NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Setting Whole Building Absolute 

Energy Use Targets for the K-12 

School, Retail, and Healthcare 

Sectors

Preprint

M. Leach, E. Bonnema, S. Pless, and 

P. Torcellini

To be presented at ACEEE Summer Study on Energy Efficiency in 

Buildings

Pacific Grove, California

August 12-17, 2012

Conference Paper

NREL/CP-5500-55131

August 2012
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1

Setting Whole-Building Absolute Energy Use Targets for the K-12 School,

Retail, and Healthcare Sectors

Matt Leach, Eric Bonnema, Shanti Pless, and Paul Torcellini, National Renewable Energy 

Laboratory1

ABSTRACT

Careful goal setting is required to design and construct high-performance buildings.

Percent savings goals are popular and can be effective but depend heavily on an often theoretical 

baseline case against which savings are measured. Specification of whole-building absolute 

energy use intensity targets can help designers and owners ensure that the desired level of 

performance for a project is achieved. Some benefits of whole-building absolute energy use 

intensity targets are that they:

• Provide a directly measureable target that enables clear and straightforward determination of

energy performance success

• Compel design and construction teams to realize energy performance goals by explicitly

including energy targets in contractual documents

• Emphasize the importance of capturing whole-building energy use, as opposed to a subset of 

building energy uses required for compliance with building codes or certification programs

This paper helps owners’ efficiency representatives to inform executive management, 

contract development, and project management staff as to how specifying and applying wholebuilding absolute energy use targets for new construction or renovation projects can improve the 

operational energy performance of commercial buildings. The absolute energy use targets 

developed for the 50% series of Advanced Energy Design Guides, which promote the use of 

economically replicable, industry-vetted, energy efficiency strategies, are emphasized. Sectorspecific absolute energy use targets that account for sector-wide programmatic variation are

presented for K-12 schools, medium- to big-box retail stores, and large hospitals.

Benefits of Whole-Building Absolute Energy Use Targets

The value of whole-building absolute energy use targets has been demonstrated through 

real-world application (Brown et al. 2010; Pless et al. 2011). The following section highlights 

ways in which the specification of such targets increases the likelihood that pitfalls associated 

with the specification of traditional energy performance targets can and will be avoided.

Importance of a Clearly Defined Goal

A clearly defined energy performance goal brings focus to a project. When energy 

performance is defined in terms of a percent savings goal, significant analysis is typically 

 1 The Alliance for Sustainable Energy, LLC (Alliance), is the manager and operator of the National Renewable 

Energy Laboratory (NREL). Employees of the Alliance for Sustainable Energy, LLC, under Contract No. DEAC36-08GO28308 with the U.S. Dept. of Energy, have authored this work. The United States Government retains 

and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a 

non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or 

allow others to do so, for United States Government purposes.
2

required to translate that goal into a specific energy use target. Establishing a baseline requires 

assumptions that allow significant individual interpretation. Even with the best of intentions, 

generating a baseline that accurately represents the project can be time consuming; the subjective 

nature of this process (especially as it relates to defining quantities not governed by codes or 

standards, such as plug and process loads [PPLs]) can also easily be exploited to game rating or 

certification procedures. Whole-building absolute energy use targets provide clear energy 

performance goals that leave no room for interpretation.

Importance of Goal Verification

Building energy performance is rarely measured (using utility bills or installed metering); 

most commonly, an energy model representing the final low-energy design is used to determine 

percent savings over the baseline model. Energy modeling is extremely valuable for defining 

energy use targets, predicting building performance throughout the design and construction 

process, and setting end-use energy budgets, but the inherent differences between simulation and 

reality make it impossible for energy modeling results to fully represent the actual building.

Thus, occupied building energy use must be measured to determine if energy performance goals 

have been met. Specification of whole-building absolute energy use performance targets shifts 

the focus of performance verification away from energy modeling and towards building 

measurement; whole-building absolute energy use can be measured with utility bills, allowing 

for simple and straightforward verification of energy performance goals.

Importance of Capturing Whole-Building Energy Use

A primary limitation of traditional goal setting, which typically measures performance 

against the requirements of a prevailing building code or recognized national standard (such as 

ASHRAE Standard 90.1), is that such goals address only a subset of the energy-using building 

systems (typically neglecting PPLs, realistic operational schedules, etc.). Depending on the 

application, nonregulated loads, such as PPLs, can dominate energy use, and must be understood 

and controlled to meet energy performance goals (Brown et al. 2010). Specification of wholebuilding absolute energy use targets necessitates that all energy-using building systems are 

considered and reflected in energy performance goals.

Consideration of whole-building energy use will often foster discussions that focus on 

often-overlooked energy use implications. Evaluation of whole-building energy use requires that

the term whole-building be defined. Does the scope of the analysis extend beyond the building to 

encompass the entire site? If the building site contains a charging station for electric vehicles, 

should the scope include transportation energy use? If the building is part of a larger campus, 

should associated district heating and cooling loads be attributed to the building? If a building 

houses a data center that serves multiple facilities, how should its energy use be assigned? Figure 

1 illustrates the connectivity between a building, its governing building codes, and its 

surroundings, and demonstrates the complexity involved in defining whole-building.

We define whole-building as the building and its immediate site. We also define energy 

targets with respect to site energy, as opposed to alternative energy use metrics such as source 

energy or carbon emissions.
3

Figure 1. Defining Whole-Building

(Credit: Marjorie Schott/NREL)

Importance of Maximizing Project Resources

Specific and measurable energy use intensity goals, as opposed to prescriptive design 

requirements, allow for design flexibility and encourage innovative, cost-effective, and 

integrated design strategies. Specifying a whole-building absolute energy use goal alleviates the 

need to create and maintain a baseline energy model; this allows the design team to focus all 

resources on developing the low-energy design. To further maximize resources, the project can 

be defined such that the design and construction team is awarded bonus fees when it reaches the 

whole-building absolute energy use target (Pless et al. 2011).

Tailoring Whole-Building Absolute Energy Use Targets to Project Parameters

Determining a project’s achievable energy performance level requires a complete 

understanding of where and how the building will use energy. The next section highlights key 

parameters that influence energy use, and provides guidance on how those parameters should 

inform the energy target selection process.
4

Defining Key Project Parameters

The following project parameters have a particularly strong impact on energy use and 

should be considered with particular care.

• Building function: Buildings are designed for the functions they will facilitate, and different 

building functions have different energy use characteristics. Retail buildings, for which 

merchandise display is a key function, typically have large lighting loads. Office buildings 

typically have high computing loads, and often require dedicated data centers. Some 

buildings may be considered as hybrids of other, single-function types (e.g., a hospital with 

medical offices). Functions such as electric vehicle charging stations and exterior lighting, 

which may be exterior to the building but still included in the immediate building site, must 

be included.

• Climate: Envelope and ventilation loads, and the effectiveness of many efficiency strategies,

vary with climate; for example, natural ventilation is most effective in mild climates. Energy 

performance of buildings with lower surface-area-to-volume ratios or lower outdoor airflow 

requirements is less affected by climate.

• PPLs: These vary with building function and can have a substantial impact on wholebuilding energy use.

• Hours of operation: Operating requirements can differ between night and day. Cooling 

loads are larger during the day, whereas heating loads (in the absence of temperature setback) 

are larger during the night. For exterior spaces, lighting equipment is typically used only at 

night. Strategies that require solar energy or daylight are beneficial only during the day. And 

some strategies require spaces to be unoccupied when employed (e.g., night economizing to 

cool thermal mass). Accordingly, hours of operation can significantly affect how a building 

uses energy and which strategies can effectively reduce energy use.

• Occupancy: Occupancy dictates ventilation requirements. Occupants can also be a 

significant source of internal loads, both sensible and latent. Understanding occupancy 

densities and patterns is critical for system sizing and control schemes. Buildings with 

significant variations in occupancy must have systems that are designed to operate efficiently 

over a wide range of loading conditions.

• Service level: Building energy use is strongly tied to the level of service for which a building 

is designed. Requirements for comfort and indoor air quality should be clearly defined.

Certain space types may have unique conditioning requirements; for example, grocery sales 

areas are often maintained at a lower-than-normal dew point to reduce refrigerated case loads 

and prevent condensation.

• Specialty space types: Some buildings have specialty space types, such as data centers or 

laboratories, with unique loads. Characteristics of such space types are often project specific 

and can be difficult to define. Accordingly, specialty space types often require separate 

energy use analysis.

Using Project Parameters to Focus the Target Selection Process

When specifying whole-building absolute energy targets for a project, it is wise to survey 

standard and best practices for the applicable building type. Case studies of projects 

demonstrating best-in-class efficiency provide insight into what can be achieved. Survey of the 
5

existing stock of a building type establishes typical energy use and provides context for best-inclass performance.

Significant information is available to inform the specification of whole-building absolute 

energy use targets (50% Advanced Energy Design Guide (AEDG) series, Commercial Buildings 

Energy Consumption Survey (CBECS), High Performance Buildings Database, ENERGY

STAR® Target Finder, portfolio data, local building utility data, etc.); the challenge is filtering 

those data to extract the most applicable information. Defining key parameters and seeking out 

comparison data and target-setting recommendations according to compatibility with those 

parameter definitions can focus the target selection process and enable better-informed decision 

making.

Using Subsystem Targets

Specialty space types may require separate analysis to determine subsystem targets. For 

example, a large, dedicated, data center represents a specialty space type that is very different 

from typical office building space types; data centers are typically thermally isolated from other 

space types and require dedicated heating, ventilation, and air-conditioning (HVAC) equipment 

and strategies. Accordingly, it may be useful to isolate the data center from the rest of the 

building and analyze it separately, seeking out case studies that highlight efficiency strategies 

specific to data centers. Wet and dry laboratories, commercial kitchens, surgery suites, and 

indoor swimming pools may also require this type of analysis.

Specialty space types may have unique energy performance metrics. For example, data 

center performance is measured with respect to power usage effectiveness, a ratio of total data 

center power consumption to computational power production.

Specifying Whole-Building Absolute Energy Use Targets

This section presents varying approaches to using building parameter definitions and 

available resources to specify aggressive and achievable whole-building absolute energy use 

targets. Each approach follows the same basic steps:

1. Define project parameters: All parameters that affect energy use should be defined; 

especially those that have a particularly strong impact on energy use.

2. Survey applicable resources: These will vary by project. For many projects, comparable 

industry best practice case studies will be available. For owners with a large portfolio of 

buildings that share a prototypical design, extensive measured data may be available for 

nearly identical projects. For projects that are more unusual, possibilities may include highlevel comparison against a building type at the national or local level, piece-wise comparison 

of building sections designed for distinct functionality, and increased reliance on energy 

modeling to predict the energy use implications of project-specific parameter definitions.

3. Select goal reference and specify target: Ideally, targets should be set based on technical 

and economic feasibility. In this respect, the whole-building energy use that the target 

represents is important, not the reference point against which it is measured. Reference points 

can provide context for energy goals, however; a target of “30% better than the previous 

building” likely has more meaning than the whole-building energy use that such a target 

represents (in kBtu/ft2

, for example).
6

Many resources may be applicable, and the design team will have to weigh options to 

select a reference point on which the target will be based. For example, many reference points 

may be available to an owner with a portfolio of buildings that share a prototypical design: 

comparable best practice projects for similar buildings, Retail AEDG energy targets, mean 

portfolio performance, best practice portfolio performance, ENERGY STAR Portfolio Manager,

and CBEC data for the appropriate building type.

The following subsections focus on Step 3.

Specifying Whole-Building Absolute Energy Use Targets According to Industry Best 

Practice

Industry projects demonstrating best practice may be excellent reference points for 

energy use target setting. Best practice performance should be identified and targeted any time it 

is cost effective or otherwise justifiable (e.g., corporate image boost). Potential issues associated 

with this approach may include:

• Best practice projects that align with the key parameter definitions of a project cannot be 

identified;

• Best practice projects that align with the key parameter definitions of a project do not align 

with the project budget; and

• Best practice projects cannot be identified that achieve the level of performance desired by 

the design team.

The K-12 School, Retail, and Large Hospital AEDGs provide guidance for specifying

whole-building absolute energy use targets to achieve 50% savings beyond ASHRAE Standard 

90.1-2004 (ASHRAE 2004); 50% AEDG energy use targets represent industry-vetted, 

economically replicable absolute reference points for industry best practice. Another resource for 

best practice is the High Performance Buildings Database.

Specifying Whole-Building Absolute Energy Use Targets According to Portfolio 

Performance

An owner may have a portfolio of buildings that share a prototypical design; building 

design may vary somewhat by climate and functionality, but is similar for many projects. In such 

cases, portfolio energy performance data are invaluable, as they provide options for selecting a 

reference point for energy use target setting. Such data enable an owner to determine typical 

performance and compare it to that for the most and least energy-efficient buildings in the 

portfolio. Poor performers represent straightforward opportunities for improvement; top 

performers represent what is possible with the current prototype design and reference points for 

efficiency improvements. These data can be used to validate or reject efficiency strategies, 

highlight opportunities for improvement, and illustrate a path of continuous improvement.

The greatest benefit of comparing a building to other buildings in a portfolio is that the 

resulting comparison projects have nearly identical project parameter definitions. The biggest 

downside is that it tends to perpetuate the design status quo. The top-performing buildings may 

fall short of industry best practice in a number of respects; considering examples of best practice

throughout the industry as a whole may shed light on design deficiencies and encourage forward 

thinking. ENERGY STAR Portfolio Manager compares building energy use to CBECS data and 
7

assigns efficiency scores that define individual building energy performance with respect to the 

CBECS dataset. The score of the top-performing buildings establishes a context for portfolio 

performance and defines the gap between current design and industry best practice.

Using High-Level Sector Data to Specify Whole-Building Absolute Energy Use Targets 

For some projects, comparable industry best practice projects may not be identifiable and 

portfolio-based comparisons may not be possible. In such cases, high-level sector data sources

such as CBECS and ENERGY STAR Target Finder may be used to inform target setting. Such 

sources can provide a high-level look at energy use across a sector and for a certain location.

Sector-average energy performance incorporates the performance of buildings of varying 

vintages and typically does not match performance characteristics of compliance with current 

codes and standards; such high-level data are useful to establish context for project goals, but 

cannot typically be benchmarked against project-specific parameter definitions to the extent 

required to ensure whole-building absolute energy use targets are achieved.

Using Energy Simulation to Specify Whole-Building Absolute Energy Use Targets 

If a project cannot be accurately characterized using industry best practice case studies, 

portfolio data, or high-level sector data, annual whole-building energy simulations can be used to 

specify absolute whole-building energy use targets. A detailed whole-building energy model can 

accurately capture any and all project-specific features and provide accurate energy use 

predictions that can be used to specify achievable, aggressive targets. The downside to energy 

modeling is that it is resource intensive and requires simulation expertise. Ideally, it should be 

used to supplement best practice case studies and/or portfolio data and be used to explore the 

impact of project-specific parameters that are not sufficiently characterized by other sources.

Using Absolute Energy Targets throughout a Project to Improve Energy 

Performance

An energy performance goal must be considered during each stage of a project, starting 

with the proposal and continuing through commissioning to building occupancy and operation.

All design and construction decisions should be considered for their energy performance 

implications. This section highlights the ways whole-building absolute energy use targets can be 

used to increase the probability of energy performance success at various stages.

This section also details how energy modeling can be used to ensure that whole-building 

absolute energy use targets represent energy performance goals and can ultimately be achieved 

during building operation. Annual whole-building energy modeling represents the most 

comprehensive way to combine all aspects of building design that affect energy use into a 

holistic analysis of whole-building energy use.

Case studies of similar projects are valuable resources for specifying these targets. They

can be used to select efficiency strategies and to predict a likely range of energy use based on 

similarity to a proposed design. A case study is rarely fully compatible with the set of parameters 

definitions for a given project, however. Energy modeling can be used to bridge this gap by 

facilitating project-specific evaluation of efficiency strategies identified through a case study 

survey.
8

Team Selection Stage

Selecting a design and construction team is critical to project success. If the owner or the 

owner’s efficiency representatives can establish whole-building absolute energy use targets 

before the team is selected, team members are much more likely to be selected for their ability to 

reach the performance goal within the specified budget.

In a design-build scenario, including whole-building absolute energy use targets in the 

request for qualifications frees respondents from prescriptive design requirements and 

encourages innovative, cost-effective solutions. Willing and positive team participation to help 

meet energy performance requirements can be further encouraged via a voluntary incentive 

program that offers an award fee of 2%-3% of the total contract fee. This can be especially 

valuable during commissioning and warranty periods because it gives the design team a financial 

stake in identifying and addressing performance issues (Pless et al. 2011).

Using energy modeling to inform the team selection process can have significant 

benefits. Although approximate energy use goals based on case study research may be minimally 

sufficient to characterize the design problem at the team selection stage, energy modeling can be 

used to focus energy use goals by accounting for project-specific parameter definitions.

Contractual inclusion of whole-building absolute energy use targets requires accurate energy use 

predictions that carefully consider all building energy uses. Greater confidence in predictions 

allows for more aggressive targets, and comprehensive whole-building energy modeling (energy 

simulation, thermal bridging calculations, daylighting modeling, natural ventilation modeling, 

thermal storage modeling, renewable generation calculations, specialty space type modeling, 

etc.) results in the most accurate predictions (Hirsch et al. 2011). Energy modeling can also be 

used to evaluate applicants’ proposed design solutions. And because energy modeling is useful 

throughout the project, this capability should be an important applicant evaluation criterion.

Early Design Stage

Traditional goal-setting exercises tend to neglect energy uses not governed by the 

relevant building code or certification process. Because whole-building absolute energy use 

targets apply to all energy uses in a building, the process of specifying aggressive energy 

performance goals using these targets often identifies a wider range of energy use considerations.

The early design phase provides an opportunity to identify and understand efficiency 

opportunities for often-overlooked programmatic energy uses. Key examples include space 

planning, equipment organization, and operational schedules. For example, space layout 

considerations can affect design flexibility later. Designing an office space to prevent exposure

to direct sunlight can alleviate elevated perimeter conditioning requirements and allow radiant 

cooling solutions to be considered.

It is important to understand the distribution of energy use types (loading type, 

operational schedule, etc.) throughout a building. Zoning spaces according to similarities in 

energy use type allows for the consolidation of HVAC equipment, reducing first costs and 

operation and maintenance costs. When considered during the early design stage, such issues can 

be resolved appropriately and cost effectively; as the design process progresses, potential 

solutions become less viable.

Energy modeling should be used in the early design stage to determine the extent to 

which whole-building absolute energy use targets need to inform the design of the building form

(Hirsch et al. 2011). Architectural decisions can be made to ensure that building orientation, 
9

massing, and layout contribute to the achievement of energy goals, often at no additional fixed or 

life cycle cost. Many efficiency strategies, such as daylighting, thermal mass distribution, natural 

ventilation, and solar shading, require integration with the building envelope and structure. By 

using energy modeling to evaluate and incorporate these simple and passive strategies into the 

early design, a design team can significantly improve the probability that targets can be met 

within budget (Pless et al. 2012). Incorporating strategies that require integration with the 

building envelope and structure becomes progressively more difficult and expensive as a project 

progresses (Pless et al. 2011). During the early design stage, energy modeling can also be used to 

answer questions about efficiency strategies as they relate to energy use targets. Is daylighting 

necessary? What types of HVAC systems can I use to reach my goals?

Construction Stage

During construction, the impact of change orders on the overall energy budget should be 

carefully considered. Where they significantly impact energy use goals, they should be 

reevaluated.

Construction contractors are typically unaware of energy performance goals, but wholebuilding absolute energy use targets can be written into contracts to provide contractors a 

financial incentive to help a project reach its energy performance goals.

As-Built Stage

Once design decisions are finalized and the building is constructed, all the necessary 

information is available to finalize end-use energy budgets. To be useful, these budgets must be 

realistic and take into account all operational details that affect energy use. Whole-building 

absolute energy use targets are a valuable reference during the specification of end-use energy 

budgets; the summation of these budgets should be no greater than the whole-building energy 

use target. An added benefit of this exercise is that the careful scrutiny required may highlight 

potential operational issues that would otherwise be overlooked (e.g., sequences of operation as 

they relate to system interactions).

As construction is completed, energy models should be updated to reflect any 

discrepancies between the final design and the constructed building. In particular, installed 

equipment power draws (including parasitic) should be measured and used to update energy 

model inputs (Hirsch et al. 2011). PPLs are notoriously difficult to predict and can have a 

significant impact on achieving an energy use target. Understanding installed loads and 

specifying energy model inputs accordingly can inform how associated control strategies may 

need to be updated to ensure that the PPL end-use energy budget will be met. As-built energy 

models should also reflect any differences between shop drawings and original plans, as well as 

the results of commissioning and testing and balancing.

As-Operated Stage

Once the building is operational, end-use energy budgets can be used to inform the 

control sequence commissioning process and to fine tune control schemes. The owner can

compare actual end uses to energy budget allowances (using real-time, submetered data), to 

identify and reconcile discrepancies between design and operation: set points can be updated to 

match actual (as opposed to predicted) occupancy patterns; operation sequences can be modified 
10

to improve synergy between strategies such as economizing, natural ventilation, and supply air 

temperature control.

Energy models should be updated to reflect any changes made to control schemes or 

operational schedules during the control sequence commissioning process. Measured data should 

ultimately be used to evaluate the success of a project with respect to whole-building absolute 

energy use targets, but the final state of whole-building energy models should also be evaluated.

Energy modeling results should be compared to measured whole-building and system-level 

(submetered) energy use data; discrepancies should be investigated and opportunities for 

improving modeling inputs should be identified. Lessons learned can inform future energy 

modeling efforts and improve the accuracy with which whole-building absolute energy use 

targets and end use energy budgets can be specified.

Comparing actual end use to energy budget allowances requires measurement and 

verification. Real-time, submetered data are required, and dashboards and displays designed to 

facilitate data analysis are strongly recommended.

AEDG Whole-Building Absolute Energy Use Targets

The U.S. Department of Energy has partnered with professional societies (ASHRAE, 

AIA, USGBC, and IES) to develop a series of AEDGs to provide cost-effective, industry-vetted 

recommendations for achieving energy performance that goes well beyond the minimum 

requirements of commercial building codes. The AEDGs offer a prescriptive path for design 

teams (building owners, architects, designers, engineers, and builders) to achieve significant 

energy savings without intensive calculations or complex analyses outside the scope of their 

normal practices. The initial series of six AEDGs provided recommendations for achieving 

energy savings of 30% beyond ASHRAE Standard 90.1-1999 (ASHRAE 1999); the series 

covered small office buildings, small retail buildings, K-12 school buildings, and small 

warehouse and self-storage buildings. A new series of AEDGs provides recommendations for 

achieving energy savings of 50% beyond ASHRAE Standard 90.1-2004 (ASHRAE 2004); 

AEDGs for small and medium office buildings, K-12 school buildings, medium to big box 

(20,000 to 100,000 ft2

) retail buildings, and large hospitals have all been published. These

provide a prescriptive path to 50% savings as well as a performance-based path; in particular, 

these AEDGs contain guidance for setting whole-building absolute energy use targets. This 

section highlights the merits of those energy targets, describes the methodology behind their 

development, and provides guidance on their applicability.

Merits of AEDG Whole-Building Absolute Energy Use Targets

Much as the AEDG prescriptive paths are designed to simplify the path to economically

replicable, industry-vetted savings, the AEDG energy use targets are designed to simplify the 

process of setting whole-building absolute energy use targets. The AEDG energy use targets are 

whole-building, absolute targets that align with 50% savings beyond current commercial 

building code (ASHRAE Standard 90.1-2004). Specifying AEDG whole-building absolute 

energy use targets and following the prescriptive recommendations of the 50% AEDGs (which 

have been demonstrated to meet or exceed the AEDG energy use targets) represents a clear, 

easy-to-follow path to specifying and achieving whole-building energy use targets that reflect 

industry best practice in energy efficiency.
11

The design team should not feel obligated to follow the prescriptive recommendations of 

the AEDGs; the prescriptive path represents one way, but not the only way, to achieve industry 

best practice energy performance. Specification of whole-building absolute energy use targets 

gives the design team the freedom to reach the performance goal with an approach that best fits 

the overall goals and constraints (including those not related to energy performance) of the 

project.

Because they embody the knowledge required to set practical, aggressive energy 

performance targets, specification of AEDG whole-building absolute energy targets can 

eliminate the majority of analysis that may otherwise be required to specify energy performance 

goals. In particular, because the AEDG energy targets are defined in terms of absolute energy 

performance (in kBtu/ft2

, rather than with respect to a theoretical baseline), they can be specified 

without the need for a baseline energy model. A design team can specify an absolute energy 

target based on the corresponding AEDG energy target and then focus analysis efforts towards 

achieving industry best practice energy performance rather than trying to define a reference point 

against which to measure performance.

Development of AEDG Whole-Building Absolute Energy Use Targets

The whole-building absolute energy use targets for the 50% AEDG series were 

developed in accordance with the following approach:

1. If possible, start with the DOE Commercial Reference Building model (Deru et al. 2011) that 

corresponds to the AEDG building type; this model is minimally compliant with ASHRAE 

Standard 90.1-2004. Where the Reference Building model did not sufficiently represent 

common practice for a building type, the AEDG project committee developed and approved 

an alternative model.

2. Update the Reference Building model according to the AEDG project committee’s expert 

guidance; special care is given to aspects of the model not prescribed by ASHRAE Standard 

90.1-2004, including schedules and unregulated PPLs. The goal is to develop a model that 

accurately captures typical (common practice) whole-building energy use for the relevant 

building type.

3. Simulate the industry-vetted model across a set of 16 climate zones that fully represent the 

variations in the eight DOE climate zones (Figure 2) (Briggs et al. 2003). Benchmark 

modeling results against available sector data (e.g., CBECS) and project committee. Make 

necessary corrections to model inputs and resimulate. Iterate until results are in line with 

sector data and industry expectations for baseline energy performance by climate zone.

4. Set climate-specific absolute targets representing 50% savings beyond ASHRAE Standard 

90.1-2004 by halving baseline whole-building energy performance results. Confirm through

whole-building energy simulation and case study survey (including committee member 

projects) that 50% savings targets are feasible and representative of industry best practice

energy performance.
12

Figure 2. U.S. Map Depicting the DOE Climate Zones

(Credit: (DOE 2005))

The following sections present the 50% AEDG energy use targets for K-12 school 

buildings, medium to big box retail buildings, and large hospital buildings; guidance on target 

applicability is provided and case-specific variations in approach are explained.

AEDG Whole-Building Absolute Energy Use Targets for K-12 Schools

This AEDG is intended to provide user-friendly, “how-to” design guidance and 

efficiency recommendations for elementary, middle, and high school buildings (ASHRAE 2011). 

The mission of a K-12 school building is to facilitate education; school buildings are designed 

accordingly, and energy-saving measures must not compromise this fundamental goal. The 

measures recommended by the 50% AEDG for K-12 school buildings are intended to avoid 

compromising, and to complement whenever possible, the delivery of educational services.

For this analysis, two building types were modeled (primary and secondary schools) and 

two sets of climate-specific, whole-building absolute energy use targets for 50% savings beyond 

ASHRAE Standard 90.1-2004 were developed (Table 1 and Table 2).

Whole-building absolute targets are supplemented with key end use energy targets (PPLs, 

lighting systems, and HVAC systems). Although the end use targets need not be met to achieve 

the whole-building target, these targets provide guidance as to how energy use is likely to be 

distributed throughout a K-12 school building; they can also inform end use energy budgets.

Programmatic requirements are relatively constant for a given school type (primary or 

secondary); accordingly, the AEDG whole-building and end use energy targets for K-12 school 

buildings are likely to apply reasonably well to most K-12 school building projects. The AEDG 

energy targets do not take into account the energy use of specialty space types such as indoor 

swimming pools, wet labs (e.g., chemistry), dirty dry labs (e.g., woodworking and auto shops), 

or other unique spaces with extraordinary heat or pollution generation. Such space types should 

be analyzed separately; their predicted energy use can be combined with the AEDG targets to 

determine an area-weighted, whole-building energy use target that correctly reflects all project 

energy uses.
13

Table 1. Primary School AEDG Absolute Energy Use Targets

Climate

Zone

Plug/Process

(kBtu/ft2∙yr)

Lighting

(kBtu/ft2∙yr)

HVAC

(kBtu/ft2∙yr)

Total

(kBtu/ft2∙yr)

1A

11 6

20 37

2A 20 37

2B 20 37

3A 15 32

3B-CA 8 25

3B 14 31

3C 10 27

4A 19 36

4B 15 32

4C 15 32

5A 22 39

5B 17 34

6A 27 44

6B 22 39

7 30 47

8 45 62

Table 2. Secondary School AEDG Absolute Energy Use Targets

Climate

Zone

Plug/Process

(kBtu/ft2∙yr)

Lighting

(kBtu/ft2∙yr)

HVAC

(kBtu/ft2∙yr)

Total

(kBtu/ft2∙yr)

1A

8 7

21 36

2A 21 36

2B 21 36

3A 18 33

3B-CA 10 25

3B 17 32

3C 13 28

4A 22 37

4B 18 33

4C 19 34

5A 25 40

5B 21 36

6A 31 46

6B 26 41

7 34 49

8 48 63

AEDG Whole-Building Absolute Energy Use Targets for Medium to Big Box Retail

This AEDG is intended to provide user-friendly, “how-to” design guidance and 

efficiency recommendations for retail stores (ASHRAE 2011). Retail buildings are designed to 

facilitate the delivery of goods and services to the public; energy-saving measures must not

compromise this fundamental goal. That stated, energy costs are typically the second-highest 

operating expense for retailers; implementing cost-effective energy-saving strategies has a direct 

and significant impact on profitability and is an essential part of a successful retail business.

Two building types were modeled for this analysis: medium box (40,000 ft2

) and big box 

(100,000 ft2). Programmatic requirements can vary greatly from application to application. A 

high-end retailer may use significant high-wattage accent lighting to display merchandise with a 
14

particular style; a discount retailer may use little or no accent lighting. Similarly, an electronics 

retailer may have significantly higher installed PPLs than a clothing retailer. Because installed 

equipment load (including accent lighting and PPLs) can vary significantly according to projectspecific requirements, AEDG energy targets were determined for a range of installed equipment 

loads. Energy targets are provided for two levels of baseline plug load requirements: Low and 

High, representing whole-building average installed plug load densities of 0.5 W/ft2 and 0.7 

W/ft2

, respectively. A general merchandise store would be a typical low-plug load case, whereas 

a dedicated electronics store would be a typical high-plug load case. Within each category of 

installed plug loads, energy targets are provided for three levels of baseline accent lighting

requirements: (1) little or no accent lighting (Low), with a value of 0.0 W/ft2

; (2) a typical level 

of accent lighting (Med), 1.6 W/ft2 for sales areas; and (3) a high level of accent lighting (High), 

representative of retail applications with specialty accent lighting requirements, such as jewelry 

sales, with a value of 3.9 W/ft2

, the maximum allowed for sales area by ASHRAE Standard 90.1-

2004. Energy targets for 50% savings beyond Standard 90.1-2004 are presented in Table 3 and 

Table 4.

Table 3. Medium-Box Retail Energy Use Targets for 50% Savings

Climate

Zone

Energy Use Intensity (kBtu/ft2∙yr)

Low-Plug High-Plug

Low

Accent

Med

Accent

High

Accent

Low

Accent

Med

Accent

High

Accent

1A 42 58 81 45 61 85

2A 41 56 77 44 59 80

2B 37 53 75 40 56 79

3A 38 51 70 40 53 73

3B-CA 31 46 67 34 49 69

3B 36 50 72 38 53 75

3C 29 43 61 32 45 64

4A 39 51 68 41 53 70

4B 36 50 70 39 53 72

4C 33 44 61 35 47 63

5A 40 50 65 42 52 67

5B 36 49 67 39 51 69

6A 43 53 66 45 54 68

6B 39 50 65 41 52 67

7 44 52 63 46 54 65

8 56 61 69 57 62 71
15

Table 4. Big-Box Retail Energy Use Targets for 50% Savings

Climate

Zone

Energy Use Intensity (kBtu/ft2∙yr)

Low-Plug High-Plug

Low

Accent

Med

Accent

High

Accent

Low

Accent

Med

Accent

High

Accent

1A 42 58 82 45 62 85

2A 41 56 77 44 58 80

2B 38 54 77 41 57 80

3A 35 49 69 38 52 72

3B-CA 30 45 66 33 48 69

3B 34 49 71 37 52 74

3C 28 41 61 30 44 63

4A 37 49 66 39 51 68

4B 34 48 68 37 51 71

4C 31 43 60 33 45 62

5A 38 49 64 40 51 66

5B 35 47 66 37 50 68

6A 41 51 64 43 52 66

6B 37 48 63 39 50 65

7 42 50 62 44 52 63

8 53 58 67 54 60 68

AEDG Whole-Building Absolute Energy Use Targets for Large Hospitals

This AEDG is intended to provide user-friendly, “how-to” design guidance and 

efficiency recommendations for large healthcare buildings (ASHRAE 2012). For healthcare 

applications, patient considerations (outcome, safety, and overall quality of experience) trump all 

cost and energy savings benefits. No efficiency strategy that would risk patient, staff, or visitor 

health is recommended by the 50% AEDG for large hospitals; on the contrary, strategies that 

reduce this risk are emphasized.

For this analysis, a single, 427,000 ft2 building was modeled; climate-specific, wholebuilding absolute energy use targets for 50% savings beyond ASHRAE Standard 90.1-2004 are 

presented in Table 5.

Whole-building absolute targets are supplemented with key end use energy targets (plug 

and process equipment, lighting systems, and HVAC systems). Although the end use targets

need not be met to achieve the whole-building target, they provide guidance as to how energy 

use is likely to be distributed throughout a large hospital building; they can also inform end-use 

energy budgets.
16

Table 5. Large Hospital Energy Use Targets for 50% Savings

Climate Zone Plug/Process Loads

(kBtu/ft2∙yr)

Lighting

(kBtu/ft2∙yr)

HVAC

(kBtu/ft2∙yr)

Total

(kBtu/ft2∙yr)

1A

38 18

67 123

2A 68 124

2B 63 119

3A 62 118

3B:CA 55 111

3B 55 111

3C 55 111

4A 65 121

4B 50 106

4C 55 111

5A 65 121

5B 50 106

6A 68 124

6B 54 110

7 67 123

8 81 137

Applicability of Whole-Building Absolute Energy Use Targets

Specifying these targets requires detailed knowledge of where and how energy will be 

used. This section highlights some scenarios in which whole-building absolute energy use targets 

may be difficult to specify.

Projects with Specialty Space Types

Because specialty space types tend to be project specific and have unique programmatic 

requirements, it can be difficult to find points of comparison to inform energy use goal setting. 

When comparison points cannot be found, energy modeling informed by a best-in-class 

technology survey is a viable approach to establishing energy use targets.

Projects with Difficult-To-Define Operational Parameters

For some projects, operational parameters may be difficult to define before occupancy.

Consider a cafeteria, for example. Accurately predicting customer occupancy patterns may be 

impossible, and because cafeteria energy use has a strong correlation with occupancy density, 

accurately predicting overall cafeteria energy use may be difficult. Design teams can still strive 

to maximize the energy performance of such projects, but initial energy use targets may need to 

be less aggressive than desirable.

Conclusions

The design and construction of high-performance buildings requires careful goal setting.

Percent savings goals are popular and can be effective, but depend heavily on the definition of an 

often theoretical baseline case against which savings are measured. Whole-building absolute 

energy use targets provide straightforward, easily understood, and directly measureable 

performance goals that focus on realized building performance rather than comparison to a 
17 

theoretical baseline. Defining the energy performance goal for a project using whole-building 

absolute energy use targets results in a specific and measureable, holistic goal and promotes

innovative, cost-effective design and construction solutions. Achieving an energy performance 

goal requires consideration of that goal during each project stage, starting with the proposal and 

continuing through building occupancy and operation. Setting aggressive targets requires careful 

consideration of project-specific parameters and a complete understanding of where and how 

energy is used in the building. There are many ways to determine whole-building absolute 

energy use targets, but all require following the same basic steps: (1) define project parameters, 

(2) survey applicable resources, and (3) select goals and specify targets. Specifying wholebuilding absolute energy use targets can help designers and owners ensure that the project’s 

desired performance goal is achieved.

References

ASHRAE. 1999. ANSI/ASHRAE/IESNA Standard 90.1-1999, Energy Standard for Buildings 

Except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, Ga.

ASHRAE. 2004. ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings 

Except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, Ga.

ASHRAE, AIA, IESNA, USGBC, and DOE. 2011. Advanced Energy Design Guide for K-12 

School Buildings: Achieving 50% Energy Savings Toward a Net Zero Energy Building. 

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, 

Ga.

ASHRAE, AIA, IESNA, USGBC, DOE (2011). Advanced Energy Design Guide for Medium to 

Big Box Retail Buildings: Achieving 50% Energy Savings Toward a Net Zero Energy 

Building. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 

Atlanta, Ga.

ASHRAE, AIA, IESNA, USGBC, DOE (2012). Advanced Energy Design Guide for Large 

Hospitals: Achieving 50% Energy Savings Toward a Net Zero Energy Building. American 

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, Ga.

Briggs R. S., R. G. Lucas, and Z. T. Taylor. (2003). “Climate Classification for Building Energy 

Codes and Standards: Part 1 - Development Process.” ASHRAE Transactions 109(1):109-

121. 

Brown, K., A. Daly, J. Elliot, C. Higgins, and J. Granderson. (2010). “Hitting the Whole Target: 

Setting and Achieving Goals for Deep Efficiency Buildings.” In Proceedings of the 2010 

ACEEE Summer Study on Energy Efficiency in Buildings, Pacific Grove, Calif.
18 

Deru, M.; Field, K.; Studer, D.; Benne, K.; Griffith, B.; Torcellini, P.; Liu, B.; Halverson, M.; 

Winiarski, D.; Rosenberg, M.; Yazdanian, M.; Huang, J.; Crawley, D. (2011). U.S. 

Department of Energy Commercial Reference Building Models of the National Building 

Stock. NREL/TP-5500-46861, National Renewable Energy Laboratory, Golden, Colo. 

DOE. (2005). “Map of DOE’s Proposed Climate Zones.” Retrieved July, 2010, from 

www.energycodes.gov/implement/pdfs/color_map_climate_zones_Mar03. 

Hirsch, A., S. Pless, R. Guglielmetti, P. A. Torcellini, D. Okada, and P. Antia. (2011). “Role of 

Modeling When Designing for Absolute Energy Use Intensity Requirements in a DesignBuild Framework: Preprint.” NREL/CP-5500-49067. National Renewable Energy 

Laboratory, Golden, Colo.

Pless, S., P. Torcellini, and D. Shelton. (2011). “Using an Energy Performance Based DesignBuild Process to Procure a Large Scale Low-Energy Building: Preprint.” NREL/CP-5500-

51323. National Renewable Energy Laboratory, Golden, Colo. 

Pless, S., P. Torcellini, and P. Macey. (2012). Controlling Capital Costs in High Performance 

Office Buildings: 15 Best Practices for Overcoming Cost Barriers in Project Acquisition, 

Design, and Construction. NREL/TP-5500-54978. National Renewable Energy Laboratory, 

Golden, Colo.