Task lights 0% Heat reject 1% Pumps 3% Refrig display 0% Ht pump supplement 0% Ext usage 0%
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reCoMMended PreliMinary enerGy analysis
Before design of the building form begins, a building massing (“simple box”) energy analysis can be used to evaluate potential energy and load reduction strategies, such as insulation levels and window performance levels. Initial modeling iterations should include the strategies in Step 5.
Site conditions. Consider options that integrate landscape components and strategies that reduce exterior lighting. Massing and orientation. Consider two fundamental building footprint shapes or two building heights (e.g.,
one-story versus two stories for the same total gross square footage). Evaluate how rotating the building 90 degrees affects energy loads.
Building envelope performance. Consider options for the following aspects:
· Solar heat gain coefficients, overall U-value of glazing systems, performance criteria for windows in low,
medium, and high ranges
· R-value (insulation) of walls, roofs, and conditioned below-grade structures in low, medium, and high ranges · Effect of orientation on energy loads
· Effect of percentage of exterior glazing (e.g., 30%, 50%, and 70%) on energy loads
Lighting levels. Consider at least two options for reasonable reductions in lighting power density, including one
aimed at a significant reduction from ASHRAE standards.
Thermal comfort ranges. Consider options for expanding the thermal comfort range.
Plug and process load needs. Consider at least two options for reasonable reductions in plug load density,
including one aimed at a significant reduction from ASHRAE standards.
Programmatic and operational parameters. Consider options aimed at reducing building size, hours of
occupancy, and/or number of occupants.
Simple massing sketches of rough configurations can be converted to simple box energy models. In both cases of this example, only a single wing of each sketch was modeled to simplify this early energy modeling, as depicted in Figures 2 and 3.
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The purpose of the modeling at this stage is to evaluate coarse-grain building configuration differences; only options that have large consequences need to be modeled (Figure 3).
Figure 2. Simple massing sketches. Image courtesy of The Design Alliance Architects, Pittsburgh, PA © 2008. Phipps Center for
Sustainable Landscapes.
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Use this early iterative conceptual energy modeling to understand the building’s heating and cooling loads and determine whether the project’s energy use is likely to be dominated by internal or external loads. Small commercial and most residential projects are frequently dominated by external loads; that is, exterior conditions tend to affect the building’s heating and cooling loads more than internal conditions. As a result, the performance of the building’s envelope tends to have a larger effect than internal loads such as lighting. Large commercial buildings tend to be dominated by internal loads: occupants, equipment, and ventilation may be far greater contributors to the overall load than the performance of the building envelope, depending on climatic conditions.
exaMPles
Example 1. Light level analysis1
During the early stages of a Schools project, the team was able to reduce the number of lighting fixtures in classrooms by 25% compared with standard practice by selecting a paint color whose light reflectance value was 75%, instead of 64% for the initial proposed paint selection, while maintaining adequate illuminance (roughly 50 footcandles) on work surfaces.
The reduction in the number of light fixtures has multiple benefits, beyond the initial savings in fixture purchases and installation: the cost of electrical energy for lighting falls by 25% over the life of the building, and since lighting produces heat, the costs for cooling (roughly 1 watt of energy for every 3 watts of lighting) are reduced.
Example 2. Determining load reduction strategies
Determining effective load reduction strategies is the first step in creating an energy-efficient building. Early focus on load reduction is important because once the space programming is completed and the building is constructed, changing certain components that affect loads becomes difficult and expensive, especially for a building dominated by external or building envelope loads.
An example of a dominant external load is a fully glazed western façade in a mixed climate like New York City. This type of façade creates large loads for both cooling and heating, resulting in excessive energy use and oversizing of HVAC systems. Example strategies to decrease envelope loads include increasing insulated opaque wall area (balanced with daylighting strategies), increasing the insulating value of the glazing and window frame system, and summer solar shading.
On the other end of the spectrum are large buildings with dominant internal loads, like hospitals. Internal loads are often cooling loads, created by a combination of heat-producing lighting, equipment, and occupants. Conditioning of outside air is another big internal load. Load reduction strategies include decreasing lighting power, providing daylighting, reducing plug loads, using economizers for free cooling, and reducing the amount of ventilation air during periods of partial occupancy with CO2 sensors.
In both cases, significant energy load reductions can be achieved. The concept model can provide feedback on which combination of strategies is likely to be the most effective and guide the design team in preparation for modeling HVAC systems. This allows HVAC systems to be properly sized and equipment efficiency improved in subsequent models; the team may be able to downsize or even eliminate equipment. The integrated approach can thus save both energy and capital costs of construction.
exaMPle WorksheeT doCuMenTaTion
Describe how research and analysis uncovered through discovery influenced the project building program, form, geometry, and/or configuration.
The architect and mechanical engineer both started with the idea that two 100-ton chillers would be necessary for the AC system but had not thoroughly considered modifications to the building envelope design. Using the energy model to inform decisions about both, they instead specified two 50-ton chillers. The project also had a “future expansion” component that was not adequately defined, so the team experienced difficulty planning for design flexibility. The team paused and specifically addressed adaptability during the goal-setting workshop and then in the OPR, including which materials would be reclaimed or reused during the future expansion phase. Although opinions differed on the best way forward, the 1. Adapted from 7group and Bill G. Reed, The Integrative Design Guide to Green Building: Redefining the Practice of Sustainability (John Wiley W Sons, Inc., 2009).
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raTinG sysTeM variaTions Core and Shell
The energy-related systems analysis should include all system loads and occupants required by EA Prerequisite Minimum Energy Performance for Core and Shell projects. The water-related systems analysis should include all system loads and occupants required by both WE Prerequisite Outdoor Water Use and WE Prerequisite Indoor Water Use for Core and Shell projects.
ProjeCT TyPe variaTions Major Renovations
The energy-related systems analysis and water-related systems analysis should include all of the same systems required for new construction projects, as described above, except for the massing and orientation component.
CaMPus Group Approach
All buildings in the group may be documented as one.
Campus Approach
Ineligible. Each LEED project may pursue the credit individually.
required doCuMenTaTion
documentation all projects
Integrative Process worksheet (energy and water analysis tabs) X
relaTed CrediT TiPs
LT Credit Quality Transit. The related credit’s methodology for calculating transit service daily trips can be used to
compare the suitability of project site locations for commuters.
LT Credit Reduced Parking Footprint. Reducing paved area and enlarging the landscaped area can expand the
potential for rainwater infiltration aid the irrigation strategies connected with the preliminary water budget analysis required for this credit. This credit also requires that at least one on-site nonpotable water supply source contribute to at least two water demands; for example, a nonpotable water supply source such as harvested rainwater used for both irrigation and toilet flushing satisfies this requirement.
SS Credit Site Assessment. Addressing the related credit together with this credit will offer a more holistic
perspective on the design opportunities and challenges. For best results, conduct the site assessment at the same time as the energy and water analyses required by this credit and present findings to the owner in one package. Climate data research and collection are recommended for both credits.
SS Credit Open Space. A larger landscaped area can increase graywater infiltration and aid irrigation—issues that
relate to the preliminary water budget analysis required for this credit. Integrate vegetated areas (including roofs) to meet the requirements of SS Credit Rainwater Management, SS Credit Heat Island Reduction, WE Prerequisite and Credit Indoor Water Use Reduction, and WE Prerequisite and Credit Outdoor Water Use Reduction as part of a
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holistic analysis. Attention to the credits’ interconnections allows optimization of the whole. Also take into account site design, building location, orientation, and massing, all of which can affect the preliminary energy-related systems analysis required for this credit—for example, using vegetation to provide solar shading.
SS Credit Rainwater Management. The preliminary water budget analysis required for this credit enables project
teams to see how associated water issues interrelate. In developing the required water analysis, look for synergies with the related credit, plus SS Credit Open Space, SS Credit Heat Island Reduction, WE Prerequisite and Credit Indoor Water Use Reduction, and WE Prerequisite and Credit Outdoor Water Use Reduction, for achieving both cost and performance improvements.
SS Credit Heat Island Reduction. Many heat island reduction strategies alter both the preliminary water budget
analysis and the preliminary energy-related systems analysis. For example, vegetated roofs that improve the energy performance of buildings are often paired with rainwater-harvesting systems.
SS Credit Light Pollution Reduction. Reducing exterior lighting power density addresses a site conditions aspect
of the preliminary energy analysis.
WE Prerequisite and Credit Outdoor Water Use Reduction. The landscape water requirement calculation
methodology of the related prerequisite and credit must be used for conducting the preliminary water budget analysis.
WE Prerequisite and Credit Indoor Water Use Reduction. The building water use and appliance and process use
calculation methodologies of the related prerequisite and credit must be used for conducting the preliminary water budget analysis.
WE Credit Cooling Tower Water Use. For projects with cooling towers or evaporative condensers, the calculation
methodologies in the related credit can be used for conducting the preliminary water budget analysis. This credit also requires that at least one on-site nonpotable water supply source contribute to at least two water demands; for example, a nonpotable water supply source such as harvested rainwater used for cooling tower cycling plus one other demand-side use satisfies this requirement.
EA Prerequisite Fundamental Commissioning and Verification. The narrative that this credit requires,
describing the preliminary energy-related systems analysis and preliminary water budget analysis, must be included in the project’s OPR and BOD, both of which are required by the related prerequisite. The purpose here is to give the commissioning authority an understanding of the process and criteria used to select the designed systems—that is, the “why,” not just the “what.”
EA Prerequisite Minimum Energy Performance and EA Credit Optimize Energy Performance. The
preliminary energy analysis required for this credit encourages project teams to focus on load reductions before analyzing system efficiencies. Using “simple box” energy modeling at an early stage, even before determining building form, gives a project team energy end-use benchmarks that directly inform design decisions during an iterative process, significantly improving energy performance and reducing operating costs.
EQ Prerequisite Minimum Indoor Air Quality Performance. The preliminary energy analysis requires project
teams to calculate basic energy end use distribution in the earliest design stages. By doing so, teams can compare the relative energy demands of different ventilation strategies while meeting minimum ventilation requirements.
EQ Credit Enhanced Indoor Air Quality Strategies. The preliminary energy-related systems analysis requires
project teams to calculate basic energy end use distribution in the earliest design stages. By doing so, teams can compare the relative energy demands of different ventilation strategies, including filtration, exhaust, demand control ventilation, and natural ventilation.
EQ Credit Thermal Comfort. Adjusting thermal comfort ranges can dramatically affect energy consumption.
The preliminary energy-related systems analysis allows project teams to study the relative energy demands of adjustments to thermal comfort in the earliest design stages. Thermal comfort depends on many interrelated issues covered by a preliminary energy-related systems analysis, such as ventilation, internal loads from lighting and
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occupants, daylighting strategies, and external loads associated with envelope performance. Early modeling allows project teams to iteratively adjust and evaluate the associated parameters before schematic design.
EQ Credit Daylight. Effective daylighting, including appropriate levels of natural light with controls that reduce
electric lighting, can dramatically affect energy consumption. The preliminary energy analysis allows project teams to compare daylighting design strategies, particularly balancing total glazing area with its effect on thermal performance and human comfort.
EQ Credit Quality Views. The preliminary energy-related systems analysis helps project teams give occupants
exterior views while balancing total glazing area with its effect on thermal performance and comfort.
ChanGes froM leed 2009
This is a new credit.
referenCed sTandards
ANSI Consensus National Standard Guide© 2.0 for Design and Construction of Sustainable Buildings and
Communities (February 2, 2012): ansi.org