Technical Report

NREL/TP-550-49213

September 2010

Technical Support Document: 

Strategies for 50% Energy Savings 

in Large Office Buildings

Matthew Leach, Chad Lobato, Adam Hirsch, 

Shanti Pless, and Paul Torcellini
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

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Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-550-49213

September 2010

Technical Support Document: 

Strategies for 50% Energy Savings 

in Large Office Buildings

Matthew Leach, Chad Lobato, Adam Hirsch, 

Shanti Pless, and Paul Torcellini

Prepared under Task No. BEC7.1309
NOTICE

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i 

Acknowledgments

This document was prepared by the National Renewable Energy Laboratory (NREL) for the U.S. 

Department of Energy’s (DOE’s) Building Technologies Program (BTP) as Deliverable 10-2.2.4 

under Task BEC7.1309 in the Commercial Buildings Statement of Work. The authors would 

like to thank the BTP Commercial Buildings Research and Development team for their dedicated 

support of this project. 

We are indebted to a number of retailers and building industry professionals for taking the time 

to provide equipment and construction cost estimates and to review our analysis assumptions and 

earlier versions of this report. John Priebe of The Abo Group arranged for the procurement of 

envelope construction cost data from Cumming Corporation and HVAC system cost data from 

RMH Group. Stefan Coca of Cumming Corporation provided us with an extensive set of 

envelope cost data for low-rise and high-rise large office constructions. Bob Stahl of RMH 

Group, with assistance from Phil Kocher and Jim Bradburn from RMH Group, provided us with 

detailed HVAC schematics, equipment lists, and overall system costs for our baseline and lowenergy HVAC systems. Bob also provided us with estimates for incremental costs associated 

with improved component efficiencies. Steven Taylor of Taylor Engineering and Fiona Cousins 

of Arup Engineering provided us very detailed review of both our analysis assumptions and our 

overall approach. David Okada of Stantec Engineering provided review of an initial list of 

possible energy efficiency measures (EEMs).

We would like to thank all of the peer reviewers for their time and constructive feedback. NREL 

colleagues Anthony Florita, Andrew Parker, Rois Langner, Daniel Studer, Michael Deru, and 

Shanti Pless all reviewed the report during its development. Stefanie Woodward and Stephanie 

Price of NREL proofread and edited the document. Carol Kerstner assisted with final edits and 

prepared the document for publication. 

Several other NREL colleagues provided valuable guidance and information during the modeling 

process, either directly or through their past work. Eric Bonnema and Brent Griffith provided 

extensive modeling assistance. Ian Doebber and Kyle Benne provided modeling assistance and 

significant insight into the modeling process, especially in regards to the setup and control of the 

radiant heating and cooling system model. Jennifer Scheib and Rob Guglielmetti provided 

electric lighting and daylighting EEM data. Nicholas Long and Eric Bonnema provided Opt-EPlus assistance. Michael Deru and Kristin Field provided review of our code compliant high-rise 

baseline, including our schedule sets. Jenni Sonnen coordinated graphic design work by Joshua 

Bauer to provide us with figures for the report. Eric Bonnema, Brent Griffith, and Michael Deru 

shared their computing resources for the optimization process.
ii

Executive Summary

This Technical Support Document (TSD) was developed by the Commercial Buildings Group at 

NREL, under the direction of the DOE Building Technologies Program. Its main goal was to

evaluate the potential for new large office buildings in the United States to achieve a 50% net 

site energy savings compared to a baseline defined by minimal compliance with respect to 

ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings Except Low-Rise 

Residential Buildings (ASHRAE 2004c). 

The work presented here extends the 50% Energy Savings Design Technology Packages for 

Medium Office Buildings TSD developed at the Pacific Northwest National Laboratory 

(Thornton, Wang et al. 2009) to encompass office buildings with larger footprints and high-rise 

design. It is a stand-alone report that is not part of a formal project under ASHRAE’s Special 

Project procedures to develop an Advanced Energy Design Guide for Large Offices. It may be 

used to support such a project in the future and should be considered a preliminary feasibility 

study for achieving 50% energy reduction in large office buildings across the different climates 

found in the United States. Detailed design recommendations were not provided in recognition 

that they will be a focus of future work to develop a corresponding Advanced Energy Design 

Guide and that many design details will likely be project specific when reaching for the 50% 

energy reduction goal. Many of the assumptions in Thornton, Wang et al. (2009) have been 

changed for this report to more accurately portray the practices followed in designing large office 

buildings, especially pertaining to heating, ventilation, and air conditioning (HVAC) design. For 

example, the baseline variable air volume (VAV) system included central chillers and boilers 

with hot and cold water coils where the Medium Office TSD assumed a rooftop VAV with direct 

expansion cooling coils and direct gas-fired heating. As in the Medium Office TSD, in-slab 

hydronic radiant heating and cooling with a dedicated outdoor air system (DOAS) was adopted 

as a primary energy-saving strategy, but with the radiant heating and cooling assumed to be via a 

slab ceiling rather than a slab floor. While this design is uncommon in the United States, it has 

been identified as a promising energy-saving strategy (Thornton, Wang et al. 2009). 

The intended audience for this report includes energy modelers who wish to simulate low-energy 

large office buildings as part of the design process and for engineers who want to delve into the 

detailed assumptions underlying the results presented in the report to inform low-energy building 

design. While ASHRAE Standard 90.1-2004 was used to define code-compliant baseline 

models, we included all building energy consumption terms in the analysis, both those regulated 

by code and so-called “unregulated” loads, such as miscellaneous plug loads and data center 

energy consumption. Energy savings was also compared to an ASHRAE 90.1-2007 compliant 

baseline to analyze how energy code changes impact energy savings. Site energy (the energy 

delivered to the building) was used as our primary energy performance metric, consistent with 

the original statement of work for this project. Source energy savings, energy cost savings, and 

energy-related emissions savings were defined in the report and presented for comparison with 

site energy savings (Torcellini 2006; Deru and Torcellini 2007). 

A 50% site energy savings was found to be feasible in all climate zones analyzed. Five-year total 

lifecycle costs were included in the results for baseline and low-energy building designs to allow 

cost comparisons. 
iii

Methodology

To account for energy interactions between building subsystems, we used EnergyPlus (DOE 

2010) to model the energy performance of baseline and low-energy buildings to verify that 50% 

net site energy savings can be achieved. EnergyPlus computes building energy use based on the 

interactions between climate, building form and fabric, internal gains, HVAC systems, and 

renewable energy systems. Percent energy savings were based on comparison with a minimally 

code-compliant building as described in Appendix G of ASHRAE 90.1-2004, and used wholebuilding net site energy use intensity (EUI) to measure performance, defined as: the amount of 

energy a building consumes for regulated and unregulated loads, minus any renewable energy 

generated within its footprint, normalized by building area. 

The following steps were used to generate low-energy building models: 

1. Architectural-program characteristics (design features not addressed by ASHRAE 90.1-

2004) for typical large office buildings were chosen to create low-rise and high-rise 

prototype models. 

2. Baseline energy models were created for each climate zone by specifying features of the 

prototype models to be minimally compliant with ASHRAE 90.1-2004. 

3. A list of candidate EEMs was defined.

4. Baseline energy model and EEM assumptions were reviewed by industry representatives. 

5. Combinations of EEMs were selected in each climate zone that achieved at least 50% net 

site energy savings. Preference was given to strategies that had low five-year total life 

cycle cost.

The simulations supporting this work were managed with the NREL commercial building energy 

analysis platform, Opt-E-Plus (NREL 2010). Opt-E-Plus employs an iterative search technique 

to find EEM combinations that achieve a given level of whole-building energy savings at the 

lowest total life cycle cost. The primary advantages of the analysis platform are its abilities to: 

(1) transform high-level building parameters (building area, internal gains per zone, HVAC 

system configuration, etc.) into a fully functional input file for EnergyPlus; (2) conduct an 

automated search to find an optimal solution, subject to assumptions made about EEM 

performance and cost; and (3) manage multiple EnergyPlus simulations run on both a local CPU

and remote supercomputer processors. The economic criterion used to filter the 

recommendations was five-year total life cycle cost (using the 2010 OMB real discount rate, 

1.6%) (OMB 2010). The five-year analysis period was established in our statement of work and 

was assumed acceptable to a majority of developers and owners. 

The building architectural prototypes that were developed for this project defined the basic 

building characteristics such as floor plate dimensions, orientation, and thermal zoning. Both 

high-rise and low-rise prototypes contained 460,800 ft2 (42,810 m2

) of total floor area and had an 

aspect ratio of 1.5. The low-rise prototype had four stories and a footprint of 115,200 ft2 (10,700 

m2); the high-rise prototype had 12 stories and a footprint of 38,400 ft2 (3,570 m2). The 

prototype envelope constructions were based on typical design practice for their respective 

building configurations: the low-rise prototype had precast concrete exterior wall panels and 

punched-hole glazing; the high-rise prototype had spandrel glass exterior wall panels (opaque 

panels with insulation) and glass curtain glazing. Both prototypes had roofs with insulation 

above deck. 
iv

Construction types and other building parameters were chosen to transform the building 

prototypes into representations of minimally code-compliant and low-energy building 

representations to calculate energy savings. Code compliant baseline models (low-rise and highrise) had a 40% window-to-wall ratio (WWR) as per minimal code compliance with ASHRAE 

Standard 90.1-2004. A non-compliant high-rise case with 69% WWR was also considered in 

order to analyze what additional investment in EEMs was required to reach the target of 50% 

better than the code-compliant baseline. For this case, all EEMs were available except for 

changes to WWR and wall insulation. The baseline HVAC system configuration was a variable 

air volume (VAV) system with hydronic heating via a natural gas-fired boiler and hydronic 

cooling via a water-cooled, electric, centrifugal chiller. A baseline plug load density of 0.9 W/ft2

(9.7 W/m2) was assumed, including the electricity consumption of a centralized data center. 

The EEMs used in this work fell into the following categories:

• Form EEMs affecting building aspect ratio, façade glazing coverage, and overhangs 

used to shade glazing. 

• Fabric EEMs addressing opaque envelope insulation, glazing construction, and envelope 

air barriers and entrance vestibules.

• Equipment EEMs specifying the properties of: the radiant heating/cooling and DOAS 

equipment, energy recovery equipment, waterside economizing, reduced lighting power 

densities, occupancy controls, daylighting controls, higher efficiency HVAC and service 

water heating (SWH) equipment, and photovoltaic (PV) electricity generation. 

Findings

The results show that 50% net site energy savings can be achieved in both low-rise and high-rise 

large office buildings in a range of climates representative of the spectrum of U.S. weather 

conditions (Table ES-1). 

Table ES-1 Standard 90.1-2004 Baseline Model Performance

Climate Zone Climate Type Representative City Low-Rise 

Savings

High-Rise 

Savings

1A Hot and Humid Miami, Florida 57.6% 57.5%

3B Hot and Dry Las Vegas, Nevada 56.7% 58.2%

4C Marine Seattle, Washington 54.1% 57.1%

5A Cold and Humid Chicago, Illinois 54.0% 55.1%

5B Cold and Dry Boulder, Colorado 55.5% 58.3%

7 Very Cold Duluth, Minnesota 55.0% 57.8%

On-site generation technology (in this case, PV) was not necessary to meet the energy savings 

goal except for the non-compliant, poorly insulated high-rise case. The following EEMs played 

important roles in reaching the 50% energy savings target: 

• The baseline hydronic VAV system was replaced with radiant heated and cooled slab 

ceilings with DOAS for ventilation. 

• The DOAS design was tailored to address climate-specific requirements as follows: 

sensible and latent energy recovery equipment was used in humid climates, sensible 

energy recovery equipment was used in marine and very cold climates, and indirect 

evaporative cooling (IDEC) was included in dry climates.
v 

• Waterside economizing was incorporated in dry climates.

• Lighting power density was reduced to 0.63 W/ft2 in offices spaces and occupancy 

sensors were assumed in infrequently occupied zones.

• Daylighting controls tuned to maintain a 27.9 fc (300 lux) set point.

• Entrance vestibules and envelope air barriers were included to reduce infiltration. These 

features were important to avoid condensation on radiant cooling surfaces in humid 

climates.

• High efficiency boilers (condensing, nominally 98% efficient), chillers (COP of 7), air 

distribution units (69% total fan efficiency), and service water heating (SWH) equipment 

(90% thermal efficiency) was installed.

• Façade WWR was reduced to 20% and window properties were modified to reduce solar 

gain, improve overall envelope insulation, and reduce construction costs. In low-rise 

buildings, double pane windows with low-emissivity film and argon fill (U-0.235, 

SHGC-0.416, VLT-0.750) were installed; in high-rise buildings, double pane windows 

with low-emissivity film and tinted glass constructions (U-0.288, SHGC-0.282, VLT0.55) were used. 

• Exterior wall insulation was added in cold climates (up to R-19.5 continuous insulation 

(c.i.) for the low-rise case and R-22.5 c.i. for the high-rise case).

• Total plug loads were reduced by 23% to 0.68 W/ft2

 (7.3 W/m2) by purchasing high 

efficiency electronic equipment and employing control strategies to eliminate plug loads 

when equipment was not being used. 

Energy use intensities for the ASHRAE 90.1-2004 baselines were similar for the code compliant 

low-rise and high-rise cases, but larger for the high-rise case with non-compliant envelope design 

(by an average of 11%). The non-compliant high-rise model EUIs were much higher in severe 

climates where already large heating and/or cooling loads were magnified by the highly glazed, 

poorly insulated building envelope. 

Energy savings was also compared to a baseline specified to minimally satisfy the requirements 

of ASHRAE 90.1-2007 rather than 90.1-2004, to analyze how code changes impact percent 

savings. The 90.1-2007 baseline models had EUIs similar to the ASHRAE 90.1-2004 baseline 

models. In climate zone 7 (Duluth), a baseline building built to satisfy ASHRAE 90.1-2007 was 

found to be slightly more expensive than one built to ASHRAE 90.1-2004 due to additional 

envelope insulation requirements; however, over five years this additional capital cost was more 

than offset by energy cost savings. In all other climates, replacing ASHRAE 90.1-2004 with 

ASHRAE 90.1-2007 as the baseline building standard resulted in little or no energy savings and 

slightly increased capital and life cycle costs.

An economic analysis calculating simple payback period was performed for the final low-energy 

EEM combinations selected in each climate zone. Low-energy high-rise large office buildings 

featuring well integrated energy efficiency measures demonstrated simple payback periods of 

less than ten years; low-energy low-rise large office buildings had simple payback periods of 
vi

between nine and 16 years; and low-energy high-rise large office buildings with high glazing 

fraction and minimal insulation had simple payback periods of greater than 20 years. 

While the energy goal for this study was defined with respect to net site energy, low-energy 

buildings were also evaluated with respect to net source energy, energy-related carbon dioxide 

emissions, and energy cost for comparison (Torcellini 2006; Deru and Torcellini 2007). A 

simplified analysis was performed using national average site-to-source and site-to-emissions 

multipliers and a national average electricity tariff. The low-energy buildings (not considering 

the non-compliant high rise case) performed well with respect to net source energy savings 

(52.8% average), energy emissions savings (52.4% average), and energy cost (50.3% average), 

but not quite as well as they performed with respect to net site energy savings (56.4% average). 

This was because these alternative metrics are heavily weighted toward electricity savings, due 

to the high site-to-source multiplier of electricity versus natural gas on average in the United 

States, reflecting the efficiency losses during electricity generation, transmission, and 

distribution (Torcellini 2006; Deru and Torcellini 2007). Peak electricity demand only decreased 

by 10%, on average. Further research is needed to analyze how design recommendations change 

when (1) energy savings using an alternative performance metric (even including peak electrical 

demand) is considered as a design objective and (2) region-to-region variability in electricity 

tariffs and conversion factors between site energy and the other metrics is included in the 

analysis. 

Future analyses of large office building energy efficiency may benefit from adopting some of the 

recommendations outlined in Section 5.0 of the report. For instance, several EEMs deserve 

attention as this work progresses to the AEDG stage but were omitted here due to lack of reliable 

input data or lack of model validation for these advanced strategies. They include: 

• Alternative HVAC systems, such as a high efficiency VAV system (as a low-energy 

alternative to the baseline VAV system), though this strategy was found to limit energy 

savings to under 50% in some climate zones in the medium office 50% savings TSD.

• Exploring the effect building thermal mass characteristics have (through manipulations of 

the constructions of exterior walls, radiant slabs and interior furnishings) on radiant 

system operation and control.

• Natural ventilation, especially cross ventilation for high aspect ratio designs. 

• Advanced daylighting strategies, including: different combinations of view glass and 

daylighting glass, with function-specific material properties; and, installation of light 

redirection devices to allow deeper penetration of daylight into the building interior. 
vii

Nomenclature

5-TLCC five-year total life cycle cost

ACH air changes per hour 

AEDG Advanced Energy Design Guide 

AHU air handling unit

ANSI American National Standards Institute

ASHRAE American Society of Heating, Refrigerating and AirConditioning Engineers 

ASTM American Society for Testing and Materials

CBECS Commercial Buildings Energy Consumption Survey 

c.i. continuous insulation

CO2 carbon dioxide 

COP coefficient of performance

DCV demand control ventilation 

DOAS dedicated outdoor air system 

DOE U.S. Department of Energy 

DX direct expansion 

EEM energy efficiency measure

EIA Energy Information Administration

EMS Energy Management System

ERV energy recovery ventilator 

EUI energy use intensity

GSD-1 general service demand

HVAC heating, ventilation, and air conditioning

IDEC indirect evaporative cooling 

IECC International Energy Conservation Code 

IESNA Illuminating Engineering Society of North America

LEED Leadership in Energy and Environmental Design 

LPD lighting power density 

MCF 1000 cubic feet

MRT mean radiant temperature

NREL National Renewable Energy Laboratory 

OA outside air

O&M operations and maintenance 

OMB Office of Management and Budget 

PC personal computer

PLR part-load ratio

PMV predicted mean vote 

PNNL Pacific Northwest National Laboratory

PUE power usage effectiveness

PV photovoltaic 

QA/QC quality assurance/quality control 

RH relative humidity

RSF Research Support Facility

SHGC solar heat gain coefficient
viii

SOW Statement of Work

SWH service water heating

TSD Technical Support Document 

UFAD under floor air distribution 

USGBC U.S. Green Building Council 

VAV variable air volume

VLT visible light transmittance

w.c. water column

WD weekday

WWR window-to-wall ratio

XML Extensible Markup Language

ZEB zero energy building
ix

Contents

Acknowledgments............................................................................................................................ i

Executive Summary ........................................................................................................................ ii

Methodology .............................................................................................................................. iii

Findings ...................................................................................................................................... iv

Nomenclature ................................................................................................................................ vii

Contents ......................................................................................................................................... ix

Figures and Tables ........................................................................................................................ xii

Figures ....................................................................................................................................... xii

Tables ........................................................................................................................................ xii

1.0 Introduction .......................................................................................................................... 1

1.1 Objectives ......................................................................................................................... 3

1.2 Scope ................................................................................................................................ 4

1.3 Report Organization ......................................................................................................... 5

2.0 Methodology ........................................................................................................................ 6

2.1 Guiding Principles ............................................................................................................ 6

2.2 Definitions ........................................................................................................................ 7

2.2.1 Energy Use ................................................................................................................... 7

2.2.2 Percent Energy Savings ................................................................................................ 8

2.2.3 ASHRAE 90.1-2004 Baseline ...................................................................................... 8

2.3 Building Energy Modeling Methodology ........................................................................ 9

2.3.1 EnergyPlus .................................................................................................................... 9

2.3.2 Climate Zones ............................................................................................................... 9

2.4 Modeling Protocol .......................................................................................................... 11

2.4.1 Baseline Model Specification ..................................................................................... 11

2.4.2 Preliminary 50% Energy Savings Design Selection................................................... 11

2.4.3 Low-Energy Model Refinement ................................................................................. 12

2.4.4 Quality Assurance/Quality Control Protocol .............................................................. 13

3.0 Model Development and Assumptions .............................................................................. 15

3.1 Analysis Assumptions .................................................................................................... 15

3.1.1 Integrity of Simulation Models................................................................................... 15

3.1.2 Economics .................................................................................................................. 15
x 

3.2 Prototype Model ............................................................................................................. 19

3.2.1 Program ...................................................................................................................... 19

3.2.2 Form............................................................................................................................ 22

3.2.3 Fabric .......................................................................................................................... 23

3.2.4 Equipment ................................................................................................................... 23

3.2.5 Prototype Model Summary ......................................................................................... 24

3.3 Baseline Model ............................................................................................................... 26

3.3.1 Program ...................................................................................................................... 26

3.3.2 Form............................................................................................................................ 28

3.3.3 Fabric .......................................................................................................................... 30

3.3.4 Equipment ................................................................................................................... 35

3.4 Energy Efficiency Measures .......................................................................................... 43

3.4.1 Program ...................................................................................................................... 44

3.4.2 Form............................................................................................................................ 45

3.4.3 Fabric .......................................................................................................................... 46

3.4.4 Equipment ................................................................................................................... 49

4.0 Results ................................................................................................................................ 66

4.1 Baseline Models ............................................................................................................. 66

4.1.1 ASHRAE 90.1-2004 Baseline Models: Performance ................................................ 66

4.1.2 ASHRAE 90.1-2007 Baseline Models: Performance ................................................ 73

4.1.3 Discussion ................................................................................................................... 77

4.2 Selected Low-Energy Models ........................................................................................ 78

4.2.1 Preliminary Low-Energy Models: Selection ............................................................. 78

4.2.2 Preliminary Low-Energy Models: Performance........................................................ 82

4.2.3 Optimized Low-Energy Models: Selection ............................................................... 82

4.2.4 Optimized Low-Energy Models: Performance .......................................................... 87

4.2.5 Discussion ................................................................................................................... 97

5.0 Suggestions for Future Work ............................................................................................. 99

5.1 Optimization Setup ......................................................................................................... 99

5.2 Energy Modeling ............................................................................................................ 99

6.0 Conclusions ...................................................................................................................... 102

7.0 References ........................................................................................................................ 104
xi

Appendix A Prototype Schedules .......................................................................................... 108

A.1 Occupancy .................................................................................................................... 108

A.2 Lighting ........................................................................................................................ 109

A.3 Plug and Process Loads ................................................................................................ 110

A.4 Service Water Heating ................................................................................................. 111

Appendix B Baseline Model Schedules ................................................................................ 112

B.1 HVAC........................................................................................................................... 112

B.2 Infiltration ..................................................................................................................... 113

B.3 Thermostat Set Points................................................................................................... 115

Appendix C Low-Energy Model Schedules .......................................................................... 117

C.1 HVAC........................................................................................................................... 117

C.2 Infiltration ..................................................................................................................... 119

C.3 Thermostat Set Points................................................................................................... 121

Appendix D Metric Unit Tables ............................................................................................ 122
xii

Figures and Tables

Figures

Figure 2-1 DOE climate zones and representative cities........................................................................... 10

Figure 2-2 Modeling Protocol Flowchart................................................................................................... 11

Figure 2-3 Example Opt-E-Plus output: climate zone 1A (Miami, Florida) ............................................. 13

Figure 3-1 Prototype weekday schedules: occupancy, plug load equipment, and lighting equipment..... 22

Figure 3-2 Baseline weekday schedules: occupancy, HVAC operation, and infiltration ......................... 27

Figure 3-3 Baseline weekday schedules: heating and cooling set points.................................................. 27

Figure 3-4 Isometric view of the low-rise baseline model......................................................................... 28

Figure 3-5 Isometric view of the code-compliant high-rise baseline model.............................................. 29

Figure 3-6 Isometric view of the common practice high-rise baseline model........................................... 29

Figure 3-7 Baseline Boiler Efficiency Curve............................................................................................. 40

Figure 3-8 Low-energy weekday schedules: occupancy, HVAC operation, and infiltration ................... 44

Figure 3-9 Low-energy weekday schedules: DOAS heating and cooling set points................................ 45

Figure 3-10 Radiant slab ceiling construction ........................................................................................... 55

Figure 3-11 “Trickle and ramp” radiant flow control ................................................................................ 56

Figure 3-12 DOAS supply air temperature control.................................................................................... 58

Figure 3-13 Boiler efficiency curves for the baseline and low-energy boilers.......................................... 61

Figure 4-1 Low-rise EUI by end use for baseline energy models.............................................................. 67

Figure 4-2 High-rise EUI by end use for baseline energy models............................................................. 68

Figure 4-3 Low-rise Energy Use Intensity by end use for low-energy models ......................................... 87

Figure 4-4 High-rise Energy Use Intensity by end use for code compliant low-energy models............... 88

Figure 4-5 High-rise Energy Use Intensity by end use for common practice low-energy models............ 89

Tables 

Table ES-1 Standard 90.1-2004 Baseline Model Performance................................................................iv

Table 3-1 Economic Parameter Values...................................................................................................... 16

Table 3-2 Electricity Tariff........................................................................................................................ 17

Table 3-3 National Average Natural Gas Tariff and Source Data in $/MCF ............................................ 17

Table 3-4 Large Office Space Types and Sizes......................................................................................... 20

Table 3-5 Occupancy Density Mapping and Peak Values......................................................................... 21

Table 3-6 Prototype Shape Characteristics................................................................................................ 22

Table 3-7 Large Office Prototype Model Characteristics and Data Sources............................................. 25

Table 3-8 Baseline Shape Characteristics.................................................................................................. 28
xiii

Table 3-9 Low-Rise Baseline Exterior Wall Constructions....................................................................... 30

Table 3-10 High-Rise Code-Compliant Baseline Exterior Wall Constructions ........................................ 31

Table 3-11 High-Rise Common Practice Baseline Exterior Wall Construction........................................ 31

Table 3-12 Low-Rise Baseline Roof Constructions................................................................................... 32

Table 3-13 Low-Rise Baseline East-, South-, and West-Facing Punched-Hole Window Constructions.. 33

Table 3-14 Low-Rise Baseline North-Facing Punched-Hole Window Constructions .............................. 33

Table 3-15 High-Rise Baseline East-, South-, and West-Facing Glass Curtain Constructions................. 33

Table 3-16 High-Rise Baseline North-Facing Glass Curtain Constructions.............................................. 34

Table 3-17 Baseline Infiltration Rates per Zone........................................................................................ 34

Table 3-18 Baseline Lighting Loads by Space Type ................................................................................. 36

Table 3-19 Peak Baseline Plug Loads........................................................................................................ 37

Table 3-20 Baseline Data Center Load per Person .................................................................................... 37

Table 3-21 Baseline Data Center EUIs...................................................................................................... 37

Table 3-22 Low-Rise and High-Rise Baseline Minimum Ventilation Rates............................................. 39

Table 3-23 Baseline HVAC System Cost Estimation Sizes ...................................................................... 41

Table 3-24 Baseline HVAC System Cost Estimate Equipment Breakdown ............................................. 42

Table 3-25 Baseline HVAC System Cost Breakdown............................................................................... 42

Table 3-26 Baseline HVAC Models Summary.......................................................................................... 43

Table 3-27 Scope of Energy Efficiency Measures Considered ................................................................. 43

Table 3-28 Low-Rise Exterior Wall EEMs................................................................................................ 47

Table 3-29 High-Rise Exterior Wall EEMs............................................................................................... 47

Table 3-30 Low-Rise Roof EEMs ............................................................................................................. 48

Table 3-31 Low-Rise Fenestration Construction EEMs............................................................................ 48

Table 3-32 High-Rise Fenestration Construction EEMs ........................................................................... 49

Table 3-33 Low-Rise Occupancy Sensor LPD Reductions....................................................................... 51

Table 3-34 High-Rise Occupancy Sensor LPD Reductions ...................................................................... 51

Table 3-35 Lighting Power Density EEMs................................................................................................ 52

Table 3-36 Plug Load Reduction Strategies .............................................................................................. 53

Table 3-37 Low-Energy Peak Plug Loads................................................................................................. 53

Table 3-38 Low-Energy Data Center Load per Person.............................................................................. 54

Table 3-39 Low-Energy Data Center EUIs................................................................................................ 54

Table 3-40 Baseline and Low-Energy HVAC System Comfort Comparison ........................................... 56

Table 3-41 Radiant System Temperatures Required for Baseline Equivalent Comfort ............................ 59

Table 3-42 Radiant System Temperatures Required for Maximum Capacity ........................................... 60

Table 3-43 Radiant System Peak Volumetric Flow Rates per Floor ......................................................... 60
xiv

Table 3-44 Low-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes............. 62

Table 3-45 High-Rise Low-Energy Radiant with DOAS HVAC System Cost Estimation Sizes............. 62

Table 3-46 Low-Energy HVAC System Cost Estimate Equipment Breakdown....................................... 62

Table 3-47 Low-Energy HVAC System Cost Estimate Breakdown ......................................................... 63

Table 3-48 Low-Energy HVAC System Operational Static Pressure Breakdown .................................... 65

Table 4-1 ASHRAE 90.1-2004 Low-Rise Baseline Model Energy Performance ..................................... 68

Table 4-2 ASHRAE 90.1-2004 Low-Rise Baseline Model Costs............................................................. 69

Table 4-3 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Energy Performance......... 69

Table 4-4 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Costs................................. 69

Table 4-5 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Energy Performance....... 70

Table 4-6 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Costs............................... 70

Table 4-7 Comparison of Low-Rise EUI by End Use Between Baseline and 50% Savings Target.......... 71

Table 4-8 Comparison of Code-Compliant High-Rise EUI by End Use Between Baseline and 50% 

Savings Target..................................................................................................................... 71

Table 4-9 Comparison of Common Practice High-Rise EUI by End Use Between Baseline and 50% 

Savings Target..................................................................................................................... 72

Table 4-10 ASHRAE 90.1-2007 Low-Rise Baseline Exterior Wall Constructions .................................. 73

Table 4-11 ASHRAE 90.1-2007 High-Rise Baseline Exterior Wall Constructions.................................. 73

Table 4-12 ASHRAE 90.1-2007 Baseline Roof Constructions................................................................. 73

Table 4-13 ASHRAE 90.1-2007 Low-Rise Baseline Window Constructions........................................... 74

Table 4-14 ASHRAE 90.1-2007 High-Rise Baseline Window Constructions.......................................... 74

Table 4-15 Low-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines............................. 75

Table 4-16 High-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines............................ 75

Table 4-17 ASHRAE 90.1-2007 Low-Rise Baseline Model Energy Performance ................................... 75

Table 4-18 ASHRAE 90.1-2007 Low-Rise Baseline Model Costs........................................................... 76

Table 4-19 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Energy Performance....... 76

Table 4-20 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Costs............................... 76

Table 4-21 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Energy Performance..... 77

Table 4-22 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Costs............................. 77

Table 4-23 Preliminary Low-Rise Low-Energy Model EEM Selections.................................................. 79

Table 4-24 Preliminary Code Compliant High-Rise Low-Energy Model EEM Selections ...................... 80

Table 4-25 Preliminary Common Practice High-rise Low-Energy Model EEM Selections..................... 81

Table 4-26 Preliminary Low-Energy Model Net Site Energy Savings...................................................... 82

Table 4-27 Optimized Low-Rise Low-Energy Model EEM Selections.................................................... 84

Table 4-28 Optimized Code Compliant High-Rise Low-Energy Models.................................................. 85
xv

Table 4-29 Optimized Common Practice High-Rise Low-Energy Model EEM Selections...................... 86

Table 4-30 Low-rise Optimized Low-Energy Model Energy Performance: Warm Climates................... 90

Table 4-31 Low-rise Optimized Low-Energy Model Energy Performance: Cold Climates ..................... 90

Table 4-32 Code Compliant High-rise Optimized Low-Energy Model Energy Performance: Warm 

Climates............................................................................................................................... 91

Table 4-33 Code Compliant High-rise Optimized Low-Energy Model Energy Performance: Cold 

Climates............................................................................................................................... 91

Table 4-34 Common Practice High-rise Optimized Low-Energy Model Energy Performance: Warm 

Climates............................................................................................................................... 92

Table 4-35 Common Practice High-rise Optimized Low-Energy Model Energy Performance: Cold 

Climates............................................................................................................................... 92

Table 4-36 Low-rise Optimized Low-Energy Model Cost Performance: Warm Climates ....................... 93

Table 4-37 Low-rise Optimized Low-Energy Model Cost Performance: Cold Climates.......................... 94

Table 4-38 Code Compliant High-rise Optimized Low-Energy Model Cost Performance: Warm 

Climates............................................................................................................................... 94

Table 4-39 Code Compliant High-rise Optimized Low-Energy Model Cost Performance: 

Cold Climates...................................................................................................................... 95

Table 4-40 Common Practice High-rise Optimized Low-Energy Model Cost Performance: 

Warm Climates.................................................................................................................... 95

Table 4-41 Common Practice High-rise Optimized Low-Energy Model Cost Performance: Cold 

Climates............................................................................................................................... 96

Table 4-42 Common Practice High-rise PV Comparison.......................................................................... 96

Table 4-43 Low-rise Simple Payback Results........................................................................................... 97

Table 4-44 Code Compliant High-rise Simple Payback Results............................................................... 97

Table 4-45 Common Practice High-rise Simple Payback Results............................................................. 97

Table A-1 Prototype Occupancy Schedule .............................................................................................. 108

Table A-2 Prototype Lighting Schedule .................................................................................................. 109

Table A-3 Prototype Plug and Process Load Schedule............................................................................ 110

Table A-4 Prototype Service Water Heating Schedule............................................................................ 111

Table B-1 Baseline HVAC Schedule....................................................................................................... 112

Table B-2 Baseline Ground Floor Infiltration Schedule .......................................................................... 113

Table B-3 Baseline Interior Floor Infiltration Schedule .......................................................................... 114

Table B-4 Baseline Heating Set Point Schedule (oC) .............................................................................. 115

Table B-5 Baseline Cooling Set Point Schedule (oC).............................................................................. 116

Table C-1 Low-Energy DOAS Schedule................................................................................................. 117

Table C-2 Low-Energy Radiant Availability Schedule ........................................................................... 118

Table C-3 Low-Energy Ground Floor Infiltration Schedule.................................................................... 119
xvi

Table C-4 Low-Energy Interior Floor Infiltration Schedule.................................................................... 120

Table C-5 Low-Energy Heating Set Point Schedule (oC)........................................................................ 121

Table D-1 National Average Natural Gas Tariff and Source Data in $/GJ.............................................. 122

Table D-2 Low-Rise Baseline Exterior Wall Constructions.................................................................... 122

Table D-3 High-Rise Code-Compliant Baseline Exterior Wall Constructions........................................ 122

Table D-4 High-Rise Common Practice Baseline Exterior Wall Construction....................................... 122

Table D-5 Low-Rise Baseline Roof Constructions.................................................................................. 123

Table D-6 Low-Rise Baseline East-, South-, and West-Facing Punched-Hole Window Constructions . 123

Table D-7 Low-Rise Baseline North-Facing Punched-Hole Window Constructions.............................. 123

Table D-8 High-Rise Baseline East-, South-, and West-Facing Glass Curtain Constructions................ 123

Table D-9 High-Rise Baseline North-Facing Glass Curtain Constructions............................................. 124

Table D-10 Baseline Data Center EUIs................................................................................................... 124

Table D-11 Baseline HVAC System Cost Estimation Sizes ................................................................... 124

Table D-12 Baseline HVAC System Cost Breakdown............................................................................ 124

Table D-13 Low-Rise Exterior Wall EEMs............................................................................................. 125

Table D-14 High-Rise Exterior Wall EEMs............................................................................................ 125

Table D-15 Low-rise Roof EEMs............................................................................................................ 125

Table D-16 Low-Rise Fenestration Construction EEMs......................................................................... 125

Table D-17 High-Rise Fenestration Construction EEMs......................................................................... 125

Table D-18 Low-Rise Occupancy Sensor LPD Reductions.................................................................... 126

Table D-19 High-Rise Occupancy Sensor LPD Reductions.................................................................... 126

Table D-20 Lighting Power Density EEMs............................................................................................. 126

Table D-21 Low-Energy Data Center EUIs............................................................................................. 126

Table D-22 Baseline and Low-Energy HVAC System Comfort Comparison......................................... 126

Table D-23 Radiant System Temperatures Required for Baseline Equivalent Comfort ......................... 127

Table D-24 Radiant System Temperatures Required for Maximum Capacity ........................................ 127

Table D-25 Radiant System Peak Volumetric Flow Rates Per Floor...................................................... 127

Table D-26 Low-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes.......... 127

Table D-27 High-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes ......... 127

Table D-28 Low-Energy HVAC System Cost Estimate Breakdown ...................................................... 127

Table D-29 Low-Energy HVAC System Operational Static Pressure Breakdown ................................. 128

Table D-30 ASHRAE 90.1-2004 Low-Rise Baseline Model Energy Performance ................................ 128

Table D-31 ASHRAE 90.1-2004 Low-Rise Baseline Model Costs........................................................ 128

Table D-32 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Energy Performance .... 128

Table D-33 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Costs............................ 129
xvii

Table D-34 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Energy Performance.. 129

Table D-35 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Costs.......................... 129

Table D-36 Comparison of Low-Rise EUI in MJ/m2

∙yr by End Use Between Baseline and 50% 

Savings Target................................................................................................................... 130

Table D-37 Comparison of Code-Compliant High-Rise EUI in MJ/m2

∙yr by End Use Between 

Baseline and 50% Savings Target ..................................................................................... 130

Table D-38 Comparison of Common Practice High-Rise EUI in MJ/m2

∙yr by End Use Between 

Baseline and 50% Savings Target ..................................................................................... 131

Table D-39 ASHRAE 90.1-2007 Low-Rise Baseline Exterior Wall Constructions................................ 132

Table D-40 ASHRAE 90.1-2007 High-Rise Baseline Exterior Wall Constructions............................... 132

Table D-41 ASHRAE 90.1-2007 Baseline Roof Constructions.............................................................. 132

Table D-42 ASHRAE 90.1-2007 Low-Rise Baseline Window Constructions........................................ 132

Table D-43 ASHRAE 90.1-2007 High-Rise Baseline Window Constructions....................................... 133

Table D-44 Low-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines.......................... 133

Table D-45 High-Rise EUI Comparison between 90.1-2004 and 90.1-2007 baselines........................... 133

Table D-46 ASHRAE 90.1-2007 Low-Rise Baseline Model Energy Performance ................................ 133

Table D-47 ASHRAE 90.1-2007 Low-Rise Baseline Model Costs........................................................ 134

Table D-48 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Energy Performance .... 134

Table D-49 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Costs............................ 134

Table D-50 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Energy Performance.. 134

Table D-51 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Costs.......................... 135

Table D-52 Low-Rise Optimized Low-Energy Model Energy Performance: Warm Climates.............. 135

Table D-53 Low-Rise Optimized Low-Energy Model Energy Performance: Cold Climates................ 135

Table D-54 Code-Compliant High-Rise Optimized Low-Energy Model Energy Performance: Warm 

Climates............................................................................................................................. 136

Table D-55 Code-Compliant High-Rise Optimized Low-Energy Model Energy Performance: Cold 

Climates............................................................................................................................. 136

Table D-56 Common Practice High-Rise Optimized Low-Energy Model Energy Performance: 

Warm Climates.................................................................................................................. 137

Table D-57 Common Practice High-Rise Optimized Low-Energy Model Energy Performance: Cold 

Climates............................................................................................................................. 137

Table D-58 Low-Rise Optimized Low-Energy Model Cost Performance: Warm Climates.................. 138

Table D-59 Low-Rise Optimized Low-Energy Model Cost Performance: Cold Climates .................... 138

Table D-60 Code-Compliant High-rise Optimized Low-Energy Model Cost Performance: Warm 

Climates............................................................................................................................. 139

Table D-61 Code-Compliant High-Rise Optimized Low-Energy Model Cost Performance: Cold 

Climates............................................................................................................................. 139
xviii

Table D-62 Common Practice High-Rise Optimized Low-Energy Model Cost Performance: Warm 

Climates............................................................................................................................. 140

Table D-63 Common Practice High-Rise Optimized Low-Energy Model Cost Performance: Cold 

Climates............................................................................................................................. 140

Table D-64 Low-Rise Simple Payback Results....................................................................................... 141

Table D-65 Code-Compliant High-Rise Simple Payback Results........................................................... 141

Table D-66 Common Practice High-Rise Simple Payback Results......................................................... 141
1 

1.0 Introduction

According to the 2003 Commercial Building Energy Consumption Survey (CBECS), office 

buildings in the United States comprise roughly 12 billion ft2 (1.1 billion m2) of floor space and 

consume about 93 kBtu/ft2·yr (1055.5 MJ/m2) of site energy (177.8 kBtu/ft2·yr [2017.8 MJ/m2] 

primary energy) on average. Office buildings represent nearly one-fifth of all delivered energy 

consumed by commercial buildings, and are therefore an important focus for energy efficiency 

improvements (EIA 2005). 

Our goal is to investigate the feasibility of reducing energy use by 50% in newly constructed 

large office buildings across the United States relative to one built to comply with the minimum 

requirements of ANSI/ASHRAE/IESNA Standard 90.1-2004 (ASHRAE 2004c). We build on 

earlier research about energy savings opportunities in small office buildings (Jarnagin, Liu et al. 

2006) and medium office buildings (Thornton, Wang et al. 2009). Additional analysis is 

required for the large office case because office buildings are designed differently depending on 

their size, especially their mechanical heating, ventilating, and air conditioning (HVAC) 

equipment. Our intended audience includes energy modelers who wish to simulate low-energy 

large office buildings as part of the design process and engineers who wish to delve into the 

detailed assumptions underlying our results as part of designing low-energy buildings. We make 

design recommendations at a conceptual level of detail as a basis for the future development of 

more detailed design and implementation recommendations for a prospective Advanced Energy 

Design Guide for Large Office Buildings. 

Large office buildings, where large refers to total floor area, are built in diverse shapes and sizes. 

This report attempts to capture energy savings in low-rise large office buildings, using a 4-floor 

prototype, and high-rise office buildings, using a 12-floor prototype. Both have the same total 

floor area of 460,800 ft2

 (42,810 m2), identical to the U.S. Department of Energy (DOE) 

Reference Building large office model (Deru, Field et al. 2010). We recognize that many factors 

drive large office building envelope design and that a glass curtain wall construction with high 

window-to-wall area ratio (WWR) is a popular architectural choice (Wilson 2010). Although 

this construction may not meet the prescriptive requirements of ASHRAE 90.1-2004 in many 

locations, we explore whether it limits the achievable whole-building energy savings.

We use Appendix G of ASHRAE 90.1-2004 (ASHRAE 2004b) to define certain aspects of our 

baseline building design, but it includes only a subset of building energy uses and specifies

energy cost as a performance metric. This report encompasses all building energy consumption 

terms and uses site energy (the energy delivered to the building) as the primary energy 

performance metric, as required by the original project mandate. Savings are also presented 

using other commonly used metrics of energy consumption. Aspects of the baseline not 

governed by ASHRAE Standards, such as miscellaneous electric loads, are defined according to 

industry feedback and industry case studies. 

Reports like this one are often referred to as Technical Support Documents, or TSDs. They are 

detailed compilations of modeling assumptions, analysis techniques, and results that provide the 

technical basis for recommending building design packages that achieve a desired level of net 

energy savings compared to a baseline model. Historically, a separate series of TSDs was 

written for a particular energy savings level covering multiple commercial building types. Some 

of these have led to the production of volumes in the American Society of Heating, Refrigerating 
2 

and Air-Conditioning Engineers (ASHRAE) Advanced Energy Design Guide (AEDG) series. 

The AEDGs are user-friendly publications containing the TSD design recommendations plus 

relevant case studies and best practices tips. The TSDs and AEDGs are part of an 

interorganizational effort to facilitate the design, construction, and operation of more efficient 

buildings, with the eventual goal of achieving buildings so efficient that their operational energy 

consumption can be cost effectively met by on-site renewable energy generation (Torcellini 

2006). The first phase of AEDGs concentrated on achieving 30% energy savings versus 

buildings designed to meet the minimum requirements of ANSI/ASHRAE/IESNA Standard 

90.1-2004 (ASHRAE 2004c). 

This study is part of a second phase to provide technical guidance that architects, designers, 

contractors, developers, owners, and lessees of large office buildings can use to achieve wholebuilding net site energy savings of at least 50% compared to a baseline defined according to the 

minimum requirements of ASHRAE Standard 90.1-2004 (and ASHRAE 62.1-2004 (ASHRAE 

2004b), needed to specify minimum ventilation requirements which also impact building energy 

use) for new construction. This TSD will result in the production of a prospective Large Office 

50% AEDG, in support of the ASHRAE Vision 2020 Committee and AEDG Scoping Committee 

goals to enable interested parties to achieve 50% energy savings by 2010 (Mitchell, Brandmuehl 

et al. 2006; Jarnagin, Watson et al. 2008). This work will also reach its intended audience 

through the DOE-sponsored Retailer Energy Alliance (DOE 2008b). 

Our recommendations are tailored by climate zone and address building envelope, including 

infiltration through walls and doors, fenestration quantities and types, electrical lighting systems, 

daylighting, HVAC systems, outside air (OA) treatment, plug load schedules, and photovoltaic 

(PV) systems. The recommendations should be used as starting points only; they are not 

intended to be part of a code or standard. Our approach can be taken as a model of a simulationbased approach to preliminary design of a large office building with a specific advanced energy 

savings target.

This TSD was developed by the Commercial Buildings Research Group at the National 

Renewable Energy Laboratory (NREL), under the direction of the DOE Building Technologies 

Program. It builds on previous work (Hale 2008; Hale, Macumber et al. 2008) at NREL that 

established a basic methodology for finding building designs that achieve 50% energy savings 

over ASHRAE 90.1-2004 using the EnergyPlus (DOE 2010) model in Opt-E-Plus (NREL 2010), 

an optimization framework developed at NREL. Fundamental energy modeling inputs have 

been vetted through internal and external reviews. The number of climate zones was reduced 

from 16 to 6 to reduce overall simulation time and allow more time for analysis. These zones

still capture climate variability across the country. 

This analysis begins with a low-energy configuration inspired by Thornton, Wang et al. (2009) 

and real case studies of high-performance office buildings rather than a “blind” sequential-search 

optimization to completely determine the low-energy design as used by Hale, Leach et al. (2009) 

and Leach, Hale et al. (2009). This choice was made for two reasons: 

• A large number of data and analyses on energy-efficient office buildings are available

from which best practices can be drawn (DOE and NREL 2010). 

• The optimization platform Opt-E-Plus, which was used in previous TSD efforts, does not 

allow substitution of HVAC mechanical systems in the same way as many other energy 

efficiency measures (EEMs). 
3 

We had to specify an HVAC system for the low-energy case a priori and then use Opt-E-Plus to 

optimize its parameters and other building features, such as wall insulation and WWR, to “tune” 

the low-energy design to maximize energy savings or achieve similar savings (at least 50%) at 

lower cost. 

The design of NREL’s Research Support Facility (RSF) is particularly relevant. This new 

220,000 ft2 (20,440 m2) four-story large office building with a central data center was designed to 

use 35 kBtu/ft2

∙yr (400 MJ/m2∙yr)—half the energy used by a minimally ASHRAE 90.1-2004 

code-compliant building in the same climate zone (Colorado) and less than 40% of that used by 

an average U.S. office building. Consistent with the recommendations of Thornton, Wang et al. 

(2009), the RSF uses a radiant in-slab heating and cooling system with a dedicated outdoor air 

system (DOAS) featuring energy recovery and demand control ventilation (DCV). The RSF also 

features a 60-ft (18.3-m)-wide cross section and high aspect ratio along an east–west axis that is 

designed to maximize access to daylight. Because the RSF represents the state-of-the-art in lowenergy large office building design, it is an excellent reference for low-energy large office 

mechanical system design and baseline and low-energy large office construction performance 

and cost specifications. Because our low-energy building configurations are largely based on the 

RSF design, an added benefit is that it allows us to assess how well the RSF design might 

perform in different climate zones. A data center is included in the baseline and low-energy 

prototypes; its energy savings are modeled based on best practices implemented in the RSF 

design. 

The radiant heating and cooling with DOAS strategy of the RSF and recommended by Thornton, 

Wang et al. (2009) represents one way, but not necessarily the only way, to achieve 50% energy 

savings. The reasons for this choice are explained in the following sections. Exploring the full 

range of possible mechanical HVAC systems for low-energy design is outside the scope of this 

study and is left to future work. 

1.1 Objectives

The modeling and analysis described in this report are intended to: 

• Develop recommendations that meet a quantitative goal. The energy savings goal is a 

specific relative energy savings value, not an approximate target. We used wholebuilding energy simulation to verify all recommendation sets to give at least 50% net site 

energy savings compared with Standard 90.1-2004. The savings are calculated on a 

whole-building energy consumption basis, which includes unregulated loads. Lowenergy building configurations exceeding 50% savings are included in the results; 

however, the final energy savings numbers are inherently uncertain. 

• Present a basic economic analysis of the selected design package. The capital and 

energy costs of the baseline and low-energy designs are compared, and simple wholebuilding payback analysis is performed for the low-energy design package. 

• Investigate and communicate the benefits of integrated design. An EnergyPlus-based 

building optimization tool, Opt-E-Plus, is used to capture the interaction between 

building systems. It enables us to identify design measures that work together to achieve 

the desired energy savings level most cost effectively, so one building subsystem is not 

optimized at the expense of others. 
4 

• Incorporate review of modeling assumptions by industry representatives. We 

circulated a condensed compilation of baseline and low-energy cost and performance 

assumptions to industry partners and engineering firms. We incorporated many of their 

comments, and will consider others for future work. 

• Explore the implications of energy metrics on low-energy building configurations. 

Although the analysis uses site energy use to determine 50% savings, low-energy 

building performance is also compared to baseline simulations using source energy, 

energy cost, and energy-related emissions to show how relative savings change when 

viewed through these metrics. 

• Compare ASHRAE 90.1-2004 to ASHRAE 90.1-2007 as they apply to large office 

buildings. Low-energy building energy use and cost are benchmarked against ASHRAE 

90.1-2007 (ASHRAE 2007b) as well as 90.1-2004 so interested parties can evaluate the 

progression of Standard 90.1. It also demonstrates how a percent energy savings target is 

influenced by a moving baseline. 

• Investigate sensitivity to building footprint. We analyzed the impact of building aspect 

ratio on energy use and building life cycle cost. We used energy simulation for the lowrise prototype to study the trade-off between increased HVAC loads caused by energy 

transfer through greater envelope area and energy savings through increased access to 

daylight when a building is stretched. 

• Assess the impact of glass curtain constructions on energy use intensity (EUI). Glass 

curtain constructions are used prevalently in large office design, especially in high-rise 

construction, to reduce construction costs and improve aesthetics. Among glass curtain 

constructions, those with high WWRs and low spandrel panel insulation values are 

especially common. We used a 12-story high-rise construction (which has the same 

whole-building floor area as the 4-story low-rise construction) to assess the impact of this 

practice. We explore how this high WWR, low wall insulation case differs from an 

ASHRAE 90.1-2004-compliant glass curtain construction case and how it affects the 

achievability of 50% net site energy savings with respect to a minimally code-compliant 

case.

1.2 Scope

We provide recommendations and technical guidance to help office design teams decrease their

fossil fuel energy use in new construction, and possibly in retrofit projects. To ease the burden 

of designing and constructing energy-efficient large office buildings, we describe a set of designs 

that reach the 50% energy savings target for each climate zone (see Section 4.2) for new 

construction. They represent one way, but not the only way, to reach 50% energy savings. 

This TSD is not intended to substitute for rating systems or other references that address the full 

range of sustainable issues, such as acoustics, productivity, indoor environmental quality, water 

efficiency, landscaping, and transportation except as they relate to operational energy 

consumption. 
5 

1.3 Report Organization

Section 2.0 introduces our modeling methodology, including definitions, analysis framework, 

post-processing of results, and industry review. Section 3.0 describes our modeling assumptions, 

starting with extensible prototype models, followed by detailed cost and performance data for 

climate-specific baseline buildings and EEMs, which may provide energy savings in one or more 

climates. Section 4.0 contains the results of the modeling study, including cost and EUI of 

baseline and low-energy models, and the EEMs chosen in different climate zones to reach the 

energy savings goal. We show how the baseline energy use changes when using ASHRAE 90.1-

2007 instead of 90.1-2004, and compare baseline results with the 2003 CBECS dataset. We also

investigate the impact of glass curtain construction on energy use and trade-offs in high-aspectratio offices between increased envelope energy transfer and increased savings from passive 

strategies such as daylighting. Section 5.0 includes suggestions for future work, and Section 6.0 

provides conclusions. The appendices contain schedules for prototypes, baseline and low-energy 

models, and metric unit tables. 
6 

2.0 Methodology

This section describes the methodology and assumptions used to develop early-stage building 

designs that achieve 50% energy savings. We begin with an overall approach to modeling 

energy savings in large office buildings, including energy and economic metrics and the scope of 

EEMs we consider. We describe how models that meet the 50% energy savings goal were 

determined and conclude with a summary of our solicitations for industry and engineering 

review and the results of that activity.

2.1 Guiding Principles

Our objective is to find large office building conceptual designs that achieve 50% energy savings 

compared to an equivalent building designed to meet the minimum requirements of ASHRAE 

90.1-2004 and ASHRAE 62.1-2004. Percent net site energy savings and Five-Year Total Life 

Cycle Cost (5-TLCC) are used as the primary performance metrics for candidate buildings. Of 

course, other objectives could be used; these choices best fit the project mandate. Careful 

attention is paid to simulated comfort indices to ensure indoor environmental quality is not 

sacrificed in the interest of energy savings or costs (see Section 2.4.4.2). 

Achieving 50% energy savings cost effectively requires an integrated building design—an

approach that analyzes buildings as holistic systems rather than as disconnected collections of 

individually engineered subsystems. We analyze the complex interactions between building 

systems and ensure the building will operate as efficiently as possible. Consider the building 

envelope, which influences energy use in multiple ways by separating the building from the 

exterior environment and by providing daylight to the interior. Integrated design weighs the 

daylighting and view benefits of increasing WWR and analyzing the impact on heat transfer. 

This enables a design team to strike an optimal balance between daylighting and heat gain or 

loss.

Candidate low-energy designs are chosen by applying one or more design features to a 

minimally code-compliant baseline building. These EEMs have an impact on energy use. We 

use the following guiding principles to develop a list of prospective EEMs: 

• We recommend off-the-shelf technologies that are available from multiple sources, as 

opposed to technologies or techniques that are available only in limited quantities or from 

one manufacturer. 

• The EEMs are limited to technologies that can be modeled with EnergyPlus. 

The methodology for developing candidate integrated designs is discussed in Sections 2.4.2 and 

2.4.3. The quality assurance and quality control (QA/QC) protocols for assessing occupant 

comfort, sizing equipment, and evaluating thermal performance are detailed in Section 2.4.4. 

The designs are also expected to be reasonably cost effective, but not necessarily the most cost 

effective, given the difficulty of obtaining accurate and timely cost data on all the technologies 

required to reach 50% savings in all climate zones. Costs can also differ dramatically by project, 

across the country, and over time. We thus do not rely heavily on cost criteria to select a lowenergy design; rather, we begin with a preliminary low-energy strategy based on energy 

efficiency best practices and then refine it with Opt-E-Plus, which optimizes net site energy 

savings with respect to life cycle cost. We then compare the life cycle cost of the optimized 50% 

design to that of the baseline building and report the results of a simple payback analysis.
7 

2.2 Definitions

This section specifies how we calculate building energy use and percent energy savings relative 

to ASHRAE 90.1-2004. We describe the site boundary used to calculate net site energy use, 

how Appendix G of ASHRAE 90.1 is applied, and how energy uses outside the scope of the 

ASHRAE Standards are incorporated. 

2.2.1 Energy Use

Building energy use can be calculated in several ways, depending on where the energy is 

assumed to originate and which categories of energy consumption are included in the calculation. 

For example, one must decide whether to measure energy consumption at the utility meter or to 

consider all the generation, transmission, and distribution losses between the extraction of the 

energy carrier and its eventual consumption. Our assumptions follow. 

2.2.1.1 Energy Metrics

The percent energy savings goal is based on net site energy use: the amount of energy (typically 

electricity or natural gas) the utility delivers to a building minus any renewable energy generated 

within its footprint and exported. Reducing building energy consumption through integrated 

design and energy efficiency is considerably more cost effective than adding renewable 

generation (see Section 4.2.5). 

Net site energy savings are the primary energy metric by which we evaluate building models; 

however, other metrics, such as source energy savings, energy cost savings, and energy emission 

savings, could also be used (Torcellini 2006; Deru and Torcellini 2007). The energy metrics 

used for this study are defined as follows:

• Site Energy. The energy directly consumed at the building. It is typically measured 

with utility meters.

• Source Energy. The sum of the energy consumed at the building and the energy 

required to extract, convert, and transmit that energy from the source to the building. To 

calculate a building’s total source energy, imported and exported energy are multiplied 

by the appropriate site-to-source conversion multiplier.

• Energy Cost. The economic cost of energy services and energy used by the building. 

• Energy Emissions. The emissions produced from the building’s energy use, including 

emissions for processes such as extraction and transportation. 

Each metric has advantages and disadvantages for calculation and interpretation, and each favors 

different technologies and fuel types. This TSD uses net site energy savings to be consistent 

with the previous TSD and AEDG work. For completeness, however, and to explore how the 

choice of an energy metric might affect the optimization results, selected low-energy building 

models are evaluated against the energy metrics of source energy savings, energy cost savings, 

and emissions savings.

We convert from site energy to source energy using multiplication factors of 3.37 for site 

electricity use and 1.09 for site natural gas use (Deru and Torcellini 2007); we convert site 

energy to energy cost using our utility tariff structure (see Section 3.1.2.5). We convert from site 

energy to energy emissions using multiplication factors of 1.574 lbCO2/kWh (0.714 

kgCO2/kWh) of electricity use and 0.134 lbCO2/1000ft3

 (2.146 kgCO2/1000m3) of natural gas 

use (0.012 lbCO2/1000ft3 [0.186 kgCO2/1000m3] for precombustion emissions and 0.122 
8 

lbCO2/1000 ft3 [1.960 kgCO2/1000 m3] for on-site combustion emissions) (Deru and Torcellini 

2007). 

2.2.1.2 Whole-Building Energy Use

Historically, energy savings have been expressed in two ways: for regulated loads only and for 

all loads (the whole building). Regulated loads do not include plug loads, which are not 

regulated by energy code. Whole-building energy savings calculations, on the other hand, 

include regulated and unregulated loads. Achieving whole-building savings is usually more 

challenging, but more accurately captures a building’s impact on the national energy system. 

We use the whole-building energy savings method to determine 50% energy savings, in line with 

the current ASHRAE and Leadership in Energy and Environmental Design (LEED) practices 

specified in Appendix G of ASHRAE 90.1-2004 and in LEED 2.2 (USGBC 2006). We do not, 

however, limit our recommendations to the regulated loads, as in the 30% AEDGs; we also make 

recommendations for plug load densities, which comprise a large fraction of large office building 

energy use. 

2.2.2 Percent Energy Savings

Percent energy savings are measured with respect to a minimally code-compliant building as 

described in Appendix G of ASHRAE 90.1-2004 (ASHRAE 2004c). We took the following 

steps to determine 50% savings: 

1. Define architectural program characteristics (design aspects not addressed by ASHRAE 

90.1-2004 such as schedules, constructions, plug load densities, and building geometry) 

for typical large office buildings, thereby defining prototype models. 

2. Create baseline energy models for each climate zone that are elaborations of the 

prototype models and are minimally compliant with ASHRAE 90.1-2004 and ASHRAE 

62.1-2004. 

3. Create a list of EEMs that can be applied to the baseline models to create candidate lowenergy models. 

4. Select low-energy models for each climate zone that achieve 50% energy savings 

compared to the baseline models, giving preference to solutions that have low 5-TLCCs. 

2.2.3 ASHRAE 90.1-2004 Baseline

The 50% savings achieved by each low-energy building model is demonstrated in comparison 

with a baseline model that minimally satisfies the requirements of ANSI/ASHRAE/IESNA 

Standard 90.1-2004 (ASHRAE 2004c). The baseline models are constructed in a manner similar 

to what was used in the previous TSDs (Hale 2008; Hale, Macumber et al. 2008), and in 

compliance with Appendix G of Standard 90.1-2004 when appropriate. Notable deviations from 

Standard 90.1-2004 Appendix G include: 

• Glazing amounts (window area and skylight area) and properties are allowed to vary 

between the baseline and low-energy models. We thereby demonstrate the effects of 

optimizing window area for daylighting and thermal considerations. 

• Net site energy use, rather than energy cost, is used to calculate energy savings.
9 

• Mass walls are modeled in the baseline and low-energy low-rise models and spandrel 

glass wall panels are modeled in the baseline and low-energy high-rise models to ensure 

our baselines accurately reflect typical design practice.

See Sections 3.3.4.2 and 3.3.4.3 for baseline assumptions regarding unregulated loads (generated 

by plug load equipment and data center). 

2.3 Building Energy Modeling Methodology

2.3.1 EnergyPlus

EnergyPlus Version 5.0 (DOE 2010), a publicly available building simulation engine, was used 

for all energy analyses. The simulations were managed with the NREL analysis platform, OptE-Plus, which transforms user-specified, high-level building parameters (building area, internal 

gains per zone, HVAC system configuration, etc.) stored in eXtensible Markup Language 

(XML) files into an input file for EnergyPlus. Opt-E-Plus can automatically generate the XML 

files, or it can manage XML files that have been assembled or modified elsewhere. Working 

with the XML files is much faster than modifying EnergyPlus input files directly, because a 

single XML parameter can map to multiple EnergyPlus inputs. 

We selected EnergyPlus because it is a detailed DOE simulation tool that computes building 

energy use based on the interactions between climate, building form and fabric, internal gains, 

HVAC systems, and renewable energy systems. The simulations were run with EnergyPlus Bug 

Fix Version 5.0.0.036 compiled on local personal computers. EnergyPlus is a heavily tested 

program with formal ASHRAE Standard 140 validation protocol repeated for every release 

(ASHRAE 2007a). 

2.3.2 Climate Zones 

The AEDGs and TSDs contain a unique set of energy efficiency recommendations for each 

International Energy Conservation Code (IECC)/ASHRAE climate zone. The 8 zones and 15 

subzones in the United States are depicted in Figure 2-1. The zones are categorized by heating 

degree days and cooling degree days, and range from the very hot zone 1 to the very cold zone 8. 

Subzones indicate varying moisture conditions. Humid subzones are designated by the letter A, 

dry subzones by B, and marine subzones by C. This document may also be beneficial for 

international users, if the location of interest can be mapped to a climate zone (ASHRAE 2006). 
10

Figure 2-1 DOE climate zones and representative cities

To provide a concrete basis for analysis, we designate the 16 specific locations (cities) used by 

Deru, Field et al. (2010) as representatives of their climate zones. The cities are marked in 

Figure 2-1 and listed here. We chose larger cities, as their weather and utility data directly apply 

to a large fraction of building floor area. Two cities are provided for Zone 3B to account for the 

microclimates in California. 

Zone 1A: Miami, Florida (hot, humid)

Zone 2A: Houston, Texas (hot, humid)

Zone 2B: Phoenix, Arizona (hot, dry)

Zone 3A: Atlanta, Georgia (hot, humid)

Zone 3B: Las Vegas, Nevada (hot, dry) and Los Angeles, California (warm, dry)

Zone 3C: San Francisco, California (marine)

Zone 4A: Baltimore, Maryland (mild, humid)

Zone 4B: Albuquerque, New Mexico (mild, dry)

Zone 4C: Seattle, Washington (marine)

Zone 5A: Chicago, Illinois (cold, humid)

Zone 5B: Denver, Colorado (cold, dry)

Zone 6A: Minneapolis, Minnesota (cold, humid)

Zone 6B: Helena, Montana (cold, dry)

Zone 7: Duluth, Minnesota (very cold)

Zone 8: Fairbanks, Alaska (extremely cold)

In a departure from previous TSD work, in which simulations were run for each of the 16 

locations, simulations in this study were run for a subset of six cities that we feel represent a 

more general, but still all-encompassing, categorization of climate types: hot and humid (Miami, 
11

1A), hot and dry (Las Vegas, 3B-NV), cold and humid (Chicago, 5A), cold and dry (Denver, 

5B), marine (Seattle, 4C), and very cold (Duluth, 7). We use the same Typical Meteorological 

Year weather files in each city for baseline and low-energy simulations. 

2.4 Modeling Protocol

Our modeling process followed a four-step sequence, each of which is described in more detail 

in Sections 2.1.4 to 2.1.4: 

1. Establish minimally code-compliant baseline models. 

2. Create a preliminary 50% energy savings model. 

3. Refine the preliminary low-energy model using Opt-E-Plus. 

4. Perform a QA/QC assessment on the baseline and low energy models to ensure the 

simulated buildings can meet their loads and provide a comfortable indoor environment; 

if not, rerun the models. Figure 2-2 visualizes the process.

Figure 2-2 Modeling Protocol Flowchart

2.4.1 Baseline Model Specification

To establish a benchmark for assessing energy savings, we chose building parameters (such as 

wall construction to provide particular minimum opaque envelope R-values and OA delivery 

rates) to meet the minimum requirements of ASHRAE 90.1-2004 and ASHRAE 62.1-2004. We 

applied these parameters to a generic high-level building prototype model to create a codecompliant building for each location, then manually added airside economizers to the baseline 

buildings in climate zones 3B-NV, 4C, 5A, 5B, and 7 (see Section 2.3.2 for climate zone 

definitions and Section 3.3) for details of the baseline model definitions. 

2.4.2 Preliminary 50% Energy Savings Design Selection

The EEMs (see Section 3.4) represent the palette of design options we considered to craft 50% 

energy saving designs. This choice was influenced by Thornton, Wang et al. (2009) and DOE 

and NREL (2010). The strategies reflect the experience of the NREL Commercial Buildings 

Group with analyzing low-energy building design and performance and the example provided by 

the RSF. 

We used engineering judgment and considered optimization engine limitations to select a subset 

from the full list of strategies to be included in all low-energy models. Opt-E-Plus is limited in 

HVAC system substitution, so we used the RSF design and the results of Thornton, Wang et al. 
12

(2009) to fix our low-energy HVAC system as a radiant heated and cooled system with DOAS. 

Because of the aggressive energy savings target, we also designed the DOAS with climatespecific energy recovery considerations. We added air barriers and vestibules to reduce 

uncontrolled OA infiltration as default options to the low-energy design to help ensure occupant 

comfort and to avoid condensation on the radiant cooling surfaces. 

We then used the results from Hale, Leach et al. (2009) and Leach, Hale et al. (2009) to construct 

preliminary low-energy designs aimed at achieving the 50% savings goal in each climate zone. 

In some cases, the preliminary designs were able to reach the 50% savings goal, so the 

optimization goal (see Section 2.4.3) was to determine the full range of energy savings available 

and to maximize cost effectiveness from a life cycle standpoint at each savings level. If the 

preliminary designs fell short of the 50% savings goal, the optimization process also helped 

determine whether 50% net site energy savings were achievable and, if so, whether it was 

possible without an on-site renewable energy source. 

2.4.3 Low-Energy Model Refinement

Once we identified preliminary 50% savings low-energy designs, we used Opt-E-Plus to alter 

design parameters (such as window solar heat gain coefficient [SHGC] or exterior wall 

insulation) and to refine those designs in each climate. This further increased net site energy 

savings and decreased 5-TLCC (see Section 3.1.2.6). The Opt-E-Plus environment generates 

new building energy models with altered designs from a specified palette of options, manages 

EnergyPlus simulations, and graphs the 5-TLCC and energy use of the many building 

permutations.

The building models are first specified in high-level XML files. The Opt-E-Plus preprocessor 

then translates them into EnergyPlus input files. The output of the optimization is a 5-TLCC 

(described in Section 3.1.2.6 and calculated using the economic data in Sections 3.1.2.4, 3.3, and 

3.4) versus percent energy savings plot (see Figure 2-3 for an example) that includes one data 

point for each building, and a curve that represents a design path from the preliminary 50% 

energy saving building to the building with maximum percent savings along which each 

incremental step represents the most cost-effective method to configure a building to achieve that 

level of energy savings. 
13 

Figure 2-3 Example Opt-E-Plus output: climate zone 1A (Miami, Florida) 

The data points (low-energy building configurations) along the portion of this curve which starts 

at the minimum cost point and continues toward higher percent energy savings are called Pareto 

points. Between Pareto points is a trade-off between energy savings and cost. For a given 

Pareto point, moving to a less expensive building necessitates that it will have a lower energy 

savings level, and moving to a more energy-efficient building necessitates higher 5-TLCC. The 

set of Pareto points determines a Pareto front, which is generally a curve that represents the most 

cost-effective pathway to achieving low-energy buildings (given the limitations of our input data 

and search algorithm). An iterative search algorithm is used to avoid an exhaustive search of all 

possible EEM combinations. Each iteration starts at the most recently found Pareto point, and 

then configures, simulates, and analyzes the full set of models that are single parameter 

perturbations from that point. The least-cost perturbation of the set becomes the next Pareto 

point. The algorithm stops when it cannot find additional Pareto points. 

2.4.4 Quality Assurance/Quality Control Protocol 

An important aspect of simulation-based analysis is establishing a protocol to manage QA/QC. 

We focused our QA/QC analysis on system sizing and operation as they relate to EnergyPlus 

simulations of conditioning capacity and control, as well as occupant comfort, safety, and wellbeing. 

2.4.4.1 System Sizing 

Sizing determines whether (1) a given system can meet thermal loads; and (2) how much energy 

it consumes. If a system is undersized, it may be unable to operate as designed; if it is oversized, 

it may use more energy than an equivalent, properly sized system. In EnergyPlus, some systems 

are sized automatically based on the results of design day-based sizing routines; others are hardsized with precalculated capacities. Regardless, we used a QA/QC protocol to ensure the 

resulting building model operates as intended and monitored the following system metrics: 

• Hours outside heating and cooling set points during occupied hours. Hours outside 

heating and cooling set points indicate space conditions are outside the desired 

Net Site Energy Percent Savings [%]

-20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Total Life Cycle Cost (TLCC) Intensity [$/ft^2]

130

128

126

124

122

120

118

116

114

112

110

108

106

104

102
14

operational dead band, possibly because of undersized system components. For cases 

with significant hours outside these set points, we examined equipment run time fraction 

(or part load ratio) values to determine if components were running at full capacity for 

extended periods (an indication of undersizing) and adjusted the sizing factors 

accordingly.

• HVAC component part-load ratios (PLRs). A component operating at PLR lower 

than 80% of sized capacity at all times throughout the year indicates oversizing. We

tracked these and adjusted the sizing factors accordingly to ensure all components 

operated at PLRs above 80% during periods of peak load.

• Space ventilation rates. Proper ventilation (as specified by ASHRAE 62.1-2004) is 

vital to occupant well-being. We confirmed that the scheduled OA delivery rates 

specified as model inputs were being supplied during all occupied and unoccupied 

periods. This is especially important with VAV systems for which flow to a given zone 

depends on load.

2.4.4.2 System Operation

Even a properly sized system must be controlled to operate as desired and use the minimum 

amount of energy. In EnergyPlus, control is often determined through scheduling; for more 

advanced control requirements, EnergyPlus features an energy management system (EMS) tool 

that allows users to update system operation based on simulated indoor and outdoor 

environmental conditions. To ensure proper system operation, we tracked the following 

conditions: 

• Time not comfortable based on simple ASHRAE 55-2004. Standard 55 (ASHRAE 

2004a) uses space air temperature and relative humidity (RH) to determine occupant 

comfort; accordingly, monitoring the number of hours outside of comfort can be useful in 

identifying humidity issues. When the number of hours in violation of Standard 55 was 

large, we used output variables to analyze RH levels. RH values above 60% (based on 

typical comfort requirements for an office space) indicated that system operation needed 

to be modified to mitigate humidity issues. This led us to implement nighttime humidity 

control logic to allow the HVAC system to cycle for humidity control (in addition to the 

standard temperature control cycling) to keep RH levels below 60% during unoccupied 

hours. It also enabled us to confirm that daytime system operation produced humidity 

levels within the comfort range. 

• Zone dew point exceeding radiant surface temperature. A major concern with radiant 

cooling as it relates to occupant safety, occupant satisfaction, and building equipment—

especially in humid climates—is condensation. If the radiant surface temperature falls

below the dew point, condensation will begin to form on the radiant surface, posing a 

potentially serious health risk to occupants. Accordingly, we used EMS to monitor for 

conditions in which condensation might be expected to occur. We specified control of 

the radiant system such that it would temporarily turn off when normal operation, as 

currently defined by our control logic (see Section 3.4.4.5.1), would result in 

condensation. In the future, we may further develop this control to allow for the system 

to continue operating during such periods; by increasing the supply water temperature to 

raise the radiant surface temperature above the space dew point, we will in many cases be 

able to provide a reduced level of cooling as opposed to none at all. 
15

3.0 Model Development and Assumptions

This section documents the development of model inputs. Section 3.1 describes assumptions 

that apply to the entire study, including our economic assumptions and methodology. Section

3.2 describes the programmatic characteristics of a typical large office building and uses them to 

develop high-level prototype models. Section 3.3 elaborates on Section 3.2 to define the 

EnergyPlus baseline models that provide a reference for determining percent energy savings and 

are minimally compliant with Standard 90.1-2004. Section 3.4 describes the EEMs used to 

create low-energy models. 

3.1 Analysis Assumptions

Most of Section 3 is concerned with the assembly of building energy and cost models, 

component by component. Here we touch on two types of assumptions that color our entire 

analysis: (1) the often implicit assumptions required to conduct building energy simulation 

studies; and (2) our economic model. 

3.1.1 Integrity of Simulation Models

We made the following assumptions:

1. The models developed in this work represent typical large office buildings well enough to 

provide climate-specific guidance for the kinds of design strategies that should be 

considered first when planning a high-performance large office building. 

2. These virtual buildings are well maintained and operated. 

The models created for this report do not represent actual buildings, and as such have not been 

tested against measured data; however, they are informed by EIA (2005), Deru, Field et al. 

(2010), and Thornton, Wang et al. (2009). They include detailed suggestions from industry 

experts. The model results are subjected to quality checking to ensure simulated comfort is not 

sacrificed to energy savings. Anticipated energy savings are often not achieved, or erode over 

time, because buildings are not properly commissioned, operated, or maintained. For example, 

economizer dampers are notorious for failing. 

3.1.2 Economics

One outcome of this project is a recommended cost-optimized design package for achieving 50% 

energy savings over code in a large office building. The objective economic function of interest 

is 5-TLCC, which is further described in Section 3.1.2.6. 

3.1.2.1 Building Economic Parameters

Our SOW mandates that the recommended design package be analyzed for cost effectiveness 

based on a five-year analysis period, which is assumed to be acceptable to a majority of 

developers and owners. The other basic economic parameters required for the life cycle cost 

calculation were taken from Balboni (2008) and OMB (2010). 

This analysis uses the real discount rate, which accounts for the projected rate of general 

inflation in the Report of the President’s Economic Advisors, Analytical Perspectives, and is 

equal to 1.6% for a five-year analysis period (OMB 2010). By using this rate, we avoid 

explicitly accounting for energy and product inflation rates. 

The economic parameters that help shape the cost side of this study are summarized in Table 3-1. 
16

Table 3-1 Economic Parameter Values

Economic Parameter Value Data Source

Analysis period 5 years DOE

Discount rate 1.6% OMB

O&M cost inflation 0% OMB

Gas cost inflation 0% OMB

Electricity cost inflation 0% OMB

Bond fee 10% RSMeans

Contractor fee 10% RSMeans

Contingency fee 12% RSMeans

Commissioning fee 0.5% Assumption

3.1.2.2 Energy Efficiency Measure Cost Parameters

Each EEM has its own cost data. The cost categories for each are the same, but the units vary: 

• Units define how the EEM is costed (e.g., $/m2, $/kW cooling, $/each). 

• Expected life is the time (in years) that the EEM is expected to last. Once that period has 

expired, the EEM is replaced; that is, the full materials and installation costs are added to 

that year’s cash flows. Note that replacement costs are negligible when using a five-year 

analysis period. 

• Capital cost is the per-unit cost of all materials and installation required for the EEM.

• Fixed operations and maintenance (O&M) is a per-unit, per-year cost.

• Variable O&M is a per-unit, per-year cost.

We report fixed and variable O&M costs as a single, fixed, annual maintenance cost.

3.1.2.3 Costing Methodology

Unless otherwise stated, all costs are in 2010 dollars. Costs originally from another year are 

adjusted according to the Consumer Price Index inflation calculator (Labor 2010). 

The cost data used for the EEMs and the baseline walls, roofs, windows, lighting systems, and 

HVAC equipment are adapted from multiple sources. The cost data sources and values are listed 

explicitly throughout Section 3.3 and Section 3.4. 

3.1.2.4 Baseline Capital Costs

Cost estimates in the early planning stages are not necessarily accurate. This report includes data 

about some technologies that are not widely implemented, so the reported costs may be less 

accurate than anticipated. To start with reasonable baseline costs, we adjust our baseline cost per 

unit area to match that found for large office buildings by Balboni (2008) ($115.77/ft2

[$1,246/m2] for low-rise buildings and $124.86/ft2 [$1,344/m2] for high-rise buildings). The cost 

is implemented in Opt-E-Plus under a category that is not affected by any EEMs. The baseline 

capital cost is therefore fixed, enabling realistic estimates of the percent change in 5-TLCC when 

the low-energy models are compared to the baselines.

3.1.2.5 Utility Tariffs

One set of utility tariffs is used for all locations to make the results from each climate zone easier 

to compare and to focus comparisons between climates on energy performance rather than utility 
17

variability. We chose Florida Power & Light’s 2008 General Service Demand (GSD-1) 

electricity tariff because of data availability, the closeness of Florida’s average commercial 

electricity rates to the national average, and the electricity demand of our models (Florida Power 

& Light 2008; EIA 2009). The tariff is summarized in Table 3-2. The tax rate is a populationweighted average of state plus average county and city sales taxes from Sales Tax Clearinghouse 

(Sales Tax Clearinghouse 2009). Even though a single tariff is used across climate zones, 

demand charges are included because they can represent a significant fraction of building 

operational costs.

Table 3-2 Electricity Tariff

Tariff Name General Service Demand

Monthly charge $33.10

Base demand charge $5.10/kW

Demand capacity charge $1.63/kW

Nonfuel energy charge $0.01392/kWh

Fuel energy charge $0.05564/kWh

Conservation energy charge $0.00133/kWh

Environmental energy charge $0.00038/kWh

Taxes 7.1%

We calculated multiple years of a national average gas tariff by averaging the Energy 

Information Administration (EIA) compilation of national average monthly prices for April 

2006 through March 2009 (EIA 2007; EIA 2009) rather than taking the previous year’s data, 

because recent prices have been volatile. The resulting tariff and source data are reproduced in 

Table 3-3 (see Table D-1 for metric units). Although using a national-average tariff might lead 

to some design solutions that are suboptimal because of regional tariff variability, it enables us to 

isolate climate variability as a driving factor in designing buildings to save energy. For specific 

case studies, we recommend considering regional tariff structures and incentives in the economic 

side of the analysis.

Table 3-3 National Average Natural Gas Tariff and Source Data in $/MCF

Month 

Year

Tariff 

2006 2007 2008 2009

January – $11.15 $11.01 $11.04 $11.07

February – $11.21 $11.32 $10.68 $11.07

March – $11.79 $11.81 $10.10 $11.23

April $11.57 $11.49 $12.44 – $11.83

May $11.61 $11.48 $13.24 – $12.11

June $11.09 $11.86 $14.39 – $12.45

July $10.98 $11.61 $15.45 – $12.68

August $11.20 $11.16 $14.04 – $12.13

September $11.16 $10.90 $13.02 – $11.69

October $10.05 $10.90 $11.83 – $10.93

November $11.05 $11.19 $11.45 – $11.23

December $11.61 $11.02 $11.32 – $11.32
18

3.1.2.6 Total Life Cycle Cost

Our objective is to simultaneously achieve 50% net site energy savings and minimize 5-TLCC. 

The 5-TLCC is the total expected cost of the whole building (capital, maintenance, and energy 

costs) over the five-year analysis period. The 5-TLCC calculation uses the real discount rate to 

account for inflation of energy and O&M costs instead of using the nominal discount rate paired 

with explicit estimates of energy and O&M inflation. 

The annual cash flow is summed over the analysis period to calculate the 5-TLCC. The annual 

energy use is assumed to be constant throughout the analysis period. Equation 3-1 defines the 

annual cash flows.

eg

J

j

Cn CCn FOM n VOM n ++ CC 













 = ∑ ++ =0

where 

Cn = cost in year n

J = total number of unique EEMs 

CCn = capital cost

FOMn = fixed O&M cost

VOMn = variable O&M cost

Cg = annual cost of gas consumption 

Ce = annual cost of electricity consumption 

The 5-TLCC is determined by Equation 3-2. 

( ) ∑= + =−

5

0 1

5 n

n

n

d

C TLCC

where

5-TLCC = present value of the 5-TLCC

Cn = cost in year n

d = annual discount rate 

3.1.2.7 Simple Payback Calculation

We also report simple payback for the low-energy models to indicate the timeframe required for 

the incremental capital and maintenance costs associated with EEM packages to be paid back by 

energy cost savings. Simple payback, in years, is determined by Equation 3-3 (Thornton, Wang 

et al. 2009). 

es

P C

CC

t 0 =

where

tP = simple payback in years 

CC0 = initial capital cost

Ces = annual energy cost savings 

(3-1)

(3-2)

(3-3)
19

Equation 3-3 assumes all incremental capital costs associated with EEM implementation are 

incurred up front and do not recur, and that overall O&M costs are consistent between the 

baseline and low-energy cases. 

3.2 Prototype Model

We surveyed a number of reports and datasets to develop typical large office building 

characteristics and obtain energy performance estimates (see individual sections for references). 

Descriptions and assumptions relevant to each building characteristic are organized into 

functional groupings. This section details aspects of the large office building models that are 

common between the baseline and low-energy cases.

We consider a 12-story high-rise prototype and a 4-story low-rise prototype. Although the highrise prototype has more floors than the low-rise prototype, its footprint area is reduced such that 

both contain the same total floor area of 460,800 (42,810 m2

), matching Deru, Field et al. (2010). 

We used CBECS 2003 data to validate the size of the floor plate for the low-rise prototype 

(115,200 ft2 [10,700 m2]). These indicate that 7 of 30 office buildings built since 1980 with total 

floor areas larger than 150,000 ft2 (13,935 m2) and five or fewer floors have floor plates between 

100,000 ft2 (9,290 m2

) and 150,000 ft2 (13,935 m2) (EIA 2005). 

We modeled the low-rise baseline building as three floors: a ground floor, a top floor, and an 

interior floor (with a multiplier of two to represent the second and third floors). The high-rise 

building, for which energy consumption is dominated by the interior floors, was modeled as a 

single interior floor with adiabatic boundary conditions on its top and bottom exterior surfaces 

(such that it represents an interior floor, as opposed to a single-story building that is exposed to 

the sky and ground on top and bottom, respectively). There are two reasons to model the highrise case:

• To explore energy implications associated with low aspect ratio high-rise constructions, 

such as energy use being dominated by interior floors that are largely isolated from the 

outside elements. 

• To assess the performance of glass curtain constructions, both in terms of common (high 

WWR, low exterior opaque envelope insulation) and best practice, code-compliant 

implementation. 

For this study, height dependence of wind speed and stack effect driven infiltration are not 

considered. 

3.2.1 Program

This section addresses building size, space types, and certain aspects of internal loads that are 

common between the baseline and low-energy models. 

3.2.1.1 Space Types

To allow building geometry (especially aspect ratio) to be manipulated during optimization, we 

modeled the prototypes such that each floor consists of a large rectangular central core zone 

surrounded by perimeter zones, measuring 20 ft (6.1 m) deep from the exterior walls on each 

side. This captures the localized thermal effects near exterior walls and the benefits of certain 

EEMs, such as daylighting, natural ventilation, and exterior wall thermal mass design. We 

selected the 20-ft [6.1-m] perimeter depth as an average characteristic length for the effects 

captured by the perimeter zones. For each category of internal loading, we calculated the overall 
20

building average and applied it to each zone. To facilitate the calculation of average building 

loads, we estimated a distribution of typical office space types for each prototype (low-rise and 

high-rise). 

Averaging space-specific ventilation requirements and internal loads across a simplified building 

geometry has drawbacks. For example, compliance with ASHRAE 62.1-2004 requires that 

space types meet ventilation requirements individually. Also, savings from strategies such as 

supply air temperature reset can be inflated when staggered loading caused by space-specific 

scheduling is not taken into account. However, the benefits associated with capturing the impact 

of aspect ratio on building energy use outweighed the drawbacks. 

The space type breakdown for each prototype is presented in Table 3-4. Space type breakdowns 

are based on the layouts of a number of large office case studies, including the RSF.

Table 3-4 Large Office Space Types and Sizes

Space Type

Low-Rise High-Rise

Floor Area 

(ft2) 

Floor Area 

(m2) 

Percent of 

Total 

Floor Area 

(ft2) 

Floor Area 

(m2) 

Percent of 

Total 

Office 393,332 36,542 85.4% 380,700 35,368 82.6%

Conference 17,992 1,672 3.9% 17,412 1,618 3.8%

Break room 7,112 661 1.5% 6,888 640 1.5%

Elevator 6,716 624 1.5% 20,148 1,872 4.4%

Restroom 11,192 1,040 2.4% 11,196 1,040 2.4%

Stairs 7,860 730 1.7% 7,860 730 1.7%

Mechanical/electrical 

room 16,596 1,542 3.6% 16,596 1,542 3.6%

Total 460,800 42,810 100% 460,800 42,810 100%

The elevator, restroom, stairwell, and mechanical room space types make up a larger fraction of 

the overall floor area in the high-rise prototype than in the low-rise prototype (12.1% versus 

9.2%). This is based on a comparison of examples of high-rise (a DOE Commercial Building 

Partnerships project) and low-rise (RSF) office floor plans, and more generally on the 

assumption that elevator floor area scales with occupancy density rather than building footprint. 

3.2.1.2 Internal Load Densities

Internal loads include the heat generated by occupants, lights, and appliances (plug and process 

loads). This section details occupancy densities, which are common between the baseline and 

low-energy models. Electric lighting and plug and process loads are detailed separately in the 

baseline and low-energy model descriptions (see Sections 3.3.4.2 and 3.4.4.3, respectively). 

3.2.1.2.1 Occupancy

Where possible, occupancy density values are defined (by space type) according to the 

prescriptions of ASHRAE Standard 62.1-2004 (ASHRAE 2004b). The mappings between space 

type and Standard and the resulting occupancy density values, both for individual space types 

and for the prototypes as a whole, are presented in Table 3-5. Values for space types without 

direct mapping to the Standard were estimated. We assumed mechanical rooms, stairways, and 

elevators would be empty most of the time, and assigned them occupancy density values of zero. 
21

Table 3-5 Occupancy Density Mapping and Peak Values

Space Type Mapping to 62.1-2004

Low-Rise High-Rise

Occupancy Density Occupancy Density

(#/1,000 ft2) (#/100 m2) (#/1,000 ft2) (#/100 m2)

Office Office::Office Space 5 5.38 5 5.38

Conference Office::Conference/Meeting 50 53.82 50 53.82

Break room Food & Beverage::Restaurant 

Dining Rooms 70 75.35 70 75.35

Elevator CUSTOM VALUE 0 0.00 0 0.00

Restroom Office::Office Space 5 5.38 5 5.38

Stairs CUSTOM VALUE 0 0.00 0 0.00

Mechanical/electrical 

room

CUSTOM VALUE 0 0.00 0 0.00

Average 7.42 7.99 7.19 7.74

The internal gains from occupants were calculated assuming 132 W (450 Btu/h) of heat per 

person (81 W [276 Btu/h] of sensible heat, and 52 W [174 Btu/h] of latent heat), which 

corresponds to the value listed for “moderately active office work” in Chapter 30 of the ASHRAE 

2005 Fundamentals Handbook (ASHRAE 2005). Occupant comfort was calculated assuming 

clothing levels of 1.0 clo October through April, and 0.7 clo May through September; and an inbuilding air velocity of 0.83 ft/s (0.25 m/s). 

3.2.1.3 Prototype Schedules

We determined our prototype schedule set through a combination of industry validated 

assumption and schedule set data from the Medium Office TSD (Thornton, Wang et al. 2009) 

and the Reference Building project (Deru, Field et al. 2010), for which schedules were largely 

based on the recommendations of ASHRAE Standard 90.1-1989 (ASHRAE 1989). Prototype 

weekday schedules for occupancy, interior equipment (plug and process loads), and lighting 

equipment are presented in Figure 3-1; the prototype schedule set is summarized in table form in 

Appendix A. 
22

Figure 3-1 Prototype weekday schedules: occupancy, plug load equipment, and lighting 

equipment 

3.2.2 Form

The number of floors, floor-to-floor height, and floor-to-ceiling height are the same in the 

baseline and low-energy cases. Aspect ratio and fenestration amount and placement, however, 

vary and are defined in Sections 3.3.2 and 3.4.2, respectively.

3.2.2.1 Building Shape

For the high-rise prototype, the floor-to-floor height and number of floors match those from

Deru, Field et al. (2010). The low-rise prototype was modeled with the same overall floor area 

as the high-rise prototype and the large office Reference Building model, but as a 4-story 

building rather than a 12-story building. The characteristics that define the shape of each 

prototype are presented in Table 3-6. 

Table 3-6 Prototype Shape Characteristics

Building Shape Characteristic Low-Rise Prototype High-Rise Prototype

Number of floors 4 12

Floor-to-floor height 13 ft (4 m) 13 ft (4 m)

Floor-to-ceiling height 13 ft (4 m) 13 ft (4 m)

 Note that the prototypes were modeled with 13-ft (4-m) floor-to-ceiling and floor-to-floor 

heights. Plenums were not explicitly modeled in the prototypes; this is because aspect ratio can 

be varied automatically by the Opt-E-Plus program during building optimization only for very 

simple geometries that do not contain plenums. Rather than specifying specific designs for the 

air distribution systems of the baseline and low-energy models, we simply assumed a 
23

prototypical mixed air condition with limited temperature stratification and made no assumptions 

regarding baseline or low-energy air distribution methods. We assumed a fixed aspect ratio for 

the high-rise prototype, which seemed appropriate based on the constraints posed by many highrise large office building sites, which tend to be in densely developed areas.

3.2.3 Fabric

This section specifies the types of envelope and interior constructions used in the prototype 

models. Specific fenestration constructions and insulation levels are listed in Sections 3.3.3, as 

prescribed by Standard 90.1-2004 (ASHRAE 2004c), and 3.4.3 for the baseline and low-energy 

models, respectively.

3.2.3.1 Exterior Constructions

The low-rise prototype, like the large office Reference Building, was modeled with punched-hole 

windows and masonry construction exterior walls. The high-rise prototype, on the other hand, 

was modeled as a glass curtain construction with insulated spandrel exterior wall panels. The 

low-rise prototype, like the large office Reference Building, was modeled with an insulationabove-deck roof. The high-rise prototype represents an interior floor and therefore was not 

modeled with a roof construction; its floor and ceiling constructions are interior constructions. 

For the low-rise office case, the ground floor was modeled with a slab-on-grade construction, 

made up of carpet pad over 8-in. (0.2-m)-thick heavyweight concrete. In addition, 20 in. (0.5 m) 

of ground (earth) was modeled below the slab to capture more accurately the temperature 

gradient that occurs between the bottom of the slab and the ground (at some depth below the 

surface) that remains unaffected by the building. Capturing the effect of the building on the 

ground below it and vice versa is important from a thermal mass and a thermal storage 

perspective. A separate program, slab.exe, was used to model the coupling between the slab-on 

grade construction, including the 20 in. (0.5 m) ground layer and the ground below it (DOE 

2008a). The program determines the ground temperature under the slab construction, based on 

the slab area and building location. It reports the perimeter and core ground monthly 

temperatures and average monthly temperatures. For this analysis, the core ground average 

monthly temperatures were passed to EnergyPlus to specify the ground temperatures under the 

slab construction. 

The high-rise large office case does not contain ground floor constructions because only an 

interior floor was modeled. 

3.2.3.2 Interior Partitions and Mass

We assumed interior wall partitions that separate core and perimeter zones are composed of 4-in. 

(0.1-m)-thick steel-frame walls covered with gypsum board, and that interior floors and ceilings 

are composed of carpet pad above 4-in. (0.1-m)-thick concrete on metal decking. Internal mass 

was modeled as 2 ft2 (~0.2 m2) of 6-in. (0.15-m)-thick wood per ft2 (m2) of floor area, totaling 

921,600 ft2 (85,620 m2) for the whole building (Deru, Field et al. 2010). 

3.2.4 Equipment

This section specifies the types of HVAC and service water heating (SWH) equipment used in 

the prototype and baseline models; performance and cost data are discussed in Sections 3.3.4.4

and 3.3.4.5, respectively. 
24

3.2.4.1 Heating, Ventilating, and Air-Conditioning 

The large office prototypes are assumed to be fully heated and cooled. Setup and setback 

schedules are implemented during unoccupied hours (nighttime), when the HVAC system is set 

to cycle to maintain temperature requirements for setup and setback and maintain RH

requirements. Although humidity may not typically be controlled during unoccupied periods, 

avoiding mold and moisture is good practice. (See Sections 3.3.4.4 and 3.4.4.5 for details about 

the specification and operation of the baseline and low-energy HVAC systems, respectively.) 

3.2.4.2 Service Water Heating

SWH is facilitated by tank storage natural gas water heaters. The type and number of hot water 

fixtures was determined from the design layout for the RSF; storage capacity was then calculated 

using the hot water demand table in the Service Water Heating chapter of the HVAC 

Applications Handbook (ASHRAE 2003). The RSF has two wings (one has a floor area of 

21,800 ft2 [2025 m2

], the other 27,360 ft2 [2542 m2]). Each has the same number of hot water 

fixtures: four lavatories, two for a men’s restroom and two for a women’s restroom; two kitchen 

sinks, one per break room; and one service sink in a janitorial closet. We used these data to

estimate the following distribution of fixtures for the large office models: 18 lavatories, 9 

kitchen sinks, and 5 service sinks for each floor of the low-rise building, and 6 lavatories, 3 

kitchen sinks, and 2 service sinks for each floor of the high-rise building. We used the hot water 

demand table in ASHRAE (2003) to calculate per-floor SWH storage capacities of 271 gal (1.03 

m3) and 96 gal (0.36 m3) for the low-rise and high-rise buildings, respectively. Accordingly, we 

specified 300 gal (1.14 m3

) of storage per floor for the low-rise building and 100 gal (0.38 m3) of 

storage per floor for the high-rise building, in increments of 100 gal (0.38 m3) units. 

Calculations were based on demands of 2 gal/h (0.008 m3/h) per lavatory, 20 gal/h (0.08 m3/h) 

per kitchen sink, and 20 gal/h (0.08 m3

/h) per service sink, an overall demand factor of 0.3, a 

storage capacity factor of 2, and a tank usable volume factor of 0.7. 

3.2.5 Prototype Model Summary

This section summarizes the building characteristics that define the large office prototype 

models. To reiterate, prototype characteristics are those not specified by ASHRAE Standards 

90.1-2004 and 62.1-2004 but that are needed to develop baseline and low-energy models. 

Prototype characteristics are summarized in Table 3–7. 
25

Table 3-7 Large Office Prototype Model Characteristics and Data Sources 

Building 

Characteristic

Low-Rise Large Office 

TSD Prototype

High-Rise Large Office 

TSD Prototype Source 

Program

Size 460,800 ft2

(42,810 m2)

460,800 ft2

(42,810 m2)

DOE Reference Building Large 

Office

Space types See Table 3-4 See Table 3-4 DOE Reference Building Large 

Office, RSF

Occupancy

See Table 3-5 

for density; 

see Table A-1 

for schedule

See Table 3-5 

for density;

see Table A-1 

for schedule

ASHRAE 90.1-1989; 

DOE Reference Building Large 

Office; 

PNNL Medium Office TSD; 

Assumption

Lighting See Table A-2 

for schedule

See Table A-2 

for schedule

ASHRAE 90.1-1989; 

DOE Reference Building Large 

Office; 

PNNL Medium Office TSD; 

Assumption

Plug and process See Table A-3 

for schedule

See Table A-3 

for schedule

DOE Reference Building Large 

Office; 

PNNL Medium Office TSD; 

Assumption

Form 

Number of floors 4 12

DOE Reference Building Large 

Office; 

Assumption

Floor-to-floor height 13 ft (4 m) 13 ft (4 m) DOE Reference Building Large 

Office

Fabric

Wall type Precast concrete Spandrel glass

DOE Reference Building Large 

Office; 

Assumption

Roof type All insulation above deck Not modeled DOE Reference Building Large 

Office 

Slab Type

Slab-on-grade: carpet 

pad on 8 in. (20 cm) 

heavyweight concrete 

above 20 in. (51 cm) of 

ground

Not modeled Assumption* 

Interior walls 2 x 4 steel-frame with 

gypsum boards

2 x 4 steel-frame with 

gypsum boards Assumption* 

Interior floors Carpet pad on 4 in. (10 

cm) concrete 

Carpet pad on 4 in. (10 

cm) concrete Assumption* 

Internal mass 921,600 ft2 (85,620 m2

) of 

6 in. (15 cm) wood

921,600 ft2 (85,620 m2) of 

6 in. (15 cm) wood

DOE Reference Building Large 

Office

Equipment

HVAC controls Setup and setback during 

unoccupied hours

Setup and setback during 

unoccupied hours

DOE Reference Building Large 

Office

SWH

Natural gas heating with 

storage tank; see 

Table A-4 for schedule

Natural gas heating with 

storage tank; see 

Table A-4 for schedule

DOE Reference Building Large 

Office; 

PNNL Medium Office TSD; 

ASHRAE 90.1-1989

* Verified by industry reviewers
26

3.3 Baseline Model

This section contains a topic-by-topic description of the baseline building models’ EnergyPlus 

inputs, including: form and footprint; envelope characteristics; internal loads; HVAC equipment 

efficiency, operation, control, and sizing; and SWH. We also list associated costs, which were 

used by Opt-E-Plus to compute 5-TLCC for each building configuration. 

For the high-rise case, two baseline models were considered: one representing common glass 

curtain construction practices and one representing minimal code compliance with respect to 

ASHRAE 90.1-2004. 

The common practice high-rise baseline was set up as a high-WWR, low-exterior insulation 

case. Many high-rise buildings are designed with floor-to-ceiling view glass in occupied spaces; 

that design style is approximated in the common practice case by a continuous band of 9-ft (2.7-

m) tall glass curtain view glass around the perimeter of each floor, resulting in an overall WWR 

of 69%. We assumed that the remaining 4 ft (1.2 m) of the 13 ft (4 m) floor-to-floor height 

would house some combination of air distribution components and electrical and mechanical 

equipment and would be finished at the perimeter with spandrel glass wall panels. Spandrel wall 

constructions were defined to provide a wall assembly insulation value of roughly R-3 in each 

climate zone. Low-energy configurations of the common practice high-rise baseline were

considered, but with fixed window and wall constructions and spatial distributions (fixed WWR 

and sill height). 

The code-compliant high-rise baseline was assigned climate-specific ASHRAE 90.1-2004-

compliant window and wall constructions and spatial distributions (defined by WWR and sill 

height values) that were allowed to vary in search of configurations that decrease energy use. 

We assessed implications of common glass curtain construction practices for achievable energy 

savings by comparing the low-energy versions of the high-rise common practice and codecompliant building configurations. Building programs and equipment were changed to save 

energy in both cases, but only the high-rise prototype with the code-compliant baseline was free 

to vary its glazing fraction and opaque envelope insulation to potentially increase those savings. 

3.3.1 Program

3.3.1.1 Baseline Schedules

Our baseline model schedule set was determined through a combination of industry validated 

assumption and schedule set data from the Medium Office TSD (Thornton, Wang et al. 2009) 

and the Reference Building project (Deru, Field et al. 2010), for which schedules were largely 

based on the recommendations of ASHRAE Standard 90.1-1989 (ASHRAE 1989). 

Baseline model weekday schedules for occupancy, HVAC operation, and infiltration are 

presented in Figure 3-2. “Ground floor” infiltration applies to the ground floor in the low-rise 

baseline and “interior floor” infiltration applies to all other low-rise baseline floors and to the 

high-rise baseline. The HVAC system is activated one hour before occupancy (to allow for ramp 

up to the desired space conditions during occupancy) and infiltration is reduced to 25% of its 

peak value during HVAC operation. For the ground floor, infiltration is increased during periods 

with above minimum occupancy to account for infiltration when doors are opened (see Section 

3.3.3.4 for details on infiltration). 
27

Baseline weekday schedules for heating and cooling set point, which include setup and setback 

during unoccupied periods, are displayed in Figure 3-3; see Section 3.3.4.4 for details on 

baseline VAV HVAC operation.

For the full set of baseline schedules, see Appendix B. 

Figure 3-2 Baseline weekday schedules: occupancy, HVAC operation, and infiltration

Figure 3-3 Baseline weekday schedules: heating and cooling set points
28

3.3.2 Form

3.3.2.1 Building Shape

For the high-rise baseline building, the aspect ratio and footprint match those for the large office 

Reference Building. For the low-rise baseline model, the aspect ratio matches that for the large 

office Reference Building, but the footprint is three times larger to accommodate the same floor 

area within 4 floors instead of 12. Table 3-8 presents the aspects of the baseline models’ shape 

that are not defined in the corresponding prototypes. 

Table 3-8 Baseline Shape Characteristics

Building Shape Characteristic Low-Rise Baseline High-Rise Baseline

Aspect ratio 1.5 1.5

Length 415.7 ft (126.7 m) 240 ft (73.2 m)

Width 277.1 ft (84.5 m) 160 ft (48.8 m)

See Figure 3-4, Figure 3-5 and Figure 3-6 for isometric views of the low-rise and high-rise 

(code-compliant and common practice) baseline models. These provide visuals of the zoning 

described in Section 3.2.1 and the envelope characteristics described in Section 3.3. 

Figure 3-4 Isometric view of the low-rise baseline model 
29

Figure 3-5 Isometric view of the code-compliant high-rise baseline model

Figure 3-6 Isometric view of the common practice high-rise baseline model

3.3.2.2 Fenestration

The WWR was set to 40% for the low-rise and code-compliant high-rise baselines; this matches 

the value in the large office Reference Building model and is the maximum value allowed for 

ASHRAE 90.1-2004 Appendix G compliance. The common practice high-rise baseline is 

modeled with a WWR of 69%, approximating a design with floor-to-ceiling glass in its occupied 

spaces. 

Sill height for the low-rise and code-compliant high-rise baselines was set to 3.61 ft (1.1 m) 

above the floor, such that the view glass reaches up to 9 ft (2.7 m) above the floor. Sill height for 

the common practice high-rise baseline was set to zero, such that the view glass in all baseline 

cases has a consistent header height of 9 ft (2.7 m). 

Per Appendix G of ASHRAE 90.1-2004, overhangs were not included in the baseline models. 

Neither prototype includes skylights or daylighting controls. 
30

3.3.3 Fabric

The exterior constructions chosen for each large office prototype were further developed to meet 

the prescriptive design option requirements of ASHRAE 90.1-2004 Section 5.5 (except for the 

exterior wall construction and WWR for the common practice high-rise baseline) (Wilson 2010). 

Layer-by-layer descriptions of the exterior surface constructions were used to model the building 

thermal envelope in EnergyPlus. 

3.3.3.1 Exterior Walls

This section details the baseline exterior wall constructions for the low-rise and high-rise large 

office baseline models. For a given prototype and construction, assembly U-factors vary based 

on the climate zone and are adjusted to account for standard film coefficients. R-values for most 

layers are derived from Appendix A of ASHRAE Standard 90.1-2004. Continuous insulation 

(c.i.) R-values were selected to meet the minimum R-value requirements of Section 5.5 in 

ASHRAE Standard 90.1-2004 (except in the common practice high-rise case), which vary by 

climate zone (ASHRAE 2004c). 

The low-rise large office baseline was modeled with precast concrete wall panels. Noninsulated 

panels are made up of 8 in. (20.3 cm) of solid heavyweight concrete (140 lb/ft3) [2,240 kg/m3]). 

Insulated panels are sandwich constructions with concrete and rigid isocyanurate insulation 

layers, arranged as follows:

• Exterior air film (calculated by EnergyPlus)

• 3-in. (7.6-cm) solid heavyweight concrete, 140 lb/ft3 (2,240 kg/m3) 

• Rigid isocyanurate insulation (R-value varies by climate)

• 6-in. (15.2-cm) solid heavyweight concrete, 140 lb/ft3 (2,240 kg/m3

) 

• Interior air film (calculated by EnergyPlus). 

The low-rise baseline exterior walls’ performance metrics, including costs, are listed in Table 3-9

(see Table D-2 for metric units). Insulation R-values were selected to meet the minimum 

requirements for mass wall constructions in Section 5.5 of ASHRAE 90.1-2004. The capital 

costs were provided by The Abo Group (Priebe 2010). 

Table 3-9 Low-Rise Baseline Exterior Wall Constructions

Properties Climate Zone 

1A

Climate Zones 

3B-NV and 4C

Climate Zones 

5A and 5B

Climate Zone 

7 

Key

Baseline Wall 

Construction 

No c.i.

Baseline Wall 

Construction 

R-5.7 c.i.

Baseline Wall 

Construction 

R-7.6 c.i.

Baseline Wall 

Construction 

R-11.4 c.i.

Assembly U-factor 

(Btu/ h·ft2

·°F) 1.010 0.173 0.137 0.097

Capital cost ($/ft2) $36.15 $44.05 $44.40 $45.10

The high-rise large office baseline was modeled as a curtain wall construction with spandrel 

glass exterior wall constructions. The layers consist of spandrel glass, rigid isocyanurate 

insulation, and gypsum board, arranged as follows: 

• Exterior air film (calculated by EnergyPlus)
31

• 0.25-in. (0.64-cm) exterior spandrel glass, 113 lb/ft3 (1,810 kg/m3) 

• Rigid isocyanurate insulation (R-value varies by climate)

• 0.5-in. (1.3-cm) thick gypsum board, 49 lb/ft3

 (785 kg/m3). 

The high-rise baseline exterior walls’ performance metrics, including costs, are listed in Table 

3-10 for the code-compliant case (according to the minimum requirements for steel-framed wall 

constructions in Section 5.5 of ASHRAE 90.1-2004) (ASHRAE 2004c) and in Table 3-11 for the 

common practice case, as required, in combination with a corresponding code-compliant window 

construction (see Section 3.3.3.3), to provide an approximate exterior wall assembly R-value of 

3. (See Table D-3 and Table D-4, respectively, for metric units.) Priebe (2010) provided the 

capital costs. 

Table 3-10 High-Rise Code-Compliant Baseline Exterior Wall Constructions

Properties Climate Zones 

1A, 3B-NV, and 4C

Climate Zones 

5A, and 5B

Climate Zone 

7 

Key

Baseline Wall 

Construction 

R-13.0

Baseline Wall 

Construction 

R-13.0 + R-3.8 c.i.

Baseline Wall 

Construction 

R-13.0 + R-7.5 c.i.

U-factor 

(Btu/ h·ft2

·°F) 0.139 0.091 0.068

Capital cost 

($/ft2

) $35.75 $36.65 $37.15

Table 3-11 High-Rise Common Practice Baseline Exterior Wall Construction

Properties All Climate Zones

Key Baseline Wall Construction 

Whole Wall Assembly R-3.0

U-factor (Btu/ h·ft2·°F) 0.173

Capital cost ($/ft2) $34.80

For each construction, the thermal performances of the interior and exterior air films were 

calculated with the EnergyPlus “detailed” algorithm for surface heat transfer film coefficients, 

which is based on linearized radiation coefficients separate from the convection coefficients 

determined by surface roughness, wind speed, and terrain. 

3.3.3.2 Roofs

For the low-rise large office case, the baseline model roofs are built up with rigid insulation 

above a structural metal deck. The layers consist of roof membrane, insulation, and metal 

decking. The assembly U-factors vary based on the climate zone and are adjusted to account for 

standard film coefficients. R-values for most of the layers were derived from Appendix A of 

ASHRAE Standard 90.1-2004. Continuous insulation R-values were selected to meet the 

minimum R-value requirements of Section 5.5 in ASHRAE Standard 90.1-2004, which vary by 

climate zone (ASHRAE 2004c). The thermal performance metrics and construction costs are 

listed by climate zone in Table 3-12 (see Table D-5 for metric units). The capital costs were

provided by Priebe (2010) and assume:
32

• A 60-mil (0.15-cm) thick, mechanically fastened ethylene propylene diene monomer 

single-ply membrane 

• Polyisocyanurate insulation, including a tapered drainage piece finished with 7/16-in. 

(1.11-cm) strand board 

• 0.05-in. (0.13-cm) base flashing and edging around the perimeter of the roof. 

Table 3-12 Low-Rise Baseline Roof Constructions

Properties Climate Zones 1–7 

Key Baseline Roof Construction, R-15 c.i.

U-factor (Btu/h·ft2·°F) 0.066

Capital cost ($/ft2) $9.15

The prescriptive portion of Standard 90.1-2004 does not specify performance characteristics such 

as roof reflectance or absorption. Appendix G of the Standard states that the reflectivity of 

reference buildings should be 0.3. We assumed the baseline roof ethylene propylene diene 

monomer membrane has a solar reflectance of 0.3, a thermal absorption of 0.9, and a visible 

absorption of 0.7. 

The high-rise large office baseline models do not contain roof constructions because only an 

interior floor was modeled. 

3.3.3.3 Fenestration

The baseline fenestration systems for the low-rise and high-rise large office buildings were 

modeled as four banded windows per floor, one for each exterior wall surface. Each banded 

window spans the width of its exterior wall surface and, as a single fenestration object, 

represents the combined fenestration area of the individual windows that would populate the 

exterior wall surface in an actual construction. To reduce model complexity and to make the 

EnergyPlus simulations run faster, we did not modeled frames explicitly; however, the window 

properties (U-factors and SHGCs) are whole-assembly values that include the effects of frames. 

Performance criteria were set to match the requirements of Appendix B in ASHRAE Standard 

90.1-2004. If the Standard does not provide an SHGC recommendation for a given climate zone, 

the SHGC value for that climate zone was set to that of the next warmest climate zone for which 

a recommendation is given.

The multipliers from Table C3.5 in ASHRAE 90.1-2004 Appendix C (ASHRAE 2004c) were

used to calculate VLT values for the baseline windows. An iterative process is used to refine the 

material properties in the layer-by-layer descriptions to just match the required assembly 

performance level. Capital costs assume punched-hole constructions for the low-rise case (Table 

3-13 and Table 3-14) and glass curtain constructions for the high-rise case (Table 3-15 and Table 

3-16); see Table D-6 to Table D-9 for metric units. Priebe (2010) provided the capital costs.
33

Table 3-13 Low-Rise Baseline East-, South-, and West-Facing Punched-Hole Window 

Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV 

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.250 0.250 0.390 0.490

VLT 0.250 0.318 0.495 0.490

U-factor 

(Btu/h·ft2

·°F) 1.21 0.570 0.570 0.570

Capital cost 

($/ft2

) $46.29 $49.81 $47.24 $47.24

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22

Table 3-14 Low-Rise Baseline North-Facing Punched-Hole Window Constructions

Properties Climate Zone 

1A

Climate Zone 

3B-NV 

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.440 0.390 0.490 0.640

VLT 0.440 0.622 0.622 0.640

U-factor 

(Btu/h·ft2

·°F) 1.21 0.570 0.570 0.570

Capital cost 

($/ft2

) $45.21 $41.39 $46.66 $40.84

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22

Table 3-15 High-Rise Baseline East-, South-, and West-Facing Glass Curtain Constructions

Properties Climate Zone 

1A

Climate Zone 

3B-NV 

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.250 0.250 0.390 0.490

VLT 0.250 0.318 0.495 0.490

U-factor 

(Btu/h·ft2

·°F) 1.21 0.570 0.570 0.570

Capital cost 

($/ft2

) $73.30 $76.82 $74.25 $74.25

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22
34

Table 3-16 High-Rise Baseline North-Facing Glass Curtain Constructions

Properties Climate Zone 

1A

Climate Zone 

3B-NV 

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.440 0.390 0.490 0.640

VLT 0.440 0.622 0.622 0.640

U-factor 

(Btu/h·ft2

·°F) 1.21 0.570 0.570 0.570

Capital cost 

($/ft2

) $72.22 $68.40 $73.67 $67.85

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22

Skylights were not considered for either the high-rise or low-rise baseline cases, as they are not 

baseline equipment. 

3.3.3.4 Infiltration

Building air infiltration is addressed indirectly in ASHRAE 90.1-2004 through requirements for 

building envelope sealing, fenestration, door air leakage, etc. The air infiltration rate, however, 

is not specified. Baseline office building envelope leakage rates are based on data taken from 

ASTM E779 fan pressurization tests on U.S. office buildings (Emmerich, McDowell et al. 2005); 

exterior door leakage rates are based on the door opening event model of Yuill et al. (2000). The 

resultant whole building baseline leakage rates for the low-rise and high-rise cases, respectively, 

are 0.080 air changes per hour (ACH) and 0.072 ACH during operating hours, when the HVAC 

system is on and occupants are entering and leaving the building, and 0.244 ACH and 0.213 

ACH at night, when the HVAC system is off and the exterior doors are closed. Envelope 

infiltration is averaged and applied evenly to each floor. Infiltration through entrances and exits 

is applied only to the ground floor. Half the infiltration on each floor is assigned to the perimeter 

zones, and half is assumed to pass beyond the 20-ft (6.1-m) deep perimeter and into the core 

zone. The per-zone infiltration rates are presented in Table 3-17. 

Table 3-17 Baseline Infiltration Rates per Zone 

Floor 

Low-Rise High-Rise

Operating 

Hours 

(ACH)

Non-Operating 

Hours 

(ACH)

Operating 

Hours 

(ACH)

Non-Operating 

Hours 

(ACH)

Ground floor core 0.088 0.158 NA NA

Ground floor perimeter 0.300 0.540 NA NA

Other floor core 0.040 0.160 0.043 0.170

Other floor perimeter 0.135 0.540 0.070 0.280

 

Ground floor zone infiltration rates were not modeled for the high-rise case because only an 

interior high-rise floor was modeled. 
35

Infiltration through an envelope surface depends on the pressure gradient acting on the surface. 

We calculated pressure gradients for both cases according to the following assumptions: 

• For each of the six climate zones used for this study, an average wind velocity was 

calculated from the weather file data for the representative city.

• An average infiltration-inducing wind pressure coefficient (0.375) was calculated using 

the findings from Akins et al. (1979) and Wiren (1984) for typical low-rise, low aspect 

ratio (less than 3) rectangular buildings and a random wind direction (all wind directions 

are assumed to be equally probable). Note that, for lack of data, we also apply these 

assumptions to high-rise and high aspect ratio (greater than 3) low-rise cases.

• Based on the assumption of random wind direction, the average infiltration-inducing 

wind pressure coefficient is the same for each exterior surface.

• Average wind speeds are similar for each climate zone (ranging from 9.0 mph to 10.5 

mph [4.0 m/s to 4.7 m/s]); for simplicity, we used a climate-averaged wind speed of 9.8 

mph (4.4 m/s) to calculate an average wind pressure coefficient of 0.375, which 

corresponds to an average infiltration driving pressure of 0.017 in. w.c. (4.33 Pa). This 

driving pressure was used in all climate zones for both the low-rise and high-rise cases.

• When the HVAC system is on, total infiltration is reduced by 75% (applied equally to 

envelope leakage infiltration and exterior door opening-event infiltration). This 

assumption is based on an EnergyPlus Airflow Network analysis, for which internal 

building pressurization during HVAC operation was approximated by creating a supply 

leak in the occupied space equivalent in flow rate to that of the space’s HVAC system 

(the supply leak flow was brought in from a secondary zone such that mass flow balance 

could be maintained for the primary HVAC loop). 

• When the HVAC system is off, the building is not pressurized with respect to the exterior 

environment. 

• The current infiltration rates do not take into account temperature-driven infiltration via 

stack effect, which is difficult to model accurately. See Section 5.2 for details. 

3.3.4 Equipment

This section describes the performance and cost of the baseline buildings’ lighting, HVAC, and 

refrigeration equipment.

3.3.4.1 Electric Lighting

The baseline interior lighting power density (LPD) for each space type was derived by using the 

space-by-space method defined in ASHRAE 90.1-2004 (ASHRAE 2004c). The space typespecific LPD values were then used to calculate an area-weighted whole-building average LPD, 

which is applied to the perimeter and core zones of the baseline models. The mappings between 

space type and Standard and the resulting LPD values, both for individual space types and for the 

baseline models as a whole, are presented in Table 3-18. 
36

Table 3-18 Baseline Lighting Loads by Space Type

Space Type Mapping to ASHRAE 90.1-2004

Low-Rise High-Rise

LPD (W/ft2) LPD (W/m2) LPD (W/ft2) LPD (W/m2)

Office Office-enclosed (or open plan) 1.1 11.84 1.1 11.84

Conference Conference/meeting/multipurpose 1.3 13.99 1.3 13.99

Break room Dining area 0.9 9.69 0.9 9.69

Elevator CUSTOM VALUE 0.0 0.0 0.0 0.0

Restroom Restrooms 0.9 9.69 0.9 9.69

Stairs Stairs-active 0.6 6.46 0.6 6.46

Mechanical/ 

electrical 

room

Electrical/mechanical 1.5 16.15 1.5 16.15

Whole 

building 1.09 11.73 1.06 11.38

The baseline cost of the lighting system for both the low-rise and high-rise large office cases is 

estimated at $10.36/ft2

 ($111.51/m2) for capital costs and $77.24/kW∙yr for maintenance, where 

kW refers to the installed lighting power. Because office space dominates the floor plan of the 

building, we used office space equipment and baseline LPD prescription to estimate building 

lighting costs. For baseline lighting equipment (32-W T8 lamps), a spacing of 80 ft2 (7.4 m2) per 

fixture would result in a space LPD of 0.8 W/ft2 (8.6 W/m2

); to achieve a space LPD of 1.1 W/ft2

(11.8 W/m2), a spacing of 58 ft2 (5.4 m2) is required. The cost of the baseline lighting fixture 

was estimated at $366 per fixture, resulting in an area-normalized fixture cost of $6.29/ft2

($67.70/m2

). For a lighting power density of 1.1 W/ft2 (11.8 W/m2), we calculated a powernormalized capital lighting cost of $9,418/kW. Likewise, we calculated an area-normalized 

maintenance cost of $0.08/ft2∙yr ($0.91/m2∙yr). The capital costs are estimated based on Balboni 

(2008); the maintenance costs are estimated using Plotner (2009). 

Exterior lighting is not included in the large office baseline models. In previous TSD work, 

1 W/ft (3.3 W/m) of exterior façade lighting was applied to the baseline models as per the 

allowance for lighting of exterior walkways in ASHRAE 90.1-2004, Table 9.4.5. Parking lot 

lighting is also not included in the current study. Compared to the interior lighting and plug and 

process loads, 1 W/ft (3.3 W/m) of exterior lighting represents a very small load that has a 

negligible effect on overall building energy usage; accordingly, we chose not to model exterior 

lighting. 

3.3.4.2 Plug and Process Loads

Peak plug and process loads are largely based on Deru, Field et al. (2010) and current NREL 

operations. The Reference Building large office model specifies a plug and process load density 

of 0.75 W/ft2 for office spaces and conference rooms; for this study, we reduced that density to 

0.404 W/ft2 for those space types. The reduction is based on the assumption that a significant 

portion of the building’s computing equipment would be housed in a central data center. We 

assume that the data center would be separated from occupied spaces (in a basement, for 

example) and that it would not influence system interactions in the rest of the building; 

accordingly, we separated data center loads (for both equipment and conditioning) from the rest 

of the building loads for modeling purposes (see Section 3.3.4.2 for details on data center loads). 

We assigned the elevator space a plug load density of zero based on the assumption that the 
37

electrical equipment associated with elevator operation would be contained within a basement 

utility room, and not affect the occupied space. We assumed that baseline plug and process loads 

costs are included in the overall baseline capital costs (see Section 3.1.2.4). The baseline plug 

and process loads are presented in Table 3-19. 

Table 3-19 Peak Baseline Plug Loads

Space Type

Low-Rise High-Rise

Plug Load 

Density (W/ft2) 

Plug Load 

Density (W/m2)

Plug Load 

Density (W/ft2)

Plug Load 

Density (W/m2) 

Office 0.40 4.35 0.40 4.35

Conference 0.40 4.35 0.40 4.35

Break room 2.60 27.99 2.60 27.99

Elevator 0.00 0.00 0.00 0.00

Restroom 0.10 1.08 0.10 1.08

Stairs 0.00 0.00 0.00 0.00

Mechanical/electrical room 0.00 0.00 0.00 0.00

Average 0.40 4.34 0.39 4.20

3.3.4.3 Data Center

 According to current NREL operations, we estimated a data center IT load of 65 W of 

computational power per building occupant. Assuming typical data center operations and an 

average Power Usage Effectiveness (PUE) of 1.9, we estimated data center HVAC 

(conditioning) and lighting loads totaling 58.5 W per person (Google 2010). Table 3-20 details 

per-occupant data center loads.

Table 3-20 Baseline Data Center Load per Person

Low-Rise High-Rise

PUE 1.90 1.90

IT equipment (W/person) 65.00 65.00

HVAC and lighting equipment (W/person) 58.50 58.50

Assuming 3,494 occupants in the low-rise office building and 3,453 occupants in the high-rise 

office building, we calculated annual baseline data center energy usage of 28.01 kBtu/ft2

∙yr 

(146.5 MJ/m2); see Table 3-21 (Table D-10 for metric units) for details. Data center energy 

usage was not explicitly modeled using EnergyPlus; it was added to the building end uses and 

overall energy consumption in postprocessing. 

Table 3-21 Baseline Data Center EUIs 

Low-Rise High-Rise

IT equipment (kBtu/ft2) 14.74 14.74

HVAC and lighting equipment (kBtu/ft2) 13.27 13.27

Total data center (kBtu/ft2) 28.01 28.01
38

3.3.4.4 HVAC Systems and Components

We assumed, in agreement with the large office Reference Building model, that a VAV system 

with hydronic heating and cooling represents an appropriate HVAC baseline for a large office 

building. 

3.3.4.4.1 Hydronic VAV: System Control

Each floor of the baseline models is conditioned by a dedicated VAV system that supplies air at 

a constant 55°F (12.8°C) to zone level reheat terminal boxes. The central hot and cold water 

coils and the hot water coils in the zone-level reheat terminal boxes are supplied by a central 

boiler and chiller. Boiler, chiller, and pump loop specifications were taken from the large office 

Reference Building. The boilers are natural gas-fired, hot water models. The chillers are watercooled, electric, centrifugal compressor models paired with a water-cooled rooftop cooling tower 

with a dual-speed fan. Central heating coils may not be needed except in very cold climates; 

however, they were included in all models for completeness. They were used sparingly (or not at 

all) in most climates and otherwise had no impact on energy use. 

We considered a lower central supply temperature (45°F [7°C]) for humid climates (Miami and 

Chicago) to ensure space RH levels would be maintained below 60%, but we determined that 

55°F (13°C) supply air was sufficient in all climates to maintain specified humidity control 

during occupied times. 

The baseline hydronic VAV system operates within a daytime dry bulb dead band of 70°–75°F 

(21°–24°C). Assuming an occupant metabolic rate of 1.27 (for moderately active office work; 

see Section 3.2.1.2.1) and clothing levels of 0.7 clo for summer and 1.0 clo for winter, this 

corresponds to predicted mean vote (PMV) values of 0.12 (at 60% RH) and –0.17 (at 50% RH) 

for summer and winter, respectively. This falls within the acceptable comfort range for PMV 

values of –0.5 on the cold side to 0.5 on the warm side, according to standard design practice. 

We specified the minimum ventilation requirement as per the prescriptions of ASHRAE 62.1-

2004 (ASHRAE 2004b) (see Section 3.3.4.4.3). We also specified a minimum total outdoor air 

fraction of 0.25 and minimum VAV terminal box flow fractions of 0.3 as per typical VAV 

design for office environments. Specifying a minimum outdoor air fraction of 25% captures the 

peak design requirements for critical zones such as conference rooms, mitigating many of the 

drawbacks associated with lumped ventilation requirements. 

Reheat at the VAV terminals is supplied according to dual maximum logic, where hot water flow 

to the reheat coil is ramped up at the minimum air flow rate until the maximum hot water flow is 

reached and the air damper is gradually opened from its minimum stop position to further 

increase heating capacity (PG&E 2007). 

During unoccupied periods (nighttime), the HVAC system cycles to maintain setup and setback 

temperature and RH requirements. If the temperature in any zone rises above the setup set point 

of 87°F (30.6°C), the HVAC system for that floor powers on and cools recirculated air until the 

temperature in every zone is reduced to at least 3°F (1.7°C) below the setup temperature. 

Likewise, if the temperature in any zone falls below the setback set point of 55°F (15.6°C), the 

HVAC system powers on and heats recirculated air until the temperature in every zone is 

increased to at least 3°F (1.7°C) above the setback temperature. If the RH in any zone rises 

above 70%, the HVAC system powers on and cools recirculated air until every zone has an RH

of 60% or lower. During nighttime humidity mitigation, the heating set point is temporarily 

raised to its daytime operation point of 70°F (21°C) to avoid overcooling. If the RH in a zone 
39

has not yet been lowered to 60% and the temperature falls below 70°F (21°C), reheat is 

employed to maintain that temperature while the cold water coils continue to remove moisture 

from the air. No OA is brought into the building during unoccupied hours; conditioning occurs 

through recirculation. 

3.3.4.4.2 Hydronic VAV: System Sizing

We used the design-day method to autosize heating (boilers, central hot water coils, and reheat 

coils in VAV terminal boxes) and cooling (chillers, central cold water coils) capacities, and air 

system flow rates. The design-day data for each climate location were developed from 

ASHRAE (2005). From the design-day data set, we chose a heating design condition based on 

99.6% annual percentiles and a cooling design condition based on 0.4% annual percentiles. The 

internal loads (occupancy, lights, plug and process loads, etc.) were set to zero throughout the 

heating design day, and to their peak values throughout the cooling design day. A global sizing 

factor of 1.2 was applied to all autosized heating and cooling capacities and air flow rates during 

initial sizing runs. The resulting baselines were evaluated for equipment operating PLRs; boiler 

and chiller sizing factors of 0.5 and 0.8, respectively, were subsequently applied to ensure max 

PLR values reached above 80% at some point during the annual baseline runs (see Section 

2.4.4.1). 

3.3.4.4.3 Outside Air

Ventilation rates by space type were defined according to the prescriptions of ASHRAE 

Standard 62.1-2004 (ASHRAE 2004b). Rates for individual space types were combined to 

calculate an area-weighted whole-building average, which was applied to the perimeter and core 

zones of the baseline models. The mappings between space type and Standard and the resulting 

ventilation rates, both for individual space types and for the baseline models as a whole, are 

presented in Table 3-22. Rates for spaces without direct mapping to the Standard were 

estimated. ASHRAE 62.1-2004 requires 50 cfm (24 L/s) of OA per toilet for restrooms; 

assuming an area of roughly 48 ft2 (4.5 m2) per toilet, we calculated a per area restroom 

ventilation requirement of 1.04 cfm/ft2 (5.28 L/s∙m2). Mechanical rooms, stairways, and 

elevators (the elevator shafts, in particular) were assigned ventilation rates of zero, based on the 

assumption that they are unoccupied most of the time. 

Table 3-22 Low-Rise and High-Rise Baseline Minimum Ventilation Rates

Space Type Mapping to ASHRAE 62.1-2004 Ventilation per Person Ventilation per Area

cfm/person L/s∙person cfm/ft2 L/s∙m2 

Office Office::Office Space 5 2.36 0.06 0.30

Conference Office::Conference/Meeting 5 2.36 0.06 0.30

Break room Food & Beverage::Restaurant 

Dining Rooms 7.5 3.54 0.18 0.91

Elevator Office::Office Space 0 0.00 0.00 0.00

Restroom Office::Office Space 0 0.00 1.04 5.28

Stairs Office::Office Space 0 0.00 0.00 0.00

Mechanical/electrical 

room

CUSTOM VALUE 0 0.00 0.00 0.00

OA intake follows the same schedule as the HVAC system, which turns on an hour before the 

building is occupied in the morning and turns off when occupants leave in the evening. No 
40

outdoor air is brought into the building during night cycling for temperature and humidity 

control. 

3.3.4.4.4 Economizers

In accordance with ASHRAE 90.1-2004, Section 6.5.1, an economizer is required in climate 

zones 2B, 3B, 3C, 4B, 4C, 5A, 5B, 6A, 6B, 7, and 8 for systems with cooling capacities larger 

than 135,000 Btu/h (40 kW). All systems for all climate zones for both cases fall into this 

category, so economizers were applied as baseline to all large office models in climate zones 3BNV, 4C, 5A, 5B, and 7 (for this study, only the baselines in climate zone 1A were not equipped 

with economizers). Economizers control is based on air enthalpy. 

3.3.4.4.5 Minimum Efficiency

The code-minimum efficiencies for heating and cooling equipment depend on system type and 

size. ASHRAE 90.1-2004 (Table 6.8.1F) requires natural gas-fired, water boilers larger than 2.5 

million Btu/h (732.7 kW) to have a minimum efficiency of 80% of the combustion efficiency 

(100% minus flue losses). We modeled baseline boiler efficiency with a cubic curve that varies 

from 79% efficiency at 15% part load up to 83% efficiency at 50% part load and back down to 

81% efficiency at full capacity (Figure 3-7). ASHRAE 90.1-2004 (Table 6.8.1C) requires 

centrifugal chiller models of this size (larger than 300 tons) to have a minimum coefficient of 

performance (COP) of 6.1 (ASHRAE 2004c). 

Figure 3-7 Baseline Boiler Efficiency Curve

We set boiler and chiller pump loop specifications to match those in the large office Reference 

Building model; the boiler and chiller pump loops each have 60 ft (18 m) of head and variablespeed pump motors with efficiencies of 87.5% and 90.0%, respectively (Deru, Field et al. 2010). 
41

Pump part load ratio (PLR) curves are cubic to accurately account for reduced power 

consumption at low PLRs.

3.3.4.4.6 Variable Air Volume Fan Power Assumptions

We modeled the baseline VAV HVAC system with supply fans only. We did, however, account 

for the static pressure drop of the return air stream (including that for return fans and exhaust 

fans); basically, we combined all system fan objects into a single supply fan for each air 

distribution unit and thus assumed the same total efficiency for each fan type. We assumed a 

nominal 4 in. w.c. (1000 Pa) of static pressure drop for the supply air path and 1.75 in. w.c. (438 

Pa) of static pressure drop for the return air path, for a total nominal static pressure drop of 5.75 

in. w.c. (1438 Pa). For a supply air path static pressure drop of 4 in. w.c. (1000 Pa), we 

calculated baseline total (supply) fan efficiencies of 52.1% and 50.1% for the low-rise and highrise cases, respectively, using the equations in Appendix G.3.1.2.9 of ASHRAE 90.1-2004. To 

account for the reduction of return air flow caused by 6 ACH of restroom exhaust, we calculated 

reduced total air path static pressure drops of 5.67 in. w.c. (1417 Pa) and 5.68 in. w.c. (1421 Pa) 

for the low-rise and high-rise baseline models, respectively. 

Installing an economizer adds 0.1 in. w.c. (25 Pa) of static pressure drop (Liu, Jarnagin et al. 

2007). We modeled static pressure reset to 0.5 in. w.c. (125 Pa) (PG&E 2007). 

3.3.4.4.7 Costs and Summary

Baseline VAV HVAC cost estimates, provided by the RMH Group, were based on the average 

sizing results from a preliminary round of EnergyPlus simulations for the baseline models of 

each building type (low-rise, high-rise code-compliant, and high-rise common practice) (Table 

3-23; see Table D-11 for metric units).

Table 3-23 Baseline HVAC System Cost Estimation Sizes

Climate

Low-Rise Baseline High-Rise Baseline:

Code-Compliant 

High-Rise Baseline:

Common Practice

Boilers 

(kBtu/h)

Chillers 

(tons)

Fans 

(cfm)

Boilers 

(kBtu/h)

Chillers 

(tons)

Fans

(cfm)

Boilers 

(kBtu/h)

Chillers 

(tons)

Fans 

(cfm)

Average 17068 925 419536 20353 1153 453438 24888 1446 542430

The cost of the baseline hydronic VAV system was estimated at $18.59/ft2

 ($200.10/m2) for the 

low-rise case and at $21.52/ft2

 ($231.63/m2) for the high-rise case. For the equipment sizes in 

Table 3-23, capacity-based costs of $9,261.49/ton of cooling ($2,633.35/kW) and $7,630.69/ton 

of cooling ($2,169.66/kW) for the low-rise and high-rise cases, respectively, were calculated and 

applied to simulations to allow for cost variations based on differences in required system 

capacities for different climate zones. The low-rise estimate assumes the use of rooftop units 

(RTUs) for the air distribution system; the high-rise estimate assumes air distribution via AHUs

(two units per floor), which is more practical from a ducting standpoint for a high-rise building. 

Table 3-24 provides an equipment breakdown and Table 3-25 (see Table D-12 for metric units) 

provides a detailed cost breakdown for the baseline VAV systems (RMH Group 2010a). 
42

 Table 3-24 Baseline HVAC System Cost Estimate Equipment Breakdown

HVAC Component

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

Low-Rise

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

High-Rise

Chillers and cooling tower (#) 3 3

Boilers (#) 5 5

Air distribution units (#) 8 24

VAV terminal boxes (#) 310 312

Pumps (#) 11 11

Table 3-25 Baseline HVAC System Cost Breakdown

HVAC Input

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

Low-Rise

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

High-Rise

Chillers and cooling tower ($/ft2) $1.40 $1.40

Boilers ($/ft2) $0.49 $0.66

Air distribution units ($/ft2) $7.59 $10.36

VAV terminal boxes ($/ft2) $0.84 $0.85

Pumps ($/ft2) $0.39 $0.39

Ductwork ($/ft2) $4.46 $4.77

Water distribution network ($/ft2) $1.88 $1.64

Life safety ($/ft2) $0.35 $0.17

Air and water balance ($/ft2) $0.20 $0.26

Temperature controls ($/ft2) $1.00 $1.00

Total ($/ft2) $18.59 $21.52

 

The cost of an economizer, including controls and an additional relief hood, is estimated at 

$100.20/ton of cooling ($28.48/kW) (RMH Group 2006). Economizers are assumed in the 

estimated HVAC system costs; accordingly, their cost is removed from the cost of the baseline 

HVAC systems in climate zone 1A (Miami, Florida), where they are not required by ASHRAE 

90.1-2004 (ASHRAE 2004c). We estimated annual HVAC maintenance costs (for repair and 

replacement) as a fixed fraction (7.8%) of the overall system costs based on maintenance cost 

estimates from previous TSD work (Hale, Leach et al. 2009; Leach, Hale et al. 2009); low-rise

and high-rise O&M costs are estimated at $767.23/ton of cooling ($218.15/kW∙yr) and 

$636.40/ton ($180.95/kW∙yr), respectively.

A summary of the primary HVAC performance characteristics for the low-rise and high-rise

large office baseline models is presented in Table 3-26. 
43

Table 3-26 Baseline HVAC Models Summary

HVAC Input

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

Low-Rise

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

High-Rise

Chiller COP 6.1 6.1

Boiler heating efficiency 79%–83% (see Figure 3-7) 79%–83% (see Figure 3-7)

Fan static pressure 5.67 in. w.c. (1418 Pa) 5.68 in. w.c. (1421 Pa)

Fan static pressure with economizer 5.77 in. w.c. (1443 Pa) 5.78 in. w.c. (1446 Pa)

Fan efficiency 52.1% 50.1%

3.3.4.5 Service Water Heating

The baseline SWH system for the large office buildings is a gas-fired storage water heater that 

meets the ASHRAE 90.1-2004 requirements; a thermal efficiency of 80% meets the 

requirements for units with rated input power greater than 75,000 Btu/h (22 kW) and expending 

less than 4000 Btu/h∙gal (309.7 kW/m3). The costs associated with the SWH system are assumed 

to be included in the baseline per unit area capital costs (see Section 3.3.4.4.7). 

3.4 Energy Efficiency Measures

The preliminary design phase and the optimization algorithm (described in Sections 2.4.2 and 

2.4.3) determined which EEMs were applied to the baseline models to create low-energy models 

that meet the 50% energy savings target. This section contains a topic-by-topic description of 

the EEMs that we considered (Table 3-27).

Table 3-27 Scope of Energy Efficiency Measures Considered

Building Form EEMs Building Fabric EEMs Building Equipment EEMs

• Varying building aspect 

ratio

• Varying levels of façade 

glazing

• Overhangs to shade the 

façade glazing

• Enhanced opaque 

envelope insulation

• Glazing constructions

• Reduced infiltration via 

an air barrier and/or 

vestibule

• Radiant heating and cooling with DOAS

• Energy recovery equipment

• Waterside and airside economizing

• Reduced LPD and occupancy controls

• Higher efficiency HVAC equipment

• Reduced plug load densities

• PV electricity generation

• Daylighting controls

• DCV

• Natural ventilation

• Higher efficiency SWH

The low-energy building models were configured by perturbing the baseline models with the 

EEMs described here. Any aspect of the building previously discussed but not mentioned here

was fixed across all models (baseline and low-energy). 
44

3.4.1 Program

3.4.1.1 Low-Energy Schedules

Our low-energy model schedule set was determined through a combination of industry validated 

assumption and schedule set data from the Medium Office TSD (Thornton, Wang et al. 2009) 

and the Reference Building project (Deru, Field et al. 2010), for which schedules were largely 

based on the recommendations of ASHRAE Standard 90.1-1989 (ASHRAE 1989). 

Low-energy model weekday schedules for occupancy, DOAS operation, infiltration, and radiant 

system availability are presented in Figure 3-8. “Ground floor” infiltration applies to the ground 

floor in the low-rise low-energy case and “interior floor” infiltration applies to all other low-rise 

low-energy floors and to the high-rise low-energy case. The DOAS system activates one hour 

before the radiant system is available (such that air temperature ramp-up is facilitated by the air 

system as opposed to the radiant system), the radiant system is available for conditioning one 

hour before occupancy (to ensure the desired space conditions) and infiltration is reduced to 25% 

of its peak value during DOAS operation. For the ground floor, infiltration is increased during 

periods with above minimum occupancy to account for infiltration from doors opening (see 

Section 3.3.3.4 for details on infiltration and Section 3.4.4.5 for details on low-energy HVAC 

operation). 

Figure 3-8 Low-energy weekday schedules: occupancy, HVAC operation, and infiltration 

The low-energy weekday schedule for the DOAS heating set point, which is measured in 

operative temperature and includes setback during unoccupied periods, is displayed in Figure 

3-9. The low-energy DOAS system does not have a cooling set point during daytime operation; 

when heating is not required during daytime operation, the DOAS supplies air at 55.0oF 

(12.8oC). At night when the radiant cooling system is unavailable, the DOAS has a dry bulb 
45

setup temperature of 87oF (30.6oC). Radiant heating and cooling set points are 70oF (21oC) and 

75oF (24oC), measured in operative temperature; radiant set point temperatures apply any time 

the radiant system is available for operation. (See Section 3.4.4.5 for details on low-energy 

HVAC operation.) 

For the full set of low-energy schedules, see Appendix C. 

Figure 3-9 Low-energy weekday schedules: DOAS heating set point 

3.4.2 Form

3.4.2.1 Fenestration

Three values for WWR were made available for selection: 20%, 30%, and 40%. The lower 

bound of 20% was based on industry feedback (personal communication with David Okada of 

Stantec) for the minimum allowable office building WWR, the 40% value represents the 

maximum allowed by Appendix G of ASHRAE 90.1-2004, and the 30% value represents an 

intermediate case. WWR was fixed in the common practice high-rise low-energy case at the 

baseline value of 69%. Varying WWR ratio has a number of implications for whole-building 

integration, including altering the levels of exterior envelope insulation, admitted solar gain, and 

the amount of visible light available for the facilitation of daylighting. We did not consider 

toplighting because of the presence of the radiant ceiling slabs (see Section 3.4.4.5). 

This EEM has no inherent cost. It affects cost indirectly by substituting exterior wall 

constructions for glazing constructions. Its effect on overall building cost depends on the 

difference in cost between the relevant exterior wall and glazing constructions. The sill height 

(4.9 ft [1.5 m]) for this EEM was raised above that for the baseline building (3.6 ft [1.1 m]) to 

ensure façade fenestration (which is shorter than baseline for 20% and 30% WWRs) would be 

placed so occupants can view the outdoors and daylight can enter. 
46

3.4.2.2 Exterior Shading Devices

An EEM that adds overhangs to shade glazed surfaces was made available for application to the 

low-rise case; we assumed installation difficulties and other practical considerations (window 

washing, for example) would preclude shaded overhangs in the high-rise case. For this EEM we 

assumed a 0.82-ft (0.25-m) offset between the top of each window and the overhang. Projection 

factors of 0.5, 1.0, and 1.5 were selectable. The size of each overhang was determined by using 

the height of the window, the offset, and the projection factor. For example, a 3-ft (0.91-m) 

wide, 2-ft (0.61-m) tall window with a 0.82-ft (0.25-m) offset and a projection factor of 0.5 

would yield a 1.41-ft (0.43-m) deep by 3-ft (0.91-m) wide overhang. Costs are based on total 

overhang area and estimated at $28.75/ft2 ($309.45/m2) (Priebe 2010). 

3.4.2.3 Aspect Ratio

For the low-rise case, building aspect ratio was allowed to vary between 1.5 and 15 (with 

selectable values of 1.5, 3, 5, 10, and 15) to explore the energy and cost trade-offs associated 

with reducing the depth of the cross section. Increasing aspect ratio increases the surface area to 

volume ratio, which increases capital costs and the effect of outdoor conditions on energy use via 

thermal conductance. It also increases the possible effectiveness of passive strategies such as 

daylighting, natural ventilation, and load shifting via thermal storage in the building’s internal 

mass. The upper limit value corresponds roughly with the RSF design, which has an aspect ratio 

of approximately 13. We assume very high aspect ratio buildings would need to be designed 

with multiple wings to allow for a practical overall footprint. We restricted aspect ratio for the 

high-rise case because of typical footprint limitations for high-rise construction sites;

accordingly, it was fixed at the baseline value of 1.5 for the high-rise case.

No explicit cost is associated with this EEM; the effect varying aspect ratio has on capital cost is 

determined by the changes in envelope and HVAC costs that result from elongating the building. 

3.4.3 Fabric

3.4.3.1 Exterior Walls

This section details the EEM exterior wall constructions for the low-rise and high-rise large 

office models. In both cases, EEM exterior wall construction layups are the same as those for 

the corresponding baseline exterior wall construction; in the EEM case, increased insulation 

thicknesses were considered to allow for superior thermal insulation. 

The precast concrete wall EEMs for the low-rise large office building are shown in Table 3-28

(see Table D-13 for metric units) along with capital costs provided by The Abo Group (Priebe 

2010). The construction layup (which has a thicker interior concrete layer than exterior concrete 

layer) maximizes the internal thermal mass available to the low-energy radiant heating and 

cooling system for thermal storage to facilitate load shifting. The low-rise exterior wall EEM 

layers are equivalent to those for the baseline exterior wall sandwich panels and are: 

• Exterior air film (calculated by EnergyPlus)

• 3-in. (7.6-cm) solid heavyweight concrete, 140 lb/ft3 (2,240 kg/m3) 

• Rigid isocyanurate insulation (R-value varies)

• 6-in. (15.2-cm) solid heavyweight concrete, 140 lb/ft3 (2,240 kg/m3

) 

• Interior air film (calculated by EnergyPlus). 
47

Table 3-28 Low-Rise Exterior Wall EEMs

Insulation R-Value, 

Nominal 

Assembly U-Factor 

(Btu/h·ft2·°F)

Capital Cost 

($/ft2) 

R-5.7 c.i. 0.173 $44.05

R-9.5 c.i. 0.114 $44.75

R-13.3 c.i. 0.086 $45.45

R-15.0 c.i. 0.077 $45.95

R-19.5 c.i. 0.061 $46.25

R-22.5 c.i. 0.053 $46.60

R-28.5 c.i. 0.043 $46.95

The spandrel glass wall EEMs for the code-compliant high-rise large office case are shown in 

Table 3-29 (see Table D-14 for metric units), along with capital costs from Priebe (2010). 

Exterior wall construction was fixed in the common practice high-rise low-energy case at the 

specified baseline construction to provide an approximate wall assembly insulation level of R-3. 

The high-rise (code-compliant case) exterior wall EEM layers are equivalent to those for the 

baseline exterior wall spandrel panels and are:

• Exterior air film (calculated by EnergyPlus)

• 0.25-in. (0.64-cm) exterior spandrel glass, 113 lb/ft3 (1,810 kg/m3) 

• Rigid isocyanurate insulation (R-value varies by climate)

• 0.5-in. (1.3-cm)-thick gypsum board, 49 lb/ft3

 (785 kg/m3). 

Table 3-29 High-Rise Exterior Wall EEMs

Insulation R-Value, 

Nominal 

Assembly U-Factor 

(Btu/h·ft2·°F)

Capital Cost 

($/ft2) 

R-13.0 0.139 $35.75

R-13.0 + R-3.8 c.i. 0.091 $36.65

R-13.0 + R-7.5 c.i. 0.068 $37.15

R-22.5 c.i. 0.043 $39.85

R-28.5 c.i. 0.034 $40.75

3.4.3.2 Roofs

The insulation-above-deck roof EEMs for the low-rise large office case are shown in Table 3-30

(see Table D-15 for metric units) along with capital costs from Priebe (2010). The construction 

of the EEM roofs in the EnergyPlus models is identical to that of the baseline roofs, except for 

the amount of c.i.; the roof EEM layers are: 

• A 60-mil (0.15-cm) thick, mechanically fastened ethylene propylene diene monomer 

single-ply membrane 
48

• Polyisocyanurate insulation, including a tapered drainage piece finished with 7/16-in. 

(1.11-cm) strand board 

• 0.05-in. (0.13-cm) base flashing and edging around the perimeter of the roof. 

Table 3-30 Low-Rise Roof EEMs

EEM Key U-Factor 

(Btu/h·ft2·°F)

Capital Cost 

($/ft2) 

R-20 c.i. 0.050 $9.59

R-30 c.i. 0.033 $10.47

R-40 c.i. 0.023 $11.36

R-60 c.i. 0.016 $13.12

We omitted high albedo roof membranes from consideration to reduce optimization simulation 

time and because they were not selected during optimization in past TSD work (Hale, Leach et 

al. 2009; Leach, Hale et al. 2009) in any climate zones.

3.4.3.3 View Glass

Table 3-31 and Table 3-32 (see Table D-16 and Table D-17 for metric units) list the window 

EEMs for the low-rise and high-rise (code-compliant) cases, respectively, including a short 

description, performance data, and cost data. The set was selected from a list of glazing systems 

compiled by The Abo Group to provide a good mix of available performances (Priebe 2006). 

Window construction was fixed in the common practice high-rise low-energy case at the 

specified baseline construction to provide an approximate wall assembly insulation level of R-3. 

Cost data were updated to 2010 dollars (Priebe 2010). 

Table 3-31 Low-Rise Fenestration Construction EEMs

EEM Key SHGC VLT U-Factor 

(Btu/h·ft2·°F)

Capital 

Cost ($/ft2) 

Fixed O&M 

Cost ($/ft2·yr)

Single pane with clear glass 0.810 0.881 1.08 $37.30 $0.21

Single pane with pyrolytic low-e 0.710 0.811 0.745 $41.80 $0.21

Double pane with low-e and argon 0.564 0.745 0.264 $50.70 $0.21

Double pane with low-e2 and 

argon

0.416 0.750 0.235 $52.70 $0.21

Triple layer with low-e polyester 

film 0.355 0.535 0.215 $72.80 $0.21

Quadruple layer with low-e 

polyester films and krypton 0.461 0.624 0.136 $93.70 $0.21
49

Table 3-32 High-Rise Fenestration Construction EEMs

EEM Key SHGC VLT U-Factor 

(Btu/h·ft2·°F)

Capital 

Cost ($/ft2) 

Fixed O&M 

Cost ($/ft2·yr)

Single pane with clear glass 0.810 0.881 1.08 $67.65 $0.21

Single pane with tinted glass 0.567 0.431 1.08 $69.64 $0.21

Single pane with pyrolytic low-e 0.710 0.811 0.745 $70.45 $0.21

Double pane with low-e and argon 0.564 0.745 0.264 $76.05 $0.21

Double pane with reflective 

coating and tinted glass 0.24 0.44 0.518 $76.60 $0.21

Double pane with low-e2 and 

argon

0.416 0.750 0.235 $78.25 $0.21

Double pane with low-e2 and 

tinted glass 0.282 0.55 0.288 $78.25 $0.21

Capital costs assume punched-hole constructions for the low-rise case and glass curtain 

constructions for the high-rise case. Constructions for the high-rise case were limited to singleand double-pane assemblies, based on industry feedback about installation feasibility. Because 

there is no window shading EEM for the high-rise case, tinted and reflective constructions were 

considered to reduce solar gain. The high-rise fenestration construction EEMs applied only to the 

code-compliant case; fenestration constructions were fixed at their baselines for low-energy 

common practice high-rise models. 

3.4.3.4 Infiltration

The infiltration reduction EEMs reduced the baseline infiltration rate by applying an envelope air 

barrier and entrance vestibules. The air barrier was assumed to reduce envelope infiltration from 

0.244 to 0.054 ACH for the low-rise case and from 0.213 to 0.047 for the high-rise case, based 

on the assumption that it would result in building envelope tightness equivalent to specifications 

for best construction practice according to CIBSE (2000). Its cost was estimated at $1.40/ft2

($15.07/m2

) of exterior wall area (Emmerich, McDowell et al. 2005). Vestibules were assumed 

to reduce the front door infiltration from 0.075 to 0.037 ACH (whole building), based on the 

door opening model of Yuill et al. (2000). Infiltration from doors being opened was not modeled 

for the high-rise case, because it included only an interior floor; however, infiltration reduction 

EEM costs include the cost of adding vestibules, based on the assumption that these would be 

included in a low-energy, high-rise construction. The cost of this EEM (based on adding one 

vestibule to each façade) was assumed to be that of adding four sets of two, 7-ft (2.13-m) tall 

swinging doors with a total surface area of 168 ft2 (15.61 m2) and adding 120 linear feet (36.6 m) 

of interior walls, based on a 15-ft. (4.6-m) deep vestibule), and corresponding to an additional 

interior wall area of 1080 ft2 (100.34 m2). The cost associated with adding vestibules is thus 

$10,786 (Waier 2008). 

3.4.4 Equipment

3.4.4.1 Daylighting Controls and Equipment

The daylighting EEM adds light sensors and dimming controls to zones with windows (perimeter 

zones). It does not add windows; rather, the EEM performance impact and cost depend on how 

many windows are installed. The perimeter zones were limited to a depth of 20 ft (6.1 m) to 

ensure quality sidelighting. 
50

To model daylighting, one light sensor is placed in each zone in the center of the zone at a height 

of 2.95 ft (0.90 m) from the floor. The dimming controls are continuous; they start dimming 

when the lighting set point is exceeded, linearly decreasing until the lighting set point is met or 

the input power decreases to 30% of its maximum (where the light output is 20% of its 

maximum), whichever comes first.

Based on industry feedback, we chose a daylighting set point of 27.9 fc (300 lux). The cost of a 

continuous dimming daylighting system for a building larger than 100,000 ft2

 (9,290 m2) is

estimated at $0.55/ft2 ($5.92/m2) of daylit area (RMH Group 2010b). 

The recommended design packages include radiant heated and cooled ceiling slabs above the 

occupied spaces, precluding skylights for daylighting of core spaces. 

3.4.4.2 Electric Lighting

A whole-building LPD reduction EEM of 42% was considered. For the low rise case, this 

corresponds to a building-average LPD of 0.63 W/ft2 (6.8 W/m2), which is the designed LPD for 

the RSF and representative of best practice for low-rise large office lighting design; for the highrise case, it corresponds to 0.61 W/ft2

 (6.6 W/m2). This reduction can be achieved by decreasing

the number of fixtures (by 27%), replacing baseline lighting equipment (32-W T8 lamps) with 

25-W T8 lamps, and adding task lights to work spaces. The T8 lamps provide ambient light with 

an average horizontal illuminance of 25 fc (270 lux); the task lights bring the average horizontal 

illuminance at the workstations to higher than 40 fc (430 lux). The T8 lamps require 0.61 W/ft2

(6.6 W/m2

) in the low-rise case; the task lights add 3–9 W per workstation. For the workstation 

distribution in the RSF, this corresponds to an LPD of 0.015–0.045 W/ft2 (0.16–0.48 W/m2). 

Assuming a total LPD of 0.63 W/ft2 (6.8 W/m2

) for the low-rise case to match that of the RSF, 

this corresponds to 4 W per task light.

For the electric lighting EEM configuration, we assumed a fixture spacing of 80 ft2 (7.4 m2

) of 

floor area per fixture (based on the interior lighting design in the RSF). The baseline lighting 

configuration assumed a fixture spacing of one fixture for every 58 ft2 (5.4 m2) of floor area. 

The LPD EEM includes an additional 9.6% overall LPD reduction, based on including

occupancy sensors in all space types where such equipment is not already considered baseline. 

Savings estimates from occupancy sensors are based on Thornton, Wang et al. (2009). 

Occupancy sensors are considered standard equipment for conference and break rooms; 

accordingly, no credit is taken for energy savings for installing occupancy sensors in those zones. 

See Table 3-33 and Table 3-34 (for low-rise and high-rise, respectively) for detailed breakdowns 

of occupancy sensor LPD reductions by space type and for the buildings as a whole (see Table 

D-18 and Table D-19 for metric units).
51

Table 3-33 Low-Rise Occupancy Sensor LPD Reductions 

Space Type Baseline LPD (W/ft2) Reduced LPD (W/ft2) LPD Reduction

Office-open 1.1 1.08 1.4%

Office-enclosed 1.1 1.04 5.7%

Conference 1.3 1.30 0.0%

Break room 0.90 0.90 0.0%

Elevator 0.00 0.00 0.0%

Restroom 0.90 0.90 0.5%

Stairs 0.60 0.60 0.0%

Mechanical/ 

electrical room 1.50 1.47 2.0%

Total 1.09 0.99 9.6%

Table 3-34 High-Rise Occupancy Sensor LPD Reductions 

Space Type Baseline LPD (W/ft2) Reduced LPD (W/ft2) LPD Reduction

Office-open 1.1 1.08 1.4%

Office-enclosed 1.1 1.04 5.7%

Conference 1.3 1.30 0.0%

Break room 0.90 0.90 0.0%

Elevator 0.00 0.00 0.0%

Restroom 0.90 0.90 0.5%

Stairs 0.60 0.60 0.0%

Mechanical/ 

electrical room 1.50 1.47 2.0%

Total 1.06 0.96 9.6%

The cost of one occupancy sensor is $150.00, including materials and labor (Greene 2008). The 

cost of a power pack, which powers the occupancy sensors and activates the lighting control 

relay, is $63.50. Two sensors and one power pack are required for every 1000 ft2 (93 m2

) (Roth, 

Westphalen et al. 2005), so the approximate cost of this EEM is $0.36/ft2

 ($3.88/m2).

The capital cost of the baseline lighting system for both cases was modeled as $10.36/ft2

($111.51/m2

). The cost of the baseline lighting fixture (with 32-W T8 lamps), installed, was 

estimated at $366 per fixture. For a spacing of one fixture for every 58 ft2 (5.4 m2) of floor area, 

this amounts to a per area cost of $6.29/ft2 ($67.70/m2). The cost of the EEM lighting fixture 

(with 25-W T8 lamps) was estimated at $566 per fixture. With one fixture for every 80 ft2 (7.4 

m

2

) of floor area, this amounts to $7.08/ft2 ($76.15/m2). Assuming other costs associated with 

the lighting system scale evenly for the baseline and EEM cases, and accounting for the addition 

of occupancy sensors, the overall cost for the lighting configuration representative of the 42% 

LPD reduction EEM was calculated at $11.51/ft2

 ($123.90/m2), an 11% increase over the cost for 

the baseline lighting system. We assumed maintenance costs for the baseline and EEM lighting 

systems to be equivalent when measured vis-a-vis lighting power installed. 

In Opt-E-Plus, lighting costs are expressed in dollars per installed kilowatt. The LPD EEM 

results in fewer installed kilowatts, so the baseline and marginal costs are summed on a wholebuilding basis, and then divided by the actual installed kilowatts to arrive at the EEM cost. The 

resulting EEM LPDs and costs are shown in Table 3-35 (see Table D-20 for metric units).
52

The LPD EEM inputs assume an 80/20 distribution of open floor plan and enclosed office 

spaces.

Table 3-35 Lighting Power Density EEMs

EEM Key LPD 

(W/ft2) 

Capital Cost 

($/kW)

Capital Cost 

($/ft2) 

Fixed O&M Cost 

($/kW·yr)

Fixed O&M Cost 

($/ft2·yr)

Baseline 1.1 $9,418 $10.36 $77.24 $0.08

42% LPD reduction 0.63 $18,270 $11.51 $77.24 $0.05

3.4.4.3 Plug and Process Loads

We developed a plug load reduction EEM according to RSF design specifications and ENERGY 

STAR® recommendations. Plug load density reduction includes: 

• Replacing a number of desktop computers with laptop computers 

• Using ENERGY STAR equipment where possible 

• Implementing control strategies such as occupancy sensors at workstations, on vending 

machines, on break room equipment, etc. 

The computing component of the plug load reduction EEM consists of replacing desktop 

computers with laptop computers and purchasing high efficiency monitors. During operation, a 

typical desktop computer consumes between 100 W and 200 W. A laptop providing equivalent 

computing power consumes 30 W. CRT monitors, as well as older LCD monitors, are replaced 

with LED backlit LCD monitors. Current LCD monitor technology provides 24-in. monitors 

that consume as little as 18 W, compared to CRT monitors that consume as much as 70 W. We 

modeled occupants as using laptop computers and separate monitors. 

The plug and process load EEM accounts for additional savings from the specification of 

ENERGY STAR equipment and other nonrated but energy-efficiency equipment. Fluorescent 

task lights (35 W each) are replaced with efficient LED task lights (6 W each). All-in-one print 

machines replace individual printers, copiers, and fax machines. Break room equipment is 

replaced with the most efficient equipment available. The vending machines are either delamped entirely, or equipped with LED display lighting controlled by motion sensors. Drinking 

fountains without coolers replace cooler equipped units. Conventional phones are replaced with 

VOIP phones. See Table 3-36 for a summary of the plug load reduction strategies. 
53

Table 3-36 Plug Load Reduction Strategies

Plug Loads Baseline Low Energy

Elevators Hydraulic design with uncontrolled 

fluorescent lighting

Traction design with controlled 

fluorescent lighting 

Break room Approximately 20 users per, nonEnergy Star equipment

Approximately 30-50 users per, 

Energy Star equipment

Task lights 35 W fluorescent task lights 6 W LED task lights

Phones 15 W conventional phones 2 W VOIP phones

Printers and copiers

Single-function devices, occupants 

with personal devices, 

approximately 15 users per shared 

device

Multi-function devices, no occupants 

with personal devices, approximately 

30-50 users per shared device

Computers 200 W desktop computers using 

screen savers

30 W Laptop Computers using 

standby mode

A third aspect of the plug and process load EEM implements control strategies to reduce plug 

and process loads during unoccupied hours. Cubicles are implemented with power strips that 

turn off equipment and eliminate parasitic losses while they are unoccupied. Computers and 

monitors are configured to go into standby when unused rather than sitting idle or running screen 

savers. Personal printers are reduced in number, or eliminated entirely, and replace by all-in-one 

machines. The number of occupants who use each all-in-one machine is maximized to limit the 

number of machines required. The number of occupants who use each all-in-one machine is 

maximized. The number of occupants per break room is also maximized. 

For a new construction case specified with the most efficient electrical equipment and equipment 

operational schedules, we assumed that the described plug and process load reductions could be 

achieved without increasing equipment costs with respect to the baseline plug and process load 

configuration.

Load densities for the plug and process load EEM are shown in Table 3-37. 

Table 3-37 Low-Energy Peak Plug Loads

Space Type

Low-Rise High-Rise

Plug Load 

Density (W/ft2)

Plug Load 

Density (W/m2)

Plug Load 

Density (W/ft2)

Plug Load 

Density (W/m2)

Office 0.31 3.34 0.31 3.34

Conference 0.31 3.34 0.31 3.34

Break room 2.60 27.99 2.60 27.99

Elevator 0.00 0.00 0.00 0.00

Restroom 0.10 1.08 0.10 1.08

Stairs 0.00 0.00 0.00 0.00

Mechanical/electrical room 0.00 0.00 0.00 0.00

Average 0.32 3.44 0.31 3.33

3.4.4.4 Data Center

Data center energy savings are achieved by replacing standard servers with blade servers and by 

improving the design of the data center’s HVAC system. Installing blade servers decreases the 

equipment load for the data center from the baseline value of 65 W per person to 48 W per 

person. Employing hot and cold aisle containment in the data center allows data center supply 
54

air temperatures to be increased, reducing the need for mechanical cooling. Additionally, 

effective cable management reduces airflow restrictions and lowers fan energy consumption. 

These strategies allow for an overall reduction in PUE from 1.9 for the baseline case to 1.2 for 

the low-energy case; see Table 3-38 for details. 

Table 3-38 Low-Energy Data Center Load per Person

Low-Rise High-Rise

PUE 1.20 1.20

IT equipment (W/person) 48.00 48.00

HVAC and lighting equipment (W/person) 9.60 9.60

Table 3-39 (see Table D-21 for metric units) presents the overall energy usage numbers for the 

low-energy data center, which indicate 53.9% energy savings with respect to the baseline 

configuration (see Table 3-21 for comparison). Again note that data center energy usage was not 

explicitly modeled using EnergyPlus; it was added to the building end uses and overall energy 

consumption in postprocessing. 

Table 3-39 Low-Energy Data Center EUIs

Low-Rise High-Rise

IT equipment (kBtu/ft2·yr) 10.76 10.76

HVAC and lighting equipment (kBtu/ft2·yr) 2.15 2.15

Total data center (kBtu/ft2·yr) 12.91 12.91

3.4.4.5 HVAC Systems and Components

For all low-energy building models, the baseline hydronic VAV system was replaced with high 

thermal mass, radiantly heated and cooled concrete ceilings, and DOAS for ventilation. DOAS 

design was location specific based on climatic considerations. 

The radiant concrete ceiling construction includes the following layers, from top to bottom: 

• 3-in. (7.6-cm) heavyweight concrete slab, 140 lb/ft3 (2240 kg/m3) 

• 5/8-in. (1.6-cm) inner diameter radiant tubing, spaced 6 in. (15.2 cm) on center 

• 1-in. (2.5-cm) heavyweight concrete slab, 140 lb/ft3 (2240 kg/m3). 

The tubing was specified to be as near to the underside of the ceiling slab as possible to reduce 

the system response time. See Figure 3-10 for a visual of the slab construction. 
55

Figure 3-10 Radiant slab ceiling construction

We did not consider airside economizing because of the nature of DOAS design, but waterside 

economizing was included as an EEM option (see Section 3.4.4.5.7).

3.4.4.5.1 Radiant Heating and Cooling with DOAS: System Control

The ability of a radiant-based heating and cooling system to deliver energy savings depends 

largely on the algorithms that control it. Accordingly, we put considerable effort into 

implementing and testing our control logic. 

First, we established temperature control dead bands appropriate for a radiant heating and 

cooling system. One benefit of a radiant conditioning system is that, because it can influence 

mean radiant temperature (MRT), it allows for a wider dry bulb dead band than does an airconditioning system. For the low-energy system with radiantly heated and cooled ceilings, we 

can achieve the same comfort levels as with the baseline VAV system with a daytime dry bulb 

range of 68o–78oF (20o–25.6oC). See Table 3-40 (Table D-22 for metric units) for details. For 

proper control of the radiant system and to ensure the comfort levels defined in Table 3-40 are 

maintained, we control the radiant system based on operative temperature (the average of MRT

and dry bulb temperature); we defined the heating set point at an operative temperature of 70oF 

(21oC) and the cooling set point at an operative temperature of 75oF (24oC). 
56

Table 3-40 Baseline and Low-Energy HVAC System Comfort Comparison 

Control 

Set 

Point

Baseline VAV System Low Energy Radiant System with DOAS

Air Temperature 

(oF) 

MRT 

(oF) PMV Air Temperature (oF) 

MRT 

(oF) PMV

Heating 70 70 –0.17 68 73 –0.17

Cooling 75 75 0.12 78 70 0.12

Second, we devised a radiant heating and cooling water mass flow control strategy with the goal 

of mitigating response time issues related to the high thermal mass of the radiant ceiling. 

Typically, the thermally massive concrete ceiling slab in which the radiant tubes are installed 

would create much slower response times for the radiant heating and cooling system than for a 

typical air system. As such, we devised our water mass flow control using a proactive approach 

to mitigate possible response time issues. Our version of a proactive radiant heating and cooling 

water mass flow control scheme is based on the work of Doebber (2010) and can be visualized as 

a “trickle and ramp” approach (Figure 3-11). The idea is to “charge” the thermally massive slab 

gradually as its temperature begins to trend toward the edges of the dead band, which eliminates

situations in which the slab’s long response time prevents it from providing space operative 

temperatures within the desired dead band and provides the potential to shift load outside periods 

of peak demand by “charging” or storing thermal energy inside the slab. It also reduces overall 

pumping energy via reduced pump power consumption during part-load operation. 

Figure 3-11 “Trickle and ramp” radiant flow control
57

In simulation, our radiant heating and cooling model operated most efficiently with a minimal 

“ramp” period and with no “trickle” period. This is likely due to shorter-than-expected response 

times; with only 4-in. (10.2-cm) thick slabs and radiant tubing placed only 1 in. (2.5 cm) from 

the ceiling surfaces, the system could quickly adjust the operative temperature. Accordingly, 

controlling with larger “trickle” and “ramp” periods increased energy consumption by reducing 

the operative temperature dead band within which the system operated. By specifying a radiant 

heating and cooling system with low effective thermal mass, response time can be shortened to 

allow for a more reactive control approach. By specifying a radiant heating and cooling system 

with high thermal mass (by using a thicker slab and placing the radiant tubing farther from the 

radiant surface, for example), response time is lengthened, allowing for more sophisticated load 

shifting strategies with properly designed proactive control. We would like to explore these 

tradeoffs more in the future (see Section 5.2). As currently specified, our radiant system begins 

to operate at 20% flow capacity when operative temperature comes to within 0.16oF (0.09oC) of 

the heating or cooling set point and ramps up to 100% flow capacity at the heating and cooling 

set points. 

Third, we designed an air system to help the radiant system meet load requirements and to ensure 

temperature set points are met when the radiant system cannot meet them alone. The air 

system’s primary function is to provide ventilation. The DOAS is operated as a 100% OA

system that is sized to meet the ventilation requirements. The averaged ventilation approach 

obscures intricacies in how variations in ventilation requirements between zones would influence 

the interaction between the DOAS and the radiant slab (see Section 5.2). Because office 

buildings have high internal loads and are typically core dominated (high core to perimeter area 

ratio), they tend to be cooling-dominated spaces. We set up our DOAS control strategy 

accordingly: the DOAS supplies ventilation air at 55oF (12.8oC) unless core zone operative 

temperature drops below 70.2oF (21.2oC), in which case ventilation supply temperature is 

ramped up to reach 85oF (29.4oC) at a core zone operative temperature of 69.4oF (20.8oC) (see 

Figure 3-12 for a visual). DOAS heating control was designed such that the DOAS supplies 

68oF (20oC) air at the heating set point. Additional heating is delivered by heating coils at the 

zone level to bring the ventilation air up to the desired supply temperature. Heating coils are 

installed only in the perimeter zones. We assume the additional (booster) heat is unnecessary in 

the core zone. If the core zone needs its ventilation air heated to help the radiant system meet the 

heating load, the DOAS supply temperature control algorithm (as previously stated) was 

designed to comply. None of the zones have secondary zone-level cooling equipment; 

accordingly, although the DOAS meets a significant portion of the cooling load, the burden is 

placed on the radiant cooling system to perform all load trimming in cooling. 
58

Figure 3-12 DOAS supply air temperature control 

 The assumption of core dominance is based on the baseline low-rise and high-rise building 

configurations, which have aspect ratios of 1.5. As aspect ratios are increased (up to 15), this 

assumption becomes less and less valid. 

We also implemented nighttime humidity control. The control scheme is identical to that for the 

baseline VAV system, except that the heating set point during dehumidification is lowered from 

70oF (21oC) to 68oF (20oC) to reflect the differences in daytime operational dry bulb dead bands 

between the baseline and low-energy HVAC systems.

3.4.4.5.2 Radiant Heating and Cooling with DOAS: System Sizing

After establishing the requirements of the radiant heating and cooling system, the next step was 

to ensure such a system could reasonably be designed and implemented. Considerations for this 

process included both system capacity and occupant comfort. The first step was to determine the 

boiler and chiller output temperatures that would be required to maintain the desired comfort 

level (PMV) at the heating and cooling set points. At a dry bulb temperature of 68oF (20oC), the 

radiant heating system is required to provide an MRT of 73oF (22.8oC) to maintain a comfort 

level (PMV of –0.17) equivalent to that for the baseline VAV system at its heating set point. At 

a dry bulb temperature of 78oF (25.6oC), the radiant cooling system is required to provide an 

MRT of 70.2oF (21.2oC) to maintain a comfort level (PMV of 0.12) equivalent to that for the 

baseline VAV system at its cooling set point. 
59

A single-zone EnergyPlus model was used to solve for the ceiling surface temperatures and 

radiant tube temperatures required to produce these MRTs at the specified dry bulb conditions 

(see Table 3-41; Table D-23 for metric units). By fixing the dry bulb temperature in the zone 

and the surface temperature on the topside of the 1-in. (2.5-cm) thick concrete slab layer between 

the radiant tubing and the zone and by specifying an adiabatic boundary condition on the other 

external surfaces to the zone, we were able to calculate the resulting temperature on the 

underside of the 1-in. (2.5-cm) thick concrete layer (the radiant surface temperature) and the 

MRT within the zone (see Figure 3-10 for a visualization of the surface layup). This was an 

iterative process in which the specified topside concrete temperature was adjusted until the 

desired MRT was reached. For this analysis, the conductivity of the ceiling slab was adjusted 

such that the uniform temperature boundary condition imposed on the topside of the 1-in. (2.5-

cm) thick concrete layer was representative of the radiant tube surface temperature (conductivity 

was reduced to account for temperature gradients through the concrete).

Radiant tube surface temperature was used to calculate supply water temperatures (hot water 

supply temperature for heating, cold water supply temperature for cooling) using the following 

assumptions: 

• Supply water temperature is roughly equivalent to the surface temperature of the radiant 

tubing. 

• Temperature differences across the radiant loop are 10oF (5.6oC) for heating and 7oF 

(3.9oC) for cooling (Olesen 2008). 

• Supply water temperature is specified to meet an average radiant tube surface 

temperature throughout the loop. 

Table 3-41 Radiant System Temperatures Required for Baseline Equivalent Comfort 

Control 

Set Point

Air 

Temperature 

(oF) 

Mean Radiant 

Temperature 

(oF) 

Supply Water

Temperature 

(oF) 

Radiant Tube 

Temperature 

(oF) 

Radiant Surface 

Temperature 

(oF) 

Heating 68 73 84 79 77

Cooling 78 70.2 57.3 60.8 65

For a radiant ceiling, maximum and minimum allowable surface temperatures for comfort are 

estimated at 80.6oF (27oC) and 62.6oF (17oC) (Olesen 2008). The radiant surface temperatures 

fall within this range; accordingly, it is feasible to design a radiant heated and cooled ceiling to 

meet the comfort requirements we specified. 

To maximize cooling capacity (and thus minimize pumping energy), a radiant system can be 

designed to the limits of the allowable comfort range; we chose to so model our radiant system to 

ascertain its maximum effectiveness, and to maximize the range of loading requirements for 

which it can satisfy the desired comfort range. The single-zone EnergyPlus model was used to 

characterize the system operation. See Table 3-42 (Table D-24 for metric units) for details. 
60

Table 3-42 Radiant System Temperatures Required for Maximum Capacity 

Control 

Set 

Point

Air 

Temperature 

(oF) 

Mean Radiant 

Temperature 

(oF) 

Supply Water

Temperature 

(oF) 

Radiant Tube 

Temperature 

(oF) 

Radiant Surface 

Temperature 

(oF) 

Heating 68 75.5 88.8 83.8 80.6

Cooling 78 68.8 54.1 57.6 62.6

The total average heat exchange coefficients for a radiant ceiling are 1.0 Btu/h∙ft2

∙F (6 W/m2∙K) 

in heating and 1.9 Btu/h∙ft2∙F (11 W/m2∙K) in cooling (Olesen 2008). For the temperature 

differences between zone air and radiant surface for maximum radiant system conditioning 

capacity at the heating and cooling set points, we calculated heating and cooling capacities of 

13.3 Btu/h∙ft2

 (42 W/m2) and 29.8 Btu/h∙ft2 (94 W/m2), respectively. For 6 in. (0.15 m) on center 

radiant tube spacing and loop temperature drops of 10oF (5.6oC) for heating and 7oF (3.9oC) for 

cooling, we calculated peak per floor water volumetric flow rates for heating and cooling for the 

low-rise and high-rise large office layouts (Table 3-43 [Table D-25 for metric units]). Larger 

values for the low-rise case reflect the larger floor area (by a factor of three).

Table 3-43 Radiant System Peak Volumetric Flow Rates per Floor 

Low-Rise Building High-Rise Building

Maximum 

Heating Flow 

(cfm)

Maximum 

Cooling Flow 

(cfm)

Maximum 

Heating Flow 

(cfm)

Maximum 

Cooling Flow 

(cfm)

40.9 130.9 13.6 43.6

 

3.4.4.5.3 Climate-Specific DOAS Configurations

To reach the aggressive 50% savings goal, we tailored HVAC equipment to each climate type 

separately. The radiant system design is climate independent; only DOAS was configured based 

on climate. For cold and marine climates (4C and 7) where latent loads are generally low, 

DOAS should be outfitted with sensible heat recovery equipment (sensible wheels). For humid 

climates (1A and 5A), latent loads are an important consideration; accordingly, both sensible and 

latent heat recovery equipment (enthalpy wheels) are beneficial. For dry climates (3B-NV and 

5B), DOAS with IDEC that can be adapted to a low-efficiency sensible heat exchanger during 

the winter is an efficient way to condition OA. 

Because of the condensation concerns associated with radiantly cooled surfaces, direct 

evaporative cooling was not considered, even in dry climates. In all climates, humidity is 

monitored and radiant cooling is temporarily halted when condensation on the radiant surface 

would otherwise occur. 

3.4.4.5.4 Cooling Efficiency

A cooling efficiency EEM increases the chiller COP from 6.1 to 7.0 and replaces the baseline 

two-speed cooling tower fan with a variable-speed model. We estimated the cost of this EEM as 

a 10% increase in chiller cost, and assumed its cost is factored into the overall low-energy 

HVAC system costs (see Section 3.4.4.5.8) (RMH Group 2010a). 
61

3.4.4.5.5 Boiler Efficiency

A boiler EEM replaces the baseline boiler with a high-efficiency condensing boiler. Condensing 

boiler efficiency depends on water supply temperature: a high efficiency boiler providing heat to 

a DOAS, for which boiler outlet temperature is near 167 oF (75 oC), has an efficiency range 

between 88% and 97%; a high efficiency boiler providing heat for radiant heating, for which 

boiler outlet temperature is near 104 oF (40 oC), has an efficiency range between 92% and 98%. 

See Figure 3-13 for a graphical comparison between the baseline and EEM boiler efficiency 

curves. We estimated the cost of this EEM as a 20% increase in boiler cost, and assumed its cost 

is factored into the overall low-energy HVAC system costs (see Section 3.4.4.5.8) (RMH Group 

2010a). 

Figure 3-13 Boiler efficiency curves for the baseline and low-energy boilers

3.4.4.5.6 Higher Efficiency Fans

Baseline fan efficiency for the RTUs and AHUs in the baseline VAV systems was set to 52.1% 

and 50.1% for the low-rise and high-rise cases, respectively, as per the requirements of Appendix

G.3.1.2.9 of ASHRAE 90.1-2004 (ASHRAE 2004c). We set our EEM fan efficiency to 75% 

(total fan efficiency of 69%, including motor efficiency), corresponding to a housed, centrifugal 

airfoil configuration. 

For the DOAS, we assumed a nominal 3.5 in. w.c. (875 Pa) of static pressure drop for the supply 

air path and 1.5 in. w.c. (375 Pa) of static pressure drop for the return air path (which is required

with the inclusion of energy recovery equipment), for a total nominal static pressure drop of 5.0 

in. w.c. (1250 Pa). We reduced nominal static pressure based on DOAS configuration (to 

account for flow required for building pressurization and/or 6 ACH of restroom exhaust) to 

obtain effective operating static pressure drops; see Section 3.4.4.6.2 for details. We modeled 

static pressure reset to 0.5 in. w.c. (125 Pa) (PG&E 2007). 
62

We estimated the cost of this EEM as a 10% increase in the cost of the air distribution units 

(RTUs or AHUs), and assumed its cost is factored into the overall low-energy HVAC system 

costs (see Section 3.4.4.5.8) (Priebe 2010). 

3.4.4.5.7 Economizers

An EEM for waterside economizing was made available. Costs to install and operate 

economizers were assumed to be included as part of the low-energy HVAC system costs. 

Airside economizing was applied to the baseline HVAC system where required by ASHRAE 

90.1-2004, but was not considered as an EEM because it is incompatible with DOAS. DOAS 

reduces the size of the air system to what is required for ventilation; oversizing it to allow for 

airside economizing defeats that purpose.

3.4.4.5.8 Radiant Heating and Cooling with DOAS: Summary and Costs

HVAC cost estimates for the low-rise and high-rise radiant heating and cooling with DOAS 

system were provided by the RMH Group based on the average sizing results from a preliminary 

set of low-energy model simulations (Table 3-44 and Table 3-45; Table D-26 and Table D-27 for 

metric units); the equipment breakdowns upon which their estimates were based are presented in 

Table 3-46 (RMH Group 2010a). In all low-energy models, radiant boiler and chiller capacities 

were hard-sized as needed to achieve the maximum heating and cooling capacities defined by 

Table 3-42 and Table 3-43 (Table D-24 and Table D-25 for metric units).

Table 3-44 Low-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes

Climate

Low-Rise Low-Energy

DOAS Boiler 

(kBtu/h)

DOAS Chiller 

(tons)

DOAS Fan 

(cfm)

Radiant Boiler 

(kBtu/h)

Radiant Chiller 

(tons)

Average 3839 177 56574 4623 867

Table 3-45 High-Rise Low-Energy Radiant with DOAS HVAC System Cost Estimation Sizes

Climate

High-Rise Low-Energy: 

Code Compliant

High-Rise Low Energy:

Common Practice

DOAS 

Boiler 

(kBtu/h)

DOAS 

Chiller 

(tons)

DOAS

Fan 

(cfm)

Radiant 

Boiler 

(kBtu/h)

Radiant 

Chiller 

(tons)

DOAS 

Boiler 

(kBtu/h)

DOAS 

Chiller 

(tons)

DOAS 

Fan 

(cfm)

Radiant 

Boiler 

(kBtu/h)

Radiant 

Chiller 

(tons)

Average 7438 175 55091 6149 1145 7438 175 55091 6149 1145

 Table 3-46 Low-Energy HVAC System Cost Estimate Equipment Breakdown

HVAC Component Radiant Heating and Cooling 

With DOAS, Low-Rise

Radiant Heating and Cooling 

With DOAS, High-Rise

Chillers and cooling tower (#) 3 3

Boilers (#) 5 5

Air distribution units (#) 2 4

Perimeter heating coils (#) 64 120

Pumps (#) 11 11
63

The cost of the low-energy HVAC system was estimated at $22.07/ft2 ($237.56/m2) for the lowrise case and at $22.51/ft2

 ($242.30/m2) for the high-rise case (see Table 3-47; Table D-28 for 

metric units). For the equipment sizes in Table 3-44 and Table 3-45, capacity-based costs of 

$9,741.25/ton of cooling ($2,769.76/kW) and $7,858.77/ton of cooling ($2,234.51/kW) for the 

low-rise and high-rise cases, respectively, were calculated and applied to simulations to allow for 

cost variation based on differences in required system capacities for different climate zones. The 

low-rise estimate assumes the use of RTUs for the air distribution system; the high-rise estimate 

assumes air distribution via AHUs (one unit per every three floors), which is more practical from 

a ducting standpoint for a high-rise building. 

Table 3-47 Low-Energy HVAC System Cost Estimate Breakdown

HVAC Input Radiant Heating and Cooling 

With DOAS, Low-Rise

Radiant Heating and Cooling 

With DOAS, High-Rise

Chillers and cooling tower ($/ft2) $1.52 $1.52

Boilers ($/ft2) $0.60 $0.60

Radiant heating and cooling ($/ft2) $10.89 $10.81

Air distribution units ($/ft2) $1.00 $1.09

Perimeter heating coils ($/ft2) $0.11 $0.21

Pumps ($/ft2) $0.39 $0.39

Ductwork ($/ft2) $3.69 $4.61

Air system water distribution ($/ft2) $2.61 $2.03

Life Safety ($/ft2) $0.09 $0.09

Air and water balance ($/ft2) $0.18 $0.18

Temperature controls ($/ft2) $1.00 $1.00

Total ($/ft2) $22.07 $22.51

3.4.4.6 Outside Air

We considered three options beyond code minimum for reducing OA loads: carbon dioxide 

(CO2) DCV, energy recovery from exhaust air, and natural ventilation. 

3.4.4.6.1 Demand Control Ventilation

DCV was not made available as an EEM because it provides only minimal energy savings in an 

office building, which has a low per-person ventilation requirement (5 cfm/person [2.36 

L/s∙person]) that amounts to roughly 0.04 cfm/ft2

 (0.20 L/s∙m2). Extensive changes would need 

to be made to implement the DOAS (replacing a constant volume ventilation system with a VAV

system, installing CO2 sensors, etc.) It would be cost prohibitive based on the high 

implementation costs.

3.4.4.6.2 Energy Recovery

Where appropriate by climate, energy recovery equipment is incorporated into DOAS design 

such that exhaust air can be used to precondition ventilation air. Humid climates can be 

equipped with sensible and latent energy recovery equipment (enthalpy wheels). Cold and 

marine climates can be equipped with sensible energy recovery equipment (sensible wheels). 

Dry climates can be equipped with an IDEC that can be converted to a low-efficiency sensible 
64

heat exchanger during winter months. Costs for energy recovery were assumed to be included as 

part of the cost of the high-efficiency DOAS in the low-energy HVAC system cost breakdown. 

An enthalpy wheel with nominal sensible effectiveness of 60% and latent effectiveness of 50% 

was available as an EEM in climate zones 1A (Miami) and 5A (Chicago). We assumed the 

pressure drop through one side of the enthalpy wheel at 0.7 in. w.c. (175 Pa) (Murphy and 

Bradley 2008). Because air passes through the wheel twice (once when it enters the building as 

unconditioned OA and once when it leaves the building as conditioned return air), an overall 

pressure drop of 1.4 in. w.c. (350 Pa) was applied to the implementation of an enthalpy wheel.

A sensible recovery wheel with nominal sensible effectiveness of 60% was available as an EEM 

in climate zones 4C (Seattle) and 7 (Duluth). Sensible heat recovery wheels (which have a latent 

effectiveness of zero) have lower pressure drops than enthalpy wheels because they do not have 

to transfer moisture. We modeled our sensible wheel as having a total added pressure drop of 1 

in. w.c. (250 Pa), assuming 0.5 in. w.c. (125 Pa) pressure drop through each side (Murphy and 

Bradley 2008). 

For dry climates (3B-NV [Las Vegas] and 5B [Boulder]), a hybrid IDEC/sensible heat recovery 

system was available as an EEM. We assumed the evaporative media could theoretically be 

dried during the winter so the IDEC unit could serve as a low effectiveness sensible heat 

exchanger. We modeled our IDEC unit with a maximum nominal wet bulb effectiveness of 75% 

and a high-efficiency (69% total efficiency) secondary (return) air stream fan that adds a total of 

1.0 in. w.c. (250 Pa) of pressure drop (0.5 in. w.c. [125 Pa] to the primary air stream and 0.5 in. 

w.c. [125 Pa] to the secondary air stream). During the winter, when the unit converts to a 

sensible heat exchanger, we assumed a nominal sensible effectiveness of 40%; this estimate was 

based on the unit operating as a low-effectiveness version of a fixed-plate heat exchanger, for 

which a typical effectiveness is 60%–70% (Murphy and Bradley 2008). 

Nominal efficiencies needed to be decreased to account for flow reduction of the return air 

stream caused by building pressurization and/or restroom exhaust. We assumed 10% of the OA

is required to pressurize the building (and reduce infiltration by 75%) during HVAC operation, 

and that the remaining 90% is available for energy recovery. For enthalpy and sensible wheels, 

leakage can occur between the entering and leaving air streams such that contamination concerns 

prevent restroom exhaust from being used for energy recovery; accordingly, we reduced the 

return air stream flow available for energy recovery by 6 ACH of restroom exhaust for DOAS 

equipped with enthalpy or sensible wheels. For IDEC, the primary and secondary air streams are 

isolated from each other such that restroom exhaust can be used for energy recovery. For the 

resulting return air to supply air flow ratios of 0.71 for DOAS with energy recovery wheels and 

0.9 for DOAS with IDEC, we calculated the following operational efficiencies: for enthalpy 

wheels, 51% sensible effectiveness, 42% latent effectiveness; for sensible wheels, 51% sensible 

effectiveness; and for IDEC, 72% maximum wet bulb effectiveness. We also used the return air 

to supply air flow ratios to reduce fan static pressure drop (as mentioned in Section 3.4.4.5.6); 

see Table 3-48 (Table D-29 for metric units) for details.
65

Table 3-48 Low-Energy HVAC System Operational Static Pressure Breakdown

Building 

Type

Low-Rise Low-Energy 

(in. w.c.)

High-Rise Low-Energy: 

Code Compliant 

(in. w.c.)

High-Rise Low Energy: 

Common Practice 

(in. w.c.)

Enthalpy 

Wheel

Sensible 

Wheel IDEC Enthalpy Wheel

Sensible 

Wheel IDEC Enthalpy Wheel

Sensible 

Wheel IDEC

Supply 

and 

return 

fans

4.58 4.58 4.85 4.57 4.57 4.85 4.57 4.57 4.85

Energy 

recovery

1.40 1.00 1.00 1.40 1.00 1.00 1.40 1.00 1.00

Total 5.98 5.58 5.85 5.97 5.57 5.84 5.97 5.57 5.84

3.4.4.6.3 Natural Ventilation

Natural ventilation was not available as an EEM because accurately capturing its effects through 

simulation is difficult. Achieving energy savings by implementing natural ventilation (in an 

actual building or a simulation model) requires accurate inputs and sophisticated control. 

Preliminary modeling indicates more efforts are necessary to validate this EEM. 

3.4.4.7 Service Water Heating

An SWH EEM increases thermal efficiency from 80% to 90%. We assigned no incremental cost 

specifically to this EEM, because we assumed SWH costs are included in our whole-building 

area-normalized capital costs.

3.4.4.8 Photovoltaic Panels

We ignore any electricity tariff changes associated with varying amounts of PV, as 5-TLCC and 

the amount of electricity generated by the PV panels vary linearly with panel area. We thus 

include a single PV EEM, then use a postprocessing step to determine the PV panel area needed 

to reach 50% energy savings (for cases where PV is selected and required to achieve the goal).

We assumed the following in all cases: 

• The panels are 13% efficient. 

• The direct current to alternating current inverters are 96% efficient. 

• The panels are installed flat on the roof. 

• The PV efficiency does not degrade with increasing temperature. 

• The panels do not shade the roof. 

• The cost is $4.00 per installed Watt for panels of this efficiency based on data collected 

through an internal PV study. 

The EEM used by Opt-E-Plus covers up to 60% of the roof area with PV panels and is sized 

assuming 1000 W/m2 incident solar radiation.
66

4.0 Results

This section presents the results of the energy modeling performed for this report. Section 4.1

includes the baseline model economic and energy use results, both for the ASHRAE 90.1-2004 

(ASHRAE 2004c) compliant baselines that serve as the standard for our percent energy savings 

calculations and ASHRAE 90.1-2007 (ASHRAE 2007b) compliant baselines that are provided 

for reference. Section 4.2 describes the selected low-energy model results (both the preliminary 

low-energy models and the selected low-energy models from the subsequent optimizations) for 

each climate zone and compares them to the baseline results. The EEMs selected for the lowenergy models in each climate zone are also listed. 

In this section, the following metrics are used to report performance: 

• Net site EUI (MJ/m2·yr or kBtu/ft2·yr). The whole-building net site yearly energy use 

(Section 2.2.1.1) divided by the building floor area. 

• Net source EUI (MJ/m2·yr or kBtu/ft2·yr). The whole-building net source yearly energy 

use (Section 2.2.1.1) divided by the building floor area. 

• Energy cost intensity ($/m2·yr or $/ft2∙yr). The cost of the yearly electrical and natural 

gas consumption divided by the building floor area. 

• Energy emissions intensity (kgCO2/ m2·yr or lbCO2/ ft2∙yr). The yearly quantity of CO2

emissions generated by the building divided by the building floor area. 

• 5-TLCC intensity ($/m2 or $/ft2). The 5-TLCC divided by the building floor area. It 

represents the total cost of the building for a five-year analysis period (see Section 

3.1.2.6).

• Electricity intensity (kWh/m2·yr or kWh/ft2·yr). The yearly electrical consumption 

divided by the building floor area. 

• Natural gas intensity (kWh/m2·yr or therms/ft2·yr). The yearly natural gas consumption 

divided by the building floor area. 

• Capital cost intensity ($/m2 or $/ft2). The total cost for materials, installation, fees, and 

commissioning divided by the building floor area. 

• Peak monthly electricity demand (kW). The maximum 15-minute net electrical 

demand, taking credit for electricity produced by PV, computed for each month of the 

annual simulation. 

4.1 Baseline Models

This section summarizes the energy and economic performance of the baseline models described 

in Section 3.3. 

4.1.1 ASHRAE 90.1-2004 Baseline Models: Performance

The energy and cost intensities of the ASHRAE 90.1-2004 baseline models are displayed in 

Figure 4-1 and Figure 4-2 for the low-rise and high-rise cases, respectively and summarized in 

Table 4-1 and Table 4–2 (Table D-30 and Table D-31 for metric units) for the low-rise case, in 

Table 4-3 and Table 4-4 (Table D-32 and Table D-33 for metric units) for the code-compliant 
67

high-rise case, and in Table 4-5 and Table 4-6 (Table D-34 and Table D-35 for metric units) for 

the common practice high-rise case.

Figure 4-1 Low-rise EUI by end use for baseline energy models
68

Figure 4-2 High-rise EUI by end use for baseline energy models

Table 4-1 ASHRAE 90.1-2004 Low-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 115.2 78.5 73.4 88.2 74.9 88.0

Source EUI (kBtu/ft2·yr) 337.4 238.1 211.8 242.3 216.9 227.6

Energy emissions intensity 

(lbCO2/ ft2

·yr) 45.6 32.3 28.6 32.5 29.3 30.3

Electricity intensity (kWh/ft2·yr) 27.3 19.6 17.0 18.8 17.4 16.9

Natural gas intensity 

(therms/ft2

·yr) 0.221 0.115 0.154 0.239 0.155 0.301

Peak demand (kW) 1984 1750 1721 1908 1690 1818
69

Table 4-2 ASHRAE 90.1-2004 Low-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $139.07 $128.90 $126.46 $134.81 $124.75 $130.66

Capital cost intensity ($/ft2) $119.51 $114.68 $113.43 $118.93 $111.99 $116.07

Annual energy cost intensity 

($/ft2

·yr) $2.60 $1.84 $1.67 $1.93 $1.70 $1.83

Annual electricity cost 

intensity ($/ft2

·yr) $2.32 $1.70 $1.48 $1.64 $1.51 $1.47

Annual natural gas cost 

intensity ($/ft2

·yr) $0.27 $0.14 $0.19 $0.30 $0.19 $0.37

Table 4-3 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 107.3 78.8 74.9 86.9 74.7 86.6

Source EUI (kBtu/ft2·yr) 315.7 238.2 213.3 239.3 216.6 225.2

Energy emissions intensity 

(lbCO2/ft2

·yr) 42.7 32.3 28.7 32.1 29.2 30.0

Electricity intensity (kWh/ft2·yr) 25.6 19.6 16.9 18.6 17.4 16.8

Natural gas intensity 

(therms/ft2

·yr) 0.200 0.118 0.170 0.233 0.153 0.291

Peak demand (kW) 1940 1758 1746 1925 1717 1872

Table 4-4 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $144.56 $137.40 $135.54 $142.35 $134.29 $139.48

Capital cost intensity ($/ft2) $127.17 $123.91 $122.99 $127.49 $122.01 $125.58

Annual energy cost intensity 

($/ft2

·yr) $2.44 $1.85 $1.69 $1.91 $1.71 $1.82

Annual electricity cost 

intensity ($/ft2

·yr) $2.19 $1.70 $1.48 $1.63 $1.52 $1.46

Annual natural gas cost 

intensity ($/ft2

·yr) $0.25 $0.15 $0.21 $0.29 $0.19 $0.36
70

Table 4-5 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 108.7 83.8 82.8 95.8 82.3 98.5

Source EUI (kBtu/ft2·yr) 322.2 250.7 226.8 255.0 230.6 242.9

Energy emissions intensity 

(kgCO2/ft2

·yr) 43.6 34.0 30.4 34.1 31.0 32.2

Electricity intensity (kWh/ft2·yr) 26.2 20.5 17.6 19.4 18.1 17.4

Natural gas intensity 

(therms/ft2

·yr) 0.191 0.138 0.227 0.296 0.205 0.390

Peak demand (kW) 1999 1868 1879 2066 1850 2036

Table 4-6 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $150.65 $145.69 $144.13 $151.04 $142.60 $149.03

Capital cost intensity ($/ft2) $132.51 $130.84 $129.96 $134.43 $128.71 $133.11

Annual energy cost intensity 

($/ft2

·yr) $2.49 $1.96 $1.83 $2.07 $1.85 $2.00

Annual electricity cost 

intensity ($/ft2

·yr) $2.25 $1.79 $1.55 $1.70 $1.60 $1.53

Annual natural gas cost 

intensity ($/ft2

·yr) $0.24 $0.17 $0.28 $0.36 $0.25 $0.48

A detailed end use breakdown of energy consumption for the ASHRAE 90.1-2004 baseline 

models is presented in Table 4-7 to Table 4-9 for the low-rise, code-compliant high-rise, and 

common practice high-rise cases, respectively (Table D-36 to Table D-38 for metric units). For 

each end use and for the building as a whole, EUIs corresponding to 50% net site energy savings 

are defined. The 50% savings value for each end use is provided as a reference for comparison 

with low-energy results; we do not imply that the low-energy models need to achieve 50% net 

site energy savings for each end use. The 50% savings goals for the high-rise cases are defined 

with respect to the code-compliant baseline case, as our goal is to find designs that achieve 50% 

net site energy savings with respect to ASHRAE 90.1-2004 and ASHRAE 62.1-2004. Thus, the 

common practice high-rise cases need to achieve larger than 50% net site EUI savings to achieve 

the low-energy savings target.
71

Table 4-7 Comparison of Low-Rise EUI by End Use Between Baseline and 50% Savings Target

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 21.4 10.7 10.7 5.4 14.4 7.2 22.8 11.4 14.4 7.2 28.8 14.4

Cooling 33.9 17.0 13.2 6.6 6.5 3.3 11.0 5.5 7.3 3.6 5.6 2.8

Interior lighting 14.8 7.4 14.8 7.4 14.8 7.4 14.8 7.4 14.8 7.4 14.8 7.4

Interior equipment 4.8 2.4 4.8 2.4 4.8 2.4 4.8 2.4 4.8 2.4 4.8 2.4

Fans 5.2 2.6 3.2 1.6 2.1 1.0 3.0 1.5 2.8 1.4 3.0 1.5

Pumps 4.1 2.1 1.9 1.0 1.1 0.6 1.7 0.9 1.2 0.6 1.2 0.6

Heat rejection 2.3 1.1 1.1 0.5 0.6 0.3 0.8 0.4 0.6 0.3 0.5 0.2

Water systems 0.7 0.3 0.8 0.4 1.1 0.5 1.1 0.6 1.1 0.6 1.3 0.7

Data center 28.0 14.0 28.0 14.0 28.0 14.0 28.0 14.0 28.0 14.0 28.0 14.0

Total end uses 115.2 57.6 78.5 39.3 73.4 36.7 88.2 44.1 74.9 37.5 88.0 44.0

Table 4-8 Comparison of Code-Compliant High-Rise EUI by End Use Between Baseline and 50% Savings Target

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 19.3 9.7 11.0 5.5 15.9 8.0 22.2 11.1 14.2 7.1 27.8 13.9

Cooling 30.1 15.0 13.9 7.0 7.0 3.5 11.3 5.6 7.9 3.9 6.1 3.0

Interior lighting 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2

Interior equipment 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3

Fans 4.9 2.4 3.2 1.6 2.2 1.1 3.0 1.5 2.9 1.5 3.0 1.5

Pumps 3.6 1.8 2.0 1.0 1.2 0.6 1.7 0.9 1.2 0.6 1.2 0.6

Heat rejection 2.0 1.0 1.1 0.6 0.6 0.3 0.8 0.4 0.6 0.3 0.5 0.2

Water systems 0.7 0.3 0.8 0.4 1.1 0.5 1.1 0.6 1.1 0.6 1.3 0.7

Data center 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8

Total end uses 107.3 53.7 78.8 39.4 74.9 37.4 86.9 43.4 74.7 37.4 86.6 43.3
72

Table 4-9 Comparison of Common Practice High-Rise EUI by End Use Between Baseline and 50% Savings Target

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 18.5 9.7 13.0 5.5 21.7 8.0 28.5 11.1 19.4 7.1 37.7 13.9

Cooling 32.2 15.0 16.1 7.0 8.4 3.5 13.2 5.6 9.5 3.9 7.3 3.0

Interior lighting 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2 14.4 7.2

Interior equipment 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3 4.7 2.3

Fans 4.6 2.4 3.5 1.6 2.7 1.1 3.3 1.5 3.5 1.5 3.5 1.5

Pumps 3.8 1.8 2.3 1.0 1.4 0.6 2.0 0.9 1.5 0.6 1.4 0.6

Heat rejection 2.1 1.0 1.3 0.6 0.7 0.3 1.0 0.4 0.7 0.3 0.6 0.2

Water systems 0.7 0.3 0.8 0.4 1.1 0.5 1.1 0.6 1.1 0.6 1.3 0.7

Data center 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8 27.7 13.8

Total end uses 108.7 53.7 83.8 39.4 82.8 37.4 95.8 43.4 82.3 37.4 98.5 43.3
73

4.1.2 ASHRAE 90.1-2007 Baseline Models: Performance

To analyze the impact of energy code changes on energy savings, baseline models were 

constructed that minimally satisfy ASHRAE 90.1-2007. Relevant differences between the 

ASHRAE 90.1-2004 and ASHRAE 90.1-2007 baselines are the window, wall, and roof 

performance requirements. Ventilation requirements are consistent between the ASHRAE 90.1-

2004 and ASHRAE 90.1-2007 baselines because ASHRAE 62.1-2004 is used as the ventilation 

Standard in both cases.

For completeness, the 90.1-2007 baseline windows, walls, and roofs are summarized in Table 

4-10 to Table 4-14 (Table D-39 to Table D-43 for metric units). To compare to the 90.1-2004 

values, see Table 3-9 to Table 3-16 (Table D-2 to Table D-9 for metric units).

Table 4-10 ASHRAE 90.1-2007 Low-Rise Baseline Exterior Wall Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zone 

4C

Climate Zones 

5A, and 5B

Climate Zone 

7 

Key

Baseline 

Wall 

Construction 

No c.i.

Baseline Wall 

Construction 

R-7.6 c.i.

Baseline Wall 

Construction 

R-9.5 c.i.

Baseline Wall 

Construction 

R-11.4 c.i.

Baseline Wall 

Construction 

R-15.2 c.i.

Assembly 

U-factor 

(Btu/h·ft2

·°F)

1.010 0.137 0.114 0.097 0.076

Capital cost 

($/ft2

) $36.15 $44.40 $44.75 $45.10 $45.80

Table 4-11 ASHRAE 90.1-2007 High-Rise Baseline Exterior Wall Constructions

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, 5B, and 7

Key

Baseline Wall 

Construction 

R-13.0

Baseline Wall 

Construction 

R-13.0 + R-3.8 c.i.

Baseline Wall 

Construction 

R-13.0 + R-7.5 c.i.

Assembly

U-factor 

(Btu/ h·ft2

·°F)

0.139 0.091 0.068

Capital cost

($/ft2

) $35.75 $36.65 $37.15

Table 4-12 ASHRAE 90.1-2007 Baseline Roof Constructions

Properties Climate Zone 

1A

Climate Zones 

3B-NV, 4C, 5A, 5B, and 7

Key Baseline Roof 

Construction R-15.0 c.i.

Baseline Roof 

Construction R-20.0 c.i.

Assembly U-factor 

(Btu/h·ft2

·°F) 0.066 0.050

Capital cost ($/ft2) $9.15 $9.59
74

Table 4-13 ASHRAE 90.1-2007 Low-Rise Baseline Window Constructions

Properties Climate Zone 

1A

Climate Zones 

3B-NV

Climate Zones

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.250 0.250 0.400 0.450

VLT 0.250 0.318 0.508 0.450

U-factor 

(Btu/h·ft2

·°F) 1.200 0.650 0.550 0.450

Capital cost 

($/ft2

) $49.67 $52.40 $47.57 $47.23

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22

Table 4-14 ASHRAE 90.1-2007 High-Rise Baseline Window Constructions

Properties Climate Zone 

1A

Climate Zones 

3B-NV

Climate Zones

4C, 5A, and 5B

Climate Zone 

7 

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.250 0.250 0.400 0.450

VLT 0.250 0.318 0.508 0.450

U-factor 

(Btu/h·ft2

·°F) 1.200 0.650 0.550 0.450

Capital cost 

($/ft2

) $76.68 $79.41 $74.58 $74.24

Fixed O&M 

cost ($/ft2

) $0.22 $0.22 $0.22 $0.22

The performance of the ASHRAE 90.1-2007 baseline models is summarized in Table 4-17 and 

Table 4-18 (Table D-46 and Table D-47 for metric units) for the low-rise case, in Table 4-19 and 

Table 4-20 (Table D-48 and Table D-49 for metric units) for the code compliant high-rise case, 

and in Table 4-21 and Table 4-22 (Table D-50 and Table D-51 for metric units) for the common 

practice high-rise case. Table 4-15 and Table 4-16 (Table D-44 and Table D-45 for metric units) 

present performance comparisons between the ASHRAE 90.1-2004 and ASHRAE 90.1-2007 

baselines for the low-rise and high-rise cases, respectively.
75

Table 4-15 Low-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines

Climate Zone

ASHRAE 90.1-2004 

Baseline Site Energy Use 

(kBtu/ft2∙yr)

ASHRAE 90.1-2007 

Baseline Site Energy Use 

(kBtu/ft2∙yr)

1A Miami 115.2 116.0

3B Las Vegas 78.5 78.6

4C Seattle 73.4 72.6

5A Chicago 88.2 87.3

5B Denver 74.9 74.1

7 Duluth 88.0 85.5

Table 4-16 High-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines

Climate Zone

ASHRAE 90.1-2004 Baseline Site 

Energy Use (kBtu/ft2∙yr)

ASHRAE 90.1-2007 Baseline Site 

Energy Use (kBtu/ft2∙yr)

Code Compliant Common Practice Code Compliant Common Practice

1A Miami 107.3 108.7 107.9 108.6

3B Las Vegas 78.8 83.8 78.8 84.7

4C Seattle 74.9 82.8 73.3 82.8

5A Chicago 86.9 95.8 86.1 95.4

5B Denver 74.7 82.3 73.9 82.1

7 Duluth 86.6 98.5 84.3 94.5

Table 4-17 ASHRAE 90.1-2007 Low-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 116.0 78.6 72.6 87.3 74.1 85.5

Source EUI (kBtu/ft2·yr) 339.1 237.9 211.1 241.5 216.0 224.8

Energy emissions (lbCO2/ ft2·yr) 45.8 32.3 28.5 32.4 29.2 30.0

Electricity intensity (kWh/ft2·yr) 27.4 19.6 17.0 18.8 17.4 16.9

Natural gas intensity (therms/ft2·yr) 0.226 0.116 0.145 0.229 0.146 0.277

Peak demand (kW) 1982 1747 1726 1908 1693 1813
76

Table 4-18 ASHRAE 90.1-2007 Low-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $139.31 $129.24 $129.24 $134.89 $124.93 $130.56

Capital cost intensity ($/ft2) $119.72 $115.06 $115.06 $119.06 $112.19 $116.16

Annual energy cost intensity 

($/ft2

·yr) $2.61 $1.84 $1.66 $1.92 $1.69 $1.80

Annual electricity cost intensity 

($/ft2

·yr) $2.33 $1.70 $1.48 $1.64 $1.51 $1.46

Annual natural gas cost intensity 

($/ft2

·yr) $0.28 $0.14 $0.18 $0.28 $0.18 $0.34

Table 4-19 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 107.9 78.8 73.3 86.1 73.9 84.3

Source EUI (kBtu/ft2·yr) 316.1 238.2 211.9 238.6 216.0 222.4

Energy emissions intensity (lbCO2/ 

ft2

·yr) 42.7 32.3 28.6 32.0 29.2 29.7

Electricity intensity (kWh/ft2·yr) 25.6 19.6 17.0 18.6 17.4 16.8

Natural gas intensity (therms/ft2·yr) 0.206 0.118 0.153 0.224 0.144 0.269

Peak demand (kW) 1934 1757 1755 1930 1723 1862

Table 4-20 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $144.87 $138.15 $136.10 $142.63 $134.60 $139.31

Capital cost intensity ($/ft2) $127.51 $124.66 $123.57 $127.78 $122.32 $125.63

Annual energy cost intensity 

($/ft2

·yr) $2.44 $1.85 $1.67 $1.90 $1.70 $1.79

Annual electricity cost intensity

($/ft2

·yr) $2.18 $1.70 $1.49 $1.63 $1.52 $1.46

Annual natural gas cost 

intensity ($/ft2

·yr) $0.26 $0.15 $0.19 $0.28 $0.18 $0.33
77

Table 4-21 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Energy Performance

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (kBtu/ft2·yr) 108.6 84.7 82.8 95.4 82.1 94.5

Source EUI (kBtu/ft2·yr) 322.2 252.4 227.5 255.2 231.0 238.2

Energy emissions intensity 

(lbCO2/ ft2

·yr) 43.6 34.2 30.5 34.1 31.1 31.6

Electricity intensity (kWh/ft2·yr) 26.2 20.6 17.7 19.5 18.2 17.4

Natural gas intensity 

(therms/ft2·yr) 0.191 0.144 0.224 0.289 0.199 0.350

Peak demand (kW) 2000 1879 1898 2082 1866 2028

Table 4-22 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Costs

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC intensity ($/ft2) $151.50 $146.75 $144.80 $151.58 $143.16 $148.55

Capital cost intensity ($/ft2) $133.35 $131.74 $130.47 $134.87 $129.15 $132.92

Annual energy cost intensity 

($/ft2·yr) $2.48 $1.98 $1.84 $2.07 $1.85 $1.95

Annual electricity cost 

intensity ($/ft2·yr) $2.25 $1.80 $1.56 $1.71 $1.61 $1.52

Annual natural gas cost 

intensity ($/ft2·yr) $0.24 $0.18 $0.28 $0.36 $0.24 $0.43

4.1.3 Discussion

EUIs for the ASHRAE 90.1-2004 baselines are similar for the low-rise (88.3 kBtu/ft2

·yr [1002 

MJ/m2

·yr] on average) and code-compliant high-rise (88.5 kBtu/ft2·yr [1004 MJ/m2·yr] on 

average) cases, but larger for the less insulated common practice high-rise case (97.8 kBtu/ft2

·yr

[1110 MJ/m2

·yr] on average), as one would expect. This is especially the case in more severe 

climates where already large heating or cooling loads are further magnified by a less insulated 

envelope. In all cases the data center is responsible for a significant fraction (averaging 28%–

32%) of total building energy consumption. 

The ASHRAE 90.1-2007 baseline energy models perform similarly to the ASHRAE 90.1-2004 

baseline models. In all but the coldest climate zone (7), EUI changed by less than 1.3% when 

replacing ASHRAE 90.1-2004 with ASHRAE 90.1-2007. In climate zone 7, ASHRAE 90.1-

2007 baselines saved 3.1%–4.6% in EUI compared to their ASHRAE 90.1-2004 counterparts. 

Capital cost and 5-TLCC values are similar between the corresponding ASHRAE 90.1-2007 and 

ASHRAE 90.1-2004 baseline models. Capital costs are slightly higher for the ASHRAE 90.1-

2007 baseline models because of the slightly more stringent envelope insulation requirements of 

ASHRAE 90.1-2007 compared to ASHRAE 90.1-2004; 5-TLCC costs are slightly higher except 

in climate zone 7, where slightly more significant energy savings for the ASHRAE 90.1-2007 

baselines were enough to offset increased capital costs during the five-year analysis period. 
78

4.2 Selected Low-Energy Models

The models described in this section meet the 50% energy savings goal over ASHRAE 90.1-

2004 and ASHRAE 62.1-2004 (see Section 2.2). The models were assembled according to the 

procedure outlined in Section 2.4: first, we applied packages of the EEMs described in Section 

3.4 to the baseline models described in Section 3.3 to identify a set of preliminary low-energy 

models aimed at achieving 50% net site energy savings; then we used the preliminary lowenergy models as starting points for optimizations that refined the package of EEM selections to 

achieve the best possible combination of net site energy savings and 5-TLCC (see Section 

3.1.2.6). 

4.2.1 Preliminary Low-Energy Models: Selection 

We assembled the preliminary low-energy models according to the procedure outlined in Section 

2.4.2. We used the design of the RSF and the results from Thornton, Wang et al. (2009) as a 

basis to define our low-energy HVAC system as a radiant heated and cooled system with DOAS. 

To mitigate concerns about condensation with radiant cooling, we minimized infiltration by 

installing an envelope air barrier and entrance vestibules. We applied climate-specific energy 

recovery strategies and then used the results from Hale, Leach et al. (2009) and Leach, Hale et al. 

(2009) and industry feedback to make the remaining EEM selections. Preliminary low-energy 

DOAS design was climate specific (see Section 3.4.4.6.2). Waterside economizing was 

implemented for all but the humid climates (Miami [1A] and Chicago [5A]), where opportunities 

for wet bulb depression are limited. Specific EEM selections are presented in Table 4-23 to

Table 4-25 for the low-rise, code-compliant high-rise, and common practice high-rise cases, 

respectively.
79

Table 4-23 Preliminary Low-Rise Low-Energy Model EEM Selections

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio 1.5 1.5 1.5 1.5 1.5 1.5

Fenestration Facade window 

fraction 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR

Shading Shading depth None None None None None None

Fabric

Fenestration Windows

Double pane 

with low-e and 

argon

Double pane 

with low-e 

and argon

Double pane 

with low-e 

and argon

Double pane 

with low-e and 

argon

Double pane 

with low-e and 

argon

Double pane 

with low-e and 

argon

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Opaque 

constructions

Walls R-22.5 c.i. 

mass walls

R-22.5 c.i. 

mass walls

R-22.5 c.i. 

mass walls

R-22.5 c.i. 

mass walls

R-22.5 c.i. 

mass walls

R-22.5 c.i. 

mass walls

Roof

R-15 c.i. 

Insulation 

above deck

R-15 c.i. 

Insulation 

above deck

R-15 c.i. 

Insulation 

above deck

R-15 c.i. 

Insulation 

above deck

R-15 c.i. 

Insulation 

above deck

R-15 c.i. 

Insulation 

above deck

Equipment

Energy generation PV None None None None None None

HVAC system System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant heated 

and cooled

ceilings and 

DOAS

Lighting

Daylighting 

Controls

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set 

point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor air ERV Enthalpy wheel 

IDEC with 

conversion 

to sensible 

heat 

recovery

Sensible 

wheel

Enthalpy 

wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible wheel

Economizer Waterside 

economizer No Yes Yes No Yes Yes
80

Table 4-24 Preliminary Code Compliant High-Rise Low-Energy Model EEM Selections

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio 1.5 1.5 1.5 1.5 1.5 1.5

Fenestration Facade window 

fraction 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR

Shading Shading depth Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Fabric

Fenestration Windows

Double pane 

with low-e and 

argon

Double pane 

with low-e 

and argon

Double pane 

with low-e 

and argon

Double pane 

with low-e and 

argon

Double pane 

with low-e and 

argon

Double pane 

with low-e and 

argon

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and

front door 

vestibule

Opaque 

constructions

Walls R-22.5 c.i. 

spandrel walls

R-22.5 c.i. 

spandrel

walls

R-22.5 c.i. 

spandrel

walls

R-22.5 c.i. 

spandrel walls

R-22.5 c.i. 

spandrel walls

R-22.5 c.i. 

spandrel walls

Roof Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Equipment

Energy generation PV None None None None None None

HVAC system System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Lighting

Daylighting 

controls

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set 

point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor air ERV Enthalpy wheel

IDEC with 

conversion 

to sensible 

heat 

recovery

Sensible 

wheel

Enthalpy 

wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible wheel

Economizer Waterside 

economizer No Yes Yes No Yes No
81

Table 4-25 Preliminary Common Practice High-rise Low-Energy Model EEM Selections

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio 1.5 1.5 1.5 1.5 1.5 1.5

Fenestration Facade window 

fraction 69% WWR 69% WWR 69% WWR 69% WWR 69% WWR 69% WWR

Shading Shading depth Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Fabric

Fenestration Windows Baseline Baseline Baseline Baseline Baseline Baseline

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope 

and front 

door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Opaque 

constructions

Walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly

R-5.8 c.i. 

spandrel

walls

Assembly

R-5.8 c.i. 

spandrel

walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly 

R-5.8 c.i. 

spandrel walls

Roof Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Equipment

Energy generation PV None None None None None None

HVAC System System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Lighting

Daylighting 

controls

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set

point

300 lux set 

point

300 lux set 

point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction 

and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor air ERV Enthalpy wheel

IDEC with 

conversion 

to sensible 

heat 

recovery

Sensible

wheel

Enthalpy 

wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible wheel

Economizer Waterside 

economizer No Yes Yes No Yes No
82

4.2.2 Preliminary Low-Energy Models: Performance

For the low-rise and code-compliant high-rise cases, the preliminary low-energy models 

achieved greater than 50% net site energy savings in all climates. This was not the case for the 

common practice high-rise preliminary low-energy models, for which the envelope restrictions 

(high WWR, low insulation wall and window constructions) were too severe to achieve that goal. 

Table 4-26 shows the preliminary low-energy model savings. 

Table 4-26 Preliminary Low-Energy Model Net Site Energy Savings

Climate Zone Low-Rise Code-Compliant High-Rise Common Practice High-Rise

1A Miami 57.2% 54.4% 45.2%

3B Las Vegas 56.3% 57.0% 40.6%

4C Seattle 54.0% 56.9% 34.3%

5A Chicago 53.7% 54.4% 33.1%

5B Denver 55.4% 57.6% 34.4%

7 Duluth 54.7% 57.3% 33.8%

4.2.3 Optimized Low-Energy Models: Selection 

After the preliminary low-energy modeling process was complete, we used the resulting lowenergy models as the starting points for Opt-E-Plus optimizations to improve energy savings 

and/or reduce 5-TLCC compared to the starting configuration. For the optimizations, we 

allowed only EEMs related to envelope (roof construction, exterior wall construction, window 

construction, WWR, and shaded overhang fraction) and PV roof coverage to vary. All others 

were fixed at their preliminary low-energy model configuration settings because we were

confident we needed to maintain those settings to achieve the 50% net site energy savings goal 

and minimize 5-TLCC. That confidence was provided by the results of Hale, Leach et al. (2009) 

and Leach, Hale et al. (2009). For the common practice high-rise case, for which all enveloperelated EEMs are fixed by definition, this optimization framework allows only PV to be applied 

as a means of achieving additional energy savings with respect to the preliminary low-energy 

models. 

In each case, the EEM package resulting in the building configuration representing the minimum 

cost point of the Pareto front was selected; the resulting EEM selections are summarized for each 

climate zone in Table 4-27 to Table 4-29 for the low-rise, code-compliant high-rise, and common 

practice high-rise cases, respectively.

4.2.3.1 Optimization Trends

We identified the following trends for the optimization results (excluding the common practice 

high-rise case):

• 20% WWR was selected in all cases, likely because of the capital cost decrease 

associated with replacing glazing with exterior opaque wall construction and because

overall envelope insulation levels improve with lower WWR. These factors outweighed

the decrease in lighting energy that might accompany larger WWR.

• In all cases, exterior wall insulation was reduced to or near baseline insulation levels 

(except in climate zone 7) and window assembly R-value was increased (with respect to 

preliminary low-energy model envelope insulation selection values). 
83

• Roof insulation was not increased above the preliminary low-energy model selection 

value (R-15 c.i.) in any case.

• Overhangs to shade glazing, when available as an EEM, were only selected in Seattle 

(4C).

• Increasing aspect ratio was not selected as a cost-effective measure in any low-rise cases. 

However, additional analysis of high aspect ratio designs is required to reach any definite 

conclusions (see Section 5.2). 

 
84

Table 4-27 Optimized Low-Rise Low-Energy Model EEM Selections

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio 1.5 1.5 1.5 1.5 1.5 1.5

Fenestration Facade 

window fraction 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR

Shading Shading depth None None

Shaded 

overhangs 

with a 0.5 

projection 

factor

None None None

Fabric

Fenestration Windows

Double pane 

with low-e2 

and argon

Double pane 

with low-e2 

and argon

Double pane 

with low-e2 

and argon

Double pane 

with low-e2 

and argon

Double pane with 

low-e2 and 

argon

Double pane 

with low-e2 and 

argon

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter envelope 

and front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Opaque 

constructions

Walls R-5.7 walls R-9.5 walls R-9.5 walls R-13.3 walls R-13.3 walls R-19.5 walls

Roof

R-15 c.i. 

insulation 

above deck

R-15 c.i. 

insulation 

above deck

R-15 c.i. 

insulation 

above deck

R-15 c.i. 

insulation 

above deck

R-15 c.i. 

insulation above 

deck

R-15 c.i. 

insulation above 

deck

Equipment

Energy generation PV None None None None None None

HVAC system System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Lighting

Daylighting 

controls

300 lux set 

point

300 lux set 

point

300 lux set 

point

300 lux set 

point 300 lux set point 300 lux set point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor Air ERV Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible 

wheel Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible wheel

Economizer Waterside 

economizer No Yes Yes No Yes Yes
85

Table 4-28 Optimized Code Compliant High-Rise Low-Energy Models

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5

Fenestration Facade 

window fraction 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR 20% WWR

Shading Shading depth Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Fabric

Fenestration Windows

Double pane 

with low-e2 

and tinted 

glass

Double pane with 

low-e2 and 

tinted glass

Double pane 

with low-e2 

and tinted 

glass

Double pane with 

low-e2 and tinted 

glass

Double pane 

with low-e2 

and tinted 

glass

Double pane 

with low-e2 

and tinted 

glass

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter envelope 

and front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter envelope 

and front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Opaque 

constructions

Walls R-13.0 

spandrel Walls

R-13.0 spandrel

Walls

R-13.0 + R7.5 c.i. 

spandrel

Walls

R-13.0 + R-3.8 

c.i. spandrel

Walls

R-13.0 + R-7.5 

c.i. spandrel

Walls

R-22.5 c.i. 

spandrel

Walls

Roof Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Equipment

Energy generation PV None None None None None None

HVAC system System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant heated 

and cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Lighting

Daylighting 

Controls

300 lux set 

point 300 lux set point 300 lux set point 300 lux set point 300 lux set point

300 lux set 

point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor air ERV Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible 

wheel Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible 

wheel

Economizer Waterside 

economizer No Yes Yes No Yes Yes
86

Table 4-29 Optimized Common Practice High-Rise Low-Energy Model EEM Selections

Form Subcategory EEM Type

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Form

Aspect ratio Aspect ratio Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5 Fixed at 1.5

Fenestration Facade 

window fraction 69% WWR 69% WWR 69% WWR 69% WWR 69% WWR 69% WWR

Shading Shading depth Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Fabric

Fenestration Windows Baseline Baseline Baseline Baseline Baseline Baseline

Infiltration Infiltration

Tighter 

envelope and 

front door 

vestibule

Tighter envelope 

and front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter envelope 

and front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Tighter 

envelope and 

front door 

vestibule

Opaque 

constructions

Walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly 

R-5.8 c.i. 

spandrel walls

Assembly

R-5.8 c.i. 

spandrel

walls

Assembly 

R-5.8 c.i. 

spandrel walls

Roof Not modeled Not modeled Not modeled Not modeled Not modeled Not modeled

Equipment

Energy generation PV 60% roof 

coverage

60% roof 

coverage

60% roof 

coverage

60% roof 

coverage

60% roof 

coverage

60% roof 

coverage

HVAC System System

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and

DOAS

Radiant heated 

and cooled 

ceilings and 

DOAS

Radiant 

heated and 

cooled

ceilings and 

DOAS

Radiant 

heated and 

cooled 

ceilings and 

DOAS

Lighting

Daylighting 

controls

300 lux set 

point 300 lux set point 300 lux set point 300 lux set point 300 lux set point

300 lux set 

point

LPD

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

42% LPD 

reduction and 

occupancy 

sensors

Outdoor air ERV Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible 

wheel Enthalpy wheel

IDEC with 

conversion to 

sensible heat 

recovery

Sensible 

wheel

Economizer Waterside 

economizer No Yes Yes No Yes No
87

4.2.4 Optimized Low-Energy Models: Performance

The energy performance of the optimized low-energy models is depicted in Figure 4-3 through 

Figure 4-5 and summarized in Table 4-30 through Table 4-35 (Table D-52 through Table D-57

for metric units). The economic performance of the optimized low-energy models is 

summarized in Table 4-36 through Table 4-41 (Table D-58 through Table D-63 for metric units). 

Table 4-42 presents a comparison between the energy savings achievable in the common practice 

high-rise case with and without the installation of PV. Table 4-43 through Table 4-45 present 

simple payback results for each of the optimized low-energy models (Table D-64 through Table 

D-66 for metric units). Note that common practice high-rise low-energy cases are measured

against the corresponding code-compliant high-rise baselines for purposes of computing energy 

and cost percent savings performance; as mentioned in Section 4.1.1, it is the goal of this study 

to seek out designs that achieve 50% net site energy savings with respect to ASHRAE 90.1-2004 

and ASHRAE 62.1-2004. 

Figure 4-3 Low-rise EUI by end use for low-energy models
88

Figure 4-4 High-rise EUI by end use for code-compliant low-energy models
89

Figure 4-5 High-rise EUI by end use for common practice low-energy models

The reductions in EUI between the preliminary low-energy cases and the optimized low-energy 

cases shown in Figure 4-5 are due to the addition of PV. 60% roof coverage by PV is modeled. 

The energy generated by PV is used to offset the electrical EUI of the data center. 
90

Table 4-30 Low-rise Optimized Low-Energy Model Energy Performance: Warm Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 115.2 48.8 57.6% 78.5 34.0 56.7% 73.4 33.7 54.1%

Source EUI 

(kBtu/ft2·yr) 337.4 162.9 51.7% 238.1 109.9 53.8% 211.8 102.1 51.8%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

45.6 22.3 51.1% 32.3 15.0 53.5% 28.6 13.8 51.6%

Electricity 

Intensity 

(kWh/ft2·yr)

27.3 14.1 48.2% 19.6 9.4 52.2% 17.0 8.4 50.4%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.221 0.007 97.0% 0.115 0.020 82.8% 0.154 0.049 68.0%

Peak Demand 

(kW) 1984 1822 8.2% 1750 1630 6.9% 1721 1385 19.5%

Table 4-31 Low-rise Optimized Low-Energy Model Energy Performance: Cold Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 88.2 40.6 54.0% 74.9 33.3 55.5% 88.0 39.6 55.0%

Source EUI 

(kBtu/ft2·yr) 242.3 122.5 49.5% 216.9 100.1 53.9% 227.6 110.8 51.3%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

32.5 16.6 48.9% 29.3 13.6 53.7% 30.3 14.9 50.9%

Electricity 

Intensity 

(kWh/ft2·yr)

18.8 10.1 46.5% 17.4 8.2 52.8% 16.9 8.7 48.6%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.239 0.062 74.2% 0.155 0.053 65.6% 0.301 0.098 67.3%

Peak Demand 

(kW) 1908 1680 11.9% 1690 1496 11.5% 1818 1704 6.3%
91

Table 4-32 Code Compliant High-rise Optimized Low-Energy Model Energy Performance: Warm 

Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 107.3 45.6 57.5% 78.8 33.0 58.2% 74.9 32.1 57.1%

Source EUI 

(kBtu/ft2·yr) 315.7 152.0 51.9% 238.2 105.0 55.9% 213.3 99.4 53.4%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

42.7 20.8 51.3% 32.3 14.3 55.7% 28.7 13.5 53.0%

Electricity 

Intensity 

(kWh/ft2·yr)

25.6 13.2 48.5% 19.6 8.9 54.7% 16.9 8.3 51.0%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.200 0.007 96.5% 0.118 0.026 77.9% 0.170 0.037 77.9%

Peak Demand 

(kW) 1940 1804 7.0% 1758 1587 9.7% 1746 1608 7.9%

Table 4-33 Code Compliant High-rise Optimized Low-Energy Model Energy Performance: Cold 

Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 86.9 39.0 55.1% 74.7 31.2 58.3% 86.6 36.6 57.8%

Source EUI 

(kBtu/ft2·yr) 239.3 117.5 50.9% 216.6 94.7 56.3% 225.2 105.4 53.2%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

32.1 15.9 50.4% 29.2 12.8 56.1% 30.0 14.2 52.7%

Electricity 

Intensity 

(kWh/ft2·yr)

18.6 9.6 48.2% 17.4 7.8 55.1% 16.8 8.4 49.9%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.233 0.061 73.9% 0.153 0.045 70.5% 0.291 0.078 73.3%

Peak Demand 

(kW) 1925 1665 13.5% 1717 1528 11.0% 1872 1729 7.6%
92

Table 4-34 Common Practice High-rise Optimized Low-Energy Model Energy Performance: Warm 

Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 107.3 55.3 48.5% 78.8 42.7 45.8% 74.9 46.8 37.5%

Source EUI 

(kBtu/ft2·yr) 315.7 180.6 42.8% 238.2 127.2 46.6% 213.3 126.0 40.9%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

42.7 24.7 42.2% 32.3 17.2 46.7% 28.7 16.9 41.3%

Electricity 

Intensity 

(kWh/ft2·yr)

25.6 15.5 39.4% 19.6 10.4 47.0% 16.9 9.6 43.1%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.200 0.024 87.9% 0.118 0.072 39.0% 0.170 0.138 18.7%

Peak Demand 

(kW) 1940 1563 19.4% 1758 1351 23.1% 1746 1378 21.0%

Table 4-35 Common Practice High-rise Optimized Low-Energy Model Energy Performance: Cold 

Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

Site EUI 

(kBtu/ft2·yr) 86.9 55.3 36.3% 74.7 45.7 38.9% 86.6 54.6 36.9%

Source EUI 

(kBtu/ft2·yr) 239.3 151.5 36.7% 216.6 119.3 44.9% 225.2 133.6 40.7%

Energy 

Emissions 

Intensity 

(lbCO2/ft2·yr)

32.1 20.3 36.7% 29.2 15.9 45.6% 30.0 17.7 41.1%

Electricity 

Intensity 

(kWh/ft2·yr)

18.6 11.7 36.9% 17.4 8.9 48.6% 16.8 9.5 43.4%

Natural Gas 

Intensity 

(Therms/ft2·yr)

0.233 0.153 34.5% 0.153 0.151 1.0% 0.291 0.221 24.0%

Peak Demand 

(kW) 1925 1454 24.5% 1717 1274 25.8% 1872 1509 19.4%

The energy savings results shown in Table 4-34 and Table 4-35 are in part due to the installation 

of a PV array that covers 60% of the roof area. 
93

Table 4-36 Low-rise Optimized Low-Energy Model Cost Performance: Warm Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC

Intensity 

($/ft2

) 

$139.07 $155.23 -11.6% $128.90 $137.71 -6.8% $126.46 $139.75 -10.5%

Capital Cost 

Intensity 

($/ft2

) 

$119.51 $136.64 -14.3% $114.68 $124.68 -8.7% $113.43 $126.67 -11.7%

Annual 

Energy Cost 

Intensity 

($/ft2

·yr)

$2.60 $1.35 47.9% $1.84 $0.91 50.8% $1.67 $0.82 51.0%

Annual 

Electricity 

Cost Intensity 

($/ft2

·yr)

$2.32 $1.35 42.1% $1.70 $0.88 48.1% $1.48 $0.76 48.8%

Annual 

Natural Gas 

Cost Intensity 

($/ft2

·yr)

$0.27 $0.01 97.1% $0.14 $0.02 83.1% $0.19 $0.06 68.1%
94

Table 4-37 Low-rise Optimized Low-Energy Model Cost Performance: Cold Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC 

Intensity ($/ft2) $134.81 $149.00 -10.5% $124.75 $134.82 -8.1% $130.66 $145.05 -11.0%

Capital Cost 

Intensity ($/ft2) $118.93 $133.10 -11.9% $111.99 $122.79 -9.6% $116.07 $130.46 -12.4%

Annual Energy 

Cost Intensity 

($/ft2

·yr)

$1.93 $1.02 47.4% $1.70 $0.82 52.0% $1.83 $0.91 50.5%

Annual 

Electricity Cost 

Intensity 

($/ft2

·yr)

$1.64 $0.94 42.6% $1.51 $0.75 50.2% $1.47 $0.79 46.2%

Annual Natural 

Gas Cost

Intensity

($/ft2

·yr)

$0.30 $0.08 74.5% $0.19 $0.07 65.9% $0.37 $0.12 67.5%

Table 4-38 Code Compliant High-rise Optimized Low-Energy Model Cost Performance: Warm 

Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC 

Intensity ($/ft2) $144.56 $154.02 -6.5% $137.40 $139.19 -1.3% $135.54 $142.28 -5.0%

Capital Cost

Intensity ($/ft2) $127.17 $137.71 -8.3% $123.91 $127.73 -3.1% $122.99 $130.48 -6.1%

Annual Energy 

Cost Intensity 

($/ft2

·yr)

$2.44 $1.29 47.0% $1.85 $0.88 52.3% $1.69 $0.81 52.0%

Annual 

Electricity Cost 

Intensity 

($/ft2

·yr)

$2.19 $1.28 41.4% $1.70 $0.85 50.0% $1.48 $0.77 48.3%

Annual Natural 

Gas Cost

Intensity

($/ft2

·yr)

$0.25 $0.01 96.6% $0.15 $0.03 78.1% $0.21 $0.05 78.0%
95

Table 4-39 Code Compliant High-rise Optimized Low-Energy Model Cost Performance: 

Cold Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC 

Intensity ($/ft2) $142.35 $149.10 -4.7% $134.29 $137.72 -2.6% $139.48 $147.03 -5.4%

Capital Cost 

Intensity ($/ft2) $127.49 $135.01 -5.9% $122.01 $127.01 -4.1% $125.58 $134.11 -6.8%

Annual Energy 

Cost Intensity 

($/ft2

·yr)

$1.91 $1.00 47.6% $1.71 $0.79 53.4% $1.82 $0.87 52.1%

Annual 

Electricity Cost 

Intensity 

($/ft2

·yr)

$1.63 $0.93 42.9% $1.52 $0.74 51.3% $1.46 $0.77 47.0%

Annual Natural 

Gas Cost 

Intensity 

($/ft2

·yr)

$0.29 $0.07 74.1% $0.19 $0.06 70.7% $0.36 $0.09 73.4%

Table 4-40 Common Practice High-rise Optimized Low-Energy Model Cost Performance: 

Warm Climates

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC 

Intensity ($/ft2

) $144.56 $165.16 -14.2% $137.40 $150.99 -9.9% $135.54 $154.47 -14.0%

Capital Cost 

Intensity ($/ft2) $127.17 $147.64 -16.1% $123.91 $138.32 -11.6% $122.99 $140.80 -14.5%

Annual Energy 

Cost Intensity 

($/ft2

·yr)

$2.44 $1.48 39.4% $1.85 $1.07 42.2% $1.69 $1.10 34.8%

Annual 

Electricity Cost 

Intensity 

($/ft2

·yr)

$2.19 $1.45 33.8% $1.70 $0.98 42.4% $1.48 $0.93 37.1%

Annual Natural 

Gas Cost 

Intensity 

($/ft2

·yr)

$0.25 $0.03 88.1% $0.15 $0.09 39.5% $0.21 $0.17 18.6%
96

Table 4-41 Common Practice High-rise Optimized Low-Energy Model Cost Performance: Cold 

Climates

Metric

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings Baseline

LowEnergyPercent 

Savings

5-TLCC 

Intensity ($/ft2) $142.35 $161.66 -13.6% $134.29 $148.86 -10.8% $139.48 $158.16 -13.4%

Capital Cost 

Intensity ($/ft2) $127.49 $145.59 -14.2% $122.01 $136.76 -12.1% $125.58 $143.29 -14.1%

Annual Energy 

Cost Intensity 

($/ft2

·yr)

$1.91 $1.31 31.3% $1.71 $1.03 39.4% $1.82 $1.18 35.2%

Annual 

Electricity Cost

Intensity

($/ft2

·yr)

$1.63 $1.13 30.6% $1.52 $0.85 44.1% $1.46 $0.91 37.9%

Annual Natural 

Gas Cost 

Intensity 

($/ft2

·yr)

$0.29 $0.19 34.8% $0.19 $0.19 1.0% $0.36 $0.27 24.0%

Table 4-42 Common Practice High-rise PV Comparison

Climate Zone Energy 

Savings

Energy 

Savings 

without PV

PV Roof 

Coverage 

PV Roof 

Coverage 

to Achieve 

50% Savings

1A Miami 48.5% 45.2% 60.0% 88.3%

3B Las Vegas 45.8% 40.6% 60.0% 108.4%

4C Seattle 37.5% 34.3% 60.0% 294.0%

5A Chicago 36.3% 33.1% 60.0% 314.1%

5B Denver 38.9% 34.4% 60.0% 210.7%

7 Duluth 36.9% 33.8% 60.0% 316.2%
97

 Table 4-43 Low-rise Simple Payback Results

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Capital Cost Increase ($/ft2) $17.13 $10.00 $13.24 $14.17 $10.80 $14.39 

Capital Cost Increase (%) 14.3 8.7 11.7 11.9 9.6 12.4

Annual Energy Cost Savings 

($/ft2·yr) $1.25 $0.93 $0.85 $0.91 $0.88 $0.92

Simple Payback Period (yr) 13.7 10.8 15.6 15.6 12.3 15.6

Table 4-44 Code Compliant High-rise Simple Payback Results

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Capital Cost Increase ($/ft2) $10.54 $3.82 $7.49 $7.52 $5.00 $8.53 

Capital Cost Increase (%) 8.3 3.1 6.1 5.9 4.1 6.8

Annual Energy Cost Savings 

($/ft2·yr) $1.15 $0.97 $0.88 $0.91 $0.92 $0.95

Simple Payback Period (yr) 9.2 3.9 8.5 8.3 5.4 9.0

Table 4-45 Common Practice High-rise Simple Payback Results

Metric

Climate Zones

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth

Capital Cost Increase ($/ft2) $20.47 $14.41 $17.81 $18.10 $14.75 $17.71

Capital Cost Increase (%) 16.1 11.6 14.5 14.2 12.1 14.1

Annual Energy Cost Savings 

($/ft2·yr)

$0.96 $0.78 $0.59 $0.60 $0.68 $0.64

Simple Payback Period (yr) 21.3 18.5 30.2 30.2 21.7 27.7

4.2.5 Discussion

The optimized low-energy models can achieve 50% net site energy savings more cost effectively 

(in terms of 5-TLCC) than their corresponding preliminary low-energy models in all instances 

for the low-rise and code-compliant high-rise cases.

The low-energy models for the common practice high-rise case cannot achieve 50% net site 

energy savings in any case, even with PV arrays that cover 60% of the roof, the maximum 

coverage allowed for this study. Table 4-42 indicates that more than 88% roof coverage would 

be required in all cases (up to a maximum coverage of more than 316%, for the Duluth [7] case) 

to reach the energy savings goal. 

For the low-rise and code-compliant high-rise cases, the optimized low-energy models could also 

achieve 50% net source energy savings in nearly all cases (except the low-rise, Chicago [5A] 

case, for which 49.5% net source energy savings were achieved). In all cases, however, net 

source energy savings were significantly lower than net site energy savings (by 3.6%, on 

average); this is due to significantly lower electricity intensity savings (50.5% on average) than 
98

natural gas intensity savings (77.1% on average) in conjunction with a higher site to source 

energy conversion factor for electricity (3.37) than for natural gas (1.09). 

A higher site to source energy conversion factor for electricity than for natural gas correlates to 

higher energy emissions and energy cost savings for electricity than for natural gas. 

Accordingly, the low-rise and code-compliant high-rise low-energy models exhibited energy 

emissions savings and energy costs savings similar to those for net source energy, and below 

those for net site energy. 

The low-energy building configurations result in significantly less reduction in peak demand 

(26% maximum) than in net site energy use. So, although such buildings would reduce total 

energy consumption by 50% or more, they provide much less reduction in capacity requirements 

for the electricity grid. 

Simple payback is longer for the low-rise case (10.8–15.6 years) than for the code-compliant 

high-rise case (3.9–9.2 years). This is likely because lowering WWR can significantly reduce 

capital costs in the high-rise case (glass curtain construction is significantly more expensive than 

spandrel panel construction), but not in the low-rise case (low-rise exterior wall and fenestration 

construction costs are very similar). Simple payback for the common practice high-rise 

optimized low-energy models is considerably longer than for the corresponding code-compliant 

high-rise models (18.5–30.2 years) because PV arrays covered 60% of the roof area in the 

common practice high-rise models. The payback for the common practice high-rise cases would 

be even longer (19.5–35.6 years) if additional PV could be added to the roof or other building 

surfaces to achieve the 50% net site energy savings goal (see Table 4-42). Although it was 

required for this analysis, a five-year analysis period seems conservative for a large office 

building; whether or not these payback periods are acceptable in practice will depend on the 

building owner and the designed use. 

Low-rise and code-compliant high-rise optimizations were initiated with EEM packages that 

produced greater than 50% net site energy savings in all cases (Table 4-26). The optimization 

algorithm precludes the selection of EEM packages that produce less energy savings than the 

EEM package with which the optimization is initialized. Accordingly, it is possible that EEM 

packages exist that would satisfy the energy savings goal at lower 5-TLCCs than the EEM 

packages selected by our optimizations; however, those packages would result in lower energy 

savings than the EEM packages with which their respective optimizations were initialized (see 

Section 5.1). 
99

5.0 Suggestions for Future Work

In this section we outline areas of improvement recommended for the AEDG stage of this 

analysis.

5.1 Optimization Setup

As mentioned in Section 4.2.5, the setup of our optimizations may have precluded the discovery 

of additional EEM packages that can create building configurations that reach the 50% net site 

energy savings goal. By initializing an optimization at an energy savings level beyond the 

savings goal, all solutions achieving savings between those of the goal and those of the 

optimization initialization point are precluded from discovery and possible selection as Pareto 

front points. To remedy this issue, we will ensure that future optimizations are initialized with 

EEM packages that result in energy savings that fall short of the energy savings goal. 

5.2 Energy Modeling

Some EEMs were not included in this study because reliable input data or modeling validation 

was lacking, or because significantly more simulation time would have been required. Other 

EEMs were included but need to be reevaluated. Measures we feel deserve increased attention 

are:

• Alternative HVAC systems. Our selected low-energy HVAC system (radiant heated 

and cooled ceiling slabs with DOAS) represents a new approach in HVAC design in the 

United States and building owners and designers may wish to reach the 50% net site 

energy savings goal with more conventional HVAC system types. We plan to consider a 

low-energy VAV case as a comparison point to out selected low-energy HVAC system 

configuration as this work progresses, although 50% energy savings was not found to be 

possible with a VAV approach in the earlier medium office TSD work.

• Building thermal mass. Building thermal mass plays an important role in influencing 

the control of the building’s HVAC system by storing energy. Low-rise low-energy 

exterior wall constructions were designed to maximize their contribution to internal 

thermal mass; however, we did not allow the internal mass characteristics of the exterior 

walls, the radiant slabs, or the interior furnishings to vary. 

• Natural ventilation. We did not include this EEM because accurately capturing its 

effects in the energy models was not possible within the scope of this project. Achieving 

energy savings by implementing natural ventilation (in an actual building or a simulation 

model) requires accurate inputs and sophisticated building controls. Preliminary 

modeling indicated that more work will be necessary to validate the impact of this EEM.

• Advanced daylighting strategies. The current daylighting configuration is based on 

using a single type of glass for both views and daylighting. More advanced daylighting 

configurations and equipment may be considered, including: different combinations of 

view glass and daylighting glass, with function-specific material properties; installation 

of light redirection devices to allow deeper penetration of daylight.

• High aspect ratio designs. We included the ability to vary aspect ratio as part of our 

low-rise low-energy optimization process in hopes of capturing the possible benefits of 

high aspect ratio design for reducing building EUI. Although increasing aspect ratio 
100

increases capital costs and the effect of outdoor conditions on energy use via thermal 

conductance, it also increases the possible effectiveness of passive strategies such as 

daylighting, natural ventilation, and load shifting through thermal storage in the 

building’s internal mass. Among these strategies, we explored only daylighting in any 

detail. To reach definite conclusions about the energy efficiency implications of high 

aspect ratio design, we need to perform more studies about passive strategies. It is 

recognized, though, that there are benefits of high aspect ratio such as connection of 

workspaces to the outdoors through proximity to windows and full daylighting of the 

workspace.

• Under floor air distribution (UFAD). A likely pairing of air distribution method with 

radiant slab ceilings is UFAD in order to avoid obstruction of the radiant surface. 

Further verification of UFAD modeling with EnergyPlus is required before this EEM can 

be used with confidence. As this large office work progresses, we would like to identify 

the inputs that will allow us to model the effects of UFAD on the energy efficiency of an 

air distribution system.

• Air flow models. Our EnergyPlus models currently assume that air masses in different 

thermal zones are isolated from one another. Modeling air transfers between zones 

would increase their accuracy and enable us to better study design features such as 

entrance vestibules and natural ventilation. For vestibules, infiltration through the front 

entrances is currently divided on an area-weighted basis between the perimeter zones and 

the central core zone, based on the assumption that the air would pass through the 

vestibules and into the core of the building. According to that division, half the air 

infiltrating through the front entrances is applied directly to the core. In reality, 

vestibules are equipped with dedicated HVAC units that precondition the infiltrated air 

before it passes through to the rest of the building. With natural ventilation, accurate air 

flow is required to capture sophisticated scenarios such as cross-ventilation, which is 

possible with high aspect ratio designs. A more accurate model (EnergyPlus’s Airflow 

Network) would enable us to capture the significance of using the vestibules to 

precondition infiltrated air. 

We also recommend that some model inputs be reevaluated and validated: 

• Radiant heating and cooling flow control. As mentioned in Section 3.4.4.5.1, we 

initially planned to control the water flow (in heating and cooling) through the radiant 

tubing network using a “trickle and ramp” approach Doebber (2010) designed to account 

for the effect of the high thermal mass of the radiant slab on system response time. 

During simulation, our radiant system behaved differently than we expected, exhibiting 

prompt enough response to thermal loads to render the “trickle and ramp” approach 

almost unnecessary. We believe this indicates the thermal mass characteristics of our 

design (for exterior walls, interior furnishings, and especially the layup of the radiant 

slab) and that revised thermal mass inputs will result in more expected system behavior, 

for which the “trickle and ramp” approach to system control will be more appropriate.

• Building model zoning. To allow aspect ratio to vary during our low-rise low-energy 

optimizations, we modeled our prototypes with simplified geometries and lumped space 
101

types. This reduced the ability of our models to capture the intricacies associated with 

space specific ventilation requirements, including how the interaction between the air 

system and the radiant system varies (and the resulting effects on system control) with 

air flow rate (which is defined by the ventilation requirement of the space for a DOAS). 

In the future, we may attempt to capture these effects through a more realistic breakdown 

of thermal zones and space type requirements. As a result, aspect ratio will be fixed, not 

varied, during a given optimization and varied between optimizations. 

• Building pressurization analysis. The model inputs for infiltration (see Section 3.3.3.4) 

and ERV (see Section 3.4.4.6.2) depend on a number of assumptions. The EnergyPlus 

Airflow Network should be used to determine the validity of those assumptions. 

• Infiltration. The building pressurization analysis through which infiltration inputs were 

developed was based on driving pressures associated with HVAC pressurization and 

wind speed. To strengthen the analysis, stack effect should be factored in. Stack effect 

was omitted from the current analysis because of its strong dependence on building 

design and ambient temperature, which make it difficult to model accurately in 

EnergyPlus. Capturing the influence of stack effect on building EUI is especially 

important for high-rise buildings; accordingly, we plan to devote time to explore this 

issue further. 
102

6.0 Conclusions

Our results suggest that fifty percent net site energy savings can be achieved in large office 

buildings (both low-rise and high-rise) in a range of climates spanning of the spectrum of U.S. 

weather conditions. Low-rise and high-rise buildings with energy efficient envelopes averaged 

56.4% net site energy savings; however, large office buildings with non-compliant envelope 

design (represented here by a high-rise case with floor-to-ceiling glazing and poorly insulated 

spandrel panels) could not reach the 50% net site energy savings goal without significant 

renewable energy generation (in this case, an average of 990 kW of installed PV). 

EUI for the ASHRAE 90.1-2004 baselines was similar for the integrated design low-rise and 

high-rise cases, but greater for the high-rise case with poor envelope design (by an average of 

11%), as one would expect; this was especially the case in more severe climates where already 

large heating or cooling loads were exacerbated by a poorly insulated, highly transparent 

envelope. 

The ASHRAE 90.1-2007 baseline energy models performed similarly to the ASHRAE 90.1-

2004 baseline models. In climate zone 7 (Duluth), replacing ASHRAE 90.1-2004 with 

ASHRAE 90.1-2007 as the baseline building standard resulted in enough energy savings (4% 

average) to offset increased capital costs associated with the implementation of the slightly more 

stringent envelope insulation requirements of ASHRAE 90.1-2007 and reduce overall 5-TLCC. 

In all other climates, replacing ASHRAE 90.1-2004 with ASHRAE 90.1-2007 as the baseline 

building standard resulted in negligible energy savings and slightly increased capital and life 

cycle costs.

For the EEM combinations that achieve the 50% net site energy savings goal with the minimum 

increase in life cycle cost, we calculated simple payback periods. Low-energy high-rise large 

office buildings with energy efficient envelopes demonstrated minimum simple payback periods 

shorter than 10 years; integrated design low-energy low-rise large office buildings demonstrated

minimum simple payback periods of 9–16 years; and low-energy high-rise large office buildings 

hampered with poor envelope design demonstrated minimum simple payback periods longer 

than 20 years. Although this study calculated life cycle cost using a five-year period, acceptable 

payback for large office buildings may be longer and will depend on the building’s owner and 

use. 

We defined the energy goal with respect to net site energy, but we also evaluated our selected 

low-energy buildings with respect to net source energy, energy emissions, and energy cost. Our 

low-energy solutions (except the poorly insulated high-rise case) resulted in greater natural gas 

intensity savings (77% average) than electricity intensity savings (51% average). As a result, our 

low-energy buildings performed less well, although still at or above 50% savings in most cases, 

with respect to net source energy savings (52.8% average), energy emissions savings (52.4% 

average), and energy cost (50.3% average) than with respect to net site energy savings (56.4% 

average). This is because source energy (and also energy emissions and energy cost, which are 

strongly related to source energy) savings is weighted toward electricity savings due to our using 

a higher site-to-source multiplier for electricity (3.37) versus natural gas (1.09). If reducing 

energy emissions and energy cost become the primary energy efficiency criteria, our analysis 

supports using source energy as the defining metric for future energy efficiency goals. However, 

using source energy introduces challenges since site-to-source conversion factors vary with both 

space and time in ways that are difficult to characterize. 
103

The 50% recommendations are intended to serve as starting points for project-specific analyses. 

They are not meant for specific design guidance on an actual project because of project-specific 

variations in economic criteria and EEM availability, cost, and performance. Project-specific 

analyses are also recommended because they can account for site-specific rebate programs that 

may improve the cost effectiveness of certain efficiency measures.

For sector-wide studies and individual projects, our approach has the advantages that it allows

for the efficient exploration of many building design options and explicitly considers economic 

factors so the most cost-effective solutions can be identified. The design features we explored

can be tailored to match a given energy savings target (regardless of the energy metric used) in a 

particular climate zone.

 
104

7.0 References

Akins, R.E.; Peterka, J.A.; Cermak, J.E. (1979). “Averaged Pressure Coefficients for Rectangular 

Buildings.” In Proceedings of the Fifth International Wind Engineering Conference, Fort Collins, CO.

ASHRAE (1989). ANSI/ASHRAE/IESNA Standard 90.1-1989, Energy Efficient Design of New 

Buildings Except Low-Rise Residential Buildings. Atlanta, Georgia, American Society of Heating, 

Refrigerating, and Air-Conditioning Engineers, Inc.

ASHRAE. (2003). HVAC Applications Handbook. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE (2004a). ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions For Human 

Occupancy. Atlanta, Georgia, American Society of Heating, Refrigerating, and Air-Conditioning 

Engineers, Inc.

ASHRAE. (2004b). ANSI/ASHRAE Standard 62.1-2004, Ventilation for Acceptable Indoor Air 

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

ASHRAE. (2004c). ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings Except 

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

ASHRAE. (2005). Fundamentals Handbook. Atlanta, GA: American Society of Heating, Refrigerating 

and Air-Conditioning Engineers, Inc.

ASHRAE. (2006). ANSI/ASHRAE Standard 169-2006, Weather Data for Building Design Standards. 

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

ASHRAE. (2007a). ANSI/ASHRAE/ASHE Standard 140, Standard Method of Test for the Evaluation 

of Building Energy Analysis Computer Programs. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. (2007b). ANSI/ASHRAE/IESNA Standard 90.1-2007, Energy Standard for Buildings Except 

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

Balboni, B., ed. (2008). Square Foot Costs, 29th Annual Edition. Kingston, MA: RSMeans.

CIBSE. (2000). CIBSE Technical Memorandum TM 23 - Testing Buildings for Air Leakage, Chartered 

Institution of Buildings Services Engineers.

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. (2010). U.S. Department of Energy 

Commercial Reference Building Models of the National Building Stock - Technical Report. Golden, CO: 

National Renewable Energy Laboratory, NREL/TP-550-46861. (To be published fall 2010.)

Deru, M.; Torcellini, P. (2007). Source Energy and Emissions Factors for Energy Use in Buildings. 

Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-38617.

DOE (2008a). EnergyPlus Energy Simulation Software. Washington, D.C.: U.S. Department of Energy. 

DOE (2008b). Retailer Energy Alliance. Washington, D.C.: U.S. Department of Energy. 

www1.eere.energy.gov/buildings/alliances/retailer_energy_alliance.html. Last accessed September 2010.

DOE (2010). EnergyPlus Energy Simulation Software, Version 5.0. Washington, D.C.: U.S. 

Department of Energy. http://apps1.eere.energy.gov/buildings/energyplus/. Last accessed September 

2010.
105

DOE and NREL (2010). High Performance Buildings Database. Washington, D.C.: U.S. Department of 

Energy and Golden, CO: National Renewable Energy Laboratory. http://eere.buildinggreen.com/. Last 

accessed September 2010.

Doebber, I. (2010). Design of a Radiant Slab Cooling System for Big Box Retail. Golden, CO, National 

Renewable Energy Laboratory. Not published.

EIA. (2005). 2003 Commercial Buildings Energy Consumption Survey. Washington, D.C.: Energy

Information Administration. 

www.eia.doe.gov/emeu/cbecs/cbecs2003/detailed_tables_2003/detailed_tables_2003.html. Last accessed 

September 2010.

EIA (2007). Natural Gas Monthly.

EIA (2009). Natural Gas Monthly.

Emmerich, S.J.; McDowell, T.; Anis, W. (2005). Investigation of the Impact of Commercial Building 

Envelope Airtightness on HVAC Energy Use. Washington, D.C.: National Institute of Standards and 

Technology. http://fire.nist.gov/bfrlpubs/build05/PDF/b05007.pdf. Last accessed September 2010.

Florida Power & Light (2008). Electric Retail Tariff Book. Miami, FL: Florida Power & Light. 

www.fpl.com/rates/index.shtml. Last accessed September 2010.

Google. (2010). Data Center Efficiency Measurements. 

www.google.com/corporate/green/datacenters/measuring.html. Last accessed September 2010.

Greene, M. (2008). Green Building: Project Planning and Cost Estimating. Dataset accessed via 

CostWorks 2008. Kingston, MA: RSMeans.

Hale, E.; Macumber, D.; Long, N.; Griffith, B.; Benne, K.; Pless, S.; Torcellini, P. (2008). Technical 

Support Document: Development of the Advanced Energy Design Guide for Medium Box Retail--50% 

Energy Savings. Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-42828.

Hale, E.T.; Leach, M.; Hirsch, A.; Torcellini, P. (2009). General Merchandise 50% Energy Savings

Technical Support Document. Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-

46100.

Hale, E.T.; Macumber, D.L.; Long, N.L.; Griffith, B.T.; Benne, K.S.; Pless, S.D.; Torcellini, P.A. (2008). 

Technical Support Document: Development of the Advanced Energy Design Guide for Grocery Stores--

50% Energy Savings. Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-42829.

Jarnagin, R.E.; Liu, B.; Winiarski. D.W.; McBride, M.F.; Suharli, L.; Walden, D. (2006). Technical 

Support Document: Development of the Advanced Energy Design Guide for Small Office Buildings. 

Richland, WA: Pacific Northwest National Laboratory, PNNL-16250.

Jarnagin, R.E.; Watson, T.E.; Burgett, L.W.; Carter, D.E; Colliver, D.G.; McMillan, H.D., III; Menzer, 

M.S.; Montgomery, J.; Olgyay, V.; Persily, A.K.; Phoenix, T.H.; Torcellini, P.A.; Balaras, C.A.; Hunn, B. 

(2008). ASHRAE Vision 2020: Producing Net Zero Energy Buildings. Atlanta, GA: American Society 

of Heating, Refrigerating and Air-Conditioning Engineers. 

www.ashrae.org/doclib/20080226_ashraevision2020.pdf. Last accessed September 2010.

Labor. (2010). Consumer Price Index Inflation Calculator. Washington, D.C.: U.S. Department of 

Labor. http://data.bls.gov/cgi-bin/cpicalc.pl. Last accessed September 2010.

Leach, M.; Hale, E.; Torcellini, P. (2009). Grocery Store 50% Energy Savings Technical Support 

Document. Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-46101.
106

Liu, B.; Jarnagin, R.E.; Jiang, W.; Gowri, K. (2007). Technical Support Document: The Development of 

the Advanced Energy Design Guide for Small Warehouse and Self-Storage Buildings. Richland, WA: 

Pacific Northwest National Laboratory, PNNL-17056.

Mitchell, J., M. Brandmuehl, et al. (2006). Final Report of the Advanced Energy Design Guides Scoping 

Committee for 50% Approach to Net Zero Energy Use in Commercial Buildings, American Society of 

Heating, Refrigerating and Air-Conditioning Engineers.

Murphy, J.; Bradley, B. (2008). Applications Engineering Manual: Air-to-Air Energy Recovery in 

HVAC Systems. Trane.

NREL. (2010). “Opt-E-Plus Software for Commercial Building Optimization. Golden, CO: National 

Renewable Energy Laboratory, NREL/FS-550-45620.

Olesen, B. (2008). “Radiant Floor Cooling Systems.” ASHRAE Journal, September. www.uponorusa.com/~/media/Files/Technical%20Documents/Commercial%20Related%20Docs/ASHRAEDAJ08Sep

200800828.aspx?sc_lang=en. Last accessed September 2010.

OMB. (2010). Appendix C: Discount Rates for Cost-Effectiveness, Lease Purchase, and Related 

Analyses. Washington, D.C.: Office of Management and Budget. 

www.whitehouse.gov/omb/circulars_a094_a94_appx-c/

PG&E (2007). Advanced Variable Air Volume System Design Guide.

Plotner, S.C., ed. (2009). Facilities Maintenance and Repair Cost Data. Kingston, MA: RSMeans.

Priebe, J. (2006). Development of Costs and Strategies for Building Design Optimization. Golden, CO, 

National Renewable Energy Laboratory.

Priebe, J. (2010). Development of Envelope Cost Data. Golden, CO, National Renewable Energy 

Laboratory. Not published.

RMH Group (2006). Building Optimization - HVAC Data. Golden, CO, National Renewable Energy 

Laboratory.

RMH Group (2010a). Building Optimization - HVAC Data. Golden, CO, National Renewable Energy 

Laboratory. Not published.

RMH Group (2010b). NREL Daylighting Controls Cost Data. Golden, CO, National Renewable Energy 

Laboratory. Not published.

Roth, K.; Westphalen, W.D.; Feng, M.Y.; Llana, P.; Quartararo, L. (2005). Energy Impact of 

Commercial Building Controls and Performance Diagnostics: Market Characterization, Energy Impact 

of Building Faults and Energy Savings Potential. Cambridge, MA: TIAX LLC.

Sales Tax Clearinghouse (2009). State sales Tax Rates Along With Average Combined City and County 

Rates. http://thestc.com/STrates.stm. Last accessed September 2010.

Thornton, B.A., Wang, W.; Lane, M.D.; Rosenberg, M.I.; Liu, B. (2009). Technical Support Document: 

50% Energy Savings Design Technology Packages for Medium Office Buildings. Richland, WA: 

Pacific Northwest National Laboratory, PNNL-18774.

Torcellini, P.; Pless, S.; Deru, M.; Crawley, D. (2006). “Zero Energy Buildings: A Critical Look at the 

Definition.” Golden, CO: National Renewable Energy Laboratory, NREL/CP-550-39833.

USGBC. (2006). New Construction and Major Renovation Version 2.2 Reference Guide. Washington, 

D.C.: U.S. Green Building Council.

Waier, P.R., ed. (2008). Building Construction Cost Data. Kingston, MA: RSMeans.

Wilson, A. (2010). “Rethinking the All-Glass Building.” Environmental Building News 19.
107

Wiren, B.G. (1984). Wind Pressure Distributions and Ventilation Losses for a Single-Family House as 

Influenced by Surrounding Buildings - A Wind Tunnel Study.” In Proceedings of Indoor Air Quality '92, 

ASHRAE/ACGIH/AIHA Conference, San Francisco, CA.

Yuill, G.K., Upham, R. Hui, C. (2000). “Air Leakage Through Automatic Doors.” ASHRAE 

Transactions 106(2):145–160.
108

Appendix A Prototype Schedules

The following schedules apply to the low-rise and high-rise large office prototypes; they were 

determined through a combination of industry-validated assumption and schedule set data from 

the Medium Office TSD (Thornton, Wang et al. 2009) and the Reference Building project (Deru, 

Field et al. 2010), for which schedules were largely based on the recommendations of ASHRAE 

Standard 90.1-1989 (ASHRAE 1989). Schedules are presented as fractions of peak, unless 

otherwise noted. The entries for total hours/day, etc. are the equivalent number of peak hours 

during the given time period. 

A.1 Occupancy

The occupancy schedule for all the prototypes is shown in Table A-1. 

Table A-1 Prototype Occupancy Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0 0 1 0 0

2 0 0 1 0 0 

3 0 0 1 0 0 

4 0 0 1 0 0 

5 0 0 1 0 0 

6 0 0 1 0 0 

7 0.05 0 1 0 0 

8 0.15 0.05 1 0 0 

9 0.2 0.2 1 0 0.05

10 0.5 0.2 1 0 0.05

11 0.5 0.2 1 0 0.05

12 0.7 0.2 1 0 0.05

13 0.7 0.1 1 0 0.05

14 0.7 0.1 1 0 0.05

15 0.7 0.1 1 0 0.05

16 0.8 0.05 1 0 0.05

17 0.7 0.05 1 0 0.05

18 0.3 0.05 1 0 0.05

19 0.1 0.05 1 0 0 

20 0.05 0 1 0 0 

21 0.05 0 1 0 0 

22 0 0 1 0 0 

23 0 0 1 0 0 

24 0 0 1 0 0 

Total 

Hours/Day 6.20 1.35 24.00 0.00 0.50

Total 

Hours/Week 32.85
109

A.2 Lighting

The lighting schedule for the prototypes is shown in Table A-2. 

Table A-2 Prototype Lighting Schedule 

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0.05 0.05 1 0 0.05

2 0.05 0.05 1 0 0.05

3 0.05 0.05 1 0 0.05

4 0.05 0.05 1 0 0.05

5 0.05 0.05 1 0 0.05

6 0.05 0.05 1 0 0.05

7 0.4 0.05 1 0 0.05

8 0.75 0.4 1 0 0.05

9 0.75 0.75 1 0 0.4

10 0.9 0.75 1 0 0.4

11 0.9 0.75 1 0 0.4

12 0.9 0.75 1 0 0.4

13 0.9 0.75 1 0 0.4

14 0.9 0.75 1 0 0.4

15 0.9 0.75 1 0 0.4

16 0.9 0.4 1 0 0.4

17 0.9 0.4 1 0 0.4

18 0.9 0.4 1 0 0.4

19 0.75 0.4 1 0 0.05

20 0.75 0.05 1 0 0.05

21 0.75 0.05 1 0 0.05

22 0.4 0.05 1 0 0.05

23 0.05 0.05 1 0 0.05

24 0.05 0.05 1 0 0.05

Total 

Hours/Day 13.05 7.85 24.00 0.00 4.70

Total 

Hours/Week 77.80
110

A.3 Plug and Process Loads

The plug and process load schedule for the prototypes is shown in Table A-3. 

Table A-3 Prototype Plug and Process Load Schedule 

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays,

Other

1 0.2 0.15 1 0 0.15

2 0.2 0.15 1 0 0.15

3 0.2 0.15 1 0 0.15

4 0.2 0.15 1 0 0.15

5 0.2 0.15 1 0 0.15

6 0.2 0.15 1 0 0.15

7 0.4 0.15 1 0 0.15

8 0.4 0.35 1 0 0.15

9 0.4 0.35 1 0 0.35

10 0.7 0.35 1 0 0.35

11 0.7 0.35 1 0 0.35

12 0.9 0.35 1 0 0.35

13 0.9 0.35 1 0 0.35

14 0.9 0.35 1 0 0.35

15 0.9 0.35 1 0 0.35

16 0.9 0.35 1 0 0.35

17 0.9 0.35 1 0 0.35

18 0.7 0.35 1 0 0.35

19 0.4 0.35 1 0 0.15

20 0.2 0.15 1 0 0.15

21 0.2 0.15 1 0 0.15

22 0.2 0.15 1 0 0.15

23 0.2 0.15 1 0 0.15

24 0.2 0.15 1 0 0.15

Total 

Hours/Day 11.30 6.00 24.00 0.00 5.60

Total 

Hours/Week 68.10
111

A.4 Service Water Heating

The SWH schedule is adopted from ASHRAE 90.1-1989 (ASHRAE 1989) and is shown in 

Table A-4. 

Table A-4 Prototype Service Water Heating Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0.04 0.11 0.04 0.11 0.07

2 0.05 0.10 0.05 0.10 0.07

3 0.05 0.08 0.05 0.08 0.07

4 0.04 0.06 0.04 0.06 0.06

5 0.04 0.06 0.04 0.06 0.06

6 0.04 0.06 0.04 0.06 0.06

7 0.04 0.07 0.04 0.07 0.07

8 0.15 0.20 0.15 0.20 0.10

9 0.23 0.24 0.23 0.24 0.12

10 0.32 0.27 0.32 0.27 0.14

11 0.41 0.42 0.41 0.42 0.29

12 0.57 0.54 0.57 0.54 0.31

13 0.62 0.59 0.62 0.59 0.36

14 0.61 0.60 0.61 0.60 0.36

15 0.50 0.49 0.50 0.49 0.34

16 0.45 0.48 0.45 0.48 0.35

17 0.46 0.47 0.46 0.47 0.37

18 0.47 0.46 0.47 0.46 0.34

19 0.42 0.44 0.42 0.44 0.25

20 0.34 0.36 0.34 0.36 0.27

21 0.33 0.29 0.33 0.29 0.21

22 0.23 0.22 0.23 0.22 0.16

23 0.13 0.16 0.13 0.16 0.10

24 0.08 0.13 0.08 0.13 0.06

Total 

Hours/Day 6.62 6.90 6.62 6.90 4.59

Total 

Hours/Week 44.59
112

Appendix B Baseline Model Schedules

The following schedules apply to the low-rise and high-rise large office baseline models; they 

were determined through a combination of industry-validated assumption and schedule set data 

from the Medium Office TSD (Thornton, Wang et al. 2009) and the Reference Building project 

(Deru, Field et al. 2010), for which schedules were largely based on the recommendation of 

ASHRAE Standard 90.1-1989 (ASHRAE 1989). Schedules are presented as fractions of peak, 

unless otherwise noted. The entries for total hours/day, etc. are the equivalent number of peak 

hours during the given time period. 

B.1 HVAC

The baseline HVAC schedule is shown in Table B-1. 

Table B-1 Baseline HVAC Schedule 

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0 0 0 0 0 

2 0 0 0 0 0 

3 0 0 0 0 0 

4 0 0 0 0 0 

5 0 0 0 0 0 

6 1 0 1 0 0 

7 1 1 1 1 0 

8 1 1 1 1 1 

9 1 1 1 1 1 

10 1 1 1 1 1 

11 1 1 1 1 1 

12 1 1 1 1 1 

13 1 1 1 1 1 

14 1 1 1 1 1 

15 1 1 1 1 1 

16 1 1 1 1 1 

17 1 1 1 1 1 

18 1 1 1 1 1 

19 1 1 1 1 0 

20 1 0 1 0 0 

21 1 0 1 0 0 

22 1 0 1 0 0 

23 0 0 0 0 0 

24 0 0 0 0 0 

Total 

Hours/Day 17 13 17 13 11

Total 

Hours/Week 109
113

B.2 Infiltration

The baseline infiltration schedule is defined for a ground floor (applies to the ground level of the 

low-rise baselines) in Table B-2 and for an interior floor (applies to all but the ground floor of 

the low-rise baselines and to the high-rise baselines) in Table B-3. 

Table B-2 Baseline Ground Floor Infiltration Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0.45 0.45 0.45 0.45 0.45

2 0.45 0.45 0.45 0.45 0.45

3 0.45 0.45 0.45 0.45 0.45

4 0.45 0.45 0.45 0.45 0.45

5 0.45 0.45 0.45 0.45 0.45

6 0.11 0.45 0.11 0.45 0.45

7 0.11 0.11 0.11 0.11 0.45

8 0.25 0.11 0.25 0.11 0.11

9 0.25 0.25 0.25 0.25 0.11

10 0.25 0.25 0.25 0.25 0.11

11 0.25 0.25 0.25 0.25 0.11

12 0.25 0.25 0.25 0.25 0.11

13 0.25 0.25 0.25 0.25 0.11

14 0.25 0.25 0.25 0.25 0.11

15 0.25 0.25 0.25 0.25 0.11

16 0.25 0.11 0.25 0.11 0.11

17 0.25 0.11 0.25 0.11 0.11

18 0.25 0.11 0.25 0.11 0.11

19 0.25 0.11 0.25 0.11 0.45

20 0.11 0.45 0.11 0.45 0.45

21 0.11 0.45 0.11 0.45 0.45

22 0.11 0.45 0.11 0.45 0.45

23 0.45 0.45 0.45 0.45 0.45

24 0.45 0.45 0.45 0.45 0.45

Total 

Hours/Day 6.70 7.36 6.70 7.36 7.06

Total 

Hours/Week 47.92
114

Table B-3 Baseline Interior Floor Infiltration Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 1 1 1 1 1 

2 1 1 1 1 1 

3 1 1 1 1 1 

4 1 1 1 1 1 

5 1 1 1 1 1 

6 0.25 1 0.25 1 1 

7 0.25 0.25 0.25 0.25 1 

8 0.25 0.25 0.25 0.25 0.25

9 0.25 0.25 0.25 0.25 0.25

10 0.25 0.25 0.25 0.25 0.25

11 0.25 0.25 0.25 0.25 0.25

12 0.25 0.25 0.25 0.25 0.25

13 0.25 0.25 0.25 0.25 0.25

14 0.25 0.25 0.25 0.25 0.25

15 0.25 0.25 0.25 0.25 0.25

16 0.25 0.25 0.25 0.25 0.25

17 0.25 0.25 0.25 0.25 0.25

18 0.25 0.25 0.25 0.25 0.25

19 0.25 0.25 0.25 0.25 1 

20 0.25 1 0.25 1 1 

21 0.25 1 0.25 1 1 

22 0.25 1 0.25 1 1 

23 1 1 1 1 1 

24 1 1 1 1 1 

Total 

Hours/Day 11.25 14.25 11.25 14.25 15.75

Total 

Hours/Week 86.25
115

B.3 Thermostat Set Points

The baseline heating and cooling set point schedules are shown in Table B-4 and Table B-5, 

respectively, which list temperatures in degrees centigrade. The baseline VAV system has dual 

thermostatic control based on dry bulb temperature in the zones. The thermostat heating set 

point is 70oF (21oC) with a setback temperature of 60.1oF (15.6oC). The thermostat cooling set 

point is 75oF (24oC) with a setup temperature of 87oF (30.6oC). 

Table B-4 Baseline Heating Set Point Schedule (oC)

Hour Weekdays Saturdays Summer 

Design

Winter 

Design

Sundays, 

Holidays, 

Other

1 15.6 15.6 15.6 15.6 15.6

2 15.6 15.6 15.6 15.6 15.6

3 15.6 15.6 15.6 15.6 15.6

4 15.6 15.6 15.6 15.6 15.6

5 15.6 15.6 15.6 15.6 15.6

6 21 15.6 15.6 21 15.6

7 21 21 15.6 21 15.6

8 21 21 15.6 21 21

9 21 21 15.6 21 21

10 21 21 15.6 21 21

11 21 21 15.6 21 21

12 21 21 15.6 21 21

13 21 21 15.6 21 21

14 21 21 15.6 21 21

15 21 21 15.6 21 21

16 21 21 15.6 21 21

17 21 21 15.6 21 21

18 21 21 15.6 21 21

19 21 21 15.6 21 15.6

20 21 15.6 15.6 21 15.6

21 21 15.6 15.6 21 15.6

22 21 15.6 15.6 21 15.6

23 15.6 15.6 15.6 15.6 15.6

24 15.6 15.6 15.6 15.6 15.6
116

Table B-5 Baseline Cooling Set Point Schedule (oC)

Hour Weekdays Saturdays Summer 

Design

Winter 

Design

Sundays, 

Holidays, 

Other

1 30.6 30.6 30.6 30.6 30.6

2 30.6 30.6 30.6 30.6 30.6

3 30.6 30.6 30.6 30.6 30.6

4 30.6 30.6 30.6 30.6 30.6

5 30.6 30.6 30.6 30.6 30.6

6 24 30.6 24 30.6 30.6

7 24 24 24 30.6 30.6

8 24 24 24 30.6 24

9 24 24 24 30.6 24

10 24 24 24 30.6 24

11 24 24 24 30.6 24

12 24 24 24 30.6 24

13 24 24 24 30.6 24

14 24 24 24 30.6 24

15 24 24 24 30.6 24

16 24 24 24 30.6 24

17 24 24 24 30.6 24

18 24 24 24 30.6 24

19 24 24 24 30.6 30.6

20 24 30.6 24 30.6 30.6

21 24 30.6 24 30.6 30.6

22 24 30.6 24 30.6 30.6

23 30.6 30.6 30.6 30.6 30.6

24 30.6 30.6 30.6 30.6 30.6
117

Appendix C Low-Energy Model Schedules

The following schedules apply to the low-rise and high-rise large office low-energy models; they 

were determined through a combination of industry-validated assumption and schedule set data 

from the Medium Office TSD (Thornton, Wang et al. 2009) and the Reference Building project 

(Deru, Field et al. 2010), for which schedules were largely based on the recommendation of 

ASHRAE Standard 90.1-1989 (ASHRAE 1989). Schedules are presented as fractions of peak, 

unless otherwise noted. The entries for total hours/day, etc. are the equivalent number of peak 

hours during the given time period.

C.1 HVAC

The low-energy DOAS schedule is shown in Table C-1. The low-energy radiant availability 

schedule is shown in Table C-2. 

Table C-1 Low-Energy DOAS Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0 0 0 0 0 

2 0 0 0 0 0 

3 0 0 0 0 0 

4 0 0 0 0 0 

5 1 0 1 0 0 

6 1 1 1 1 0 

7 1 1 1 1 1 

8 1 1 1 1 1 

9 1 1 1 1 1 

10 1 1 1 1 1 

11 1 1 1 1 1 

12 1 1 1 1 1 

13 1 1 1 1 1 

14 1 1 1 1 1 

15 1 1 1 1 1 

16 1 1 1 1 1 

17 1 1 1 1 1 

18 1 1 1 1 1 

19 1 1 1 1 0 

20 1 0 1 0 0 

21 1 0 1 0 0 

22 1 0 1 0 0 

23 0 0 0 0 0 

24 0 0 0 0 0 

Total 

Hours/Day 18 14 18 14 12

Total 

Hours/Week 116
118

Table C-2 Low-Energy Radiant Availability Schedule 

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0 0 0 0 0 

2 0 0 0 0 0 

3 0 0 0 0 0 

4 0 0 0 0 0 

5 0 0 0 0 0 

6 1 0 1 0 0 

7 1 1 1 1 0 

8 1 1 1 1 1 

9 1 1 1 1 1 

10 1 1 1 1 1 

11 1 1 1 1 1 

12 1 1 1 1 1 

13 1 1 1 1 1 

14 1 1 1 1 1 

15 1 1 1 1 1 

16 1 1 1 1 1 

17 1 1 1 1 1 

18 1 1 1 1 0 

19 1 0 1 0 0 

20 1 0 1 0 0 

21 1 0 1 0 0 

22 0 0 0 0 0 

23 0 0 0 0 0 

24 0 0 0 0 0 

Total 

Hours/Day 16 12 16 12 10

Total 

Hours/Week 102
119

C.2 Infiltration

The low-energy infiltration schedule is defined for a ground floor (applies to the ground level of 

the low-rise baselines) in Table C-3 and for an interior floor (applies to all but the ground floor 

of the low-rise baselines and to the high-rise baselines) in Table C-4. 

Table C-3 Low-Energy Ground Floor Infiltration Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 0.27 0.27 0.27 0.27 0.27

2 0.27 0.27 0.27 0.27 0.27

3 0.27 0.27 0.27 0.27 0.27

4 0.27 0.27 0.27 0.27 0.27

5 0.07 0.27 0.07 0.27 0.27

6 0.07 0.07 0.07 0.07 0.27

7 0.07 0.07 0.07 0.07 0.07

8 0.25 0.07 0.25 0.07 0.07

9 0.25 0.25 0.25 0.25 0.07

10 0.25 0.25 0.25 0.25 0.07

11 0.25 0.25 0.25 0.25 0.07

12 0.25 0.25 0.25 0.25 0.07

13 0.25 0.25 0.25 0.25 0.07

14 0.25 0.25 0.25 0.25 0.07

15 0.25 0.25 0.25 0.25 0.07

16 0.25 0.07 0.25 0.07 0.07

17 0.25 0.07 0.25 0.07 0.07

18 0.25 0.07 0.25 0.07 0.07

19 0.25 0.07 0.25 0.07 0.27

20 0.07 0.27 0.07 0.27 0.27

21 0.07 0.27 0.07 0.27 0.27

22 0.07 0.27 0.07 0.27 0.27

23 0.27 0.27 0.27 0.27 0.27

24 0.27 0.27 0.27 0.27 0.27

Total 

Hours/Day 5.04 4.94 5.04 4.94 4.08

Total 

Hours/Week 34.22
120

Table C-4 Low-Energy Interior Floor Infiltration Schedule

Hour Weekdays Saturdays Summer Design Winter Design Sundays, Holidays, 

Other

1 1 1 1 1 1 

2 1 1 1 1 1 

3 1 1 1 1 1 

4 1 1 1 1 1 

5 0.25 1 0.25 1 1 

6 0.25 0.25 0.25 0.25 1 

7 0.25 0.25 0.25 0.25 0.25

8 0.25 0.25 0.25 0.25 0.25

9 0.25 0.25 0.25 0.25 0.25

10 0.25 0.25 0.25 0.25 0.25

11 0.25 0.25 0.25 0.25 0.25

12 0.25 0.25 0.25 0.25 0.25

13 0.25 0.25 0.25 0.25 0.25

14 0.25 0.25 0.25 0.25 0.25

15 0.25 0.25 0.25 0.25 0.25

16 0.25 0.25 0.25 0.25 0.25

17 0.25 0.25 0.25 0.25 0.25

18 0.25 0.25 0.25 0.25 0.25

19 0.25 0.25 0.25 0.25 1 

20 0.25 1 0.25 1 1 

21 0.25 1 0.25 1 1 

22 0.25 1 0.25 1 1 

23 1 1 1 1 1 

24 1 1 1 1 1 

Total 

Hours/Day 10.50 13.50 10.50 13.50 15.00

Total 

Hours/Week 81.00
121

C.3 Thermostat Set Points

The low-energy heating set point schedule for the DOAS is shown in Table C-5, which lists 

temperatures in degrees centigrade. The low-energy DOAS system has heating control as 

described in Section 3.4.4.5.1 based on operative temperature in the zones. The thermostat 

heating set point is an operative temperature 70.2oF (21.2oC) with a dry bulb setback temperature 

of 60.1oF (15.6oC). The DOAS does not have a day time cooling set point; when heating is not 

required during day time operation, the DOAS supplies air at 55.0oF (12.8oC). At night when the 

radiant cooling system is unavailable, the DOAS has a dry bulb set up temperature of 87oF 

(30.6oC). Radiant heating and cooling set points are 70oF (21oC) and 75oF (24oC), measured in 

operative temperature; radiant set point temperatures apply any time the radiant system is 

available for operation. 

Table C-5 Low-Energy Heating Set Point Schedule (oC)

Hour Weekdays Saturdays Summer 

Design

Winter 

Design

Sundays, 

Holidays, 

Other

1 15.6 15.6 15.6 15.6 15.6

2 15.6 15.6 15.6 15.6 15.6

3 15.6 15.6 15.6 15.6 15.6

4 15.6 15.6 15.6 15.6 15.6

5 21.2 15.6 15.6 21.2 15.6

6 21.2 21.2 15.6 21.2 15.6

7 21.2 21.2 15.6 21.2 21.2

8 21.2 21.2 15.6 21.2 21.2

9 21.2 21.2 15.6 21.2 21.2

10 21.2 21.2 15.6 21.2 21.2

11 21.2 21.2 15.6 21.2 21.2

12 21.2 21.2 15.6 21.2 21.2

13 21.2 21.2 15.6 21.2 21.2

14 21.2 21.2 15.6 21.2 21.2

15 21.2 21.2 15.6 21.2 21.2

16 21.2 21.2 15.6 21.2 21.2

17 21.2 21.2 15.6 21.2 21.2

18 21.2 21.2 15.6 21.2 21.2

19 21.2 21.2 15.6 21.2 15.6

20 21.2 15.6 15.6 21.2 15.6

21 21.2 15.6 15.6 21.2 15.6

22 21.2 15.6 15.6 21.2 15.6

23 15.6 15.6 15.6 15.6 15.6

24 15.6 15.6 15.6 15.6 15.6
122

Appendix D Metric Unit Tables

Table D-1 National Average Natural Gas Tariff and Source Data in $/GJ 

Month 

Year

Tariff 

2006 2007 2008 2009

January – $10.57 $10.44 $10.46 $10.49

February – $10.63 $10.73 $10.12 $10.49

March – $11.17 $11.19 $9.57 $10.65

April $10.97 $10.89 $11.79 – $11.22

May $11.00 $10.88 $12.55 – $11.48

June $10.51 $11.24 $13.64 – $11.80

July $10.41 $11.00 $14.64 – $12.02

August $10.62 $10.58 $13.31 – $11.50

September $10.58 $10.33 $12.34 – $11.08

October $9.53 $10.33 $11.21 – $10.36

November $10.47 $10.61 $10.85 – $10.64

December $11.00 $10.44 $10.73 – $10.73

Table D-2 Low-Rise Baseline Exterior Wall Constructions 

Properties Climate Zone 

1A

Climate Zones 

3B-NV and 4C

Climate Zones 

5A and 5B

Climate Zone 

7

Key

Baseline Wall 

Construction 

No c.i.

Baseline Wall 

Construction 

R-5.7 c.i.

Baseline Wall 

Construction 

R-7.6 c.i.

Baseline Wall 

Construction 

R-11.4 c.i.

Assembly Ufactor 

(W/K·m2)

5.735 0.982 0.778 0.551

Capital cost 

($/m2) $389.12 $474.15 $477.92 $485.45

Table D-3 High-Rise Code-Compliant Baseline Exterior Wall Constructions 

Properties Climate Zones 

1A, 3B-NV, and 4C

Climate Zones 

5A, and 5B

Climate Zone 

7

Key

Baseline Wall 

Construction 

R-13.0

Baseline Wall 

Construction 

R-13.0 + R-3.8 c.i.

Baseline Wall 

Construction 

R-13.0 + R-7.5 c.i.

Assembly 

U-factor 

(W/K·m2)

0.789 0.517 0.386

Capital 

cost ($/m2) $384.81 $394.50 $399.88

Table D-4 High-Rise Common Practice Baseline Exterior Wall Construction 

Properties All Climate Zones

Key Baseline Wall Construction, 

Whole Wall Assembly R-3.0

U-factor (W/K·m2) 0.982

Capital cost ($/m2) $374.58
123

Table D-5 Low-Rise Baseline Roof Constructions 

Properties Climate Zones 1–7

Key Baseline Roof Construction, R-15 c.i.

U-factor (W/K·m2) 0.375

Capital cost ($/m2) $98.49 

Table D-6 Low-Rise Baseline East-, South-, and West-Facing Punched-Hole Window 

Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.25 0.25 0.39 0.49

VLT 0.25 0.318 0.495 0.49

U-factor 

(W/K·m2) 6.871 3.237 3.237 3.237

Capital cost 

($/m2) $498.26 $536.15 $508.49 $508.49

Fixed O&M 

cost ($/m2) $2.37 $2.37 $2.37 $2.37

Table D-7 Low-Rise Baseline North-Facing Punched-Hole Window Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.44 0.39 0.49 0.64

VLT 0.44 0.622 0.622 0.64

U-factor 

(W/K·m2) 6.871 3.237 3.237 3.237

Capital cost 

($/m2) $486.64 $445.52 $502.24 $439.60

Fixed O&M 

cost ($/m2) $2.37 $2.37 $2.37 $2.37

Table D-8 High-Rise Baseline East-, South-, and West-Facing Glass Curtain Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.25 0.25 0.39 0.49

VLT 0.25 0.318 0.495 0.49

U-factor 

(W/K·m2) 6.871 3.237 3.237 3.237

Capital cost 

($/m2) $788.99 $826.88 $799.22 $799.22

Fixed O&M 

cost ($/m2) $2.37 $2.37 $2.37 $2.37
124

Table D-9 High-Rise Baseline North-Facing Glass Curtain Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.44 0.39 0.49 0.64

VLT 0.44 0.622 0.622 0.64

U-factor 

(W/K·m2) 6.871 3.237 3.237 3.237

Capital cost 

($/m2) $777.37 $736.25 $792.98 $730.33

Fixed O&M 

cost ($/m2) $2.37 $2.37 $2.37 $2.37

Table D-10 Baseline Data Center EUIs 

Low-Rise High-Rise

IT equipment (MJ/m2·yr) 167.3 167.3

HVAC and lighting equipment (MJ/m2·yr) 150.6 150.6

Total data center (MJ/m2·yr) 317.9 317.9

Table D-11 Baseline HVAC System Cost Estimation Sizes 

Climate

Low-Rise Baseline High-Rise Baseline:

Code-Compliant

High-Rise Baseline:

Common Practice

Boilers 

(kW)

Chillers 

(kW)

Fans 

(m3/s)

Boilers 

(kW)

Chillers 

(kW)

Fans 

(m3/s)

Boilers 

(kW)

Chillers 

(kW)

Fans 

(m3/s)

Average 5002 3253 198 5965 4055 214 7294 5085 256

Table D-12 Baseline HVAC System Cost Breakdown 

HVAC Input

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

Low-rise

ASHRAE 90.1-2004 Baseline 

Hydronic VAV 

High-Rise

Chillers and cooling tower ($/m2) $15.07 $15.07

Boilers ($/m2) $5.27 $7.10

Air distribution units ($/m2) $81.70 $111.51

VAV terminal boxes ($/m2) $9.04 $9.15

Pumps ($/m2) $4.20 $4.20

Ductwork ($/m2) $48.01 $51.34

Water distribution network ($/m2) $20.24 $17.65

Life safety ($/m2) $3.77 $1.83

Air and water balance ($/m2) $2.15 $2.80

Temperature controls ($/m2) $10.76 $10.76

Total ($/m2) $200.10 $231.64
125

Table D-13 Low-Rise Exterior Wall EEMs 

Insulation R-value, 

Nominal

Assembly U-Factor 

(W/K·m2)

Capital Cost 

($/m2)

R-5.7 c.i. 0.982 $474.15

R-9.5 c.i. 0.647 $481.68

R-13.3 c.i. 0.488 $489.22

R-15.0 c.i. 0.437 $494.60

R-19.5 c.i. 0.346 $497.83

R-22.5 c.i. 0.301 $501.60

R-28.5 c.i. 0.244 $505.37

Table D-14 High-Rise Exterior Wall EEMs 

Insulation R-value, 

Nominal

Assembly U-Factor 

(W/K·m2)

Capital Cost 

($/m2)

R-13.0 0.789 $384.81

R-13.0 + R-3.8 c.i. 0.517 $394.50

R-13.0 + R-7.5 c.i. 0.386 $399.88

R-22.5 c.i. 0.244 $428.94

R-28.5 c.i. 0.193 $438.63

Table D-15 Low-rise Roof EEMs 

EEM Key U-Factor 

(W/K·m2)

Capital Cost 

($/m2)

R-20 c.i. 0.284 $103.23

R-30 c.i. 0.187 $112.70

R-40 c.i. 0.131 $122.28

R-60 c.i. 0.091 $141.22

Table D-16 Low-Rise Fenestration Construction EEMs 

EEM Key SHGC VLT U-Factor 

(W/K·m2)

Capital Cost 

($/m2)

Fixed O&M 

Cost ($/m2·yr)

Single pane with clear glass 0.81 0.881 6.133 $401.49 $2.26

Single pane with pyrolytic low-e 0.71 0.811 4.230 $449.93 $2.26

Double pane with low-e and argon 0.564 0.745 1.499 $545.73 $2.26

Double pane with low-e2 and argon 0.416 0.75 1.334 $567.26 $2.26

Triple layer with low-e polyester film 0.355 0.535 1.221 $783.61 $2.26

Quadruple layer with low-e polyester 

films and krypton 0.461 0.624 0.772 $1,008.58 $2.26

Table D-17 High-Rise Fenestration Construction EEMs 

EEM Key SHGC VLT U-Factor 

(W/K·m2)

Capital Cost 

($/m2)

Fixed O&M 

Cost ($/m2·yr)

Single pane with clear glass 0.81 0.881 6.133 $728.18 $2.26

Single pane with tinted glass 0.567 0.431 6.133 $749.60 $2.26

Single pane with pyrolytic low-e 0.71 0.811 4.230 $758.32 $2.26

Double pane with low-e and argon 0.564 0.745 1.499 $818.60 $2.26

Double pane with reflective coating and 

tinted glass 0.24 0.44 2.941 $824.52 $2.26

Double pane with low-e2 and argon 0.416 0.75 1.334 $842.28 $2.26

Double pane with low-e2 and tinted glass 0.282 0.55 1.635 $842.28 $2.26
126

Table D-18 Low-Rise Occupancy Sensor LPD Reductions 

 

Space Type Baseline LPD 

(W/m2)

Reduced LPD 

(W/m2)

LPD Reduction 

(Total %)

Office-open 11.84 11.63 1.40%

Office-enclosed 11.84 11.19 5.70%

Conference 13.99 13.99 0.00%

Break room 9.69 9.69 0.00%

Elevator 0.00 0.00 0.00%

Restroom 9.69 9.69 0.50%

Stairs 6.46 6.46 0.00%

Mechanical/electrical room 16.15 15.82 2.00%

Total 11.73 10.66 9.60%

Table D-19 High-Rise Occupancy Sensor LPD Reductions 

Space Type Baseline LPD 

(W/m2)

Reduced LPD 

(W/m2)

LPD Reduction 

(Total %)

Office-open 11.84 11.63 1.40%

Office-enclosed 11.84 11.19 5.70%

Conference 13.99 13.99 0.00%

Break room 9.69 9.69 0.00%

Elevator 0.00 0.00 0.00%

Restroom 9.69 9.69 0.50%

Stairs 6.46 6.46 0.00%

Mechanical/electrical room 16.15 15.82 2.00%

Total 11.41 10.33 9.60%

Table D-20 Lighting Power Density EEMs 

EEM Key LPD 

(W/m2)

Capital Cost 

($/kW)

Capital Cost 

($/m2)

Fixed O&M Cost 

($/kW·yr)

Fixed O&M Cost 

($/m2·yr)

Baseline 11.84 $9,418 $112 $77.24 $0.86

42% LPD reduction 6.78 $18,270 $124 $77.24 $0.54

Table D-21 Low-Energy Data Center EUIs 

Low-Rise High-Rise

IT equipment (MJ/m2·yr) 122.1 122.1

HVAC and lighting equipment (MJ/m2·yr) 24.4 24.4

Total data center (MJ/m2·yr) 146.5 146.5

Table D-22 Baseline and Low-Energy HVAC System Comfort Comparison 

Control 

Set 

Point

Baseline VAV System Low Energy Radiant System With DOAS

Air 

Temperature 

(oC )

Mean Radiant 

Temperature 

(oC)

PMV

Air 

Temperature 

(oC)

Mean Radiant 

Temperature 

(oC)

PMV

Heating 21.1 21.1 –0.17 20.0 22.8 –0.17

Cooling 23.9 23.9 0.12 25.6 21.1 0.12
127

Table D-23 Radiant System Temperatures Required for Baseline Equivalent Comfort 

Control 

Set 

Point

Air 

Temperature 

(oC)

Mean Radiant 

Temperature 

(oC)

Supply Equipment 

Outlet Temperature

(oC )

Radiant Tube 

Temperature 

(oC )

Radiant Surface 

Temperature 

(oC)

Heating 20.0 22.8 28.9 26.1 25.0

Cooling 25.6 21.2 14.1 16.0 18.3

Table D-24 Radiant System Temperatures Required for Maximum Capacity 

Control 

Set 

Point

Air 

Temperature 

(oC)

Mean Radiant 

Temperature 

(oC)

Supply Equipment 

Outlet Temperature

(oC )

Radiant Tube 

Temperature 

(oC )

Radiant Surface 

Temperature 

(oC)

Heating 20.0 24.2 31.6 28.8 27.0

Cooling 25.6 20.4 12.3 14.2 17.0

Table D-25 Radiant System Peak Volumetric Flow Rates Per Floor 

Low-Rise Building High-Rise Building

Maximum Heating Flow

(m3/s)

Maximum Cooling Flow

(m3/s)

Maximum Heating Flow

(m3/s)

Maximum Cooling Flow

(m3/s)

0.0193 0.0618 0.0064 0.0206

Table D-26 Low-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes 

Climate

Low-rise Low-Energy

DOAS Boiler 

(kW)

DOAS Chiller 

(kW)

DOAS Fan 

(m3/s)

Radiant 

Boiler (kW)

Radiant 

Chiller (kW)

Average 1125 622 26.7 1355 3049

Table D-27 High-Rise Low-Energy Radiant With DOAS HVAC System Cost Estimation Sizes 

Climate

High-Rise Low-Energy: 

Code-Compliant

High-Rise Low Energy:

Common Practice

DOAS 

Boiler 

(kW)

DOAS 

Chiller 

(kW)

DOAS 

Fan 

(m3/s)

Radiant 

Boiler 

(kW)

Radiant 

Chiller 

(kW)

DOAS 

Boiler 

(kW)

DOAS 

Chiller 

(kW)

DOAS 

Fan 

(m3/s)

Radiant 

Boiler 

(kW)

Radiant 

Chiller 

(kW)

Average 2180 615 26 1802 2180 2180 2180 26 1802 2180

Table D-28 Low-Energy HVAC System Cost Estimate Breakdown 

HVAC Input Radiant Heating and Cooling 

With DOAS, Low-Rise

Radiant Heating and Cooling 

With DOAS, High-Rise

Chillers and cooling tower ($/m2) $16.36 $16.36

Boilers ($/m2) $6.46 $6.46

Radiant heating and cooling ($/m2) $117.22 $116.36

Air distribution units ($/m2) $10.76 $11.73

Perimeter heating coils ($/m2) $1.18 $2.26

Pumps ($/m2) $4.20 $4.20

Ductwork ($/m2) $39.72 $49.62

Air system water distribution ($/m2) $28.09 $21.85

Life safety ($/m2) $0.97 $0.97

Air and water balance ($/m2) $1.94 $1.94

Temperature controls ($/m2) $10.76 $10.76

Total ($/m2) $237.56 $242.30
128

Table D-29 Low-Energy HVAC System Operational Static Pressure Breakdown 

Building 

Type

Low-Rise Low-Energy 

(Pa) 

High-Rise Low-Energy: 

Code-Compliant 

(Pa)

High-Rise Low Energy: 

Common Practice 

(Pa)

Enthalpy 

Wheel

Sensibl

e Wheel IDEC Enthalpy Wheel

Sensible 

Wheel IDEC Enthalpy Wheel

Sensible 

Wheel IDEC

Supply

and return 

fans

1140.8 1140.8 1208.1 1138.3 1138.3 1208.1 1138.3 1138.3 1208.1

Energy 

recovery

348.7 249.1 249.1 348.7 249.1 249.1 348.7 249.1 249.1

Total 1489.6 1389.9 1457.2 1487.1 1387.4 1454.7 1487.1 1387.4 1454.7

Table D-30 ASHRAE 90.1-2004 Low-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Site EUI (MJ/m2·yr) 1307 891 833 1001 851 998

Source EUI (MJ/m2·yr) 3829 2702 2404 2750 2461 2583

Energy emissions intensity

(kgCO2/m2·yr) 223 158 140 159 143 148

Electricity intensity (MJ/m2·yr) 1057 760 658 729 674 657

Natural gas intensity (MJ/m2·yr) 251 131 175 272 176 342

Peak demand (kW) 1984 1750 1721 1908 1690 1818

Table D-31 ASHRAE 90.1-2004 Low-Rise Baseline Model Costs 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B

Boulder

7 

Duluth

5-TLCC ($/m2) $1,496.92 $1,387.43 $1,361.22 $1,451.06 $1,342.80 $1,406.39

Capital cost ($/m2) $1,286.44 $1,234.46 $1,220.95 $1,280.20 $1,205.44 $1,249.34

Annual energy cost intensity 

($/m2·yr) $27.96 $19.83 $17.94 $20.81 $18.32 $19.75

Annual electricity cost intensity 

($/m2·yr) $25.00 $18.29 $15.90 $17.64 $16.26 $15.77

Annual natural gas cost 

intensity ($/m2·yr) $2.96 $1.54 $2.04 $3.18 $2.06 $3.97

Table D-32 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Site EUI (MJ/m2·yr) 1218 894 850 986 848 983

Source EUI (MJ/m2·yr) 3583 2704 2421 2716 2458 2556

Energy emissions intensity 

(kgCO2/m2·yr) 208 158 140 157 143 147

Electricity intensity (MJ/m2·yr) 991 760 657 721 674 653

Natural gas intensity (MJ/m2·yr) 227 134 193 265 173 330

Peak demand (kW) 1940 1758 1746 1925 1717 1872
129

Table D-33 ASHRAE 90.1-2004 Code-Compliant High-Rise Baseline Model Costs 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC ($/m2) $1,556.06 $1,478.98 $1,458.92 $1,532.21 $1,445.48 $1,501.32

Capital cost ($/m2) $1,368.85 $1,333.73 $1,323.85 $1,372.30 $1,313.34 $1,351.77

Annual energy cost intensity 

($/m2

·yr) $26.22 $19.88 $18.19 $20.59 $18.35 $19.56

Annual electricity cost intensity 

($/m2·yr) $23.55 $18.31 $15.94 $17.49 $16.33 $15.73

Annual natural gas cost 

intensity ($/m2·yr) $2.67 $1.57 $2.25 $3.09 $2.02 $3.83

Table D-34 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Site EUI (MJ/m2·yr) 1234 951 939 1087 934 1118

Source EUI (MJ/m2·yr) 3657 2845 2574 2894 2616 2757

Energy emissions intensity

(kgCO2/m2·yr) 213 166 149 166 151 157

Electricity intensity (MJ/m2·yr) 1016 795 681 751 702 676

Natural gas intensity (MJ/m2·yr) 217 156 258 336 232 442

Peak demand (kW) 1999 1868 1879 2066 1850 2036

Table D-35 ASHRAE 90.1-2004 Common Practice High-Rise Baseline Model Costs 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC ($/m2) $1,621.62 $1,568.21 $1,551.41 $1,625.77 $1,534.98 $1,604.17

Capital cost ($/m2) $1,426.30 $1,408.34 $1,398.82 $1,447.02 $1,385.40 $1,432.80

Annual energy cost intensity 

($/m2·yr) $26.75 $21.09 $19.69 $22.26 $19.89 $21.57

Annual electricity cost intensity 

($/m2·yr) $24.19 $19.26 $16.69 $18.35 $17.19 $16.44

Annual natural gas cost intensity 

($/m2·yr) $2.56 $1.82 $3.01 $3.91 $2.70 $5.14
130

Table D-36 Comparison of Low-Rise EUI in MJ/m2∙yr by End Use Between Baseline and 50% Savings Target 

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth 

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 243.3 121.6 121.7 60.9 162.9 81.5 259.3 129.6 163.9 81.9 326.8 163.4

Cooling 385.0 192.5 149.2 74.6 73.8 36.9 125.0 62.5 82.3 41.1 63.8 31.9

Interior lighting 168.1 84.1 168.1 84.1 168.1 84.1 168.1 84.1 168.1 84.1 168.1 84.1

Interior equipment 54.7 27.3 54.7 27.3 54.7 27.3 54.7 27.3 54.7 27.3 54.7 27.3

Fans 58.6 29.3 36.3 18.1 23.6 11.8 34.4 17.2 31.5 15.7 33.5 16.7

Pumps 46.6 23.3 22.1 11.1 12.8 6.4 19.5 9.7 13.1 6.5 13.4 6.7

Heat rejection 25.6 12.8 12.1 6.0 6.7 3.4 9.5 4.7 6.6 3.3 5.3 2.6

Water systems 7.6 3.8 9.3 4.6 12.3 6.1 12.7 6.3 12.6 6.3 15.0 7.5

Data center 317.9 158.9 317.9 158.9 317.9 158.9 317.9 158.9 317.9 158.9 317.9 158.9

Total end uses 1307.4 653.7 891.4 445.7 832.7 416.4 1000.9 500.5 850.6 425.3 998.4 499.2

Table D-37 Comparison of Code-Compliant High-Rise EUI in MJ/m2

∙yr by End Use Between Baseline and 50% Savings Target 

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth 

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 219.2 109.6 124.7 62.4 180.7 90.4 252.3 126.1 160.9 80.4 315.0 157.5

Cooling 341.3 170.6 158.0 79.0 79.9 39.9 127.7 63.9 89.5 44.7 68.9 34.4

Interior lighting 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7

Interior equipment 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5

Fans 55.6 27.8 35.9 17.9 25.5 12.7 33.8 16.9 33.1 16.6 33.7 16.9

Pumps 41.1 20.6 23.0 11.5 13.6 6.8 19.6 9.8 14.1 7.0 13.8 6.9

Heat rejection 22.6 11.3 12.6 6.3 7.1 3.6 9.5 4.8 7.1 3.5 5.6 2.8

Water systems 7.6 3.8 9.3 4.6 12.3 6.1 12.7 6.3 12.6 6.3 15.0 7.5

Data center 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1

Total end uses 1218.0 609.0 894.0 447.0 849.7 424.8 986.1 493.0 847.8 423.9 982.5 491.3
131

Table D-38 Comparison of Common Practice High-Rise EUI in MJ/m2∙yr by End Use Between Baseline and 50% Savings Target 

EDM Key

1A Miami 3B Las Vegas 4C Seattle 5A Chicago 5B Boulder 7 Duluth 

Baseline 50% 

Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings Baseline 50% Savings

Heating 209.8 104.9 147.0 73.5 245.8 122.9 323.1 161.5 219.6 109.8 427.4 213.7

Cooling 365.2 182.6 183.2 91.6 95.7 47.9 149.3 74.6 107.3 53.6 83.4 41.7

Interior lighting 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7 163.5 81.7

Interior equipment 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5 52.9 26.5

Fans 52.7 26.4 40.1 20.1 30.3 15.2 38.0 19.0 39.3 19.7 39.5 19.8

Pumps 43.7 21.8 26.5 13.2 16.1 8.0 22.3 11.1 16.5 8.3 15.6 7.8

Heat rejection 24.0 12.0 14.5 7.2 8.5 4.2 11.0 5.5 8.4 4.2 6.7 3.4

Water systems 7.6 3.8 9.3 4.6 12.3 6.1 12.7 6.3 12.6 6.3 15.0 7.5

Data center 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1 314.1 157.1

Total end uses 1233.6 616.8 951.1 475.5 939.2 469.6 1086.9 543.4 934.4 467.2 1118.1 559.1
132

Table D-39 ASHRAE 90.1-2007 Low-Rise Baseline Exterior Wall Constructions

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zone 

4C

Climate Zones 

5A, and 5B

Climate Zone 

7

Key

Baseline Wall 

Construction 

No c.i.

Baseline Wall 

Construction 

R-7.6 c.i.

Baseline Wall 

Construction 

R-9.5 c.i.

Baseline Wall

Construction 

R-11.4 c.i.

Baseline Wall 

Construction 

R-15.2 c.i.

Assembly Ufactor 

(W/K·m2)

5.735 0.778 0.647 0.551 0.432

Capital cost 

($/m2) $389.12 $477.92 $481.68 $485.45 $492.99

Table D-40 ASHRAE 90.1-2007 High-Rise Baseline Exterior Wall Constructions 

Properties Climate Zone 

1A

Climate Zone 

3B-NV

Climate Zones 

4C, 5A, 5B, and 7

Key

Baseline Wall 

Construction 

R-13.0

Baseline Wall 

Construction 

R-13.0 + R-3.8 c.i.

Baseline Wall 

Construction 

R-13.0 + R-7.5 c.i.

Assembly U-factor (W/K·m2) 0.789 0.517 0.386

Capital cost ($/m2) $384.81 $394.50 $399.88

Table D-41 ASHRAE 90.1-2007 Baseline Roof Constructions 

Properties Climate Zone 

1A

Climate Zones 

3B-NV, 4C, 5A, 5B, and 7

Key Baseline Roof 

Construction R-15.0 c.i.

Baseline Roof 

Construction R-20.0 c.i.

Assembly U-factor 

(W/K·m2) 0.375 0.284

Capital cost ($/m2) $98.49 $103.23

Table D-42 ASHRAE 90.1-2007 Low-Rise Baseline Window Constructions

Properties Climate Zone 

1A

Climate Zones 

3B-NV

Climate Zones

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.25 0.25 0.4 0.45

VLT 0.25 0.318 0.508 0.45

U-factor 

(W/K·m2) 6.814 3.691 3.123 2.555

Capital cost 

($/m2) $534.64 $564.03 $512.04 $508.38

Fixed O&M cost 

($/m2) $2.37 $2.37 $2.37 $2.37
133

Table D-43 ASHRAE 90.1-2007 High-Rise Baseline Window Constructions 

Properties Climate Zone 

1A

Climate Zones 

3B-NV

Climate Zones

4C, 5A, and 5B

Climate Zone 

7

Key Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

Baseline Window 

Construction

SHGC 0.25 0.25 0.4 0.45

VLT 0.25 0.318 0.508 0.45

U-factor 

(W/K·m2) 6.814 3.691 3.123 2.555

Capital cost 

($/m2) $825.38 $854.76 $802.77 $799.11

Fixed O&M cost 

($/m2) $2.37 $2.37 $2.37 $2.37

Table D-44 Low-Rise EUI Comparison Between 90.1-2004 and 90.1-2007 Baselines 

Climate Zone

ASHRAE 90.1-2004 Baseline 

Site Energy Use 

(MJ/m2∙yr)

ASHRAE 90.1-2007 Baseline 

Site Energy Use 

(MJ/m2∙yr)

1A Miami 1307.4 1316.8

3B Las Vegas 891.4 891.8

4C Seattle 832.7 823.5

5A Chicago 1000.9 990.4

5B Denver 850.6 840.5

7 Duluth 998.4 970.7

Table D-45 High-Rise EUI Comparison between 90.1-2004 and 90.1-2007 baselines 

Climate Zone

ASHRAE 90.1-2004 Baseline 

Site Energy Use 

(MJ/m2∙yr)

ASHRAE 90.1-2007 Baseline 

Site Energy Use 

(MJ/m2∙yr)

Code-Compliant Common Practice Code-Compliant Common Practice

1A Miami 1218.0 1233.6 1224.4 1233.0

3B Las Vegas 894.0 951.1 894.3 961.6

4C Seattle 849.7 939.2 831.8 939.2

5A Chicago 986.1 1086.9 976.7 1082.7

5B Denver 847.8 934.4 838.9 931.4

7 Duluth 982.5 1118.1 956.6 1072.0

Table D-46 ASHRAE 90.1-2007 Low-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (MJ/m2·yr) 1317 892 823 990 840 971

Source EUI (MJ/m2·yr) 3848 2700 2396 2741 2451 2552

Energy emissions intensity 

(kgCO2/m2·yr) 224 158 139 158 142 147

Electricity intensity (MJ/m2·yr) 1060 760 659 730 675 656

Natural gas intensity (MJ/m2·yr) 256 132 165 260 166 314

Peak demand (kW) 1982 1747 1726 1908 1693 1813
134

Table D-47 ASHRAE 90.1-2007 Low-Rise Baseline Model Costs 

Metric

Climate Zones

1A

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC ($/m2) $1,499.52 $1,391.18 $1,391.18 $1,451.91 $1,344.76 $1,405.34

Capital cost ($/m2) $1,288.69 $1,238.53 $1,238.53 $1,281.55 $1,207.63 $1,250.31

Annual energy cost 

intensity ($/m2

·yr) $28.10 $19.82 $17.85 $20.70 $18.21 $19.42

Annual electricity cost 

intensity ($/m2·yr) $25.08 $18.26 $15.93 $17.66 $16.28 $15.76

Annual natural gas cost 

intensity ($/m2·yr) $3.02 $1.55 $1.93 $3.04 $1.93 $3.66

Table D-48 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Site EUI (MJ/m2·yr) 1224 894 832 977 839 957

Source EUI (MJ/m2·yr) 3588 2704 2405 2708 2451 2524

Energy emissions intensity 

(kgCO2/m2·yr) 209 158 140 156 142 145

Electricity intensity (MJ/m2·yr) 990 760 658 722 676 651

Natural gas intensity (MJ/m2·yr) 234 134 173 255 163 306

Peak demand (kW) 1934 1757 1755 1930 1723 1862

Table D-49 ASHRAE 90.1-2007 Code-Compliant High-Rise Baseline Model Costs 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC ($/m2) $1,559.36 $1,486.99 $1,464.99 $1,535.23 $1,448.79 $1,499.50

Capital cost ($/m2) $1,372.51 $1,341.78 $1,330.11 $1,375.41 $1,316.62 $1,352.22

Annual energy cost intensity 

($/m2·yr) $26.27 $19.88 $18.01 $20.49 $18.28 $19.23

Annual electricity cost 

intensity ($/m2·yr) $23.51 $18.31 $15.99 $17.52 $16.37 $15.69

Annual natural gas cost 

intensity ($/m2·yr) $2.76 $1.57 $2.02 $2.97 $1.90 $3.55

Table D-50 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Energy Performance 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

Site EUI (MJ/m2·yr) 1233 962 939 1083 931 1072

Source EUI (MJ/m2·yr) 3656 2865 2582 2897 2622 2703

Energy emissions intensity 

(kgCO2/m2·yr) 213 167 149 167 152 154

Electricity intensity (MJ/m2·yr) 1016 798 685 754 706 674

Natural gas intensity (MJ/m2·yr) 217 163 254 328 226 398

Peak demand (kW) 2000 1879 1898 2082 1866 2028
135

Table D-51 ASHRAE 90.1-2007 Common Practice High-Rise Baseline Model Costs 

Metric 

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7 

Duluth

5-TLCC ($/m2) $1,630.73 $1,579.57 $1,558.58 $1,631.64 $1,541.00 $1,598.94

Capital cost ($/m2) $1,435.40 $1,418.04 $1,404.32 $1,451.74 $1,390.13 $1,430.78

Annual energy cost intensity 

($/m2·yr) $26.74 $21.26 $19.76 $22.27 $19.93 $21.01

Annual electricity cost intensity 

($/m2·yr) $24.19 $19.36 $16.80 $18.44 $17.30 $16.40

Annual natural gas cost 

intensity ($/m2·yr) $2.55 $1.90 $2.96 $3.82 $2.63 $4.62

Table D-52 Low-Rise Optimized Low-Energy Model Energy Performance: Warm Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 1307 554 57.6% 891 386 56.7% 833 382 54.1%

Source EUI 

(MJ/m2·yr) 3829 1848 51.7% 2702 1248 53.8% 2404 1158 51.8%

Energy 

emissions 

intensity

(kgCO2/m2·yr)

223 109 51.1% 158 73 53.5% 140 68 51.6%

Electricity 

intensity 

(MJ/m2·yr)

1057 547 48.2% 760 363 52.2% 658 326 50.4%

Natural gas 

intensity 

(MJ/m2·yr)

251 7 97.0% 131 23 82.8% 175 56 68.0%

Peak demand 

(kW) 1984 1822 8.2% 1750 1630 6.9% 1721 1385 19.5%

Table D-53 Low-Rise Optimized Low-Energy Model Energy Performance: Cold Climates 

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 1001 460 54.0% 851 378 55.5% 998 449 55.0%

Source EUI 

(MJ/m2·yr) 2750 1390 49.5% 2461 1136 53.9% 2583 1258 51.3%

Energy 

emissions 

intensity 

(kgCO2/m2·yr)

159 81 48.9% 143 66 53.7% 148 73 50.9%

Electricity 

intensity 

(MJ/m2·yr)

729 390 46.5% 674 318 52.8% 657 338 48.6%

Natural gas 

intensity 

(MJ/m2·yr)

272 70 74.2% 176 61 65.6% 342 112 67.3%

Peak demand 

(kW) 1908 1680 11.9% 1690 1496 11.5% 1818 1704 6.3%
136

Table D-54 Code-Compliant High-Rise Optimized Low-Energy Model Energy Performance: Warm 

Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 1218 518 57.5% 894 374 58.2% 850 364 57.1%

Source EUI 

(MJ/m2·yr) 3583 1725 51.9% 2704 1191 55.9% 2421 1129 53.4%

Energy 

emissions 

intensity 

(kgCO2/m2·yr)

208 102 51.3% 158 70 55.7% 140 66 53.0%

Electricity 

intensity 

(MJ/m2·yr)

991 510 48.5% 760 344 54.7% 657 322 51.0%

Natural gas 

intensity 

(MJ/m2·yr)

227 8 96.5% 134 30 77.9% 193 43 77.9%

Peak demand 

(kW) 1940 1804 7.0% 1758 1587 9.7% 1746 1608 7.9%

Table D-55 Code-Compliant High-Rise Optimized Low-Energy Model Energy Performance: Cold 

Climates 

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 986 443 55.1% 848 354 58.3% 983 415 57.8%

Source EUI 

(MJ/m2·yr) 2716 1333 50.9% 2458 1074 56.3% 2556 1196 53.2%

Energy 

emissions 

intensity 

(kgCO2/m2·yr)

157 78 50.4% 143 63 56.1% 147 69 52.7%

Electricity 

intensity 

(MJ/m2·yr)

721 374 48.2% 674 303 55.1% 653 327 49.9%

Natural gas 

intensity 

(MJ/m2·yr)

265 69 73.9% 173 51 70.5% 330 88 73.3%

Peak demand 

(kW) 1925 1665 13.5% 1717 1528 11.0% 1872 1729 7.6%
137

Table D-56 Common Practice High-Rise Optimized Low-Energy Model Energy Performance: 

Warm Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 1218 628 48.5% 894 484 45.8% 850 531 37.5%

Source EUI 

(MJ/m2·yr) 3583 2050 42.8% 2704 1444 46.6% 2421 1429 40.9%

Energy 

emissions 

intensity 

(kgCO2/m2·yr)

208 120 42.2% 158 84 46.7% 140 82 41.3%

Electricity 

intensity 

(MJ/m2·yr)

991 600 39.4% 760 403 47.0% 657 374 43.1%

Natural gas 

intensity 

(MJ/m2·yr)

227 27 87.9% 134 82 39.0% 193 157 18.7%

Peak demand 

(kW) 1940 1563 19.4% 1758 1351 23.1% 1746 1378 21.0%

Table D-57 Common Practice High-Rise Optimized Low-Energy Model Energy Performance: Cold 

Climates

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

Site EUI 

(MJ/m2·yr) 986 628 36.3% 848 518 38.9% 983 620 36.9%

Source EUI 

(MJ/m2·yr) 2716 1719 36.7% 2458 1354 44.9% 2556 1517 40.7%

Energy 

emissions 

intensity 

(kgCO2/m2·yr)

157 99 36.7% 143 78 45.6% 147 86 41.1%

Electricity 

intensity 

(MJ/m2·yr)

721 455 36.9% 674 347 48.6% 653 369 43.4%

Natural gas 

intensity 

(MJ/m2·yr)

265 173 34.5% 173 172 1.0% 330 251 24.0%

Peak demand 

(kW) 1925 1454 24.5% 1717 1274 25.8% 1872 1509 19.4%
138

Table D-58 Low-Rise Optimized Low-Energy Model Cost Performance: Warm Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2

) $1,496.92 $1,670.85 –11.6% $1,387.43 $1,482.28 –6.8% $1,361.22 $1,504.28 –10.5%

Capital 

cost 

($/m2)

$1,286.44 $1,470.79 –14.3% $1,234.46 $1,342.07 –8.7% $1,220.95 $1,363.42 –11.7%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$27.96 $14.57 47.9% $19.83 $9.75 50.8% $17.94 $8.79 51.0%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$25.00 $14.48 42.1% $18.29 $9.49 48.1% $15.90 $8.14 48.8%

Annual 

natural 

gas cost 

intensity 

($/m2

·yr)

$2.96 $0.09 97.1% $1.54 $0.26 83.1% $2.04 $0.65 68.1%

Table D-59 Low-Rise Optimized Low-Energy Model Cost Performance: Cold Climates 

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2) $1,451.06 $1,603.81 –10.5% $1,342.80 $1,451.21 –8.1% $1,406.39 $1,561.34 –11.0%

Capital 

cost 

($/m2)

$1,280.20 $1,432.63 –11.9% $1,205.44 $1,321.68 –9.6% $1,249.34 $1,404.21 –12.4%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$20.81 $10.94 47.4% $18.32 $8.80 52.0% $19.75 $9.77 50.5%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$17.64 $10.13 42.6% $16.26 $8.10 50.2% $15.77 $8.48 46.2%

Annual 

natural 

gas cost 

intensity 

($/m2·yr)

$3.18 $0.81 74.5% $2.06 $0.70 65.9% $3.97 $1.29 67.5%
139

Table D-60 Code-Compliant High-rise Optimized Low-Energy Model Cost Performance: Warm 

Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2) $1,556.06 $1,657.89 -6.5% $1,478.98 $1,498.23 -1.3% $1,458.92 $1,531.48 -5.0%

Capital 

cost 

($/m2)

$1,368.85 $1,482.30 -8.3% $1,333.73 $1,374.90 -3.1% $1,323.85 $1,404.43 -6.1%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$26.22 $13.88 47.0% $19.88 $9.49 52.3% $18.19 $8.73 52.0%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$23.55 $13.79 41.4% $18.31 $9.15 50.0% $15.94 $8.24 48.3%

Annual 

natural 

gas cost 

intensity 

($/m2·yr)

$2.67 $0.09 96.6% $1.57 $0.34 78.1% $2.25 $0.50 78.0%

Table D-61 Code-Compliant High-Rise Optimized Low-Energy Model Cost Performance: Cold 

Climates 

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2) $1,532.21 $1,604.86 -4.7% $1,445.48 $1,482.45 -2.6% $1,501.32 $1,582.63 -5.4%

Capital 

cost 

($/m2)

$1,372.30 $1,453.28 -5.9% $1,313.34 $1,367.15 -4.1% $1,351.77 $1,443.58 -6.8%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$20.59 $10.79 47.6% $18.35 $8.55 53.4% $19.56 $9.36 52.1%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$17.49 $9.99 42.9% $16.33 $7.95 51.3% $15.73 $8.34 47.0%

Annual 

natural 

gas cost 

intensity 

($/m2·yr)

$3.09 $0.80 74.1% $2.02 $0.59 70.7% $3.83 $1.02 73.4%
140

Table D-62 Common Practice High-Rise Optimized Low-Energy Model Cost Performance: Warm 

Climates 

Metric 

Climate Zones

1A Miami 3B Las Vegas 4C Seattle

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2) $1,556.06 $1,777.80 -14.2% $1,478.98 $1,625.28 -9.9% $1,458.92 $1,662.68 -14.0%

Capital 

cost 

($/m2)

$1,368.85 $1,589.23 -16.1% $1,333.73 $1,488.91 -11.6% $1,323.85 $1,515.60 -14.5%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$26.22 $15.90 39.4% $19.88 $11.49 42.2% $18.19 $11.86 34.8%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$23.55 $15.58 33.8% $18.31 $10.54 42.4% $15.94 $10.03 37.1%

Annual 

natural 

gas cost 

intensity 

($/m2·yr)

$2.67 $0.32 88.1% $1.57 $0.95 39.5% $2.25 $1.83 18.6%

Table D-63 Common Practice High-Rise Optimized Low-Energy Model Cost Performance: Cold 

Climates 

Metric 

Climate Zones

5A Chicago 5B Boulder 7 Duluth

Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings Baseline LowEnergy

Percent 

Savings

5-TLCC 

($/m2) $1,532.21 $1,740.09 -13.6% $1,445.48 $1,602.31 -10.8% $1,501.32 $1,702.42 -13.4%

Capital 

cost 

($/m2)

$1,372.30 $1,567.13 -14.2% $1,313.34 $1,472.03 -12.1% $1,351.77 $1,542.32 -14.1%

Annual 

energy 

cost 

intensity 

($/m2·yr)

$20.59 $14.15 31.3% $18.35 $11.13 39.4% $19.56 $12.68 35.2%

Annual 

electricity 

cost 

intensity 

($/m2·yr)

$17.49 $12.14 30.6% $16.33 $9.13 44.1% $15.73 $9.77 37.9%

Annual 

natural 

gas cost 

intensity 

($/m2·yr)

$3.09 $2.01 34.8% $2.02 $2.00 1.0% $3.83 $2.91 24.0%
141

Table D-64 Low-Rise Simple Payback Results 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Capital cost increase ($/m2) $184.39 $107.64 $142.51 $152.52 $116.25 $154.89

Capital cost increase (%) 14.3 8.7 11.7 11.9 9.6 12.4

Annual energy cost savings ($/m2·yr) $13.45 $10.01 $9.15 $9.80 $9.47 $9.90

Simple payback period (yr) 13.7 10.8 15.6 15.6 12.3 15.6

Table D-65 Code-Compliant High-Rise Simple Payback Results 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Capital cost increase ($/m2) $113.45 $41.12 $80.62 $80.94 $53.82 $91.82

Capital cost increase (%) 8.3 3.1 6.1 5.9 4.1 6.8

Annual energy cost savings ($/m2·yr) $12.38 $10.44 $9.47 $9.80 $9.90 $10.23

Simple payback period (yr) 9.2 3.9 8.5 8.3 5.4 9

Table D-66 Common Practice High-Rise Simple Payback Results 

Metric

Climate Zones

1A 

Miami

3B 

Las Vegas

4C 

Seattle

5A 

Chicago

5B 

Boulder

7

Duluth

Capital cost increase ($/m2) $220.34 $155.11 $191.71 $194.83 $158.77 $190.63

Capital cost increase (%) 16.1 11.6 14.5 14.2 12.1 14.1

Annual energy cost savings ($/m2·yr) $10.33 $8.40 $6.35 $6.46 $7.32 $6.89

Simple payback period (yr) 21.3 18.5 30.2 30.2 21.7 27.7
F1147-E(10/2008)

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Technical Support Document: Strategies for 50% Energy Savings in 

Large Office Buildings

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6. AUTHOR(S)

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BEC7.1309

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This Technical Support Document (TSD) documents technical analysis that informs design guidance for designing 

and constructing large office buildings that achieve 50% net site energy savings over baseline buildings defined by 

minimal compliance with respect to ANSI/ASHRAE/IESNA Standard 90.1-2004. This report also represents a step 

toward developing a methodology for using energy modeling in the design process to achieve aggressive energy 

savings targets. This report documents the modeling and analysis methods used to identify design 

recommendations for six climate zones that capture the range of U.S. climate variability; demonstrates how energy 

savings change between ASHRAE Standard 90.1-2007 and Standard 90.1-2004 to determine baseline energy use; 

uses a four-story “low-rise” prototype to analyze the effect of building aspect ratio on energy use intensity; explores 

comparisons between baseline and low-energy building energy use for alternate energy metrics (net source energy, 

energy emissions, and energy cost); and examines the extent to which glass curtain construction limits achieve 

energy savings by using a 12-story “high-rise” prototype.

15. SUBJECT TERMS

technical support document; tsd; energy modeling; climate zone; energy use intensity; eui; aspect ratio; glass curtain; 

large office

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