4.0 CONCLUSIONS
4.1 General
The most startling result of this study is that total life cycle
energy of a new residential home can be reduced by a factor of
2.8 by making incremental design changes that reduce the embodied
energy, and the use-phase energy consumption of the home. This
was achieved largely with an improved thermal envelope, and an
improved HVAC system, and with energy efficient appliances.
While the main focus of this study was life cycle energy and GWP,
which are closely linked and mostly parallel functions of each
other, mortgage payments are one of the most important factors
to a home buyer. The cost analyses performed in this study were
based on design modifications made to lower life cycle energy.
The EEH model was developed for analytic purposes and would need
more engineering design, and cost analysis before it could be
used in the market place. The analysis does show that despite
a 9.5% increase in the purchase price of an energy efficient home,
lower annual energy expenditures make the present value (discounted
at 4% over 50-years) nearly equivalent to the more energy consumptive
version. Additional sensitivity runs are also needed to find optimal
wall thickness, glazing area, and ventilation parameters, both
in terms of costs, and environmental impacts. Reductions in the
amount of structural framing lumber can also be made.
The applied EEH design modifications employ practices not yet
widely used in the US. References to the Saskatchewan wall system
used fiber-glass, not cellulose insulation. Wood basement walls
lower the embedded energy of the home unit, but most home buyers
might be suspect of wood's ability to last the life of the home.
Wood basements have been built in Michigan for a number of years
however. There is considerable opportunity in the residential
home construction industry for cost effective construction methods
integrating the energy efficient strategies (refer to tables 2-7
through 2-21) discussed in the study.
Given that life cycle energy use and global warming potential
can be reduced by a factor of nearly three without compromising
the home as a financial investment, it is natural to ponder why
it is not happening. Several possibilities are:
- The home buying market does not consider reduction of environmental
burdens as a significant element in evaluating home selection.
- Given that over the life of the home reduced energy costs compensate
for higher financing costs, home buyers, who on an average, move
about every eight years, do not believe the added cost of energy
efficiency will be appraised in future transactions.
- There are no "green" regulatory or market incentives
to motivate property developers.
- There is an insufficient volume of low energy homes being built
to force the home design and construction industries into developing
lower cost, higher efficiency homes. If there was a sufficiently
high volume, the market would quickly focus on the life cycle
energy savings of EEH- type residences.
4.2 Potential Follow-on Research
Several follow-on research projects, building on the work presented
here, are suggested below. Each would need to investigate performance,
life cycle energy and cost.
One EEH scenario increased EEH glazing by 100% to determine natural
gas heating and electrical cooling cost changes. The incremental
cost of installing the windows was $7,000. The additional windows
reduced heating energy due to increased solar heat gain. This
was offset however by an increase in electricity for space cooling.
The combination of heating and cooling costs led to an overall
life cycle cost increase of $360. The present value increase (discount-rate
= 10%) of the additional windows is $2,200. If window replacement
(in 25 years) is factored in, the discounted (10%) present value
increase of additional windows is $4,600. Impacts to GWP were
not calculated.
4.3 Analysis Tools
More thorough cost/benefit design iterations are needed, comparing
functionality, durability, marketability, life cycle energy, and
cost. This requires a greater understanding of the architectural
design and construction process. The spreadsheets developed during
this project combined material quantities, embodied energy data
for specific materials, annual heating and electrical requirements,
life cycle energy, GWP data, and cost. These were somewhat cumbersome
to use, and made analysis of design changes time consuming. Needed
is a software program designed to allow greater flexibility in
comparing various options while keeping track of different scenarios
and maintaining consistency of units.
Such an ideal product would have the following features:
Development of a software program that meets these overarching
requirements would be costly. But without it, the process of assessing
design changes in terms of life cycle energy and cost, are extremely
laborious and prevent many architects from doing so.
FOOTNOTES
[83] "Energy-10, Release 1.2" - January
1998, Passive Solar Industries Council, 1511 K Street, NW, Suite
600, Washington D.C. 20005
[84] "3D Home Architect® DELUXE", Copyright 1993-1997,
Broderbund Software, Inc. and Advanced Relational Technology,
Novato, CA
[85] AutoCAD®, Copyright 1998, Autodesk, Inc., San Rafael,
CA
[86] Kiley, M.D., Allyn, M., "1997 National Construction
Estimator, Labor & Material Costs, Manhours and City Cost
Adjustments For All Residential, Commercial and Industrial Construction",
Craftsman Book Company, Carlsbad, CA, 1996
[87] Building for Environmental and Economic Sustainability software
(BEES), National Institute of Standards and Technology, April
1998, U.S. Green Building Council, San Francisco, California
[88] Life-Cycle Advantage™, Batelle
End of section 4.0 Conclusions
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Last updated October, 9th '98, National Pollution Prevention Center