Technical Report

NREL/TP-550-44547

November 2008

Maximizing Residential Energy 

Savings: Net Zero Energy Home 

Technology Pathways 

R. Anderson and D. Roberts
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

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

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-550-44547

November 2008

Maximizing Residential Energy 

Savings: Net Zero Energy Home 

Technology Pathways 

R. Anderson and D. Roberts

Prepared under Task No. BET98001
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iii

Executive Summary

To meet current U.S. Department of Energy zero-energy home (ZEH) performance goals, 

new technologies and solutions must increase whole-house efficiency savings by an 

additional 40% relative to those provided by best available components and systems. An 

expanded research program is needed to develop the key ZEH technologies and systems 

to fill this performance gap. 

This report identifies a range of technology options to fill the residential efficiency gap in 

two categories:

• Improved systems based on modifications of existing products 

• High-risk advanced system concepts. 

Three sequential levels of market maturity and risk reduction must be accomplished

before a new ZEH technology can be successfully used by builders, contractors, and 

homeowners:

1. Level 1 Risk Reduction – The technology must meet minimum builder, contractor, 

and homeowner performance and reliability requirements to be used in new and 

existing homes. 

2. Level 2 Risk Reduction – The design, construction, and commissioning details for 

integrating the new technology into homes must be understood and validated. 

3. Level 3 Risk Reduction – The field training, quality assurance/quality control, 

commissioning, and operations and maintenance requirements for the technology 

must be integrated as part of a production construction process to ensure that potential 

savings and benefits are achieved when the technologies are broadly implemented. 

Ignoring these risk reduction requirements can significantly increase costs, homeowner 

complaints, and building or component failures and reduce near- and long-term energy 

savings. 

At least $4 million per year is needed for research on low- to medium-risk ZEH systems 

and $8 million per year for research on high risk ZEH systems to achieve current U.S. 

Department of Energy ZEH performance goals. This estimate is based on the assumption 

that 10 projects per year will be supported in each risk category, with an average annual 

cost of $400K/year for each low- to medium-risk project and an average annual cost of 

$800K/year for each high-risk project. Based on research progress, the initial set of 

technology opportunities presented in this report will be downselected over time to focus 

on the subset of projects and solutions that are expected to provide the greatest overall 

cost and performance benefits. The final development of ZEH systems for Building 

America research homes from this expanded research program is required by 2015 to 

achieve the Department’s net ZEH goal by 2020. 
iv

Acronyms

A/C air conditioning

AFUE annual fuel utilization efficiency

CFL compact fluorescent lamp

dc direct current

DHW domestic hot water

EER energy efficiency ratio

EF emissions factor

HSPF heating season performance factor

HVAC heating, ventilation, and air conditioning

MEL miscellaneous electrical load

O&M operations and maintenance 

PV photovoltaic 

SDHW solar domestic hot water

SEER Seasonal Energy Efficiency Ratio

SHGC solar heat gain coefficient

SLA specific leakage area

VHP very high-performance 

ZEH zero-energy home
v

Contents

Executive Summary ........................................................................................................... iii

Acronyms ........................................................................................................................... iv

Introduction ......................................................................................................................... 1

Objective ......................................................................................................................... 1

Critical Zero-Energy Home Performance Gaps .............................................................. 1

Zero-Energy Home Technology Barriers and Risk Reduction Requirements .................... 3

Zero-Energy Home Critical Path ........................................................................................ 5

Overview of Key Zero-Energy Home Technology Pathways ............................................ 6

Multi-Year Zero-Energy Home Research Plan................................................................. 15

Recommended Criteria for Selecting Projects for Expanded Zero-Energy Home 

Technology Research Program .................................................................................... 16

Conclusions ....................................................................................................................... 18

Appendix A – Reference Technology Packages for 50% Homes .................................... 19

Appendix B – Residential Efficiency Gap ........................................................................ 22

Appendix C – Overview of Zero-Energy Home Technology Energy Saving Goals ........ 28

Appendix D – Source Energy End-Use Consumption in 50% Reference Homes ............ 31

Appendix E – Climate Sensitivity of Zero-Energy Home Pathways ................................ 34

Appendix F – Impact of Energy Cost on Consumer Adoption of Zero-Energy Home 

Technologies ................................................................................................................ 40
1

Introduction

Objective

Significant increases in residential energy efficiency are required to meet emerging 

global and U.S. energy efficiency goals. The objective of this report is to provide an 

overview of the key residential efficiency technology opportunities and barriers that must 

be addressed to successfully develop cost-neutral net zero-energy homes (ZEHs). New 

technologies and systems must increase whole-house energy savings by an additional 

40% relative to those that can be currently provided by best available residential 

components and systems. 

Critical Zero-Energy Home Performance Gaps

Critical ZEH performance gaps1,2,3

New residential system solutions that provide an additional 40% in whole-house 

efficiency savings (relative to the 50% homes currently being developed by the 

program)

are defined in terms of the incremental source energy 

savings and incremental costs that must be achieved by new systems to successfully 

compete with current best available system solutions. New systems must provide 

significant cost and performance benefits relative to available systems to fill the energy 

savings gaps that currently limit the achievement of net ZEHs. For ZEHs to expand 

beyond high-value niche markets and achieve broad market acceptance, the total 

amortized annual incremental cost of the engineered energy technology package for a 

ZEH must be comparable to the annual utility bill savings that are provided by a ZEH

(see Figure 1). 

4

 must be developed between 2009 and 2015 in order to achieve net ZEHs by 

2020. The following systems represent a minimum5

• High-R Wall Systems – Durable high-R wall systems for cold, northern marine, and 

mixed climates, leading to development of an R-30+ wall assembly with an 

incremental cost of $2/ft2 floor area relative to an R-19 2 × 6 wall.

set of efficiency improvements 

required to achieve cost-effective net ZEHs: 

• Cold Climate Domestic Hot Water (DHW) – DHW system with $2000 incremental 

system cost and 30% reduction in annual energy use relative to a gas tankless hot 

water system with efficiency factor (EF) = 0.8. 

• Cold Climate R-10 Window Assembly – R-10 window assembly with a minimum 

solar heat gain coefficient (SHGC) of 0.3 and a cost of $20/ft2 (incremental cost of 

$4/ft2 relative to current low-e windows). 

 

1 FY 2009 Residential AOP Evaluation Criteria, 3/30/2008.

2 Critical Building America Technology Targets and Example Gate 1A Technology Packages, 3/30/2008. 3 Cost performance targets were established using BEopt default cost data, assuming future PV costs of 

$3.30/W. Analysis was done for a west-facing 2500-ft2 house with 18% window area. “Neutral cost” means 

that a homeowner moving from a 1990s house into a new home will have the same energy-related costs 

(utility bills plus financing costs for energy upgrades) as they had in their old house (utility bills only). 

Incremental home costs were evaluated relative to IECC 2003.

4 Examples of the technologies that will be used to achieve Building America 50% homes are included in 

Appendix A.

5 This is a minimum set because only space conditioning, hot water, and miscellaneous electrical loads 

(MELs) have been targeted. An additional 3%–5% of savings will be contributed by solid-state lighting as 

light-emitting diode price points and performance continue to improve. 
2

• Very High Performance (VHP) A/C System6

• MEL Reduction – 30% reduction in miscellaneous electrical energy use with an 

incremental cost of $1000. 

 – A VHP A/C system with 30% 

reduction in annual energy use and an incremental cost of $1000 relative to a current 

SEER) 18/energy efficiency ratio (EER) 13.4 twospeed system with tight ducts in conditioned space. Seasonal Energy Efficiency Ratio (

High-performance homes that meet these specifications can also be easily operated to 

minimize energy use during periods of peak utility electric demand, resulting in reduced 

peak loads and increased grid stability.7,8

Figure 1. ZEH Whole-House Cost/Performance Target

 

 

6 The VHP A/C performance goal is an overall system performance goal and includes savings from 

efficiency (improvements in coefficient of performance [COP]), zoning, night cooling, evaporative cooling, 

heat recovery, and capacity modulation.

7

Anderson, R.; Christensen, C.; Horowitz, S. “Program Design Analysis Using BEopt Building Energy 

Optimization Software: Defining a Technology Pathway Leading to New Homes with Zero Peak Cooling 

Demand.” In proceedings 2006 ACEEE Summer Study on Energy Efficiency in Buildings: Less Is MoreEn Route to Zero Energy Buildings, August 2006. 8

Anderson, R., Hammon. R., Keesee, M. “Maximizing the Benefits of Zero Energy Homes.” Home 

Energy Magazine Special Edition on Solar and Efficiency: Meeting the Energy Needs of the 21st Century, 

March 2006. 

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

Neutral Cost Goal 

Incremental, EnergyRelated Mortgage, and 

Replacement Costs 

Minimum 

Cost Point

Least Cost Curve, 

Using Current Best 

Available Systems

Source Energy Savings

50

Reference 

Building
3

Zero-Energy Home Technology Barriers and Risk Reduction

Requirements

Homeowners, homebuilders, and contractors tend to avoid technologies that 

• Increase risks

• Increase overall costs

• Have the potential to cause customer complaints 

• Require additional training or oversight of subcontractors 

• Require use of new and unfamiliar suppliers, materials, or equipment 

• Require additional planning steps or code approvals 

• Have the potential to increase future home warranty and callback costs.

Builders, in their role as residential system integrators, are often viewed as being risk 

averse with respect to adoption of new technologies. However, long-term trends in 

building construction practices do not support this conclusion. For example, builders’ use 

of premanufactured framing components and panelized wall systems is expected to 

nearly double by 2010 compared to 1990 levels.9

• Level 1 Risk Reduction – The technology must meet minimum builder, contractor, 

and homeowner performance and reliability requirements for use in new and existing 

homes.

It is more accurate to say that builders 

tend to avoid risky technologies that do not have a high likelihood of delivering proven 

benefits. 

As builders and contractors respond to increased consumer and policy-driven demand for 

energy-efficient and sustainable homes, they need credible information to decide if they 

can successfully use a broad range of new products and systems with unknown risks and 

unproven benefits. The U.S. Department of Energy Building Technologies Program is the 

only national research program that is currently developing this information.

In addition to achieving ZEH energy efficiency objectives, three levels of risk reduction 

must be achieved before a new technology can be successfully used by builders, 

contractors, and homeowners: 

• Level 2 Risk Reduction – The design, construction, and commissioning details for 

integrating the new technology into homes must be well understood and validated. 

• Level 3 Risk Reduction – The field training, construction, and installation quality 

assurance/quality control, commissioning, and operations and maintenance (O&M) 

procedures for the technology must be successfully applied as integral parts of the 

construction process to ensure that potential savings and benefits are achieved when 

the technologies are broadly implemented. 

 

9 Shuler, A. “The Factory Built Components Industry Is Almost as Large as the Softwood Lumber 

Industry.” Structural Building Components Magazine, April 2003.
4

Ignoring these risk reduction requirements significantly increases costs, homeowner 

complaints, and building failures, and reduces chances of achieving near- and long-term

energy savings. These three levels of residential technology maturity are summarized in 

more detail in Figure 2. 

The first level of risk reduction must be reached before the technology can be included in 

initial pilot projects with builders. The second level of risk reduction must be reached 

before innovative builders of high-performance homes can evaluate overall costs, 

benefits, and house redesign requirements. The third level of risk reduction must be 

reached before broad use can be achieved with mainstream production builders. 

Figure 2. The Three Levels of Risk Reduction That Must Be Achieved by 

Technologies and Systems Developed for Use in ZEHs

1. Meets minimum residential performance requirements.

Technology meets minimum cost, reliability, O&M, and durability 

requirements and provides high potential value to builders, 

contractors, and homeowners.

2. Can be integrated with the residential construction process.

Builders, contractors, and code officials understand best 

practice design details, commissioning, construction

sequencing, costs, and benefits. 

3. Can be implemented on a production basis.

Suppliers, builders, and contractors understand and accept 

responsibility for quality assurance, quality control, training, and 

commissioning.
5

Zero-Energy Home Critical Path

Multiple approaches must be explored during the initial stages of research on ZEH 

technologies and systems to ensure a robust solution set that meets residential market risk 

reduction requirements. In addition, because of the lead time required to move from 

Level 1 to Level 3 maturity, ZEH technology solutions with Level 1 maturity must be 

developed by 2015 in order to achieve cost-effective whole-house Level 3 ZEH system 

solutions by 2020.

Figure 3. ZEH Critical System Research Path (G1 = passes Level 1 risk reduction 

requirement, G2 = passes Level 2 risk reduction requirement, G3 = passes Level 3 risk 

reduction requirement)

The ZEH critical research path focuses on the development of ZEH-ready envelopes10

 

10 For an excellent review of the history of development of high-R envelopes, see Lstiburek, J., “Building 

America.” ASHRAE Journal, December 2008, pp 60–65.

combined with current best available equipment to achieve 50% homes by 2015. Initial 

production of advanced ZEH equipment and systems that provide an additional 40% in 

energy savings relative to a 50% home are also required by 2015 to achieve ZEHs by 

2020. An expanded ZEH technology research program is needed to target ZEH 

technology opportunities that have a high potential for reaching Level 1 maturity within 

the next six years. The set of technology opportunities that are investigated will be 

downselected over time to focus on the subset of projects and solutions that have been 

demonstrated to provide the highest overall cost and performance benefits relative to 

multi-year ZEH cost and performance goals. 

 

 

G3: 50% Whole-House Savings 

Level: Current best available 

equipment integrated with a ZEH 

envelope. 

G1: 70% Savings Level: 

Expanded ZEH technology 

research program required to

develop ZEH systems by 2015. 

G2: ZEH Prototype Houses

G3: Neutral Cost ZEH 

Communities 

G1 ZEH Equipment and

Systems

G3 ZEH-Ready 

Envelope

2009 2015 2018 2020
6

Figure 4. Linkage Between Expanded ZEH Technology Research and Building America 

Whole-House ZEH System Research

Overview of Key Zero-Energy Home Technology Pathways 

The residential research program is evaluating the potential impacts of a broad range of 

technology options to determine their expected incremental, whole-building cost and 

performance benefits compared to system solutions for high-performance homes that 

achieve 50% in source energy savings relative to the Building America Benchmark.

11

The technology opportunities are prioritized within each system category according to the 

estimated chance of successfully achieving ZEH system cost, performance, and risk 

reduction requirements by 2015. 

Options that appear to provide the highest marginal benefits (highest incremental energy 

savings at least incremental cost) will be recommended for further study. The system 

performance impact assessments will be updated as additional research results are 

developed from initial proof-of-concept studies and developmental research efforts (see 

Figure 4). 

The ZEH technology opportunities discussed in this report are grouped into six major 

system categories: Energy Storage Systems; Envelope Systems; Hot Water Systems; 

Lighting, Appliance, and Miscellaneous Electric Systems; Space Conditioning/HVAC 

Systems; and Community Systems. 

 

11 Examples of the technology packages for 50% homes that are being used to determine incremental 

benefits are included in Appendix A.

ZEH Technology Research:

System Impact Assessments

Fundamental Building Science

 Small-Scale Validation

 Scale-Up R&D

 Pilot Production

 

 BA G1-G3

 System R&D 

2009

2020

2015

2015
7

Modifications of current products are estimated to have a medium to high chance of 

success (low to medium risk) relative to their ability to achieve ZEH system performance 

requirements by 2015. Depending on the level of R&D investments, advanced concepts 

are expected to have a more difficult time achieving ZEH reliability and performance 

requirements by 2015 (higher risk). 

Updates to system impact assessments and/or additional exploratory research should be 

considered in cases where specific opportunities for improving system benefits have been 

identified. As more detailed performance information is developed, impact assessments 

will be based on full performance maps that are implemented as technology options 

within the BEopt12,13,14,15 analysis software. In cases where full performance maps are not 

available, simplifying assumptions may be used to provide initial impact assessments.16

• Characteristics of Priority 1 Technology Opportunities – Technologies in this 

group are based on modifications of current products to meet ZEH cost and 

performance requirements and are given the highest priority because they are 

expected to have the lowest overall risk of failure, highest chance of resulting in 

significant cost sharing from industry partners, and lowest time to market. 

 

• Characteristics of Priority 2 Technology Opportunities – Technologies in this 

group are based on advanced concepts rather than on modifications of existing 

products and are estimated to have higher risk of failure than Priority 1 technologies. 

They are also expected to be less likely to attract large investments from industry 

partners. 

The overall results of the ZEH risk and benefit evaluation are summarized in Figure 5 

and in Table 1 through Table 6. In these tables, the options within each risk level that are 

expected to have the highest system benefits are indicated in bold type. Options that may 

have promise but need additional development and evaluation to determine incremental 

system benefits are underlined

 

12 Anderson, R.; Christensen, C.; Horowitz, S. “Analysis of Residential Systems Targeting Least-Cost 

Solutions Leading to Net Zero Energy Homes,” ASHRAE Transactions, 2006. 13 Anderson, R. “Determining Technology Options and Performance Goals for Future SMUD Residential 

Energy Programs Using Advanced Energy Efficiency Measure Screening and Evaluation Tools.” SMUD, 

July 2006.

. Options that are currently expected to have low 

incremental system benefits are italicized. 

14 Christensen, C.; Anderson, R.; Horowitz, S.; Courtney, A.; Spencer, J. BEopt(TM) Software for Building 

Energy Optimization: Features and Capabilities. 21 pp.; NREL Report No. TP-550-39929, 2006. 15 Horowitz, S.; Christensen, C.; Brandemuehl, M.; Krarti, M. Enhanced Sequential Search Methodology 

for Identifying Cost-Optimal Building Pathways. NREL Report No. CP-550-43238, 2008. 16 Note: The NREL analysis team is interested in adding performance data for options included in this 

report and including additional options that may have been inadvertently omitted from this report. Please 

e-mail information to: Ren_Anderson@nrel.gov.
8

Figure 5. Overview of Option Risks and Benefits Relative to ZEH Technology Gaps

Low

Low

High

High

High

SEER A/C/

Heat Pump

Low-Cost

Ground Source

Heat Pump

Electrochromic

Windows

Switchable 

Wall 

Coatings High-R 

Windows 

BuildingIntegrated 

Thermal 

Storage 

CommunityScale 

Seasonal 

Storage 

Low-Cost

Cold Climate

SDHW

Cool

Attics

Residential

Ice Storage

Battery

Storage 

MELs Control/

Residential 

Energy Management

System

Next Generation 

Storage/Individual 

House 

Integrated Desiccant/

Indirect Evaporative 

Exchanger 

(DEvap) 

Solar-Assisted 

Heat Pumps

(heating, hot 

water) 

Low Loss

Hot Water

Distribution 

Hot Water

Heat Recovery

Small, High-Efficiency 

Condensing Combo Hot

Water/Space Heating

System

Residential dc

Power System

Efficient 

Clothes 

Dryer

A/C With

Dehumidification 

Mode 

Small-Volume

ZEH Air Handler

Attic-Integrated 

Night Sky

Radiative Cooling

Ductless

Mini-Splits

Cold Climate

Air Source

Heat Pump

Community-Scale 

Combined Heat 

and Power

ZEH Benefit

ZEH Risk
9

Table 1. Category 1 – ZEH Energy Storage Systems 

Opportunity/Need:

• Short-term thermal storage (4–6 hours) is needed to reduce afternoon peak electric 

demand. 

• Diurnal storage is needed to use winter solar gains to meet nighttime heating loads and 

to shift summer daytime cooling loads to night ventilation cooling. 

• Seasonal storage is needed to use excess summer solar thermal energy to offset winter 

heating loads. 

Overall Risks: 

• Sensible energy storage materials are more expensive than lightweight construction 

materials. 

• Phase change materials and thermochemical storage materials are expensive, difficult to 

contain, and may increase chemical exposure and smoke and fire hazards.

Cost/Performance Goal:

TBD

Priority 1: Modifications of Existing

Systems (Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)* 

Building-integrated thermal storage (4–8 ton 

hours) for homes with very high 

performance envelopes. Maximize use of 

existing sensible storage by locating 

insulation outside the structure of the 

building. 

 

Efficient, low-capacity (4–8 ton hour) residential 

ice storage for peak cooling demand reduction.

* bold = high system benefits, 

Desiccant-based thermal storage for 

simultaneous increased energy density of heat 

storage and cooling storage on single-home 

scale. Super capacitor storage. Flywheel 

storage. Super-efficient battery storage. Plug-in 

electric or hybrid vehicles with controls to allow 

user to optimize overall energy use and cost 

benefits of vehicle battery storage. 

underlined = system benefits not clear, italics = low system benefits
10

Table 2. Category 2 – ZEH Envelope Systems

Opportunity/Need: 

Envelope systems are difficult and expensive to replace after initial construction. The impacts of initial 

design decisions are felt for 50–100 years. Current U.S. energy codes do not target the most cost-effective 

insulation levels based on homeowner energy costs and financial risks.

Overall Risks:

Increased levels of insulation also increase wall thickness and require new design details for window 

installation, trim, siding installation, door installations, vapor retarders, air barriers, and drainage planes.

Overall Cost/Performance Goals:

30% reduction in the cooling and heating loads of a 50% reference house at an incremental cost of $5000.

Priority 1: Modifications of Existing Systems 

(Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)*

R-7 to R-10 window systems (whole window Rvalue including insulating glass unit, edge seals, 

and frame)

17

Durable, R-30+ wall systems (framing, vapor 

retarder, insulation, drainage plane) rated as a 

complete system, rather than a series of 

components. Needs to address thermal, 

moisture, air, structural, and bugs. Insulating 

wall sheathing that eliminates need to use 

oriented strand board for structural purposes 

(structural external insulating sheathing). 

Efficient siding attachment systems for use with 

thick insulating sheathing. Low-cost structural 

insulated panels.

Windows with variable solar heat gain capability for 

cold and mixed climates: low SHGC during cooling 

season (<0.1) and high SHGC during heating 

season (>0.5). 

Automated insulating shades or blinds. 

Durable R-10+ basement foundation systems 

with integrated moisture control. Durable, lowcost slab insulation systems with integral under 

slab and edge capillary break. 

Very high R (R-40+) sealed attic insulation/roof 

replacement retrofit strategies for existing 

homes in hot/dry climates with A/C and ducts in 

attic. 

Low-cost, easy-to-install raised heel roof truss 

systems for high-R attic insulation systems, 

optimized approach using high- or low-density 

perimeter foam plus blow-in fiber insulation. 

Fast, perimeter air sealing techniques for new 

and retrofit applications: recyclable, easy to use 

foam packs, etc.

18

Durable, dynamic external solar shading, wall and 

roof venting, and radiant insulation systems. Smart 

building materials and components that meet 

residential durability and reliability requirements 

(variable R, variable emissivity, variable absorptivity, 

variable permeability, variable transmissivity, 

variable reflectivity)

Thin, high R-value insulation materials that eliminate 

thermal bridges in wall framing and fastening 

systems (aerogel materials, etc.). 

* bold = high system benefits, underlined

 

17 R10 window assembly with a minimum SHGC of 0.3 and cost of $20/ft2 (incremental cost of $4/ft2

relative to current low-e windows).

18 Durable high R wall systems for cold, northern marine, and mixed climates, leading to development of an 

R-30+ whole wall assembly with an incremental cost of $2/ft2

-floor area relative to an R-19 2 × 6 wall.

= system benefits not clear, italics = low system benefits
11

Table 3. Category 3 – ZEH Hot Water Systems

Opportunity/Need: 

Current best available hot water systems are about 70%–90% efficient (gas) or have COPs of 

about 1.5–2 (heat pump water heaters). Integration with renewable energy sources can increase 

energy savings. 

Overall Risks: 

Hot water energy usage patterns vary dramatically from one household to another. Low hot water 

users will not benefit from expensive systems. Complicated systems are difficult to install and 

operate correctly, reducing delivered savings. Risk of shading from mature trees may reduce 

future performance of solar hot water systems.

Overall Cost/Performance Goal:

30% reduction in annual hot water energy used in a 50% reference house at an incremental cost 

of $2000.

Priority 1: Modifications of Existing 

Systems (Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)*

High-performance condensing hot water 

heating systems with integrated solar 

storage, hydronic heating and EF 0.95+ 

when used in space heating mode. 

Simple, low-cost, standardized, combined 

solar hot water (70% solar fraction) and 

space heating (30% solar fraction) systems 

for cold climates. Gas tankless, gas 

tankless/electric hybrid, or super-efficient 

small tank gas DHW systems that work well 

with solar pre-heat systems. 

Low-loss hot water distribution systems with 

occupancy based control to minimize stranded 

energy losses. Efficient, low-cost waste water 

heat recovery systems.

Low-lift CO2 heat pump water heater, COP 

2.0+, 130°–150°F delivery temperature, for 

combined hot water and space heating 

applications.

* bold = high system benefits, 

Solar-assisted heat pumps for hot water 

applications with variable lift control to optimize 

performance over a broad range of input 

temperatures.

underlined = system benefits not clear, italics = low system benefits
12

Table 4. Category 4 – ZEH Lighting, Appliances, and Miscellaneous Electrical Systems

Opportunity/Need: 

Significant amounts of electricity are used in standby modes for home office, home entertainment, 

lighting, and appliances. Advanced controls, combined with occupant feedback, can provide 

significant energy savings. Home controls are an emerging feature of utility smart grid and 

demand-response programs. Research on efficient lighting sources is not included within the 

scope of expanded research on ZEH technologies because the solid-state lighting program is 

already addressing this area.

Overall Risks: 

Current wired control systems are prohibitively expensive. Occupants will not use control systems 

that are difficult to program. Savings will be highly variable depending on occupant behavior, 

climate, and usage profiles. The numerous appliances and miscellaneous electricity uses make it 

difficult to achieve uniform levels of energy savings across all end uses.

Overall Cost/Performance Goal: 

20% reduction in the combined annual electrical energy used by a 50% reference house for 

lighting, appliances, and miscellaneous electrical uses at an incremental cost of $2000.

Priority 1: Modifications of Existing 

Systems (Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)* 

Low-cost, whole-house, occupancy-based 

energy control systems with integrated 

Tstat, ventilation, lighting, home office, 

peak electric demand, home entertainment 

control, whole house sleep mode, and low 

standby power requirements (self-powered 

wireless) with standardized dashboard 

allowing for centralized viewing and control 

of all electricity usage (e.g. lighting, 

appliances) with the ability to program 

appliance usage (daily, weekly, monthly, 

vacation).

19

Improved occupancy sensors (reducing false 

positives and negatives) for plug, HVAC 

zoning, and lighting control.

Efficient direct dc power systems for HVAC, 

home entertainment and home office 

equipment. Including standardized lowvoltage protocol and wiring system with 

central efficient rectification for dc 

electronics and lighting as well as battery 

recharging applications. 

Efficient clothes dryers. Closed-cycle, unvented 

desiccant-based, condensing, or heat pump

clothes dryer. 

* bold = high system benefits, 

Efficient, smart grid-capable appliances and 

HVAC equipment with integrated diagnostics

and energy control modes.

underlined

 

19 A multi-year research plan has been developed for MELs. Initial work will begin in January 2009. The 

MEL goal is a 30% reduction in miscellaneous electrical energy use with an incremental cost of $1000.

= system benefits not clear, italics = low system 

benefits
13

Table 5. Category 5 – ZEH Space Conditioning/HVAC Systems

Opportunity/Need: 

Heating and cooling loads in ZEHs will be less than half those in conventional homes and will allow the use 

of efficient, downsized systems with ducts located in conditioned space. There are broad opportunities to 

increase energy savings by reducing parasitic loads and developing hybrid cooling systems that integrate 

night vent cooling, indirect evaporative cooling, and waste heat recovery.

Overall Risks: 

Reduced cooling loads in ZEHs will reduce A/C operating hours and increase internal relative humidity 

during the swing seasons in hot humid and mixed humid climates. New systems may have increased 

maintenance requirements, provide reduced levels of comfort, or have reduced reliability relative to current 

systems.

Overall Cost/Performance Goal:

Very high performance (VHP) systems that use 30% less energy than the systems in a 50% reference 

house.

Priority 1: Modifications of Existing Systems 

(Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)* 

A/C with efficient dehumidification mode to limit

high interior relative humidity excursions when 

space cooling is not required.

Indirect evaporative coolers with integrated direct 

exchange or desiccant backup for hot/dry climates 

with monsoon seasons.

Efficient, low-volume air handlers with airtight 

box and durable, airtight dampers. Integrated 

ventilation air heat recovery and night vent 

capabilities for low load homes. With smalldiameter (3.5 in.), high-velocity (600 fpm) air 

distribution systems for easy I-joist integration. 

Durable. Low leakage. Low noise. Modest 

pressure drop. With installation guidelines to 

ensure adequate air distribution and air mixing 

for thermal comfort. Integrated with low capacity 

(20 kBtu) 95%+ efficient furnace. 

High-efficiency, low-capacity (1-2 ton) variable

capacity/variable refrigerant-flow heat pumps and air 

conditioners with occupancy-based zoning control. 

Ductless mini-splits with efficient air distribution and 

low-cost refrigerant lines that are cost competitive 

with ducted systems. 

Compact, integrated desiccant dehumidifier and 

evaporative cooling heat and mass exchanger

driven by solar and waste heat (DEvap).

Cold climate heat pumps.

Low fan power heat/energy recovery ventilation 

systems including occupancy-based demand control 

with homeowner feedback clearly showing operating 

status.

Less expensive and more efficient ground-source 

heat pumps with parasitic energy use comparable to 

best air source systems.

20

Solar-assisted heat pumps for space heating 

applications with variable lift control to optimize 

performance over a broad range of input 

temperatures.

* bold = high system benefits, 

Roof-integrated photovoltaic (PV)/thermal space 

heating and night cooling systems (collector +

balance of system).

Attic integrated night sky radiation cooling systems.

underlined

 

20 The VHP A/C system goal is a 30% reduction in annual energy use at an incremental cost of $1000 

relative to a current SEER 18/EER 13.4 two-speed system with tight ducts in conditioned space.

= system benefits not clear, italics = low system benefits
14

Table 6. Category 6 – Community-Scale ZEH Systems

Opportunity/Need: 

Seasonal thermal storage systems and combined heating cooling and power systems are most 

cost-effective when implemented on a community-scale.

Overall Risks: 

Increased first costs and O&M requirements may be barriers for builders, developers, and 

homeowners.

Overall Cost/Performance Goals:

TBD 

Priority 1: Modifications of Existing 

Systems (Low to Medium Risk)*

Priority 2: Advanced Systems (High Risk)*

* bold = high system benefits, 

Efficient community-scale residential energy 

systems including generation, distribution and 

energy storage (cogen, district heating and 

cooling, wind power, concentrating solar 

thermal, biomass power systems, solar thermal 

systems with seasonal storage, etc.). 

underlined = system benefits not clear, italics = low system benefits
15

Multi-Year Zero-Energy Home Research Plan

The initial research required to develop ZEH technologies and systems must be

completed by 2015 in order to achieve net ZEHs by 2020. Because of the higher risks 

associated with advanced ZEH systems, the Building America Program is also initiating 

lab homes starting in 2009 to allow detailed evaluation of advanced systems under 

controlled operating conditions. At least one lab home at the 50%+ savings level will be 

built by industry partners in each of the five Building America climate regions. The lab 

homes will be monitored for up to two years before being sold and replaced by lab homes 

with additional advanced systems. 

The overall schedule for ZEH technology research and building integration research is 

summarized in Figure 6. Best available systems and materials will be used to achieve the 

50% savings level in 2015, including initial development of a ZEH-ready envelope. 

Successful projects from the expanded ZEH technology research program will be used to 

achieve the 70% savings level in 2018 and net ZEH by 2020. Key ZEH technology 

research outcomes on the critical path are noted with arrows in Figure 6. 

Figure 6. Multi-Year ZEH Research Plan

ZEH-Ready Envelope

ZEH Equipment

ZEH Prototypes
16

Recommended Criteria for Selecting Projects for Expanded 

Zero-Energy Home Technology Research Program

At least $4 million per year for six years is required for research on low- to medium-risk 

ZEH systems and $8 million per year for six years is required for research on high risk 

ZEH systems to achieve U.S. Department of Energy ZEH performance goals by 2020. 

This estimate is based on the assumption that 10 high potential projects will be included 

in the research program within each risk category, with an average annual cost of 

$400K/year for each low- to medium-risk project and an average annual cost of 

$800K/year for each high-risk project. Assuming a 20% chance of success for high-risk 

projects and a 60% chance of success for low- to medium-risk projects over the six-year 

life of the program, the expanded ZEH technology research program will result in six 

successful low-risk projects and two successful high-risk projects. The corresponding 

requirement for the minimum energy savings that must be delivered by each successful

project can be found by dividing the required 40% in incremental energy savings relative 

to a 50% house by the number of successful projects that are expected to be completed by 

2015, 

(40% incremental savings)/8 successful projects = 5% minimum savings per project. 

To increase chances of success, projects that can provide savings greater than 5% should 

be given highest priority. Based on research progress, the initial set of technology 

opportunities that are included in the expanded research program can be downselected 

over time to focus on the subset of projects and solutions that are expected to provide the 

highest overall cost and performance benefits.

In addition to demonstrating the potential to achieve the 5% minimum incremental

energy savings goal, each project must also demonstrate:

• A high likelihood of resolving technical barriers based on basic building science 

• Validation of operating principles based on evaluation of a small-scale mockup

• Confirmation of performance based on evaluation of a full-scale prototype 

• The identification and resolution of Level 1 to Level 3 risks

• The ability to implement the technology on a pilot production basis by 2015 

• The ability to meet ZEH neutral cost criteria. 

The energy used by a 50% reference home in a cold climate is shown in Figure 7. The 

largest energy targets of opportunity are large appliances, miscellaneous electrical uses, 

space heating, and lighting. The cold climate energy savings that must be delivered by an 

expanded ZEH technology research program are shown in Figure 8. Summaries for end 

uses and savings targets for other climates are included in Appendices C and D.
17

Figure 7. Cold Climate Source Energy Uses to be Targeted by an Expanded ZEH 

Technology Research Program (See Appendix D for end use targets in other climates)

Figure 7. Cold Climate Source Energy Uses to Be Targeted by an Expanded ZEH 

Technology Research Program (see Appendix D for end use targets in other climates)

Figure 8. Energy Savings to Be Provided by an Expanded ZEH Technology Research 

Program (see Appendix C for a summary of energy saving opportunities in other climates)

Cold Climate ZEH Technology Savings Goal

0

50

100

150

200

50% Reference ZEH

Source Energy (MBtu/year)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

40%

Distribution of Energy Uses in 50% Reference Cold 

Climate Home

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Misc. (G)
18

Conclusions

Significant increases in residential energy efficiency are required to meet emerging 

global and U.S. energy efficiency goals. New technologies and systems are required that, 

in combination, increase whole-house energy savings by 40% relative to the savings 

provided by current best available components and systems (Figure 9). 

Figure 9. Minimum Energy Savings Requirement for ZEH Technologies Projects 

In addition to providing significant energy savings, new technologies and systems must 

also directly address the risks that limit broad use of new products by builders, 

contractors, and homeowners:

• Level 1 Risk Reduction – The technology must meet minimum builder, contractor, 

and homeowner performance and reliability, O&M, and durability requirements to be 

used in new and existing homes. It must provide high potential value to builders, 

contractors, and homeowners.

• Level 2 Risk Reduction – The design, construction, and commissioning 

requirements for integrating the new technology into homes must be understood and 

validated. Builders, contractors, and code officials must understand best practice 

design details, commissioning procedures, construction sequencing, costs, and 

benefits.

• Level 3 Risk Reduction – The field training, quality assurance/quality control, and 

commissioning requirements for the technology must be understood and included as 

part of a production construction process to ensure that potential savings and benefits 

are achieved when the technology is broadly implemented.

An expanded residential energy efficiency research program that includes system impact 

assessments, exploratory research, and component development research is required to 

achieve the U.S. Department of Energy goal of cost-neutral net ZEHs by 2020. 

Potential Savings vs. Target Savings

0

20

40

60

80

100

120

140

Source Energy Use (MBtu/Year)

50% Reference Potential Savings ZEH Target

Misc. (G)

Lg. Appl. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

40% 

Savings

Goal

Proposed Project

Individual Technology Savings Must Exceed 5%
19

Appendix A – 

Reference Technology Packages for 50% Homes

This appendix provides reference whole-house technology packages21 that target the 

Building America 50% savings level for cities within each major climate region. An 

additional 20% in whole-house efficiency savings relative to the Building America

benchmark (equivalent to 40% in additional savings relative to a 50% house) is required 

to achieve net ZEHs by 2020. The 50% technology packages combine a ZEH-ready 

envelope with best available equipment. Building America research on these packages is 

scheduled to be completed by 2015. 

These reference packages were developed for a two-story, three-bedroom, 2500-ft2

, westfacing house with an 18% window-to-floor area ratio using BEopt version 0.8.7 cost and 

performance values and Building America occupant usage profiles. For the optimizations, 

energy costs are based on current Energy Information Administration average annual 

values and are assumed to increase at the same rate as general inflation. 

 

21 These technology packages are provided as examples, not as prescriptive specifications or requirements. 

Alternative or equivalent approaches may also be appropriate, depending on building type, location, and 

builder and homeowner preferences. 

50% Reference: Marine Climate Region (Seattle)

• 2 × 6 + R-21 cavity + 1.5-in. exterior insulating sheathing 

• R-50 ceiling assembly

• .00015 SLA (2.6 ACH50) 

• Low-e/std SHGC glazing, argon fill (0.29 U-value, 0.30 SHGC)

• 90% compact fluorescent lamp (CFL) lighting

• SEER 15+ A/C 

• Annual fuel utilization efficiency (AFUE) 90+ furnace OR heating 

season performance factor (HSPF) 8.8+ heat pump

• Ducts in conditioned space

• Gas tankless hot water, EF 0.8+ OR premium electric, EF 0.95+ and

64-ft2 closed-loop solar system

• ENERGY STAR® appliances

 

 
20

50% Reference: Hot Humid Climate Region (Houston)

• 2 × 6, R-21 cavity 

• R-30 ceiling assembly

• .00015 SLA (2.6 ACH50) 

• Low-e/low-SHGC glazing (0.30 U-value, 0.26 SHGC)

• 90% CFL lighting

• SEER 15+ A/C 

• AFUE 90+ furnace OR HSPF 8.8+ heat pump

• Ducts in conditioned space

• Gas tankless hot water, EF 0.8+ OR premium electric, EF 0.95+ and

32-ft2 integrated collector/storage solar system

• ENERGY STAR appliances

50% Reference: Hot/Mixed Dry (Phoenix)

• 2 × 6 + R-19 cavity

• R-30 ceiling assembly

• .0003 SLA (5.3 ACH50) 

• Low-e/low-SHGC glazing (0.30 U-value, 0.26 SHGC)

• 90% CFL lighting

• SEER 13 A/C 

• AFUE 80 furnace OR HSPF 8.1 heat pump

• Ducts in conditioned space

• Gas tankless hot water, EF 0.8+ OR electric, EF 0.9+

• ENERGY STAR appliances
21

50% Reference: Mixed Humid (Atlanta)

• 2 × 6 + R-21 cavity 

• R-40 ceiling assembly

• .00015 SLA (2.6 ACH50) 

• Low-e/low-SHGC glazing (0.30 U-value, 0.26 SHGC)

• 90% CFL lighting

• SEER 15+ A/C 

• AFUE 90+ furnace OR HSPF 8.8+ heat pump

• Ducts in conditioned space

• Gas tankless hot water, EF 0.8+ OR premium electric, EF 0.95+ and

64-ft2 closed-loop solar system

• ENERGY STAR appliances

50% Reference: Cold Climate Region (Chicago)

• 2 × 6, R-21 cavity +1 in. exterior insulating sheathing

• R-50 ceiling assembly

• R-10 basement 

• .00015 SLA (2.6 ACH50) 

• Triple-pane, low-e (0.25 U-value, 0.35 SHGC)

• 90% CFL lighting

• SEER 18 AC

• AFUE 90+ furnace OR HSPF 9.2 heat pump

• Ducts in conditioned space

• Gas tankless hot water, EF 0.8+ OR premium electric, EF 0.95+ and

64-ft2 closed-loop solar system

• ENERGY STAR appliances
22

Appendix B – 

Residential Efficiency Gap

Figure B-1. Example Cost/Performance Curve

The cost and performance curves in this appendix show the magnitude of the efficiency 

gap that that must be filled to achieve net ZEHs by 2020 in different climates. This 

analysis used the same assumptions, building geometry, and cities as Appendix A. 

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

0

500

1,000

1,500

2,000

2,500

0% 100%

Energy Savings (%)

Total Annual Costs ($/year)

mortgage

utility bills

cash flow

1

2

3

4

 Neutral Cost Goal 

Incremental, EnergyRelated Mortgage, 

and Replacement 

Costs

Minimum 

Cost Point Least Cost Curve, 

Current Options 

Source Energy 

50

Building America 

Benchmark

Efficiency 

Gap 
23

Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-2. Marine Climate Region (Seattle), Gas Space Heating Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-3. Marine Climate Region (Seattle), Electric Space Heating

Efficiency Gap

Efficiency Gap
24

Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-4. Hot Humid Climate Region (Houston), Gas Space Heating Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-5. Hot Humid Climate Region (Houston), Electric Space Heating

Efficiency Gap

Efficiency Gap
25

Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-6. Hot/Mixed Dry Climate Region (Phoenix), Gas Space Heating Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-7. Hot/Mixed Dry Climate Region (Phoenix), Electric Space Heating

Efficiency Gap

Efficiency Gap
26

Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-8. Mixed Humid Climate Region (Atlanta), Gas Space Heating Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-9. Mixed Humid Climate Region (Atlanta), Electric Space Heating

Efficiency Gap

Efficiency Gap
27

Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-10. Cold Climate Region (Chicago), Gas Space Heating Mortgage + Utilities ($/yr)

 

Source Energy Savings (%)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 10 20 30 40 50 60 70 80 90 100

Figure B-11. Cold Climate Region (Chicago), Electric Space Heating

Efficiency Gap

Efficiency Gap
28

Appendix C – 

Overview of Zero-Energy Home Technology Energy Saving 

Goals

Appendix C summarizes the additional savings by end use22 that must be achieved over 

the next six years to fill the efficiency gaps shown in appendix B. A uniform savings goal 

of 20%23

ZEH Target Savings

0

50

100

150

200

250

300

Benchmark 50% Reference ZEH Target

Source Energy Use (MMBtu/yr)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

Target 

Savings

 was used for all climates to develop these graphs. The gaps shown in Appendix 

B vary from 15% to 25%, depending on climate. 

Figure C-1. Northern Marine Climate Region (Seattle), Gas Space Heating

 

22 Calculations are based on the same assumptions, building type, and locations used in Appendix A. 23 The 20% savings goal is measured relative to the energy used by the Building America Benchmark 

house. These savings correspond to 40% of the source energy used by a 50% house.
29

ZEH Target Savings

0

50

100

150

200

250

300

350

Benchmark 50% Reference ZEH Target

Source Energy Use (MMBtu/yr)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

Target 

Savings

Figure C-2. Hot Humid Climate Region (Houston), Gas Space Heating

ZEH Target Savings

0

50

100

150

200

250

300

350

400

Benchmark 50% Reference ZEH Target

Source Energy Use (MMBtu/yr)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

Target 

Savings

Figure C-3. Hot/Mixed Dry Climate Region (Phoenix), Gas Space Heating
30

ZEH Target Savings

0

50

100

150

200

250

300

Benchmark 50% Reference ZEH Target

Source Energy Use (MMBtu/yr)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

Target 

Savings

Figure C-4. Mixed Humid Climate Region (Atlanta), Gas Space Heating

ZEH Target Savings

0

50

100

150

200

250

300

350

400

Benchmark 50% Reference ZEH Target

Source Energy Use (MMBtu/yr)

Misc. (G)

Hot Water (G)

Heating (G)

Cooling (E)

Cool Fan (E)

Heat Fan (E)

Lights (E)

Lg. Appl. (E)

Misc. (E)

Target 

Savings

Figure C-5. Cold Climate Region (Chicago), Gas Space Heating
31

Appendix D – 

Source Energy End-Use Consumption in 50% Reference

Homes 

Appendix D summarizes the relative magnitudes of the energy end uses24 in homes that 

save 50% relative the Building America Benchmark in different climates.

25

Source Energy Use (Total: 136 MMBtu/yr)

27%

13%

10%

29%

10%

3%

0% 3%

1% 4%

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Lg. Appl. (G)

Misc. (G)

Large 

appliances, space conditioning, and miscellaneous electrical uses represent the largest 

individual targets of opportunity for additional energy savings in all climates. Lighting 

accounts for about 10% of whole-house energy use. Hot water energy use varies from 5% 

in warm climates to 9% in cold climates.

Figure D-1. Marine Climate Region (Seattle), Gas Space Heating

 

24 Calculations are based on the same assumptions, building geometry, and locations used in Appendix A. 25 Research leading to initial community-scale implementation of 50% homes is currently scheduled to be 

completed in 2015.
32

Source Energy Use (Total: 151 MMBtu/yr)

28%

16%

9%

17%

6% 1%

1%

3%

19%

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Misc. (G)

Figure D-2. Hot Humid Climate Region (Houston), Gas Space Heating

Source Energy Use (Total: 164 MMBtu/yr)

22%

15%

9%

9%

5% 1%

6% 1%

32%

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Misc. (G)

Figure D-3. Hot/Mixed Dry Climate Region (Phoenix), Gas Space Heating
33

Source Energy Use (Total: 136 MMBtu/yr)

27%

13%

10%

20%

8%

14%

1% 2%

1% 4%

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Lg. Appl. (G)

Misc. (G)

Figure D-4. Mixed Humid Climate Region (Atlanta), Gas Space Heating

Source Energy Use (Total: 181 MMBtu/yr)

26%

14%

4% 10%

34%

9% 1%

2%

0%

Misc. (E)

Lg. Appl. (E)

Lights (E)

Heat Fan (E)

Cool Fan (E)

Cooling (E)

Heating (G)

Hot Water (G)

Misc. (G)

Figure D-5. Cold Climate Region (Chicago), Gas Space Heating
34

Appendix E – 

Climate Sensitivity of Zero-Energy Home Pathways 

Critical ZEH performance gaps26,27,28,29 are defined in terms of the incremental source 

energy savings and incremental costs that must be achieved by new systems to 

successfully compete with the homes that are expected to be completed by the program in 

2015.30 New systems need to provide significant cost and/or performance benefits 

relative to the system solutions shown in Appendix A in order to fill the efficiency gaps 

shown in Appendix B. In addition to providing energy savings, the total amortized 

incremental cost of the engineered energy technology package in a ZEH must be 

comparable to the utility bill savings provided by the home to enable ZEHs to expand 

beyond high-value niche markets and achieve broad market acceptance. New residential 

system solutions that provide an additional 40% in savings relative to a 50% house must 

be developed between 2009 and 2015 in order to achieve net ZEHs by 2020. The 

following systems represent a minimum31

• High-R Wall Systems – Durable high-R wall systems for cold, northern marine, and 

mixed climates, leading to development of an R-30 wall assembly with an 

incremental cost of $2/ft2-floor area relative to an R-19 2 × 6 wall.

 set of efficiency improvements required to 

achieve cost-neutral net ZEHs: 

• Cold Climate DHW – DHW system with $2000 incremental system cost and 30% 

reduction in annual energy relative to a gas tankless hot water system with EF = 0.8. 

• Cold Climate R-10 Window Assembly – R-10 window assembly with a minimum 

SHGC of 0.3 and cost of $20/ft2 (incremental cost of $4/ft2 of window area relative to 

current low-e windows). 

• VHP A/C System32

• MEL Reduction – 30% reduction in miscellaneous electrical energy use with an 

incremental cost of $1000. 

 – A/C system with 30% reduction in annual energy use and an 

incremental cost increase of $1000 relative to a current two-speed SEER 18/EER 13.4 

system with tight ducts in conditioned space. 

 

26 The technology pathways shown in this appendix assume that the minimum set of cost and performance 

targets summarized above have been met. In addition, these packages assume that the installed PV system 

cost has been reduced to $3.30/W. Yellow highlighted items indicate advanced systems that will be 

developed by an expanded ZEH technology research program.

27 FY 2009 Residential AOP Evaluation Criteria, 3/30/2008. 28 Critical Building America Technology Targets and Example Gate 1A Technology Packages, 3/30/2008. 29 Cost performance targets were established using BEopt default cost data, assuming future PV costs of 

$3.30/Watt. Analysis was done for a west-facing 2500-ft2 house with 16% window area. “Neutral cost” 

means that a homeowner moving from a 1990s house into a new home will have the same energy-related 

costs (utility bills plus financing costs for energy upgrades) as they had in their old house (utility bills 

only). Incremental costs were evaluated relative to IECC 2003.

30 Examples of the technologies that will be used in these homes are shown in Appendix A. 31 This is a minimum set because only space conditioning, hot water, and MELs have been targeted. An 

additional 3%–5% of savings will be contributed by solid-state lighting if LED price points and 

performance continue to improve. 

32 The A/C performance goal is an overall installed system performance goal and includes savings from 

efficiency (improvements in COP), zoning, night cooling, evaporative cooling, heat recovery, and capacity 

modulation.
35

Hot/Dry, 90% Savings

 Technology Option

Walls 2 ×6 + R-21 cavity (R-15 assembly)

Ceiling R-40

Infiltration 0.0002 SLA (4 ACH50)

Windows: Glass Type Low-e/low-SHGC glazing (0.30 U-value, 0.26 

SHGC)

Refrigerator ENERGY STAR

Dishwasher ENERGY STAR

Washer/Dryer ENERGY STAR

Lighting LED 

HVAC AFUE 90+ furnace, VHP A/C System 

Ducts Tight (mastic, 5% leakage), in conditioned space

Water Heater Gas tankless, EF 0.8+

Other 30% reduction in MELs

PV 5.5-kW dc PV system

Incremental Cost

(relative to code house) $12/ft2 
36

Cold, 90% Savings

Technology Option

Walls

2 × 6 + R-19 cavity+ 2-in. foam sheathing (R-30 

wall assembly)

Ceiling R-50

Foundation R-15 basement

Infiltration 0.0001 SLA (2 ACH50)

Windows: Glass Type R-10 window, std SHGC (0.3 SHGC)

Refrigerator ENERGY STAR

Dishwasher ENERGY STAR

Washer/Dryer ENERGY STAR

Lighting LED

HVAC AFUE 90+ furnace; VHP A/C System

Ducts Tight (mastic, 5% leakage), in conditioned space

Water Heater Gas tankless; EF 0.8+

Other 30% reduction in MELs

SDHW Low-cost SDHW

PV 5.5-kW dc PV system

Incremental Cost

(relative to code house) $20/ft2
37

Marine, 80% Savings

Technology Option

Walls

2 × 6 + R-19 cavity+ 2-in. foam sheathing (R-30 

wall assembly)

Ceiling R-40

Infiltration 0.0001 SLA (2 ACH50)

Windows: Glass Type R-10 window, std SHGC (0.3 SHGC)

Refrigerator ENERGY STAR

Dishwasher ENERGY STAR

Washer/Dryer ENERGY STAR

Lighting LED

HVAC AFUE 90+ furnace, SEER 18 A/C

Ducts Tight (mastic, 5% leakage), in conditioned space

Water Heater Gas tankless hot water, EF 0.8+

Other 30% reduction in MELs

PV 3.5-kW dc PV system

Incremental Cost

(relative to code house) $12/ft2
38

Hot/Humid, 90% Savings

Technology Option

Walls

2 × 6 + R-19 cavity + 2in. foam sheathing (R-30 

wall assembly)

Ceiling R-40

Infiltration 0.0002 SLA (4 ACH50)

Windows: Glass Type

Low-e/std SHGC glazing, argon fill (0.30 U Value, 

0.26 SHGC)

Refrigerator ENERGY STAR

Dishwasher ENERGY STAR

Washer/Dryer ENERGY STAR

Lighting LED

HVAC AFUE 90+ furnace, VHP A/C system

Ducts Tight (mastic, 5% leakage), in conditioned space

Water Heater Gas tankless, EF 0.8+

Other 30% reduction in MELs

PV 5.5-kW dc PV system

Incremental Cost

(relative to code house) $15/ft2
39

Mixed Humid, 90% Savings

Technology Option

Walls

2 × 6 + R-21 cavity + 2-in. foam sheathing (R-30 

wall assembly)

Ceiling R-40

Foundation R-10 basement

Infiltration 0.0002 SLA (4 ACH50)

Windows: Glass Type

Low-e/std SHGC glazing, argon fill (0.30 U 

Value, 0.26 SHGC)

Refrigerator ENERGY STAR

Dishwasher ENERGY STAR

Washer/Dryer ENERGY STAR

Lighting LED

HVAC AFUE 90+ furnace, VHP A/C System

Ducts Tight (mastic, 5% leakage), in conditioned space

Water Heater Gas tankless, EF 0.8+

Other 30% reduction in MELs

PV 4.5-kW dc PV system

Incremental Cost

(relative to code house) $15/ft2
40

Appendix F – 

Impact of Energy Cost on Consumer Adoption of ZeroEnergy Home Technologies

This graph shows that current residential energy codes (point A) do not minimize a 

homeowner’s energy-related costs. Homes built to minimum code also put homeowners 

at risk when energy costs increase and household incomes are fixed.

In this simple example, energy costs are increased by 40%; all other costs are held 

constant. Homes with energy savings beyond the minimum cost point (to the right of 

point B) experience smaller percentage increases in energy-related costs than homes with 

low energy savings. The change in the location of the neutral cost point is directly 

proportional to the change in energy cost. 

Because of the shape of the least cost curve, large increases in energy cost have very little 

impact on the location of the minimum cost point. This figure demonstrates that a

consumer on a fixed income has a very strong motivation to move from an inefficient 

code-level home into an efficient home at the minimum cost point when energy costs 

increase. These results also suggest that the best value and economic security for 

homeowners would be provided by requiring energy codes to target the minimum cost 

point. 

Source Savings (%)

Impact of 40% Increase in 

Energy Cost on Least Cost Curve

Efficient Home at 

Minimum Cost Point

Code 

A

B

Location of neutral cost 

point changes with 

energy cost

Location of minimum 

cost point is 

relatively 

independent of 

energy cost
F1147-E(10/2008) 

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November 2008

2. REPORT TYPE

Technical Report

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4. TITLE AND SUBTITLE

Maximizing Residential Energy Savings: Net Zero-Energy Home 

Technology Pathways

5a. CONTRACT NUMBER

DE-AC36-08-GO28308

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6. AUTHOR(S)

R. Anderson and D. Roberts

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NREL/TP-550-44547

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BET98001

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National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

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NREL/TP-550-44547

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14. ABSTRACT (Maximum 200 Words)

To meet current U.S. Department of Energy zero-energy home performance goals, new technologies and solutions 

must increase whole-house efficiency savings by an additional 40% relative to those provided by best available 

components and systems. An expanded research program is needed to develop the key technologies and systems to 

fill this performance gap. This report identifies a range of technology options to fill the residential efficiency gap in 

improved systems based on modifications of existing products and high-risk advanced system concepts. 

15. SUBJECT TERMS

zero-energy home; zeh; building america

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