and correctly solve future operation problems.
3.2 Performance Results
The anticipated energy cost savings are approximately 80%, based on the simulation
models of the building performance (Figure 6). These savings do not include savings from
the PV system. The building is currently being monitored to validate these expectations.
DHW
5%
Lights
5%
Fix Chrg
3%
Fans
32%
Fans
0%
Heating
6%
DHW
4%
Fix Chrg
3%
Cooling
32%
Cooling
0%
Heating
10%
Lights
18%
Savings
82%
Figure 6. Expected Energy Cost Savings by Category, not Including the PV System Contribution
Figure 7 illustrates the parametric analysis results. Trends indicated by this analysis show
that the cooling load dominates the building energy load. Eliminating the solar gains (no sun
parametric) reduced the cooling load the most. This observation directed the design team to
evaluate strategies that reduced solar gain through solar gain avoidance. Reducing internal
gains also improved the cooling loads. The internal load that offered the most opportunity for
reduction by the design team was the lighting load. As a result, the design team incorporated
aggressive daylighting strategies and was careful that the daylighting design avoided solar
gains during the cooling season.
The building envelope design, which eliminates summer solar gains and optimizes the
daylighting, did not offset the entire cooling load. Natural ventilation cooling was then
integrated with the daylighting design by adding automatic window actuators to the clerestory
windows. The cooling loads that could not be met by natural ventilation are offset by the
evaporative cooling system through use of the cooltowers that were discussed earlier.
The parametric analysis showed that eliminating the solar gains (no sun parametric)
negatively impacted the building heating loads substantially. It became obvious to the design
team that winter solar contribution was required to manage the heating loads. The resulting
design solution was to incorporate a Trombe wall into the entire south wall of the building. A
properly sized window overhang allows the low winter sun to heat the wall while shading the
wall during the cooling season so as not to induce a cooling load on the building. Overhangs
for all south-facing windows were also engineered to allow direct solar gain in the winter and
eliminate summer solar gains. Because it is desirable to maximize solar gains through the
south-facing windows, these windows were specified to have a high SHGC. All west-facing
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The Energy Design Process for Designing and Constructing High-Performance Buildings
1
cool
0.9
heat
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
25 x internal mass
5 x internal mass
no sun (SHGC=0)
no infiltration
Qfloor = 0
Qroof = 0
Qwall = 0
Qwin = 0
no internal gains
0
base case
Energy Comparison (%) (Base-Case Building = 100%)
glass was specified to have a low SHGC because it is extremely difficult to shade these
windows during the cooling season using building envelope elements.
Finally, the parametric analysis showed that eliminating heat transfer through the windows
eliminated the heating load and reduced the cooling load. This led the design team to specify
low U-value windows throughout the building.
Parametric Alternative
Figure 7. Parametric Analysis Results
The total building electrical loads were reduced because of the integrated design process.
As a result, the 7.2-kW PV-UPS system is able to offset approximately 30% of the total
building electrical load that otherwise would have been met by the power from the utility grid.
The PV system is also capable of meeting all functional requirements of the building during a
daytime power outage. The PV system will operate the cash registers, security system,
building automation system, cooltower pumps, and other essential equipment. The
daylighting design provides approximately 50% of the total lighting load and is sufficient to
maintain operational lighting levels during a power outage.
The total cost to construct this building was 30% less than the original program plan
building. The integration of the energy features into the envelope increased the envelope cost
of the building, however, the reduction of infrastructure and mechanical systems (including
elimination of the mechanical room) reduced the cost. This project demonstrates that it is
possible to construct sustainable buildings for less cost than buildings not optimized for
energy efficiency.
3.3 Lessons Learned
Several lessons were learned after construction and commissioning. During the first
summer the building was occupied, comfort was maintained except in two isolated offices.
Clima 2000/Napoli 2001 World Congress – Napoli (I), 15-18 September 2001
The Energy Design Process for Designing and Constructing High-Performance Buildings
The downdraft cooltowers with natural ventilation work best in open spaces. The occupants
of these offices prefer to keep the doors shut and they prefer to keep the windows shut for
privacy and security reasons. It is then impossible for natural ventilation cooling to take place
in these areas. The design team is committed to making these spaces comfortable and is
engineering solutions to account for the observed variations. The concern is isolated to only
9.2 m2 (100 ft2) of the total building area.
A second lesson learned is related to the daylighting. Designers intentionally chose to
incorporate diffuse light in the space to reflect the lighting characteristics within the narrow
slot canyon of the Park, making the interior seem cooler. The architect also decided to use a
light pine, tongue-and-groove ceiling finish instead of a bright white ceiling, as was
recommended by the energy consultant. The darker ceiling drastically decreases the
daylighting effectiveness in the space. In addition, up-lighting fixtures were selected to
provide supplement lighting when needed. These fixtures were installed level to the
horizontal beams in the space, some distance below the ceiling. The natural wood-colored
ceiling and the distance between it and the up-lighting fixtures decreases the effectiveness of
these fixtures. The design team determined that a brighter ceiling and an alternative lighting
fixture selection would have improved the daylighting performance in the space. In addition,
task lighting was not installed in areas requiring detail work, resulting in lighting complaints.
This task lighting problem is being corrected.
4. CONCLUSIONS
An integrated design approach that included the design team and building users was
followed from the onset of the conceptual design phase through building commissioning and
occupation. An energy cost reduction goal of 70% was established early and maintained
throughout the design process. Using the microclimatic phenomena of the canyon as a model,
an integrated set of solutions for architectural design and energy efficiency was determined,
including extensive daylighting, natural ventilation, evaporative cooling, and passive solar
radiant heating using a Trombe wall. It is key to design a building that works with the
environment in which it is located to minimize the use of fossil fuels. The building
architecture was formed based on the programmatic and energy goals for the project. Tall
vertical elements were preferred by the architect to harmonize the building with the
surrounding natural environment. These towers were also used to passively cool the building.
An HVAC system was designed to work with the building. A PV system was installed to
provide emergency power and supplemental power when utility power is available. The
building construction cost was 30% less and its energy costs are 80% less than a conventional
Visitor Center. The ZNP Visitor Center shows that sustainable buildings need not cost more.
Research is underway to evaluate all the elements of the building and validate the actual
energy savings.
5. ACKNOWLEDGMENTS
This research project was funded as part of the High-Performance Buildings Research
Program (DOE 2001). Funding is provided to the National Renewable Energy Laboratory
(NREL) by the U.S. Department of Energy (DOE) Office of Building Technology State and
Community Programs, Dru Crawley, Program Manager.
The NREL/DOE High-Performance Buildings Research Program was responsible for
optimizing the design of the low-energy building described in this paper. The project
Clima 2000/Napoli 2001 World Congress – Napoli (I), 15-18 September 2001
The Energy Design Process for Designing and Constructing High-Performance Buildings
manager, architect, and mechanical engineer were Patrick Shea, James Crockett, AIA and
Mark Golnar, P.E., respectively, of the U.S. National Park Service, Denver Service Center.
Paul A. Torcellini and Ron Judkoff, NREL, were primarily responsible for the energy design
and performance monitoring of the building and acted as the project energy consultants.
The Kansas Energy Extension Service, Kansas State University, provided additional
support for this paper.
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