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

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Conference Paper

NREL/CP-5500-77412 

September 2020

Moving Zero Energy Office Buildings to 

the Mainstream: Establishing Design 

Guidelines and Energy Targets

Preprint

Korbaga F. Woldekidan, Paul A. Torcellini, Rois Langner, 

and Noah Pflaum

National Renewable Energy Laboratory

Presented at the 2020 ACEEE Summer Study on Energy Efficiency in 

Buildings

August 17-21, 2020
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

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Conference Paper

NREL/CP-5500-77412 

September 2020

Moving Zero Energy Office Buildings to 

the Mainstream: Establishing Design

Guidelines and Energy Targets

Preprint

Korbaga F. Woldekidan, Paul A. Torcellini, Rois Langner, 

and Noah Pflaum

National Renewable Energy Laboratory

Suggested Citation 

Woldekidan, Korbaga F., Paul A. Torcellini, Rois Langner, and Noah Pflaum. 2020. 

Moving Zero Energy Office Buildings to the Mainstream: Establishing Design Guidelines 

and Energy Targets: Preprint. Golden, CO: National Renewable Energy Laboratory. 

NREL/CP-5500-77412. https://www.nrel.gov/docs/fy20osti/77412.pdf. 
NOTICE

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable 

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding 

provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Building

Technologies Office. The views expressed herein do not necessarily represent the views of the DOE or the U.S. 

Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges 

that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce 

the published form of this work, or allow others to do so, for U.S. Government purposes.

This report is available at no cost from the National Renewable 

Energy Laboratory (NREL) at www.nrel.gov/publications. 

U.S. Department of Energy (DOE) reports produced after 1991 

and a growing number of pre-1991 documents are available 

free via www.OSTI.gov. 

Cover Photos by Dennis Schroeder: (clockwise, left to right) NREL 51934, NREL 45897, NREL 42160, NREL 45891, NREL 48097, 

NREL 46526.

NREL prints on paper that contains recycled content. 
1 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Moving Zero Energy Office Buildings to the Mainstream:

Establishing Design Guidelines and Energy Targets

Korbaga F. Woldekidan, NREL

Paul A. Torcellini, NREL

Rois Langner, NREL

Noah Pflaum, NREL 

ABSTRACT

Office buildings represent a significant portion of the commercial sector and are ideal 

candidates to lead the market towards achieving zero energy and zero energy ready buildings. 

The variety of sizes and uses for office buildings make them challenging to determine set design 

guidance that can be deployed across the market. The project committee for the 

ASHRAE/AIA/USGBC/IES Zero Energy - Advanced Energy Design Guide (ZE-AEDG) for 

small and medium office buildings, comprised of members from four major professional 

societies with market-pull in commercial buildings, created design guidance for achieving zero 

energy office buildings for new construction and major retrofit. This design guidance focuses on 

the process, providing a pathway for both office owners and design teams to achieve zero energy 

status. Climate specific energy use intensity targets ranging from 16 kBtu/ft2·yr to 36 kBtu/ft2·yr 

were established such that office buildings can be “zero-ready,” that is, having low energy 

consumption that can easily be offset with renewables, preferably on-site. The design guidance 

was rooted in extensive energy modeling, as well as case studies of actual office buildings that 

have achieved high levels of energy performance and met zero energy or zero energy ready 

status. A unique aspect of the zero-energy guide is that it is not compared against a baseline but 

focuses on achieving an absolute target. The paper presents process of creating the targets, the 

selection of strategies to achieve the targets, and sample case studies that show how the costsensitive solutions are achievable for the design community. It also presents outreach strategies 

to deploy market achievable zero energy measures.

Background

Commercial buildings have become increasingly efficient through continuous 

improvements in performance of heating, ventilating, and air-conditioning (HVAC) systems; 

lighting systems; and electrical equipment combined with tighter, better-insulated thermal 

envelopes with advanced glazing system. These improvements are also in part due to more 

stringent performance requirements from regulatory bodies that have adopted energy standards, 

such as those developed by the American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE). Over the past few decades, most of the work related to 

minimizing building energy impacts have been focused on reducing energy use intensity (EUI). 

Considering energy efficiency in every design decision and evaluating its impact on overall EUI 

reduction are critical strategies in any building and particularly important for zero energy 

buildings. 

As commercial buildings become more and more efficient, zero energy (ZE) buildings

were envisioned: buildings that can offset their energy requirement by adding on-site renewable 

energy resources. In line with this, Griffith et al. (2006, 2007, 2008) examined the entire 
2 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

commercial sector with a comprehensive energy model to determine which building types could 

achieve ZE and what levels of energy efficiency were needed to achieve that goal. The study 

found that the concept was technically feasible for significant portions of the commercial sector, 

including office buildings. 

DOE published a common definition in 2015 (DOE 2015): “An energy-efficient building 

where, on a source energy basis, the actual annual delivered energy is less than or equal to the 

on-site renewable exported energy.” This definition applies to individual buildings, campuses, 

communities, portfolios, or any other specified boundary. In locations where on-site renewables 

installations are limited by utilities, policies, or economics, the building can be designed to be ZE 

ready—that is, it is extremely energy-efficient and ready to accept a solar system when 

circumstances allow. 

 As thinking about ZE evolved, so did the Advanced Energy Design Guides (AEDGs). 

Published by ASHRAE, this popular series of books—more than 680,000 are in circulation as of 

June 2020—offers recommendations for achieving energy savings beyond current norms in new 

construction and major retrofits. The AEDGs were based on extensive energy simulation to 

develop energy efficiency solutions that result in energy savings compared with a current

ASHRAE energy standard. From 2004 to 2009, AEDGs that provide guidance for achieving a 

30% energy savings compared with ASHRAE Standard 90.1-1999 were produced for six 

building types. From 2011 to 2015, five guides were produced that demonstrated how to achieve 

a 50% savings from ASHRAE Standard 90.1-2004. The eleven guides covered a number of 

building types; most relevant to this discussion, 30% guide for small office buildings and 50% 

guides for small to medium office buildings were developed ((ASHRAE 2008); (ASHRAE 

2011)).

The AEDGs are focused on providing simulation-based energy solutions that are 

achievable using widely available technologies. Advances in technology and integrated design 

together with sharp reductions in the cost of renewable energy now make ZE possible and 

affordable. These trends are corroborated by a dramatic increase in the number of documented 

ZE buildings (NBI 2018). Office buildings are the second largest category of ZE buildings next 

to primary and secondary schools. 

So far two ZE AEDGs are published: Advanced Energy Design Guide for K–12 Schools: 

Achieving Zero Energy (K–12 ZE AEDG) (ASHRAE 2018) and Advanced Energy Design Guide 

for Small to Medium Office Buildings (ASHRAE, 2019). These AEDGs lay out a pathway to 

achieving ZE buildings and are based on work done during a feasibility study that showed it was 

possible to get to ZE using the U.S. Department of Energy’s (DOE’s) ZE definition (Pless et. al. 

2016; DOE 2015). The AEDGs use prescriptive and performance-based recommendations for 

envelope, fenestration, lighting, HVAC, renewable integration, outside air treatment, and service 

water heating, along with practical how-to tips and climate-specific strategies.

The interest in very low energy buildings and ZE buildings is growing. For example, 

California adopted ZE targets for 50% of the floor area of existing state-owned buildings by 

2025 and for all new or renovated state buildings beginning design after 2025 (SAM 2017). 

California has also set a target of making all new commercial buildings ZE by 2030 (CPUC 

2011). Several other states are thinking along the same lines and have established task forces that 

are working on the issue. 
3 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

The Process of Creating Design Guidance

Much has been written about what ZE buildings are, and the idea of a measurable, 

achievable ZE goal is taking hold in the marketplace (Liu et al. 2017; Torcellini et al. 2016). ZE

buildings use an EUI target rather than comparing energy savings with a predetermined base case 

such as a code-compliant building. The small to medium office buildings ZE AEDG, therefore, 

unlike the office guides in the 30% and 50% AEDG series, provides no reference building or 

comparison. Rather, it includes clear guidance on how to achieve an absolute EUI target. 

Another key difference relative to previous AEDGs is that ZE is an operational goal; success is 

measured after a minimum of one year of energy performance. 

Like the other AEDGs, a steering committee made up of members of five organizations 

(ASHRAE, IES, USGBC, AIA, and DOE) created a scope for the new ZE AEDG to focus on 

small to medium office buildings. The steering committee formed a special project committee 

that consisted of technical experts in HVAC, envelope, architecture, and lighting, with a strong 

emphasis on experience delivering or operating ZE small to medium office buildings. The 

project committee helped establish relevant model inputs based on their professional practices 

and experiences. In addition, project committee members collected case studies with measured 

energy data and examined those projects’ energy efficiency strategies and operational EUIs. 

They also conducted a demand-side analysis that looked at energy efficiency strategies used in 

ZE office case studies and evaluated energy simulation results to develop consumption EUIs 

such that on-site renewable resources could balance the consumption. These results were 

determined for each climate zone. This approach kept the emphasis on energy efficiency as the 

prime design driver. 

This information formed the inputs for running hourly simulation of energy 

consumptions for representative small to medium office buildings using OpenStudio energy 

modeling platform OpenStudio 2020). OpenStudio uses EnergyPlus as the simulation engine 

(EnergyPlus 2020). Multiple variants of the building energy models can be run in parallel using 

cloud computing. Using these models, it is possible to evaluate many different scenarios and 

identify optimal combinations of design strategies and technologies to achieve ZE. These 

parametric studies offered insights that the project committee used to identify the solutions 

included in the small to medium office buildings ZE AEDG. Using the industry-based committee 

review process grounded the theoretical nature of a simulation-based analysis in the reality of 

industry practices and norms. 

Energy Modeling Summary

The extensive energy modeling helped determine the impact of the strategies considered 

in this design guide. A “typical” prototype building is an energy model that is a representative 

example of a small to medium office building. The modelers developed a prototype model based 

on the DOE Commercial Prototype Buildings Models (Deru et al. 2011; DOE 2014) as well as

models from previous AEDG work (ASHRAE 2011). In previous AEDGs for office buildings, 

two prototypes were used—one to represent smaller buildings and one to represent buildings 

with deep floor plates. However, advancements in lighting have reduced building’s sensitivity to 

the ratio of interior to exterior office spaces and, as a result, limited energy performance 

differences are seen between the two prototype models. Therefore, one prototype building was 
4 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

assembled to represent office building construction, with information drawn from the sources 

above. 

The project committee then provided changes to the space layouts based on current 

industry perspectives and practices. The major changes were to: 

• Increase the window-to-wall ratio

• Expand the number of HVAC system types 

• Update climate zones to ASHRAE Standard 169-2013, with new representative cities and 

climate zone 0 

• Make minor changes to internal loads 

• Make minor changes to envelope to comply with ASHRAE Standard 90.1-2016. 

Table 1 highlights high-level parameters of office buildings. Table 2 provides detailed 

information about the space types considered. All the ASHRAE climate zones were considered 

as part of the modeling, because different climate zones yield different solutions and energy 

targets. Table 3 provides the representative cities for each climate zone (ASHRAE 2013). 

Table 1. Office characteristics used in modeling

Characteristic Values

Size 20,000 ft2

Number of floors 2

Window-to-wall 

ratio 40% 

Wall construction Metal-framed

Roof construction Insulation entirely above deck

Table 2. Space type breakdown in design guide simulations 

Space Type Area 

(ft2)

Percentage 

of Total

Open Office 8,000 40%

Private Office 2,400 12%

Conference 2,400 12%

Corridor 2,000 10%

Active Storage 1,000 5%

Restrooms 800 4%

Lounge 800 4%

Electrical/Mechanical 400 2%

Stairway 600 3%

Lobby 1,200 6%

Data 400 2%

Total 20,000 100%
5 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table 3. Climate zones represented in the design guide 

Climate 

Zone

Location Energy Plus Weather (EPW) Filenames

0A Hanoi VNM_Hanoi.488200_IWEC.epw

0B Abu Dhabi ARE_Abu.Dhabi.412170_IWEC.epw

1A Honolulu USA_HI_Honolulu.Intl.AP.911820_TMY3.epw

1B New Delhi IND_New.Delhi.421820_ISHRAE.epw

2A Tampa USA_FL_MacDill.AFB.747880_TMY3.epw

2B Tucson USA_AZ_Davis-Monthan.AFB.722745_TMY3.epw

3A Atlanta USA_GA_Atlanta-HartsfieldJackson.Intl.AP.722190_TMY3.epw

3B El Paso USA_TX_El.Paso.Intl.AP.722700_TMY3.epw

3C San Diego USA_CA_Chula.VistaBrown.Field.Muni.AP.722904_TMY3.epw

4A New York USA_NY_New.YorkJ.F.Kennedy.Intl.AP.744860_TMY3.epw

4B Albuquerque USA_NM_Albuquerque.Intl.AP.723650_TMY3.epw

4C Seattle USA_WA_Seattle-Tacoma.Intl.AP.727930_TMY3.epw

5A Buffalo USA_NY_BuffaloGreater.Buffalo.Intl.AP.725280_TMY3.epw

5B Aurora USA_CO_Aurora-Buckley.Field.ANGB.724695_TMY3.epw

5C Port Angeles USA_WA_Port.AngelesWilliam.R.Fairchild.Intl.AP.727885_TMY3.epw

6A Rochester USA_MN_Rochester.Intl.AP.726440_TMY3.epw

6B Great Falls USA_MT_Great.Falls.Intl.AP.727750_TMY3.epw

7 International 

Falls USA_MN_International.Falls.Intl.AP.727470_TMY3.epw 

8 Fairbanks USA_AK_Fairbanks Intl.AP.702610_TMY3.epw

Getting to Zero Energy

To develop the small to medium office buildings ZE AEDG, project committee members built 

on the technologies and strategies used to achieve a 50% energy reduction in small to medium 

offices (ASHRAE 2011), recommendations from Main Street Net-Zero Energy buildings 

(Torcellini et al. 2010) and successful design and construction approaches from existing high 

performance and ZE offices (NBI 2018). The new guide contains additional efficiency 

technologies, equipment parameter improvements, design refinements, and other guidance to 

help project teams get to zero. Here are a few examples. 

Plug Loads 

As building energy efficiency increases, plug loads account for a larger percentage of 

building loads. Plug loads include anything that is not HVAC or lighting, including computers, 

coffee makers, elevators, security systems, audio/visual equipment. Considerable plug loads 

reduction can be achieved through use of ENERGY STAR equipment where possible and 

implementation of control strategies such as occupancy sensors at workstations, on vending 
6 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

machines, and on break room equipment. The objective is to have the building “turn off” when 

the building is not occupied, which is 50% to 70% of the year. 

Lighting

The ZE small to medium office buildings AEDG recommends an average LPD of 

0.4 W/ft2. This can be achieved through the use of 100% LEDs with an efficacy of 125 LPW or 

more. Daylighting is an important component of a ZE small to medium office buildings lighting 

strategy, and is typically employed in the perimeter zones near view windows, while the rest of 

the zones are electrically lit. As lower lighting power densities become achievable, the need for 

aggressive daylighting design strategies with light shelves, clerestories, or skylights can be

reduced. 

LEDs also provide exterior lighting in ZE office buildings. Controls turn the lights on 

based on sunrise and sunset. Another energy-saving feature is to reduce lighting to 25% of 

typical output from midnight to 6 a.m. LEDs turn on quickly, so motion sensors can be used to

increase and decrease lighting levels with minimal occupant disruption. 

Envelope 

A tight, well-insulated envelope is a critical element in any energy-efficient building. 

Setting an absolute energy goal (Leach et al. 2012) before design begins shifts the burden of 

responsibility for meeting that goal from the owner to the project team. The ZE small to medium 

office buildings AEDG contains detailed information on designing a building envelope for a ZE 

offices, including recommendations for envelope infiltration rates. All envelope penetrations 

used for ingress and egress or lighting such as windows, doors, and skylights must also be 

carefully designed and selected. 

Heating, Ventilating, and Air Conditioning 

Several different types of HVAC systems are used in office buildings. Various factors 

affect system selection including building configuration, owner preference, zone configuration, 

and the magnitude of the loads to be served. While many innovative systems can be considered, 

the systems recommended in the ZE AEDG are common and readily available in order to 

encourage zero energy adoption for a larger audience of building owners. 

 Four HVAC system are discussed in the guide as a candidate for office buildings: 

Multizone Variable Air Volume (VAV) with Hydronic Heating/ Cooling, Air-Source Variable 

Refrigerant Flow (VRF) Heat Pump with Dedicated Outdoor Air System (DOAS), GroundSource Heat Pump (GSHP) with DOAS, and Sensible Cooling Chilled-Water Fan-Coils with 

DOAS.

Building Shape 

 Building planning, including massing and site layout were also examined. Long eastwest axis which increases the amount of glazing on the north and south facades can help with 

daylighting (coupled with lighting controls) and solar heat gain (coupled with appropriate 

awnings). East and west glazing can be minimized as it is difficult to control glare which hurts 

daylighting and solar heat gains increasing air conditioning loads. Note that in northern climates 
7 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

there is a slight benefit from passive solar gains; however, the south overhang is critical to 

minimize the solar gains in the summer. This is also balanced with the solar heat gain coefficient 

on the glazing. Building shape has less of an impact with the zero energy guide in part because 

of highly efficient glazing systems and highly efficient lighting systems; however, it will provide 

a positive impact to the energy consumption without much, if any, additional cost. 

Analysis Methodology

The objective of the analysis was to create a set of climate specific EUI targets for ZE

ready office buildings with a focus on energy efficiency. Once the building is as energy-efficient 

as it can be cost-effectively, project teams must determine how much solar is required to get to 

ZE. To provide guidance for this process, project committee members examined solar radiation

levels in each climate zone. Assuming 50% roof coverage by solar panels (to allow for roof 

access, HVAC equipment, daylighting penetrations, and plumbing vents), an initial EUI was 

established for each climate zone. 

Some energy efficiency solutions are independent of climate, such as plug load 

management and electric lighting design. Daylighting solutions are climate dependent, but to a 

lesser degree. These solutions were fixed across the other climate zones while project committee 

members examined further possible improvements in envelope and HVAC design. The result 

was that less than 50% of the roof area was required to achieve ZE in many climate zones. In the 

extreme north zones (climate zone 8), the solar resource is greatly diminished, making it difficult 

to achieve ZE, but these climates show the largest energy savings of any of the climate zones

when compared to ASHRAE 90.1-2016 (ASHRAE 2016). In contrast, in the extreme hot and 

humid climate (climate zone 0A), it is difficult to achieve ZE due to very high cooling demand. 

Source EUI target, site EUI target, and percentage of roof area required for PV for each climate 

zone is given in Table 4. Both site EUI and source EUI are given in the table because the sitesource conversion is an important part of achieving ZE using DOE’s ZE definition (DOE 2015). 

Note that the target EUI values are based on the office building models utilizing variable air 

volume (VAV) systems with hydronic heating and cooling. 

The DOE ZE definition allows for a tradeoff with different on-site fuel sources including 

natural gas, propane, and fuel oil as an offset in those fuels being used for power generation. 

Most ZE buildings tend towards all-electric to comply with utility requirements on the amount of 

exported electricity compared to purchased electricity. In this case, using a site energy and the 

corresponding source energy target will yield the same result. The modeling examined both gasfired heating and heat pump technologies to determine the energy targets. In general, the heat 

pumps have larger EUIs for the very cold climates compared to gas-fired equipment and 

therefore it is harder to achieve ZE in the cold climates for all-electric especially when combined 

with less solar availability.

Derivative Works

Because the measures used in the small to medium office building ZE AEDG were 

modeled with standard code elements, the design community can use the same basis for further 

simulations and introduce improvements by investigating alternative strategies while continuing 

to achieve the design EUI goal. This allows the design community to apply the prescriptive 

recommendations to their own building layouts and operational schedules. For example, this was 
8 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

useful during a DOE-sponsored university Solar Decathlon Build Challenge. In this effort 

students designed a ZE ready office building and the teams had to demonstrate an ability to 

perform analysis (DOE 2019). In addition, online learning modules for continuing education 

credits are being developed for architects and engineers, expected to be available during the fall 

of 2020.

Table 4. Small to medium office buildings energy use intensities: zero energy ready targets

Climate 

Zone

Site Energy

(kBtu/ft2·yr)

Source Energy

(kBtu/ft2·yr)

% of Roof Area 

for PV

0A 23.2 73.1 63

0B 27.6 86.9 50

1A 23.4 73.9 45

1B 25.7 81.1 56

2A 22.2 69.9 44

2B 22.8 71.8 40

3A 21.4 67.3 42

3B 21.1 66.6 35

3C 16.0 50.3 31

4A 21.7 68.5 44

4B 20.6 64.9 34

4C 17.3 54.4 43

5A 23.2 73.0 46

5B 22.9 72.0 37

5C 17.5 55.2 40

6A 27.7 87.3 48

6B 24.7 77.8 46

7 30.3 95.5 54

8 36.0 113.5 79

Consistencies with Other Methods of Setting Energy Goals

The project committee identified existing ZE ready office buildings and compared the 

EUIs and systems deployed with the analysis results. A sampling of these case studies and their 

climate zones and EUIs are show in Table 5. These offices were designed and built before the 

small to medium office buildings ZE AEDG was developed but achieved low operational EUIs, 

so they were good examples of how offices could be operated within the recommended EUIs for 

a ZE ready small to medium offices. 

As another point of reference, the EUIs were compared against different versions of 

ASHRAE Standard 90.1, CBECS (EIA 2012a; EIA 2012b), and the 30% and 50% series of 

Advanced Energy Design Guides. The ASHRAE Standard 90.1 values are weighted by climate 

zone based on the actual number of buildings in each climate zone. These results point to a 

highly energy-efficient building, so the project committee also performed an analysis comparing 

CBECS and ASHRAE standards. Results indicate that ZE ready offices perform, on average, 

14% better than ASHRAE Standard 90.1-2016 as shown by the black line in Figure 1. Note that 
9 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

climate specific values for the 30% AEDGs are not available by climate zone based on the 

analysis performed.

 Table 5. Energy use intensity recommendations and achieved values for office buildings 

Offices Site EUI

(kBtu/ft2·yr)

ZE Small to Medium office

AEDG Recommended Site

EUI (kBtu/ft2·yr)

Climate 

Zone 

DPR Construction Regional 

Office (Phoenix, AZ) 

26 22.8 2B

DPR Construction Regional 

Office (San Diego, CA)

14 21.1 3B

CMTA INC

(Lexington, Kentucky)

15.5 21.7 4A

NREL Research Support 

Facility (RSF) (Golden, CO) 

20.9 (without 

data center)

22.9 5B

Results from the ENERGY STAR® Target Finder were also compared with the EUI 

targets. Meeting EUI targets in the small to medium office buildings ZE AEDG required an 

ENERGY STAR score ranging from 85 to 100, depending on the climate zone. 

 

Figure 1. Comparison of energy use intensities for the Commercial Buildings Energy Consumption Survey, 

ASHRAE Standard 90.1, and the Advanced Energy Design Guides

0

25

50

75

100

125

150

175

200

2012 CBECS

Education

90.1-2007 90.1-2010 90.1-2016 30% AEDG 50% AEDG ZE AEDG

Source Energy Use Intensity (kBtu/ft2) 

Range shows high/low for 

different climate zones 

with the average shown as 

the black lines
10 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Conclusion 

As part of the development of the small to medium office buildings ZE AEDG, energy 

use intensity targets for zero energy ready performance were determined for 19 climate zones. 

Buildings that achieve these EUI’s are well positioned to have on-site renewables provide the 

same amount of energy as consumed by the building. The target values were compared with 

ASHRAE Standard 90.1-2016 and shown to be substantially lower than the standard. The target 

values were consistent with case studies of operating ZE offices. Finally, these values were 

compared with the ENERGY STAR® Target Finder scoring system. 

This analysis established that it is technically possible for new office building projects to 

achieve ZE ready status in all climate zones across the continental United States. Including 

climate zone 0 and climate zone 8 extends the analysis to most of the developed portion of the 

world. Temperate climates require a smaller percentage of solar panel coverage than very hot or 

very cold climates. In extremely cold climates (climate zone 8), roof space alone is not sufficient 

to get to ZE ready, but it can be achieved with additional solar panels installed outside the 

building footprint to balance energy demand. It is noteworthy that the largest energy savings can 

be achieved for these cold climate zones. 

The target EUIs developed in this study provide excellent starting points for all office 

building owners who want their projects to be as energy efficient as possible. These values have 

been incorporated into energy models for industry use, so that design teams can start with viable 

pathways to ZE and adjust those pathways based on local market conditions and needs. 

Acknowledgments 

This work was authored in part by Alliance for Sustainable Energy, LLC, the manager 

and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy 

(DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by the U.S. 

Department of Energy Office of Energy Efficiency and Building Technology Office. The views 

expressed in this paper do not necessarily represent the views of the DOE or the U.S. 

Government. The U.S. Government retains and the publisher, by accepting the article for 

publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, 

irrevocable, worldwide license to publish or reproduce the published form of this work, or allow 

others to do so, for U.S. Government purposes. 

The authors would also like to acknowledge the various stakeholders engaged in the 

development of this work, including members of the project’s Steering and Project Committees. 

The Steering and Project Committee organizations include ASHRAE, DOE, the American 

Institution of Architects (AIA), the U.S. Green Building Council (USGBC), and the Illuminating 

Engineering Society (IES). 

References

ASHRAE. 2008. Advanced Energy Design Guide for Small Office Buildings: Achieving 30% 

Energy Savings Toward a Net Zero Energy Building. ASHRAE, Atlanta, GA. 

https://www.ashrae.org/aedg. 
11 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

ASHRAE. 2011. Advanced Energy Design Guide for Small to Medium Office Buildings: 

Achieving 50% Energy Savings Toward a Net Zero Energy Building. ASHRAE, Atlanta, GA. 

https://www.ashrae.org/aedg. 

ASHRAE. 2013. ASHRAE Standard 169-2013—Climatic Data for Building Design Standards

(ANSI Approved). Atlanta, GA: ASHRAE. 

ASHRAE. 2016. ANSI/ASHRAE/ Illuminating Engineering Society of North America (IESNA) 

Standard 90.1-2016—Energy Standard for Buildings Except Low-Rise Residential Buildings. 

Atlanta, GA: ASHRAE.

ASHRAE. 2019. Advanced Energy Design Guide for Small to Medium Office Buildings: 

Achieving Zero Energy. ASHRAE, Atlanta, GA. https://www.ashrae.org/aedg. 

Bonnema, E., M. Leach, S. Pless, B. Liu, W. Wang, B. Thornton, and J. Williams. 2012. “50% 

Advanced Energy Design Guides.” ACEEE Summer Study on Energy Efficiency in 

Buildings. August 12–17, 2012. Pacific Grove, CA: ACEEE.

http://www.nrel.gov/docs/fy12osti/55470.pdf.

CPUC (California Public Utilities Commission). 2011. California Energy Efficiency Strategic 

Plan [update]. www.cpuc.ca.gov/WorkArea/DownloadAsset.aspx?id=5303. 

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

Winiarski, M. Rosenberg, M. Yazdanian, J. Huang, and D. Crawley. 2011. U.S. Department 

of Energy Commercial Reference Building Models of the National Building Stock. (Technical 

Report). NREL/TP-5500-46861. Golden, CO: National Renewable Energy Laboratory. 

www.nrel.gov/docs/fy11osti/46861.pdf. 

DOE (U.S. Department of Energy). 2014. Commercial Prototype Building Models. Last 

modified July 23. 2014. 

https://www.energycodes.gov/development/commercial/prototype_models. 

DOE. 2015. A Common Definition for ZE Buildings. DOE/EE-1247. Washington, DC: DOE. 

https://www.energy.gov/sites/prod/files/2015/09/f26/A Common Definition for Zero Energy 

Buildings.pdf. 

DOE. 2018. U.S. Department of Energy Race to Zero Student Design Competition Guide. 

https://www.energy.gov/eere/buildings/downloads/2018-us-department-energy-race-zerostudent-design-competition-guide. 

EnergyPlus. 2020. EnergyPlus Simulation Program. Accessed March 2020. U.S. Department of 

Energy Building Technologies Office. https://energyplus.net 

EIA. (Energy Information Administration). 2012a. Commercial Buildings Energy Consumption 

Survey (CBECS). www.eia.gov/consumption/commercial. 

EIA. 2012b. Commercial Buildings Energy Consumption Survey: Energy Usage Summary. 

www.eia.gov/consumption/commercial/reports/2012/energyusage. 
12 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Fisher, S., N. Sultan, and R. Stromquist. 2006. “Plug Load Reduction for a Net Zero Energy

Building.” Proceedings of the 2006 ACEEE Summer Study on Energy Efficiency in Buildings

9:119–123. ACEEE. Washington, DC: ACEEE. 

http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel9_Paper11.pdf. 

Griffith, B., P. Torcellini, N. Long, D. Crawley, and J. Ryan. 2006. Assessment of the Technical 

Potential for Achieving Zero-Energy Commercial Buildings: Preprint. (Conference Paper). 

NREL/CP-550-39830. Golden, CO: National Renewable Energy Laboratory. 

https://www.nrel.gov/docs/fy06osti/39830.pdf. 

Griffith, B., N. Long, P. Torcellini, R. Judkoff, D. Crawley, and J. Ryan. 2007. Assessment of the 

Technical Potential for Achieving Zero-Energy Commercial Buildings. NREL/TP-550-

41957. Golden, CO: National Renewable Energy Laboratory. 

https://www.nrel.gov/docs/fy07osti/41957.pdf. 

Griffith, B., N. Long, P. Torcellini, R. Judkoff, D. Crawley, and J. Ryan. 2008. Methodology for 

Modeling Building Energy Performance across the Commercial Sector. NREL/TP-550-

41956. Golden, CO: National Renewable Energy Laboratory. 

https://www.nrel.gov/docs/fy08osti/41956.pdf. 

Liu, B., C. Eley, S. Gupta, C. Higgins, J. Iplikci, J. McHugh, M. Rosenberg, P. Torcellini. 2017. 

“A conversation on zero net energy buildings.” ASHRAE Journal 59(6):38–49. 

New Buildings Institute. 2018. Getting to Zero Status Update and List of ZE Projects. Accessed 

March 2020. https://newbuildings.org/wpcontent/uploads/2018/01/GTZ_StatusUpdate_ZE_BuildingList_2018.pdf. 

OpenStudio. 2020. OpenStudio Platform. Accessed March 2020. NREL, Golden, CO. 

https://www.openstudio.net 

Peterson, K., P. Torcellini, C. Taylor, and R. Grant. 2016. “Establishing a Common Definition 

for ZE Buildings: Time to Move the Market.” NREL/CP-5500-67080, Proceedings of the 

2016 ACEEE Summer Study on Energy Efficiency in Buildings 10:1-11. Washington, DC: 

ACEEE. https://aceee.org/files/proceedings/2016/data/papers/10_815.pdf. 

Pless, S., and P. Torcellini. 2010. Net-Zero Energy Buildings: A Classification System Based on 

Renewable Energy Supply Options, NREL/TP-550-44586, Golden, CO: National Renewable 

Energy Laboratory. https://www.nrel.gov/docs/fy10osti/44586.pdf. 

Pless, S., P. Torcellini, E. Bonnema, and D. Goldwasser. 2016. “Technical Feasibility Study for 

Zero Energy K–12 Schools.” Proceedings of the 2016 ACEEE Summer Study on Energy 

Efficiency in Buildings 10:1-15. Washington, DC: ACEEE. 

https://aceee.org/files/proceedings/2016/data/papers/10_809.pdf. 
13 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

SAM ([California] State Administrative Manual). 2017. Energy and Sustainability: Zero Net 

Energy for New and Existing State Buildings. 

https://www.documents.dgs.ca.gov/osp/sam/mmemos/MM17_04.pdf, 

https://www.documents.dgs.ca.gov/sam/SamPrint/new/sam_master/sam_master_file/chap180

0/1815.31.pdf. 

Torcellini, P., E. Bonnema, D. Goldwasser, and S. Pless. 2016. “Analysis of Different Methods 

for Computing Source Energy in the Context of Zero Energy Buildings.” Proceedings of the 

2016 ACEEE Summer Study on Energy Efficiency in Buildings 10:1-12. Washington, DC: 

ACEEE. 

Torcellini, P., Pless, S., Lobato, C. 2010. “Main Street Net-Zero Energy Buildings: The Zero 

Energy Method in Concept and Practice” NREL/CP-550-47870, Proceedings of the 4th 

International Conference on Energy Sustainability. Phoenix, Arizona: ASME.