Introduction
Low cost housing producers have, for well over a decade, been
asking the question: What are the most cost-effective energy
measures for our type of construction?
Dozens of organizations have leaped forward over the years to
offer their version of the answer to this question. This has
caused a Tower of Babel effect, leaving many home builders confused.
The problem is - the true answer to the question is "It
Depends." It depends on what the organization is building
now, depending on local conditions. It depends on what products
are available at an affordable price. It depends on who is building
the homes - volunteers, owner-builders or contracted home builders.
These are all dynamic aspects of construction - they change with
personnel changes, market
changes and many other factors.
In the early 1980s, it was documented that low cost housing could
be built that was High Performance housing - it could use under
$200 per year for space heat in our nation's coldest climates
while providing improved indoor air quality and health features.
And, the best part was that it was very affordable to build this
way, because the energy features were designed into the plan
from the beginning, rather than as an afterthought. But, it did
require some changes in practice, a few new products and a willingness
to let go of unnecessary measures that don't pan out in the field
studies or that clash with the new approach being taken. As a
response to these findings, over time in the Northwest thousands
of high performance homes were built, and two states went so
far as to change their codes to the new high performance level,
a level that exceeds the proposed energy star levels. Yet, most
of the United States and the other two Northwest states have
not made the transition to this level of performance.
In 1994, the National Affordable Housing Network was founded
to represent the consumer's interest in affordable housing production
- and work toward bringing the best possible energy efficiency
improvements to affordable housing in Texas. NAHN partnered with
Habitat affiliates in Texas and began seeking resources to transfer
solutions known and explore new solutions appropriate to current
markets in Texas.
Habitat for Humanity International is a global organization that
partners with low-income families to build simple, decent housing.
Habitat cares about the value it is providing the homebuyer,
and it also has an abiding concern for keeping first costs at
their lowest to spread charitable dollars the farthest. Habitat
is a grass-roots organization, a network of independent yet coordinating
organizations that make all decisions on the local level. In
the United States, San Antonio Texas is the oldest affiliate
of Habitat International and consistently one of the nation's
top Habitat home producers. Texas has many strong Habitat affiliates.
Dallas City Homes is one of a wave of new non-profit housing
producers who work at the local level using federal HOME funds
to make housing affordable. Dallas City Homes uses a variety
of contracted labor, while Habitat uses volunteer, owner-builder
and contractor labor for various elements of the construction
process.
The purpose of the partnerships developed was to define affordable
energy approaches for Habitat and non-profit housing producers
that would provide the best value at the lowest possible first
cost. Another purpose was to provide educational opportunities
and field information to Habitat home builders.
Given that there are approximately 60,000 independent home builders
nationwide, and Habitat and the non-profit sector may represent
5,000 of this number, it is clear that there would be wide divergence
between approaches taken by various builders. In 1996, Texas
State Energy Conservation Office funded an oil-overcharge project
to bring solutions to Habitat homebuilders across the state,
who produce as many as 400 volunteer-built homes a year.
The project had three phases - the current practice study, the
design and build stage, and the measurement stage. This report
is the final deliverable on the Texas SECO contract, and provides
an update for participants and an introduction for those who
may wish to participate with the High
Performance Housing Partnership (Hp2) in the future.
ACKNOWLEDGEMENTS
The High Performance Housing
Partnership (Hp2) is a program of the National Affordable Housing
Network, a non-profit organization dedicated to representing
low-income consumers in the design and development of affordable
housing. Staff of NAHN working on this effort included Barbara
Miller, project director, and Bob Corbett, chief of design and
product evaluation. Simulation, data analysis and collection
was performed by Ecotope Inc., under Larry Palmiter, senior scientist
and Paul Francisco, with Jack Bartholomew conducting data verification
and one-time measurements from the Texas sample. 2000 marks the
22nd year that that Miller, Palmiter and Corbett have worked
together on development of high-performance low-cost housing.
Because this report is a milestone in a multi-year effort, we
have seen a complete staff change at nearly all the participating
building projects in the Hp2 effort. In other words, we have
two groups of people to thank and acknowledge for their participation
in this work. First, the project would not have been possible
without Regina Nobles, of Dallas City Homes (and formerly of
Habitat) who shares the mission of wanting to develop the best
possible home for the funds available to families who have the
support to make the dream of homeownership possible. She sits
on the Habitat regional council, and is a frequent support contractor
and volunteer to Habitat. Within Habitat, San Antonio Habitat,
including Jim Grant, Amy Hartman, and former ED Duane Beechey
and Jim Brewer, Paul Blakely at Longview Habitat, Kevin Coleman
of Abilene Habitat, Karl Dreher of El Paso Habitat, Gail Ryan
of Fort Worth Habitat, NAHN board member and former Habitat International
Board Member Carl Umland and Joe Gatlin, regional director for
Habitat International. Other former participant staffers at the
housing non-profit organizations include Brenda Coleman of Abilene,
Wink Dickey of Dallas and Gene Ruckle of Dallas.
Executive
Summary
In 1996, Habitat for Humanity in Texas joined with other housing
non-profit organizations to study and improve energy practices
in their current construction and new building. The National
Affordable Housing Network, a non-profit housing research organization,
submitted and was approved to conduct an oil-overcharge funded
project to pave the way for better understanding of energy practices
that represent the best public and consumer value in new affordable
housing construction.
The effort included volunteer-constructed homes as well as contractor-built
homes. It included a current practice study of more than 100
units statewide. Review of what is currently being done was the
basis of the next phase - the study of best-practice - best value
elements for three locations in the state, using a variety of
fuels and technologies. Then, model plans and guidebooks were
developed around three types of space conditioning - natural
gas, all-electric, and evaporative cooling. The plans were all
under 1,230 SF, with the average home being approximately 1,100
SF, three-bedroom. The project included the construction and
performance testing of more than 40 new homes in San Antonio,
Longview, Abilene, Dallas and El Paso. The project included the
production of approximately 30 educational information pieces
and house plans.
The largest sample with the most data collected to date is in
San Antonio. The performance of the natural gas homes in first
San Antonio sample is to within two percent of the modeling projection
for the project. The best performing home had total annual utility
cost of under $490 a year for all uses, with the best group having
an average consumption of $16 for annual space heat and $191
for annual cooling. This represents a 42 percent savings over
the San Antonio current practice ($849) average in 1996.
Across the other sites, a wide range of performance was seen.
The biggest percentage savings were seen in Longview and Dallas/FW,
which had the higher energy bills in the 1996 sample. Contractor
built homes tended to have the greatest absolute consumption.
The Habitat-built homes employed a wide range of technologies
and approaches. The best performing of these homes followed the
recommended Hp2 specifications closely. A variety of measurements
were taken across the sample, to maximize understanding of the
data and report the information in a way that would make it useful
to others.
When a home performed differently than expected, reviews were
conducted. Consumer behavior had the biggest overall impact on
performance, followed by product substitution, changing the specification
in a way that affected performance, or workmanship that needed
improvement from the energy performance standpoint. Appropriate
builder execution of the specification and product selection
were key aspects of performance. Occasionally, warranty-covered
product failure could be a cause of performance issues. Homes
that performed best closely followed all aspects of the specification,
were certified to meet the performance benchmarks and had occupants
who had appropriate expectations of performance and consumption
behaviors within predicted performance levels.
The Design
And Build Stage of Hp2 and the Features of the Design
with the lowest overall consumption performance
Coming to the Current "Right
Answer" for San Antonio's Habitat -
Optimization results
Cooling loads are the dominant energy consumption concern, but
heating is also an issue. The goal was to identify which cooling
solutions had the drawback of increasing heating costs and vice
versa. In this regard, the problem to solve for was the proper
balance of heating and cooling related measures.
The following items had cost and performance characteristics
that appear to have the lowest first cost and lowest operation
cost, compared to other packages.
The San Antonio plan has 1,045 square feet, slab on grade. This
house plan has three bedrooms. The home uses natural gas for
hot water and space heat. The following listing shows the features
of the home that had the lowest consumption data in our sample:
1) ENVELOPE INSULATION UPGRADE - Minimum insulation Levels are
R-30 in the attic and R-18 in the walls (R-13 batt, with R-3
or R-4 tongue-in-groove exterior foam insulation (1/2 inch to
¾-inch); slab edge is insulated; Roofing is the lightest
acceptable color. In Dallas, structural insulated panels (SIP)
were used for walls. Energy trusses were used to allow maximum
insulation values in the attic.
2) WINDOW UPGRADE - HEAT REJECTION AND GLAZING UPGRADE - All
windows meet the tightness specification. All windows have heat
rejection glazing, double glazed, vinyl frames.
3) MOISTURE CONTROL PACKAGE - Because of the impact of humidity
on cooling loads and comfort levels, controlling indoor relative
humidity levels can save cooling costs. Moisture transmission
through slab is reduced through an under slab moisture barrier,
and the building is tightly constructed to avoid moisture transmission
through ambient infiltration. A continuous vapor barrier is installed
above the ceiling sheetrock to stop air leakage and control moisture.
4) VENTILATION - INDOOR AIR QUALITY PACKAGE - Controlled continuous
ventilation is performed with high-performance fan, located in
the bathroom, wired directly to the panel. which does triple
duty of spot moisture control, on-going moisture discharge and
meeting ventilation recommendations. Is automatic and extremely
affordable.
5) "PERFORMANCE TESTED COMFORT SYSTEM" HVAC (system
downsizing and verification, including duct testing). Due to
the low consumption predictions, the HVAC system was downsized
to a point source, with air mixing through controlled exhaust
ventilation. Air tightness level was verified to match HVAC system.
Ductwork (if any) is checked for air leakage as part of verification
activities. All combustion heating equipment is sealed combustion,
to insure air quality and safety. Heating systems included sealed
combustion gas fireplaces, small gas wall furnaces sealed combustion,
and heat pumps. Cooling systems included small through-the-wall
air conditioners, central heat pumps and central room heat pumps.
Hp2 emphasized the lowest cost approaches to equipment selection
for heating-cooling equipment. Only sealed combustion was recommended.
Measures
that were not included for cost or performance reasons
It is very much a sifting process to determine what the consumer's
best value is, at a given point in time. Value is also relative
to what the consumer's preferences are. In housing, there are
several choices that consumers and appraisers feel are improvements
versus those that are thought to be "downgrades" or
economy models. Many times the economy model will work just fine,
and if it doesn't have other problems, it can be quite acceptable.
For this reason, in San Antonio it was considered an upgrade
to switch to sealed combustion gas heaters, from the prior product,
which was a centrally located gas furnace with no ductwork. In
other locations, the need for central heat and air was dominant,
and less cost effective approaches were employed due to consumer
preference. People have strong tastes and preferences when it
comes to space conditioning choices, and Hp2 was flexible with
those builders who would allow follow-up testing and correction,
if previous standards were employed.
Generally, Hp2 avoided ducted systems and relying instead on
a combination of tight construction with a point source of space
conditioning to achieve comfort at the lowest first and on-going
cost. In this system, these small houses are built tightly enough
that wind has virtually no impact on them. (See Appendix 1: Data
from Abilene) Thus, air temperatures were similar throughout
the house without ducted air handling. This is possible when
better levels of insulation, air tightening, heat rejection and
other envelope features are employed.
Low-income housing long has been associated with inadequate heating
and cooling systems, and some people still see a point source
of heating or cooling in this negative light. Indeed, point sources
of space conditioning combined with leaky construction can make
for comfort call-backs. An alternate system is the smallest available
forced air system with all ductwork within the conditioned space
and kept to a minimum. If outside the conditioned space, they
must be insulated to the maximum degree possible and checked
for air leakage and proof of performance. Also, this approach
must avoid products or installations that have combustion transfer
to the conditioned space. These systems cost more, and may cost
more to operate over time.
Where's the
"whole house fan?"
Whole house fans employ cooler night air to reduce indoor temperatures.
They tend to be located in the center of the house plan, and
field tests have shown them to leak air year-round, giving them
an energy penalty in this regard. They can work well when used,
but most require occupant action, and any system that requires
occupant action is likely to not be used much or at all. In the
end, the savings from not using the air conditioner would not
justify the measure, particularly when the air leakage is considered.
High-Performance
ventilation instead
Because of the need year round to control indoor moisture and
remove indoor-generated pollutants, a high performance fan was
identified that would run continuously and use under approximately
$10 a year in energy to operate. Moreover, the fan is so quiet
and efficient, that it cannot be heard when operated and is virtually
silent. This quantum advance in fan technology has been coming
for a long time. Thus, a small fan can run continuously in the
bathroom, and with tight construction, the air from the entire
home is slowly ventilated out the bathroom fan exhaust. A second
low-energy fan can be employed elsewhere for a "boost"
or for a second bathroom when additional whole house ventilation
is required or occupancy in the home increases. Because of the
specific performance of this piece of equipment, very few substitutes
would work.
Cooling Strategy
The cooling loads were cut to such a low level that a single
central room conditioner could readily handle the small cooling
load for the whole house. Measured cooling consumption in San
Antonio had a mean cost of $160 per household per YEAR. ($191
average). A combination of small steps leads to this performance.
This was accomplished through the combination of humidity control
and heat rejection, with improved insulation.
The cooling strategy included reducing heat gains through windows,
larger roof overhangs for shading, along with uniform, tightly
constructed, well-insulated walls and roof. Exterior wall insulation
is employed for air tightness and moisture control under the
siding. The slab on grade construction has a moisture barrier
underneath the concrete. This reduces water vapor from migrating
into the building through the concrete. This allows the concrete
to become a large cooling component that doesn't add to cooling
loads because of unwanted moisture transmission. Supplemental
cooling, including compression-driven dehumidification, is accomplished
by a central-room through the wall cooler, needed only during
the hotter hours. The ground-coupled high-mass floor staves off
the cooling demand, reducing the amount of compression-driven
cooling that is required. Overhead fans are installed in most
rooms to provide additional comfort. Passive cooling measures
are joined with moisture removal through the on-going ventilation
by the low-energy fan system.
Special products in this situation include long-life plastics
under the floor slab, and heat rejection glazing and tight window
construction. The wall air conditioner should have a SEER of
10 EER or greater to meet the Model Energy Code.
Evaporative
Cooling has lowest consumption, but limited applicability
El Paso Habitat was alone in its use of evaporative cooling,
a move that further reduces simulated energy consumption by approximately
$100 a year under the San Antonio consumption. Data from El Paso
had shown this performance level in the current practice study.
Humidity levels in most of the rest of Texas do not readily allow
for this approach. Thus, while homes using evaporative cooling
in El Paso using the Hp2 specification can expect to use under
$400 a year for all uses, based on the consumption seen in San
Antonio. The San Antonio model has the wider applicability, being
possible anywhere gas is available to the development, with possible
annual costs of $500 for all end uses. The all-electric model
has reduced its consumption to under $600-700 a year for all
end uses, down from a high average of $1,500 a year in Longview
in the current practice review in 1996.
MARGINAL
COST INFORMATION
Marginal cost depends on where the particular builder is starting
from. In several cases, it was clear that the HP2 specification
combined in the plan form or guidebook as recommended was likely
less expensive than what the builder was currently building.
On the other hand, the better windows and other features can
add to cost if the builder is already building at the tightest
possible margin. Because of the HVAC downsizing, it is possible
to reduce the marginal cost of better insulation, windows, doors,
and moisture control features in most cases. Each builder in
Hp2 was compensated $2,000 per unit for participation costs including
energy measures. Other programs currently set a limit of $1,500
per unit for marginal costs for energy measures.
Two of the project builders chose to spend significantly more
than the baseline (San Antonio) house by adding much more glazing
area or adding a large central ducted HVAC system. Habitat and
independent builders are working with local markets, and they
may wish to take a certain approach with full knowledge that
the costs may be greater based on occupant preferences.
Hp2 aimed at demonstrating a benchmark of the lowest first cost
combined with the best overall performance possible. It is always
possible to "solve" energy issues with money - similar
performance can be purchased for approximately $7,000 in the
form of a geothermal heat pump system. But, Habitat cannot afford
this route on a routine basis, so Hp2 focused on getting similar
performance from a system of low-cost changes. |
