Technology Installation Review 

A New Technology Demonstration Publication 

DOE/EE-0318 

Leading Leading by example,

saving energy and saving energy and 

taxpayer dollars

in federal facilities

Bringing you a prosperous Bringing you a prosperous 

future where energy is

clean, abundant abundant, reliable,

and affordable

Energy Savings from 

Small Near-Zero-Energy Houses 

Introduction 

This technology installation review provides an overview of the construction and monitoring of four 

small single-family houses that achieve dramatic reductions in energy consumption and approach 

the goal of “net zero energy use” that the U.S. Department of Energy’s (DOE’s) Building Technology 

Office has set for itself. (A net-zero-energy building is one that produces as much energy from on-site 

renewable energy as it consumes on an annual basis.) This study discusses the construction methods, 

building products, appliances and equipment, and data collection methodologies used in the houses 

and provides data on energy savings gathered through the monitoring effort. 

The houses discussed in this study were built through a collaboration among the Loudon County, 

TN, affiliate of Habitat for Humanity, DOE’s Building America program1, Oak Ridge National 

Laboratory (ORNL), the Tennessee Valley Authority (TVA), and the building and appliance 

industries. The houses were designed by ORNL and Building America teams and constructed 

by volunteers from the Loudon County Habitat affiliate. Building trade associations and product 

manufacturers donated some materials and equipment and helped with installation. 

During the construction of the houses, researchers from the Buildings Technology Center (BTC) at 

ORNL and members of the Florida Solar Energy Center (FSEC) Building America team installed 

extensive sensor systems that constantly measure interior and exterior conditions and the energy 

consumption and output of the houses. The data are used in detailed analyses. This review uses those 

data to document the energy performance of each of the houses and compare it with that of a “base 

house” — a Habitat house of similar size and built in the same subdivision, but without the advanced 

energy-saving features of the “net-zero-energy” houses. 

Energy consumption of the base house and the four test houses are summarized in Figure 1. The data 

show that during the monitoring periods the first of the four houses built (ZEH1) used about 46% 

less energy from the grid than the base house, and the second, third, and fourth houses built (ZEH2, 

3, and 4) used between 52 and 54% less energy than the base house. (The values shown in Figure 1 

are adjusted for observed anomalies. See “Energy Savings and Costs” section.) 

1

Building America is a public–private partnership dedicated to improving the energy efficiency of housing through conducting research and working to change 

production housing construction practices. Building America forms teams of professionals that traditionally work independently of each other (architects, engineers, builders, manufacturers and suppliers, and others). The teams use a systems engineering approach in research, design, and testing of improved building 

practices and components. For more information go to www.eere.energy.gov/buildings/building_america/. 

Internet: www.eere.energy.gov/femp/ 

No portion of this publication may be altered in any form without 

prior written consent from the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, and the authoring national laboratory. 

U.S. Department of Energy 

Energy Efficiency 

and Renewable Energy 
Technology Installation Review 

Energy costs per day for these houses 

were $1.01 for ZEH1, $0.88 for ZEH2, 

$0.79 for ZEH3, and $0.75 for ZEH4. 

These costs are based on the actual 

current residential electric rate in 2004­

2005 of $0.068/kWh and TVA’s solar 

credit of $0.15/kWh for all AC power 

produced by the houses. The percentage 

of total energy load supplied by the 

photovoltaic (PV) systems for these 

houses increased from 20% in ZEH1 to 

27% in ZEH4. To reach true net zero, 

future houses will have to be even more 

energy efficient, or larger solar systems 

will have to be installed. 

One of the goals of the research effort 

is to help the building industry develop 

building methods and materials that 

will make possible low-cost zero-energy 

residences by 2010. A number of 

builders across the United States are 

building near-net-zero-energy houses, 

but most are large houses at the high 

end of the housing market. For the 

efficiency technologies to achieve wide 

market penetration and become 

common in more affordable homes, 

the first-cost premium must be reduced 

enough for the utility bill savings to 

match or nearly match the amount that 

the energy-saving technologies add to 

the mortgage payment. 

Technology Description 

The four near-zero-energy houses studied 

are in Lenoir City, Tennessee, a small 

town a few miles south of ORNL in 

East Tennessee. They are similar in size 

and appearance to other houses built in 

the East Tennessee area by Habitat for 

Humanity, a non-profit organization 

that uses supervised volunteer labor to 

build modest homes that can be sold 

at an affordable cost to qualifying 

families. The houses are part of a small 

subdivision of Habitat houses called 

Harmony Heights. 

kWh/year 

cost/day 

Figure 1. Comparison of the energy consumption of the base house and the four 

test houses. 

The four dwellings were built between 

the summer of 2002 and the summer 

of 2004. The size ranges from 1060 to 

1200 ft2. ZEH1 and ZEH4 have a bath 

and a half-bath; ZEH2 and ZEH3 have 

just one bath. Three of the houses have 

crawl spaces; the other has a walk-out 

full basement that contains the bedrooms. All four are finished with vinyl 

siding. All were designed specifically 

for the mixed humid climate of 

East Tennessee. 

Most of the construction labor on the 

homes was provided by volunteers 

working under the direction of a 

trained construction supervisor from 

the Loudon County Habitat affiliate. 

Subcontractors were hired for the 

plumbing; heating, ventilation, and 

air-conditioning (HVAC) systems; 

site work and foundations; drywall; 

and concrete. 

Design Process 

These four near-zero-energy houses were 

designed to surpass by 50% the energy 

efficiency achieved in the DOE Building 

America Research Benchmark (Hendron 

2005). The design process started in 

the laboratory. For example, hundreds 

of hot box tests and evaluations were 

examined to select a wall system with 

minimum thermal shorts (Christian and 

Kosny 1995) and inherent air-tightness 

potential (Christian and Kosny 1996). 

The results from multi-year tests of 

HVAC systems in test houses of similar 

size in identical climatic conditions led 

the design teams to locate the HVAC 

distribution systems inside the insulating envelope instead of in uninsulated 

parts of the structure (Vineyard et al. 

2003). One of the Building America 

Research Teams participated in designing each of the houses, bringing to the 

process the advances and experience 

gained from hundreds of BA test houses. 

Before specific building components 

were selected, design optimizations were 

done using whole-house building 

computer simulation software, either 

Energy Gauge or Rem/Rate. 

Several constraints affected the design 

process. Natural gas was not available at 

the site, so these are all-electric houses 

by necessity. The designs were also 

restricted by Habitat International’s 

guidelines governing house size, number 

of bathrooms, number of windows, and 

other features. And because these houses 

are located in a subdivision comprised 

wholly of Habitat houses, the amenities 

in the test houses could not be substantially different from those in the other 

houses in the neighborhood. A major 

. 

2 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Technology Installation Review 

constraint was cost. The design team 

selected only technologies that were 

believed to have the potential to be 

affordable in houses for typical homeowners by 2010, based on assumptions 

that technology development, market 

growth and economies of scale, and 

utility, state, and federal incentives would 

all lead to lower costs in the near future. 

Energy-Efficiency Technologies 

Each house includes a number of 

energy-efficiency technologies, and no 

two houses have the same combination. 

The building envelope and mechanical 

features of the houses are listed in Tables 

1 and 2. 

Each house has a rooftop solar photovoltaic (PV) system with a power rating 

of about 2 kWp that is connected to 

the local utility grid. The PV systems 

produce between 20 and 27% of the 

electricity used by each house. A netmeter allows the surplus energy to flow 

into the utility grid when a house is 

using less electricity than the PV system 

produces (usually on sunny afternoons). 

The power consumed by the household 

and generated by the PV system is 

metered, and the homeowner is paid 

$0.15 per kWh by the local TVA-affiliated distribution utility for all the solar 

power produced, including that used by 

the house. 

Key energy-efficiency technologies 

employed in building all the houses 

include the following. 

•	 All houses were built with structural 

insulated panels (SIPs). SIPS are 

made of thick sheets of foam 

insulation sandwiched between two 

sheets of oriented strand board 

(Figure 2). The panels are made in 

custom sizes, and rough openings 

for windows and doors and 

channels for wiring are cut into 

them at the factory. SIPs are highly 

insulating. They generally form 

more airtight building envelopes 

than conventional building systems 

and, because they combine 

insulation and sheathing in one 

unit, can be erected more 

quickly. The SIPs used in these 

houses generally were 8 ft high 

and of various lengths. 

•	 Energy use is minimized by airtight building envelopes. SIPs are 

joined with splines and well sealed 

with caulk, tape, and foam at every 

edge where panels meet. While 

the typical frame houses build by 

the same contractor next to the 

near-zero-energy houses have a 

level of air leakage equivalent to a 

hole of about 60 square inches, 

large enough to slam a volleyball 

through, the near-zero-energy 

houses have air leakage equivalent to an area of about 13.5 square 

inches, not even large enough to 

toss a softball through. Each house 

underwent a blower door test before 

completion to test airtightness and 

identify any significant leaks that 

needed to be sealed. The natural 

air infiltration rate in the houses 

is less than 0.1 air change per hour 

(ACH) (the average for a same-size 

conventional new frame house built 

by the same Habitat affiliate ranges 

from 0.2 to 0.25 ACH). 

•	 All the houses use high-efficiency 

HVAC systems, but no two houses 

have the same system. Each house 

has an electric heat pump with a 

high seasonal energy-efficiency 

ratio (SEER) rating—the lowest 13 

SEER and the highest 17 SEER. 

Two of the heat pumps used have 

two-stage compressors and 

variable-speed fans, which allow 

Figure 2. Wall/ceiling SIP 

them to control humidity more 

efficiently during the cooling 

season. One house is equipped with 

a horizontal-trench ground-source 

heat pump, which uses the 

subsurface earth as a heat source 

for heating and a heat sink for the 

cooling system. Because the 

temperature 5 feet below ground 

is warmer in winter (55°F) and 

cooler in summer (70°F) than the 

air temperature, a ground-source 

heat pump is significantly more 

efficient than a conventional 

air-source heat pump. 

•	 Heating/cooling ducts are located 

inside the conditioned space to 

minimize heat transfer between 

ducts and the surroundings. 

•	 Supply mechanical ventilation 

ensures that the houses receive 

the amount of fresh air prescribed 

by American Society of Heating, 

Refrigerating and Air-Conditioning 

Engineers Standard 62.2 

(ASHRAE 2004) for ventilation 

and indoor air quality. In one 

house CO2 monitoring is used to 

determine when even more fresh air 

is needed to accommodate the 

number of people in the house and 

the level of activity (e.g., CO2 levels 

would rise during a large family 

gathering, signaling the ventilation 

system to admit more fresh air). 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 3 
Technology Installation Review 

•	 Three units have heat pump water 

heaters (HPWHs), which use heat 

pump technology to produce hot 

water. (The HPWHs also produce 

cool, dry air that supplements the 

cooling system during the cooling 

season.) Detailed measurements 

taken at 15-minute intervals by 

instruments installed with the 

HPWHs in these houses show 

that they are twice as efficient as 

conventional electric water heaters 

(Christian 2006). One unit has a 

highly efficient conventional 

electric resistance water heater. 

•	 Reflective metal roofs reduce heat 

gain through the roof during hot 

weather. Once all reflective roofs 

were light in color, but now even 

dark roofs can be reflective because 

pigments are available that 

minimize solar radiation absorption 

outside the visible electromagnetic 

spectrum. Two of the houses have 

dark green metal roofs and two have 

light-colored roofs. 

•	 All the windows used are highefficiency windows and have a 

National Fenestration Rating 

Council (labeled) U-factor of 0.34 

and a solar heat gain coefficient 

(SHGC) of 0.33. (U-factor 

measures heat transfer; the SHGC 

measures how well the window 

blocks heat from the sun.) The 

glazing is double-pane, lowemissivity glass filled with argon gas. 

•	 Passive-solar principles applied 

include placing most of the 

windows on the south side of the 

house and using roof overhangs to 

block solar heat gain during the 

warm months. 

•	 All appliances are Energy Star® 

appliances, with the possible 

exception of the washing machines, 

4 –– FEDERAL ENERGY MANAGEMENT PROGRAM 

which were purchased by the 

homeowners. 

•	 Sixty to ninety percent of the 

lighting in each house is fluorescent. 

In addition to the energy-saving 

features, there was an emphasis on 

moisture management to avoid mold, 

mildew, and general moisture damage 

to the building and to control relative 

humidity levels that affect thermal 

comfort. The technologies employed 

include moisture barriers in the crawl 

spaces and basement. The HVAC 

systems avoid introducing large 

quantities of humid outdoor air, 

pressure-neutralize distribution systems, 

and have programmable thermostats 

that also help control summer humidity. 

Table 1 lists building envelope features 

used in the four near-zero-energy houses 

and in a baseline Habitat house used for 

comparison. Table 2 lists mechanical 

features used in the test houses and the 

base house. The base house itself is 

unusually energy-efficient, as measured by 

a Home Energy Rating System (HERS) 

rating of 84, which indicates about 

20% better performance than a typical 

American house of the same size 

and layout. 

Principles of Operation 

A net-zero-energy house is one that 

produces enough, or more than enough, 

renewable energy on site to meet all the 

dwelling’s power needs on an annual 

basis. Currently the on-site energy 

source of choice is rooftop PV and solar 

water heating systems. A small, grid-tied 

PV system cannot produce enough energy to constantly supply all the electricity needed—on cloudy days or at night, 

the house must still use power from 

the utility grid. However, in periods of 

intense sunlight, a small PV system may 

produce mor . e energy than the house 

needs. The excess power can be fed into 

the utility grid and purchased by the 

local utility to balance the electricity 

purchased during less sunny times. 

To reach the net-zero-energy goal, a 

house must be super energy-efficient, 

consuming no more power annually 

than a small PV system can supply. 

Otherwise, the PV system would have 

to be prohibitively large and expensive. 

That means cutting energy consumption 

by at least 70% compared with a 

conventionally built house of comparable 

size, according to DOE Building 

America. Advanced energy-saving 

technologies thus are indispensable to 

making net-zero-energy houses feasible. 

A net-zero-energy house is not a single 

technology but a suite of closely 

integrated technologies. An essential 

principle of the zero-energy design 

and building process is whole-house 

integration—careful planning to make 

all the components work together to 

achieve maximum energy savings 

(e.g., recovering waste heat to enhance 

the efficiency of a water heater). In the 

houses in this study, PV energy production is combined with several key 

building energy-efficiency principles— 

air-tightness, high-R-value insulation, 

high-efficiency appliances, reflective 

roofs, energy-efficient fenestration, 

passive solar techniques, recovery of 

waste heat, and humidity control—to 

move toward the net-zero-energy goal. 

Because zero-net-energy building is a 

new field, an essential part of this 

integration process is applying the 

lessons learned from building each 

dwelling to subsequent ones. 

Maintenance, Service, 

and Operation 

In the future each net-zero-energy house 

will employ a similar set of products, 
Technology Installation Review 

Table 1. Building envelope features of near-zero-energy houses and a base energy-efficient house 

House ZEH1 ZEH2 ZEH3 ZEH4 Base 

Floors 1 1 1 2 1 

Area (ft2) 1056 1060 1060 1200 1060 

Occupancy Nov 2001 Dec 2003 Dec 2003 July 2004 June 2000 

Foundation Unvented crawlspace Mechanically vented 

crawlspace in winter only 

with insulated walls, 2-in. 

polyisocyanurate boards 

(R-12) 

Unvented crawl space 

with insulated walls, 

2-in. polyisocyanurate 

boards (R-12) 

Walkout basement with 

insulated precast (nominal 

steady-state R-16) 

Vented 

crawlspace 

First floor 6.5-in. SIPs 1# 

expanded polystyrene 

(EPS) (R-20) structural 

splines 

R-19 glass fiber batts, 

3⁄4-in. extruded polystyrene boards installed on 

bottom side of 91⁄2 in. 

I-joist (R-24) 

R-19 glass fiber batts, 

3⁄4-in extruded polystyrene boards installed on 

bottom side of 91⁄2 in. 

I-joist (R-24) 

Concrete slab R-19 glass fiber 

batts (R-17.9) 

Walls 4.5-in. SIPs 1#EPS 

(R-15) surface splines, 

house wrap, vinyl 

4.5-in. SIPs 2#EPS 

(R-15.5) structural 

splines, house wrap, vinyl 

6.5-in. SIPs 1#EPS 

(R-21), structural 

splines, house wrap, 

vinyl 

2nd floor 4.5-in. SIPs 

polyisocyanurate pentane 

blown (R-27), surface 

splines 

2×4 frame with 

R-11 glass 

fiber batts, OSB 

sheathing, 

(R-10.6) 

Windows 9 windows, 0.34 

U-factor, 0.33 SHGC, 

sill seal pans 

8 windows, 0.34 U-factor, 

0.33 SHGC, sill seal pans 

8 windows, 

0.34 U-factor, 0.33 

SHGC, sill seal pans 

10 windows, 0.34 U-factor, 

0.33 SHGC, 

sill seal pans 

7 windows, 

U-factor 0.538 

Doors 2 doors, one solid 

insulated, 

one half-view 

2 doors, one solid insulated, one half-view 2 doors, one solid 

insulated, one half-view 

3 doors, one solid 

insulated, one full-view, 

one half-view 

2 doors, one 

solid insulated, 

one half-view 

Roof 8 in. SIPs 1#EPS 

(R-28), surface splines 

6.5-in. SIPs 2#EPS 

(R-23), structural splines 

10-in. SIPs 1#EPS 

(R-35), surface splines 

8-in. SIPs, polyisocyanurate, 

pentane blown (R-45), 

surface splines 

Attic floor blown 

glass fiber 

(R-28.4) 

Roofing Light grey hidden 

raised metal seam, 

0.31 reflectivity 

(http://www.energystar. 

gov/ia/products/prod_ 

lists/roof_prods_prod_ 

list.pdf) 

15-in. green standing 

24-GA steel seam, 

0.17 reflectivity 

15-in. green standing 

24-GA steel seam, 

0.23 reflectivity 

Light gray metal simulated 

tile, 0.032 aluminum, 0.31 

reflectivity 

(http://portal.atas.com/dnn/ 

Portals/57ad7180-c5e7-

49f5-b282-c6475cdb7ee7/ 

ATAS%20Standard%20Color 

s%20Reflect_Emitt.pdf) 

Gray asphalt 

shingles, 0.18 

reflectivity 

(Parker 1993) 

Notes for tables 1 and 2: ECM = electronically commuted motor; EF = energy factor; 


EPS = expanded polystyrene; HP = heat pump; HPWH = heat pump water heater; HSPF = heating 


seasonal performance factor; OSB = oriented strandboard; SEER = seasonal energy efficiency rating; 


SHGC = solar heat gain coefficient; SIP = structural insulated panel; XPS = extruded polystyrene


equipment, and building techniques, 

which will lead to very predictable 

maintenance and operating expectations. The equipment installed in the 

homes will require regular maintenance 

according to the manufacturers’ 

guidelines. 

Makers of the building materials 

(e.g., SIPs, high performance windows, 

solar panels) and equipment (e.g, heat 

pumps, HPWHs) used in zero-energy 

houses offer warranties and service 

contracts on their products. Individual 

construction subcontractors (e.g., 

plumbers, HVAC installers) generally 

offer limited warranties that cover 

specific problems arising from mistakes 

or poor workmanship on their part, as 

do general contractors. As packaged kits 

of house parts become more common, 

warranties and maintenance requirements will grow more standardized and 

similar for each construction project. 

A general observation based on experience from building the homes discussed 

in this study is that it is essential to 

apply the experience and knowledge 

gained from previous houses with this 

advanced equipment. Most of the 

problems documented for these houses 

were of the same sort that could arise 

during construction of any house. The 

experience of rapidly evolving advanced 

technologies in this series of four 

houses underlines the importance of 

maximizing premanufactured components, systematically inspecting all work, 

and checking equipment for proper 

operation after contractor installation. 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 5 
Technology Installation Review 

Table 2. Mechanical features of near-zero-energy houses and energy-efficient base house 

House ZEH1 ZEH2 ZEH3 ZEH4 Base 

Solar system 48 43-W amorphous 

silicon PV modules, 2.06 

12 165-W multi-crystal 

silicon PV modules, 

12 165-W multi-crystal 

silicon PV modules, 

20 110- polycrystalline, 

2.2 kWp, 10.6% efficient 

None 

kWp, 5.3% efficient 12.68% efficient, 12.68% efficient, 

1.98 kWp 1.98 kWp 

Heating and cooling 1.5-ton air-to-air HP, 2-ton air-to-air HP, 2-ton direct exchange 2-ton air-to-air HP, SEER 17, Air-to-air 2-ton HP, 

SEER 13.7, 2-speed 2-speed compressor, geothermal HP, R-417a, variable-speed compressor, SEER 12 

ECM indoor fan SEER-14, HSPF-7.8, 

CFM cooling 700, 

variable-speed ECM 

indoor fan, 

variable speed ECM indoor and 

outdoor fan, 8.1 HSPF 

variable-speed ECM 3.7 COP@36 F for region IV 

indoor fan 

Mechanical ventilation Supply to return side Supply to return side of Supply to return side of Supply to return side of coil, None 

of coil coil, CO2 sensor, bath coil, bath fan exhaust bath fan exhaust 

fan exhaust 

Duct location Inside conditioned space Inside conditioned space Inside conditioned space Inside conditioned space In crawlspace 

Water heater Integrated HPWH linked Integrated HPWH, linked Desuperheater for hot HPWH vented to half-bath that Electric EF~0.89 

to unvented crawlspace to crawl-space that has water, EF 0.94 is exhausted for ventilation 

motorized damper 

Another general observation is that 

continuous monitoring of performance 

is important to indicate operating 

problems and correct them in a timely 

manner. For example, although the solar 

PV systems themselves performed well, 

a faulty inverter on one system significantly reduced the amount of power 

produced until it was replaced. Regular 

monitoring of the PV system output 

indicated a performance problem; 

otherwise, the inverter problem 

might have gone undiscovered for a 

longer time. 

A third observation is that even the 

most energy-efficient equipment may 

not save energy if it is not functioning 

properly. A low refrigerant charge in the 

heat pump in one house caused it to use 

far more energy than it would have with 

a proper charge, almost doubling the 

energy use of that house’s HVAC 

system until it was corrected. 

A blower door was used to test the 

airtightness of each house during and 

after construction. Infiltration testing 

reveals leaks that would be overlooked 

otherwise and is a critical element of 

Figure 3. Airtight assembly of the SIP 

envelope is essential for energy 

ensuring energy efficiency by preventing 

incursions of cold air during the heating 

season and unconditioned humid air 

during the cooling season. 

Measures of Efficiency 

The overall measure of efficiency used to 

evaluate the performance of each of the 

near-zero-energy houses in this study 

is the amount of energy consumed in 

relation to the energy consumed in a 

conventionally built house of the same 

size. This measure is an imperfect 

comparison because the number and 

ages of the people in the different 

houses and their energy use patterns 

vary and the test houses vary. However, 

it does show a clear difference between 

the four subject houses and the 

base house. 

Energy consumption data were gathered 

for the main categories of consumption: 

heating, cooling, hot water, and plug 

loads (including lighting loads). 

Measures of efficiency are established 

by trade groups, building codes, and 

government agencies for all the building 

materials and equipment used in these 

four houses. PV systems, for example, 

are rated in terms of the amount of peak 

power they can produce and their 

efficiency in converting sunlight to 

electricity. SIPs are rated according to 

R-value. Windows are rated by the 

National Fenestration Rating Council 

for several factors, including heat 

transfer rate and solar heat gain. Heat 

pumps are assigned a SEER rating for 

energy efficiency according to standards 

established by DOE and the HVAC 

industry. The energy efficiency of water 

. 

6 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Technology Installation Review 

heaters is rated by coefficient of performance. Household appliances are rated 

according to standards set by DOE and 

the various industries. 

Energy Savings 

Energy consumption and equipment 

performance were monitored in each 

ZEH for a full year of occupation. The 

data that was collected was used to 

compare these houses to three different 

standards of energy efficiency. 

One respected tool for evaluating the 

energy efficiency of a home is the Home 

Energy Rating System (HERS). HERS 

compares the energy performance of a 

specific house with that of a computersimulated reference house, identical in 

layout and size, that complies with 

the 2003 International Energy 

Conservation Code (IECC). The 

reference house is rated at HERS 80. 

Each 5% reduction in energy use compared with the reference house increases 

the HERS score by one point. The 

HERS scores for ZEH1, 2, 3, and 

4 were 90.2, 91.4, 91.5, and 92.5, 

respectively, which is 40 to 60% more 

efficient on an annual basis than the 

reference house. (The “base house” 

that was built the same size and in the 

same subdivision as the ZEH1 – 4, and 

to which these houses are compared 

throughout this document, is a HERS 

84 house, 20% more efficient than the 

IECC reference house.) 

To gain DOE Energy Star® certification, 

a house must attain a HERS score of at 

least 86. The data showed that ZEH1 

– 4 are 20 to 26% more efficient than 

an Energy Star house of the same size. 

Cost-Effectiveness 

The cost-effectiveness of near net-zeroenergy houses will vary with energy 

costs, climate, the energy-consumption 

habits of the occupants, utility, state, 

and federal incentives for PV systems, 

and the cost of the particular set of 

technologies used in a particular dwelling. 

The electricity rate in Lenoir City, 

Tennessee, in 2004–2005 was $0.068 

per kWh, well below the national 

average of around $0.086 per kWh. 

Energy cost savings would be greater 

in regions with higher electricity rates. 

Because they were built partly as 

research units and mostly by volunteers, 

the four houses studied did not benefit 

from economies that would be possible 

with production units. Production 

houses are expected to cost substantially 

less—particularly as the construction 

techniques used become more familiar 

and standardized and as the materials 

are produced in greater volume. Federal 

agencies, especially, should be able to 

negotiate large discounts on materials 

and equipment for large-scale projects 

involving a few standard house plans 

(e.g., military housing). 

The economic justification for net-zeroenergy houses is that energy savings plus 

revenue from renewable energy sold to 

the utility grid help offset the added 

price of construction. For these four 

houses, utility bills averaged less than 

$1 per day—around $25 per month 

after credit for the sale of solar power 

back to the utility. The fourth house 

built had an average daily cost for 

electricity of 75 cents per day. A 

conventionally built house of similar 

size in the same community would be 

expected to average $4 to $5 per day for 

electricity. Figure 4 shows utility costs 

for ZEH1 and the base house over a 

period of a year. 

2

 Information about incentives to promote renewable energy is available through the Database of State Incentives for Renewable 

Energy (DSIRE) at www.dsireusa.org. 

Table 3 shows the building costs for all 

four houses and for a base house of 

similar size in the same locale. The costs 

of volunteer labor and donated materials are factored in. The costs of building 

the four study houses (not including the 

cost of land and infrastructure, which is 

the same for all, and the cost of the PV 

systems) ranged from about $79,000 to 

$88,000. The cost of building the base 

house was about $59,300. Thus the cost 

of the highly energy-efficient research 

houses, without the PV system added, 

ranged from about 33–66% more than 

the cost of the base house. The higher 

costs of the experimental houses are due 

to use of prototype or customized equipment and the extra effort required to 

install non-standard equipment, as well 

as the costs of installing instrumentation 

to continuously monitor and measure 

performance of the equipment and 

temperature and humidity in the houses. 

With the cost of the PV systems included, 

the construction cost ranged from about 

$100,000 to about $104,000, or from 

69 to 75% more than the cost of the 

base house. However, the cost of the PV 

systems had dropped from $22,000 in 

2002, when the first house was built, 

to about $15,000 for a slightly largercapacity system when the fourth house 

was completed in mid-2004. By late 

2004, the market cost for a similar-size 

system was under $14,000. Over the 

long term the cost of PV systems is 

expected to continue to drop as 

production volume increases. 

Photovoltaic systems are cost-effective 

only if utility and government incentive 

programs, such as purchase of solar 

energy from the PV systems, or 

mandatory renewable-generation 

directives, are in place.2 If TVA raises 

the rate it pays for energy from the PV 

systems from 15 cents to, say, 20 cents 

per kWh, that would lower net energy 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 7 
Technology Installation Review 

costs for these houses by about $0.25 

per day, which would increase their 

cost-effectiveness. 

Additional reductions in first cost are 

necessary to bring the life-cycle costs of 

net-zero-energy houses into line with 

requirements for federal housing. 

However, the local Habitat affiliate 

collaborating with this project is now 

attaining HERS ratings higher than 

86 for houses they build for less 

than $60,000. 

Field Demonstration 

Test Site 

The construction and demonstration 

of these four near-zero-energy houses 

evolved from an existing partnership 

between DOE and Loudon County, 

Tennessee, affiliate of Habitat for 

Humanity. For several years, ORNL 

researchers and Building America had 

been working with Habitat to improve 

the energy efficiency of Habitat houses. 

As Habitat International is one of the 

largest home builders in the United 

States, the partnership helped DOE 

meet goals for reducing the energy intensity of U.S. housing. The partnership 

helped Habitat add value and comfort 

to its homes, helped Habitat homeowners save money on energy bills, 

gave the building industry a platform 

to test new energy-efficient products, 

and provided DOE and ORNL a field 

laboratory for energy-efficiency research. 

When net-zero-energy houses became 

a the major goal of the DOE Building 

Technology Office, the partnership with 

Habitat Loudon County offered an ideal 

setting for incorporating ultra-efficient 

technologies into houses that working 

families could afford. The partnership 

made plans to build a series of five 

houses, using the lessons learned from 

each one to move from near-zero-energy 

8 –– FEDERAL ENERGY MANAGEMENT PROGRAM 

Figure 4. Comparison of utility bills for ZEH1 and the base house over a year. 

to net-zero-energy while exploring 

ways to reduce building costs for the 

super-efficient houses. The four nearzero-energy houses in this demonstration are the first four. 

The four houses studied are located 

in a small subdivision in Lenoir City, 

Tennessee, which contains several dozen 

other Habitat for Humanity houses. The 

terrain is hilly, and the building lots are 

mostly clear of large trees. Lenoir City 

Utilities Board, affiliated with TVA, is 

the local electrical power distributor. 

ORNL staff and representatives from 

companies donating materials and 

equipment helped direct the assembly 

of the structures, the weather-proofing, 

and the installation of specialized 

equipment. Contractors were hired for 

more skilled tasks which included site 

preparation and foundations, plumbing, 

installing HVAC and PV systems, 

hanging and finishing drywall, and 

pouring and finishing concrete. 

The monitoring of each house for energy 

consumption began after the owners 

had moved in. Each house was occupied 

by three to four people. The homeowners received no training in household 

energy conservation in conjunction with 

the purchase of the houses. Because 

the occupants own the houses, they are 

free to use energy as they wish. They 

set the thermostats to their preferences 

and decide whether to use additional 

energy-saving methods such as compact 

fluorescent light bulbs. Therefore, the 

demonstration reflects how these houses 

will perform in real life. 

The Test Houses 

All four houses are constructed with 

SIPs that are caulked, foamed and/or 

sealed with tape, simplified thermal 

distribution systems with ducts inside 

the conditioned space, controlled 

mechanical ventilation, insulated 

windows with a 0.34 U-factor and 

Table 3. Construction cost of test houses 1–4 and the base house ($) 

Base 1 2 3 4 

House 59,295 78,914 83,953 87,889 85,189 

Land and infrastructure 14,500 14,500 14,500 14,500 14,500 

PV system 0 22,388 16,000 16,000 14,935 

Total cost 73,795 115,802 115,953 122,329 114,624 

. 
Technology Installation Review 

0.33 SHGC, extended roof overhangs, 

mostly south-facing windows, and 

Energy Star appliances. Other energyefficiency features, such as the type of 

HVAC system or water heater, vary 

from house to house. 

ZEH1 is a one-story dwelling containing 

1056 ft2. It has three bedrooms, a livingdining room, a kitchen, and 1.5 baths. 

Its 4.5 in.-thick walls, 6-in. floors, 

and 8-in. ceiling are all constructed of 

SIPs made with expanded polystyrene 

insulation. The ACH rate (at a pressure 

of 4 Pascals) is 0.08. The HVAC unit 

is a 13.7 SEER 1.5-ton air-source heat 

pump with a 2-speed indoor circulating 

fan. The occupants kept the temperature 

at about 75° year-around, on average. 

The roof is gray reflective metal, hidden 

raised seam, with a 4/12 pitch. On the 

roof is a 2-kWp 48-panel solar 

PV system. 

Hot water is supplied by a 50-gal 

HPWH located in a utility closet by 

the kitchen. During the cooling season, 

warm air from the refrigerator compressor is pulled into the utility closet 

to allow heat recovery to increase the 

HPWH thermal efficiency. The HPWH 

exhausts cool, dehumidified air, which 

is returned to the conditioned space 

during the cooling season. (During the 

heating season, the HPWH draws input 

air from the crawl space and exhausts 

cool air to the outside.) ZEH1 also has 

a heat recovery shower that captures 

the waste heat from warm water going 

down the drain to preheat the cold water 

before it flows into the water heater. The 

house was equipped with energy-saving 

compact fluorescent light bulbs in about 

75% of its light fixtures. 

ZEH2 is one story with 1060 ft

2

. Its 

wall and ceiling SIPs have slightly higher 

density and R-value than in ZEH1, and 

its ACH rate at 4 Pascals is 0.07. Unlike 

ZEH1, ZEH2 has an insulated crawl 

space. The 14 SEER air-source heat 

pump is a 2-ton unit with a two-stage 

compressor and variable-speed indoor 

circulating fan. The two-stage compressor 

was selected to provide better humidity 

control during the summer months. 

The temperature was kept at about 75° 

year-around. The humidistat was set at 

55% RH during the summer months. 

The 50-gal. HPWH performed at a 

higher efficiency (2 compared to 1.7) 

than the unit in ZEH1; the setup for 

the air supply to the HPWH is more 

compact. This house has 1.25-ft overhanging eaves instead of the 2-ft overhangs in the three other ZEH houses. 

The ceiling is 6.5-in.-thick SIPs, and the 

roof is green metal standing seam with 

a 6/12 pitch. The PV system is rated 

at 1.98 kWp and has higher efficiency 

modules than used in ZEH1, resulting 

in only 12 modules, compared to 

48 in ZEH1. This house initially used 

incandescent light bulbs; they were later 

replaced with compact fluorescent bulbs. 

ZEH3 is one story with 1060 ft2. 

The biggest difference between it and 

the other three houses is that its heating/cooling system (2 ton, 16.6 SEER) 

is a geothermal or ground-source heat 

pump, which directly absorbs heat 

from and rejects it to the underground 

instead of to the air. The heat exchanger 

is three refrigerant loops of copper pipe 

buried in 5-ft-deep, 200-ft-long 

trenches behind the house. 

The system includes soaker hoses buried 

in the trenches in case the ground should 

ever become too warm to accept the 

rejected heat; but that is not expected to 

happen unless much drier than normal 

summer conditions prevail. 

ZEH3 has 6.5-in.-thick SIP walls and 

10-in.-thick SIP ceiling panels. The 

ACH rate at 4 Pascals is 0.04. The green 

metal standing-seam roof is painted 

with an infrared-reflective pigmented 

paint that makes it 35% more reflective 

than the similar-looking green roof 

of ZEH2. It has the same 6/12 pitch 

(26.6°) as ZEH2. 

The PV system, like the one in ZEH2, 

is a 12-panel system rated at 1.98 kWp. 

The water heater is not a HPWH but a 

50-gal. electric resistance unit with an 

efficiency rating of 94%, the highest 

available in fall 2003 when the house 

was built. Water heating is augmented 

by a desuperheater, a heat exchanger 

that uses superheated exhaust from the 

heat pump compressor to heat water for 

the hot water supply. The occupants of 

ZEH3 kept the temperature at around 

72° year around. 

ZEH4, the only two-story house, 

contains 1139 ft2. It was built in two 

stories because of the steepness of the 

lot. Instead of a crawl space, it has a 

walk-out basement, opening on the 

south side, that contains three bedrooms. The basement walls are four 

Tmass® pre-cast panels of polyisocyanurate insulation sandwiched in concrete. 

The walls were precast with electrical 

chases and receptacle boxes installed and 

with rough openings provided for the 

windows and doors. On below-grade 

surfaces, 60-mil waterproofing was 

sprayed and covered by 3⁄4-in. glass fiber 

drainage boards. Tmass walls were 

chosen because they provide thermal 

mass to store and release heat, aiding 

in heating and cooling; because they 

are airtight; and because they aid in 

moisture management. The SIPs used 

in ZEH4 are made of polyisocyanurate, 

which has a higher R-value than the 

expanded polystyrene SIPs used in the 

other three houses. The ACH rate at 

4 Pascals is 0.07. The roof is light gray 

aluminum simulated tiles and has a 4/12 

pitch. The PV system has 20 panels and 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 9 
Technology Installation Review 

Figure 5. ZEH1 

is rated at 2.2 kWp, about 10% more 

capacity than the PV systems on ZEH1, 

2, and 3. 

The heating/cooling system is a 17 

SEER, 2-ton air source heat pump 

with a two-speed compressor and DC 

commutating indoor fan motor. The 

water heater is an HPWH. Unlike the 

other HPWHs in ZEH1 and 2, it 

draws warm air from the refrigerator 

compressor year-around; also unlike 

the others, it exhausts cool, dry air 

into an adjacent half-bath year-around. 

The ventilation scheme for the house 

prevents the cool, dry HPWH exhaust 

from being a comfort issue during the 

heating season. Every 20 minutes the 

fresh air inlet opens and the half-bath 

exhausts about 100 cfm. Continuous 

temperature measurements were not 

made in this bathroom; however, the 

homeowner’s response to being asked 

several times if this space was too cold 

indicates that the fan noise is more 

noticeable than too-cool temperatures. 

ZEH4 has compact fluorescent bulbs in 

about 75% of its light fixtures. 

The Test Houses 

Each of the demonstration houses was 

equipped during construction with an 

array of sensors to record values such 

as indoor, crawl space, and ambient 

temperature; indoor, crawl space, 

and ambient relative humidity; water 

temperature in the water heater; heat 

pump operation; and indoor CO2 level. 

The number of sensors installed in each 

house ranges from 32 to 53. Each house 

contains thermocouples to measure the 

temperature of the HVAC equipment, 

duty-cycle valves to monitor equipment 

usage, and transducers to track the 

energy being used throughout 

the house. 

At ZEH3, which has a geothermal heat 

pump, thermocouples were installed 

to measure the underground temperature 1, 6, 12, and 24 in. away from the 

buried copper heat exchanger pipeline 

and at 15 ft away from one of the three 

buried copper tubes. These thermocouples are buried at the same depth as the 

copper pipe, at a distance of 50 ft from 

the compressor outlet loops. 

Each house is equipped with two 

electric utility meters, one to track the 

total amount of electricity the solar PV 

system is producing and another to 

track whether the house is using more 

energy than it produces, or vice versa. 

The sum of these two meters equals the 

whole-house energy consumption. 

The thermal performance sensors continuously measure data that is recorded 

in a computer located in each house 

every 15 minutes. At 2:00 a.m. daily, 

a laboratory computer calls the data 

acquisition system at each house and 

downloads the recorded data from the 

previous 24 hours. 

The data are analyzed extensively to 

determine product performance and 

energy consumption and to validate 

computer models. These validated 

models can be used to accurately simulate situations such as how modifying 

the mix of technologies might affect the 

energy usage of a house or how varying 

inputs would change overall energy 

performance. For example, a house 

could be modeled in another climate 

or with lower or higher plug loads, or 

a larger PV system on a house could 

be simulated to determine whether the 

added PV production would bring the 

house to net-zero-energy status. Simulations such as these provide information 

to researchers about what technology 

mix might provide the most energy 

efficiency for the money. 

Energy Savings and Costs 

The calculations of energy cost in this 

section are based on electricity costs of 

$0.068/kWh. A contractual arrangement specifies that the local utility will 

pay the homeowner $0.15/kWh for all 

the solar power produced by the PV 

system for 10 years whether the 

homeowner uses it or not. Eighteen 

states have some type of production 

incentive program similar to TVA’s 

green power switch generation. 

ZEH1. Monitoring data show that 

ZEH1, built in 2002, used 10,216 kWh 

of electricity between March 2003 and 

February 2004. That is about 40% less 

than the base Habitat house, which is 

itself more efficient than the average 

house. The energy cost (electricity 

purchased from the utility minus the 

amount of surplus solar power sold 

to the utility) amounted to about 

$1.01 per day. 

The rooftop solar PV system supplied 

2006 kWh, about 20% of the energy 

used over the year. About 40% of the 

PV power was produced at a time in 

which it was not needed in the house. 

The PV power was produced mostly on 

hot summer afternoons and reduced the 

house’s peak load by a daily average of 

40% between June and August. 

Table 4 shows the monthly measured 

energy usage for ZEH1 during the 

monitoring year March 2003 through 

. 

10–– FEDERAL ENERGY MANAGEMENT PROGRAM 
Technology Installation Review 

February 2004. As in all the houses, 

lighting and plug loads (“other”) 

accounted for about 60% of the energy 

used. The occupants of ZEH1 used less 

than 40 gallons of hot water per day, 

about 43% less than the national 

average of 64 gallons estimated from a 

national survey of hot water usage 

(U.S. DOE 2004). The low hot water 

draws are due in part to reduced 

distribution losses resulting from the 

compact plumbing system—because hot 

water does not have as far to travel, less 

of the heat is lost. Water distribution 

losses in a typical house are thought to 

be around 30%. 

ZEH2. During the one-year period 

from April 1, 2004, through March 31, 

2005, ZEH2 occupants consumed a 

total of 12,207 kWh. During this same 

12-month measurement period the PV 

system generated 2305 kWh. About 

34% of the solar energy was collected 

at a time when it was not needed in the 

house. Table 5 shows the energy usage 

broken down into heating, cooling, hot 

water, and other. 

The measured net daily cost of off-site 

energy to run this all-electric house was 

$1.32, compared to the daily energy 

cost of $1.01 for ZEH1. The higher 

energy cost is attributable to a low coolant charge on the heat pump. Although 

the heat pump was recharged on June 

6, 2004 and again on February 23, 

2005, average daily energy cost for the 

14-SEER, two-speed compressor with 

a variable-speed fan motor was $1.30, 

compared to $0.52 per day for ZEH1, 

which had a 13.7 SEER heat pump with 

a single-speed compressor, and $0.44 

per day for ZEH3 with the geothermal 

heat pump. 

Based on measurements of the heat 

pump supply and return temperatures, 

the kWh of the indoor and outdoor 

heat pump units, and ambient air 

temperatures, the HVAC system’s COP 

for January 17, which had an average 

daily temperature very close to the rated 

ambient performance test conditions of 

17°F, was calculated. Researchers found 

that the heat pump was delivering only 

47% of its rated performance. Using 

this calculation, heating season HVAC 

power requirements from the beginning 

of the heating season until the unit was 

recharged in late February 2005 were 

adjusted, assuming a properly performing heat pump. The resulting adjusted 

energy use for October 2004 until the 

end of February 2005 is 2370 kWh or 

$161 per year, which equals $0.44 per 

day. This reduction in heating energy 

for ZEH2 was 2544 kWh. The resulting 

adjusted daily HVAC cost is $0.85 per 

day, which yields a total whole-house 

daily energy cost after solar credits of 

$0.88. 

Assuming a properly functioning heat 

pump, the solar energy collected on site 

amounts to 23% of the house’s total 

electric demand of 9837 kWh/year, an 

improvement of 3% over the 20% of 

total electric demand supplied by PV in 

the first house. 

ZEH3. During the one-year period 

from March 1, 2004 until February 28, 

2005, ZEH3 occupants consumed a 

total of 11,014 kWh. During the same 

year the PV system generated 2241 

kWh, including 29% collected during 

times when the energy was not needed 

in the house. Table 6 shows the actual 

energy usage in ZEH3. 

The net daily cost for off-site energy to 

run this all-electric house was $1.13. 

The “other” loads in this house of 7388 

kWh, were much higher than ZEH1 

(5907 kWh/year), ZEH2 (4314 kWh/ 

year), and the suggested internal loads 

from the Building America Benchmark house (6512 kWh/year). In part 

this is explained by the house being 

mostly occupied during the day 7 days 

a week. Also a significant load was due 

to unusually extensive outdoor holiday 

decorations during November through 

January. To be able to more directly 

compare ZEH3 with the other houses 

and the Building America Benchmark, 

the kWh for “other” loads for ZEH3 is 

reduced. The average for “other” loads 

of ZEH1, ZEH2, and two Building 

America Benchmark houses is 5604 

Figure 6. Air flow to and from the heat-pump water heater in ZEH2. 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 11 
Technology Installation Review 

Figure 7. ZEH3. 

kWh/year, or $1.04 /day. This 

would reduce the “other” load 

by 1784 kWh, which would 

represent a cost reduction to 

the homeowner for off-site 

energy shown in Table 6 of 

$0.34/day, resulting in an 

average daily net-cost for offsite energy of $0.79. 

This compares to $1.01/day 

for ZEH1 (Christian 2005), and 

$0.88/day for ZEH2 (Christian 2006a). 

The HVAC cost on ZEH3 with the 

geothermal heat pump averaged only 

$0.44/day, compared to $0.51 per day 

on ZEH1 with a 13.7 SEER, singlespeed compressor. The final adjusted 

daily HVAC cost for ZEH2 came to 

$0.85/day. 

With an adjusted “other” load for ZEH3 

of 5604 kWh/year, this all-electric 

house’s fraction of solar energy collected 

on site amounts to 24% of the total 

electric demand of 9230 kWh/year, 

an improvement of 4% over ZEH1. 

ZEH2 attained 23% of it’s total energy 

needs from the solar PV system. 

ZEH4. ZEH4 occupants consumed 

a total of 9843 kWh for one complete 

year from August 1, 2004, through 

July 31, 2005. During this same period 

the solar system generated 2627 kWh. 

About 46% of the solar was collected 

at a time when it was not needed in the 

Figure 8. GHP trenches behind ZEH3. 

house. Table 7 shows the energy usage 

broken down into heating, cooling, hot 

water, and other. 

The net daily cost for off-site energy to 

run this all electric house was $0.75. 

This compares to $1.01 per day for 

ZEH1 (Christian 2005), $0.88 per day 

for ZEH2 (Christian 2006a), and $0.79 

per day for ZEH3 (Christian 2006b). 

The HVAC cost for ZEH4 with the 

SEER 17 air source HP averaged 

$0.51/day. 

Table 4. ZEH1 measured energy use, March 2003 through February 2004 

Month Space heat 

(kWh) 

Space cool 

(kWh) 

Hot water 

(kWh) 

Other (kWh) Total electric 

(kWh) 

Solar 

generated 

(kWh) 

Solar sold to 

utility (kWh) 

March 127 0 124 325 575 167 91 

April 64 0 146 419 629 195 100 

May 0 94 109 460 663 188 90 

June 0 204 87 490 781 213 88 

July 0 314 74 494 882 209 79 

Aug 0 359 70 536 966 219 76 

Sept 0 187 82 491 760 195 95 

Oct 34 17 117 518 686 159 77 

Nov 141 0 138 518 797 121 45 

Dec 401 0 187 650 1238 115 15 

Jan 473 0 219 540 1232 120 23 

Feb (2004) 344 0 196 466 1006 104 25 

Total 1584 1175 1549 5907 10216 2006 804 

% of total 15.5% 11.5% 15% 58% 100% 20% 

Annual cost $100a $74 b $98 $372 $644 –$301 

Daily cost $0.51a $0.44 b $0.27 $1.02 $1.76 -$0.82 

a Heating days only. . b Cooling days only. 

12 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Technology Installation Review 

The HVAC cost on ZEH1 with a 13.7 

SEER single speed compressor came to 

the same $0.51/day. The final adjusted 

HVAC daily cost for ZEH2 came to 

$0.85/day. The HVAC cost on the 

ZEH3 with the geothermal HP averaged only $0.44/day. 

This all-electric house’s fraction of solar 

energy collected on site amounts to 

27% of the total electric demand of 

9843 kWh/year, the highest fraction 

of on-site generation among the fourhouse set. 

Summary 

Four near-zero-energy houses were built 

to demonstrate the feasibility of making 

net-zero-energy housing affordable in 

moderately priced housing. The houses, 

built between 2002 and 2004, cost 

between $115,000 and $122,000, 

including the cost of the rooftop solar 

PV systems on all the houses. Their 

energy efficiency, documented by an 

elaborate monitoring system, was 

notable — energy consumption in the 

first house built was 40% less than in an 

energy-efficient base house and 62% less 

than in a conventional frame house of 

the same size. 

The technology is performing well and 

the energy savings make the houses less 

expensive to operate, but they do not 

currently meet federal procurement 

guidelines for payback periods without 

utility and government incentives. 

Additional improvement in energy 

efficiency and lower costs are necessary to 

make the technology broadly appropriate 

for federal building programs. However, 

promising improvements in energy 

efficiency, more policies to encourage 

incentives, and high-volume production 

Figure 9. ZEH4 

of energy efficient key components of 

zero-energy houses are likely to accelerate the progress toward a vibrant ZEH 

market in both the federal and private 

sectors. The cost of solar PV systems 

dropped from $22,000 to $14,000 

during the two years when these houses 

were being built. 

A key to bringing down the costs of netzero-energy houses is increased demand 

Table 5. ZEH2 measured energy use, April 2004 through March 2005 

Month Space heat 

(kWh) 

Space cool 

(kWh) 

Hot water 

(kWh) 

Other (kWh) Total electric 

(kWh) 

Solar 

generated 

(kWh) 

Solar sold 

to utility 

(kWh) 

April 0 159 87 418 664 203 99 

May 0 488 66 359 913 234 78 

June 0 498 57 336 891 215 76 

July 0 347 59 325 731 250 110 

August 0 280 60 344 684 233 86 

Sept. 0 246 56 299 601 217 102 

October 280 0 70 346 696 159 65 

Nov. 624 0 78 359 1061 145 30 

Dec. 1420 0 109 403 1932 148 19 

January 1392 0 118 382 1892 136 15 

February 756 0 99 352 1207 142 34 

March 442 0 102 391 935 223 81 

Total 4914 2018 961 4314 12207 2305 795 

% of total 40% 17% 8% 35% 100% 

Annual cost $334a $137b $65 $293 $830 -$346 

Daily cost $1.83a $0.75b $0.18 $0.80 $2.27 -$0.95 

Adjusted daily 

cost 

$0.95c $1.83c 

a Heating days only. b Cooling days only. c Based on correctly charged heat pump using 2544 kWh rather than actual 4914 kWh used by incorrectly charged heat pump. 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 13 
Technology Installation Review 

leading to mass production. Building researchers at ORNL and utility partners 

are encouraging the building industry to 

develop net-zero-energy housing “kits” 

containing the materials needed to 

construct a small house in a particular 

climate zone. The kits would encourage 

both mass production and standardization of panels and other components. 

Next Steps 

Good progress toward net zero is being 

made. Construction of ZEH5 is 

complete, and from Nov. 1, 2005, until 

October 31, 2007, work in this test 

facility is focused on making the next set 

of research breakthroughs to attain the 

DOE goal of 70% whole-house energy 

savings. The house has a very promising 

lower cost geothermal system, a solar 

water heater, and anticipated 3.5-kWp 

solar PV system. This will be sufficient 

to reach the energy performance goals, 

leaving the challenging affordability 

issue, which will be addressed by a 

robust R&D focus on the most promising technologies and not exclusively on 

rapidly escalating energy costs. 

Federal Sector Potential 

Military family housing, public housing, and the Department of Housing 

and Urban Development are good 

candidates for net-zero-energy housing. 

Especially in remote areas with high 

solar incidence, military housing and 

other small structures are an opportunity for using net-zero-energy technologies. The cost-effectiveness of net-zeroenergy housing would be enhanced in 

remote areas because of the high cost of 

establishing electric transmission and 

distribution infrastructure there and its 

vulnerability to disruption. The modular panel construction can go up in a 

few days using a workforce with limited 

skills. These houses would be excellent 

candidates for rebuilding after military 

conflicts and natural disasters. 

The life-cycle cost of building these 

houses must fit within the procurement 

requirements of the federal government. Without utility and government 

incentives, which are on the increase, 

the energy savings may not offset the 

first costs sufficiently to offer acceptable 

payback periods. However, increasing 

demand for high-efficiency materials 

and equipment is expected to bring 

prices down gradually as production 

volumes increase. Continued energy 

cost escalation such as the 30 – 50% 

increase anticipated for natural gas in 

the 2005–06 heating season could close 

this gap in a very short timeframe. Mass 

purchasing of the building components 

for a large number of housing units 

Table 6. ZEH3 measured energy use, March 2004 through February 2005 

Month Space heat 

(kWh) 

Space cool 

(kWh) 

Hot water 

(kWh) 

Other (kWh) Total electric 

(kWh) 

Solar 

generated 

(kWh) 

Solar sold to 

utility (kWh) 

March 69 108 486 663 231 116 

April 0 77 108 489 674 226 100 

May 0 319 90 560 969 221 48 

June 0 346 76 511 933 213 56 

July 0 394 76 569 1039 232 48 

August 0 352 76 603 1031 222 41 

Sept. 0 290 79 483 852 201 55 

October 57 0 99 560 716 154 49 

Nov. 50 0 104 738 892 135 37 

Dec. 132 0 148 1174 1454 142 28 

January 176 0 144 620 940 131 40 

February 85 0 171 595 851 133 41 

Total 569 1778 1279 7388 11014 2241 659 

% of total 5% 16% 12% 67% 100% 

Annual Cost $39a $121b $87 $502 $749 –$336 

Daily cost $0.22a $0.66 b $0.24 $1.38 $2.05 –$0.92 

Adjusted 

daily cost 

$1.04c $1.71c 

a Heating days only.
 b Cooling days only. .
 c Based on normalized “other” usage of 5604 kWh rather than the actual 7388 kWh.


14 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Technology Installation Review 

might be a means of attaining acceptable life-cycle costs. The federal government has the buying power to push 

cost-reduction measures such as largevolume production of SIP zero-energy 

houses in standard sizes. 

Utility support for energy-efficient 

housing is growing because of the cost 

of building new power generation, the 

need to reduce peak loads, and the need 

to reduce power plant emissions. 

Increased reimbursement levels for the 

PV power produced, which can be sold 

at a premium green power rate, could 

significantly offset cost differentials. 

Other issues may work to make netzero-energy building attractive for the 

federal sector, even considering high 

first cost: 

• Environmental need for such 

housing could offset cost issues 

in some communities, for example, 

areas that are not meeting Clean Air 

standards and need to reduce 

emissions from power plants. 

• Rising energy costs make energyefficiency measures more costeffective. Record fossil fuel prices 

and forecasts of continuing high 

prices put pressure on the 

government to make long-term 

investments to cut energy 

consumption. 

• Energy conservation decreases 

U.S. dependence on foreign oil 

and enhances national security. 

Should the federal government adopt 

the net-zero-energy concept for a large 

number of housing units, its mass 

purchasing power probably would 

enable it to negotiate significantly 

lower prices for the components. If 

construction costs can be brought 

into line with federal requirements, 

potential federal sector applications of 

small net-zero-energy houses or other 

buildings include military housing and 

base structures. 

Much future U.S. military construction 

is likely to be in parts of the world with 

bright sunlight year-round and without 

widespread infrastructure for electricity transmission and distribution. For 

such areas, net-zero-energy construction might prove more feasible than 

conventional approaches. The speed 

with which panelized houses can be put 

together by workers with limited skills 

would enhance their value for building 

housing in remote areas and for 

rebuilding housing on a large scale 

after man made or natural disasters. 

Table 7. ZEH4 measured energy use, August 2004 through July 2005 

Space heat 

(kWh) 

Space cool 

(kWh) 

Hot water 

(kWh) 

Other (kWh) Total electric 

(kWh) 

Solar 

generated 

(kWh) 

Solar sold to 

utility (kWh) 

August 2004 0 204 168 503 875 279 126 

Sept 0 145 114 580 839 236 77 

Oct 73 0 115 474 663 176 87 

Nov 152 0 138 449 739 144 70 

Dec 429 0 186 425 1041 146 62 

Jan 438 0 190 441 1068 137 62 

Feb 322 0 162 359 843 146 67 

March 297 0 196 439 932 247 126 

April 0 99 169 422 690 255 134 

May 0 102 144 376 622 324 201 

June 0 199 116 402 717 286 120 

July 2005 0 267 120 427 814 251 87 

Total 1711 1016 1819 5297 9843 2627 1219 

% of total 17% 10% 18% 54% 100% 

Annual cost $116a $69b $124 $360 $669 –$394 

Daily cost $0.32a $0.19b $0.34 $0.99 $1.83 -$1.08 

a Heating days only. b Cooling days only. 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 15 
92

William Lintner

New Technology Demonstration

 Program Manager

Federal Energy Management 

 Program

U,S. Department of Energy

1000 Independence Ave, SW, EEWashington, DC 20585

Phone: (202) 586-3120

Fax: (202) 586-3000

william.lintner@ee.doe.gov

Steven A. Parker

Pacific Northwest National

 Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contact

Michael Kintner-Meyer

Pacific Northwest National

Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-4306

Fax: (509) 375-3614

Michael.Kintner Meyer@pnl.gov

Produced for the U.S. Department

of Energy, Energy Efficiency and

Renewable Energy, by the Pacific

Northwest National Laboratory

DOE/EE-0000

xxxx 2006 

General Contacts

References 

ASHRAE, 2004. ANSI/ASHRAE 62.2-2004: Ventilation and Acceptable Indoor Air Quality in 


Low-Rise Residential Buildings, American Society of Heating, Refrigerating and Air-Conditioning 


Engineers (ASHRAE), 1791 Tullie Circle N.E., Atlanta, GA 30329-2305.


Christian, Jeff, 2005. “Ultra-Low-Energy Residences,” ASHRAE Journal (January 2005).


Christian, Jeffrey E., and Jan Kosny, 1995. “Towards a National Opaque Wall Rating Label,” 


ASHRAE/DOE Thermal Performance of the Exterior Envelope of Buildings Conference VI, 


Clearwater Beach, FL, December 4-8, 1995.


Christian, Jeffrey E., and Jan Kosny, 1996. “Thermal Performance and Wall Ratings,” 


ASHRAE Journal, Volume 38, Number 3, March 1996.


Christian, Jeff, Paige Pate, Phil Childs, and Jerry Atchley, 2006a. “Small House with Construction 


Cost of $100K, Total Energy Cost of $0.88 a Day,” to be presented at the 2006 ASHRAE Winter 


Meeting and published in ASHRAE Transactions, Volume 112, Part 1.


Christian, Jeff, Lauren Richards, Phil Childs, Jerry Atchley, and Hyeun Moon, 2006b. “Energy 


Efficiency, SIPS, Geothermal, and Solar PV Team Up to Near-Zero-Energy House,” to be presented 


at the 2006 ASHRAE Summer Meeting and published in ASHRAE Transactions 2006, Volume 2.


Hendron, Robert, 2005. Building America Research Benchmark Definition, Version 4,


Updated July 14, 2004. [Current version.] NREL/TP-550-36429, 


National Renewable Energy Laboratory. www.nrel.gov/docs/fy05osti/36429.pdf


Hendron, R., et al., 2004. Building America Performance Analysis Procedures, Rev. 1. 


NREL/TP-550-35567, NREL, Golden, CO. 


Parker, D. S., J. E. R. McIlvaine, S. F. Barkaszi, and D. J. Beal, 1993. Laboratory Testing of 


Reflectance Properties of Roofing Materials, Report No. FSEC-CR-670-93, Florida Solar Energy Center, 


300 State Rd. 401, Cape Canaveral, FL 32920.


U.S. Department of Energy (DOE), 2004. DOE 2004 Buildings Energy Databook, Table 7.2, 

“Typical Appliance Usage.” 

Vineyard, E. A., et al., 2003. “Measured Performance of Conventional and High-Velocity Distribution 

Systems in Attic and Space Locations,” ASHRAE Transactions, Volume 109, Part 2, June 2003. 

Log on to FEMP’s Web site for information about New Technology Demonstrations 

www.eere.energy.gov/femp/ 

You will find links to 

• A New Technology Demonstration Overview 

• Information on technology demonstrations 

• Downloadable versions of publications in Adobe Portable Document Format (pdf) 

• A list of new technology projects under way 

• Electronic access to a regular mailing list for new products when they become available 

• How Federal agencies may submit requests to us to assess new and emerging technologies 

DISCLAIMER 

This report was sponsored by the United States Department of Energy, Energy Efficiency and Renewable 

Energy, Federal Energy Management Program. Neither the United States Government nor any agency or 

contractor thereof, nor any of their employees, makes any warranty, express or implied, or 

assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any 

information, apparatus, product, or process disclosed, or represents that its use would not 

infringe privately owned rights. Reference herein to any specific commercial product, process, or 

service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its 

endorsement, recommendation, or favoring by the United States Government or any agency or 

contractor thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those 

of the United States Government or any agency or contractor thereof. 

A Strong Energy Portfolio 

for a Strong America 

Energy efficiency and clean, renewable 

energy will mean a stronger economy, 

cleaner environment, and greater 

energy independence for America. 

Working with a wide array of state, 

community, industry, and university 

partners, the U.S. Department of 

Energy’s Office of Energy Efficiency 

and Renewable Energy invests in a 

diverse portfolio of energy technologies. 

For More Information 

EERE Information Center 

1-877-EERE-INF 

1-877-337-3464 

www.eere.energy.gov/femp 

General Contacts 

Will Lintner 

Team Lead, RSTT 

Federal Energy 

Management Program 

U.S. Department of Energy 

1000 Independence Ave, SW 

EE-92 

Washington, DC 20585 

Phone: (202) 586-3120 

Fax: (202) 586-3000 

william.lintner@ee.doe.gov 

Technical Author 

Jeff Christian 

Oak Ridge National Laboratory 

865-574-5207 

christianje@ornl.gov 

DOE/EE-0318 

May 2007 

-

U.S. Department of Energy 

No portion of this publication may be altered in any form without Energy Efficiency prior written consent from the U.S. Department of Energy, Energy and Renewable Energy Efficiency and Renewable Energy, and the authoring national laboratory.