1.0 INTRODUCTION
1.1 Overview
Annually, 24 % percent of the natural gas, and 35% of the electricity
in the US, is consumed by the residential housing sector [10,
11]. As a result, 1.3 million metric tons of green-house gases
are emitted annually. This is equal to 31% of the green-house
gases emitted from electricity and natural gas consumption by
all sectors in the US.
The above figures represent energy consumption and emissions data
for residential utility services. Of these, natural gas and grid
electricity combine for over 90% of all energy used for space
and water heating, lighting, ventilation and appliances in 1990.
Coal, fuel oil, wood, and liquefied propane gas account for the
remainder. In 1994, CO2 emissions associated with the
residential housing sector contributed approximately 19% of total
CO2 emissions released by all US sectors combined [12].
What is conventionally not considered in determining residential
energy consumption is the energy required to make building materials
and home appliances. This is the energy required to extract the
raw materials (mining, oil extraction, timber cutting), refine
those resources (smelting, refining, cutting), and manufacture
ready-to-use construction materials. This last item, for example
includes extrusion, molding, punching and assembly of metal, plastic,
and other material into usable shapes, as well as combining different
materials into composite forms such as windows, doors, pre-assembled
panels, floor coverings, electrical and plumbing fixtures, and
the many appliances found in modern homes.
Life cycle analysis (LCA) quantifies the environmental impacts
caused by the energy and material flows in all stages of a product's
life cycle. Some of the impact categories widely used to compare
product systems are global warming potential (GWP), ozone depletion,
nutrification, acidification, and ground-level ozone creation
potential. In LCA research, the product system being investigated
is structured into several stages [13]. Conventionally, these
are 1) raw material acquisition, 2) parts fabrication, assembly,
and construction, 3) use, and 4) retirement (or end-of-life).
Life cycle assessment is commonly referred to as a cradle-to-cradle
analysis because it looks at all inputs and outflows in a product
system over its entire life history. In a full LCA, all inputs
(material, energy, water) and outflows (air and water emissions
and solid wastes) are accounted for. In this project, only primary
energy and the global warming potential (GWP) will be evaluated.
Primary energy is the energy that is embodied in resources
as they exist in nature: the chemical energy embodied in fossil
fuels or biomass, the potential energy of a water reservoir, the
electromagnetic energy of solar radiation, and the energy released
in nuclear reactions. For the most part, primary energy is not
used directly but is first converted and transformed into electricity
and fuels such as gasoline, jet fuel, heating oil, or charcoal.
This statement applies to raw material extraction, transportation,
manufacturing and home energy consumption as well.
While quantification of resource consumption, water emissions
and solid waste resulting from material manufacturing and product
use are important, the project scope focused on primary energy
and GWP, which are two important indicators of the overall environmental
impact of home construction and use. Using a similar approach,
life cycle costing is used to determine all costs in monetary
terms associated with a product. The life cycle costs in this
study are all costs borne by the owner. These include all finance
costs associated with:
Understanding energy consumption, GWP, and cost from a life cycle
perspective is essential if a systematic and comprehensive reduction
of environmental impacts is desired. All three are linked. Changes
to the energy intensity of building products will change the GWP.
Reductions in home energy consumption will reduce utility costs
and GWP. Use of building materials with lower embodied energy
may or may not affect use phase energy. Accordingly, an inventory
of the product's life cycle, identifying mass and energy flows,
helps in understanding the complexity of the various interactions.
1.2 Purpose of Study
The goal for undertaking the project was to determine the relationship
between material production/construction (pre-use) phase energy,
and use phase energy, as energy efficiency strategies are applied
to various home systems. It is commonly believed that to achieve
higher energy efficiency, more materials are needed in the initial
construction. Thicker walls are needed obtain lower thermal conductance
properties (i.e., higher R values). More windows of higher quality
optimize solar heat gain. Additional internal thermal mass is
required to allow for temporary storage of the increased solar
heat for release at night. While these energy efficient strategies
lower the building's heating fuel requirements, it is not entirely
intuitive whether they actually lower total life cycle energy
consumption. For example, is the additional energy required to
manufacture the glass for more windows recovered with lowered
heating requirements?
Other research questions to be addressed in this study include:
1.3 Similar Studies
FOOTNOTES
[10] "Table 8.9 Electric Utility Retail Sales
of Electricity by End-Use Sector, 1949-1997", Energy Information
Administration, Office of Energy Markets and End Use, U.S. Department
of Energy, <http://www.iea.ord.gov/pub/energy.overview/aer/aer0809.txt>,
8/13/1998
[11] "Table 6.6 Natural Gas Consumption by Use Sector, 1949-1997",
Energy Information Administration, Office of Energy Markets
and End Use, U.S. Department of Energy, <http://www.iea.ord.gov/pub/energy.overview/aer/aer0606.txt>,
8/13/1998
[12] "Annual Energy Review 1994, July 1995", DOE/EIA-0384
(94), Energy Information Administration, Office of Energy Markets
and End Use, U.S. Department of Energy, Washington, DC 20585,
pg. 337
[13] Life Cycle Assessment: Inventory Guidelines and Principles
(EPA 600/R-92/245). Cincinnati, OH: U.S. EPA, Office of Research
and Development, Risk Reduction Engineering Laboratory, February
1993
End of section 1.0 Introduction
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0.0 Abstract and Executive Summary
2.0 Methods
3.0 Results
4.0 Conclusions
Last updated October, 9th '98, National Pollution Prevention Center