Environmental Engineering Reference
In-Depth Information
stores, restaurants, hotels, motels, and industrial buildings
need 10-13 GJ/m
2
, and hospitals and office build-
ings need 18-20 GJ/m
2
, mainly because of more metals
in structures, elevators, and finishing (EIA 1998). A
detailed analysis of two Hong Kong high-rise designs
showed energy costs of 6.5-7 GJ/m
2
, with steel ac-
counting for about 70% of the total (Chen, Burnett, and
Chau 2001). As a result, a five-story building with 75
apartments embodies as little as 25 TJ, a luxury 30-story
building with 1000 m
2
/floor needs 300 TJ. As expected,
life cycle assessments show lower shares of embodied en-
ergy for buildings in colder climates. For a large 200-m
2
Canadian house that uses about 25 W/m
2
for heating
and lighting (see section 9.3) and embodies about 1.5
TJ, the ratio of construction to operation energy will
be only 0.16 over a 50-year period. For detached and
semidetached houses in temperate climates, the ratios
are 0.3-0.4 and rise to more than 0.75 for superinsulated
structures (Mithraratne and Vale 2004; CWC 2004).
After a house, the second most valuable possession of
modern households is a car. Steel components have tra-
ditionally made up the largest proportion of a car's mass
and hence of its energy cost. Berry and Fels (1972) put
the average late-1960s American car production cost at
about 134 GJ, or roughly 85 GJ/t. Several opposing
trends have been at work since that time. Continuing
substitutions of steel and iron by aluminum, plastics,
ceramics, and composites have introduced increasing
amounts of lighter but more energy-intensive materials.
Cast or machined aluminum and its alloys (see section
10.2) are at least four times, and up to eight times,
more energy-intensive than most steel components, and
the plastics used in cars typically require about 100
GJ/t, or two or three times as much energy as rolled
steel.
The declining energy costs of steel and other basic
materials have lowered the specific energies of major
inputs, and robotic assembly has further lowered produc-
tion costs, but these gains have been largely negated by
the increased average mass and power of passenger cars.
U.S. data show a steady post-WW II increase in the av-
erage mass of passenger cars to nearly 1.8 t by the mid-
1970s, followed by a decline to 1.35 t by 1986, and
then by steady growth to 1.49 t by 2004 (NHTSA
2005). This trend was reinforced by rapid market pene-
tration of vans, light trucks, and SUVs (mostly in excess
of 2 t/vehicle), and it has prevented any notable declines
in the specific energy cost of car making.
During the 1990s total energy needed to produce car
body parts from steel sheet was about 65 GJ/t for pri-
mary metal and 52 GJ/t for recycled steel (Stodolsky
et al. 1995). An LCA of a 1990 Ford Taurus (1.4 t) put
the vehicle's embodied energy at 120 GJ, or 86 GJ/t, a
rate virtually identical with the typical value for the early
1970s (MacLean and Lave 1998). At the turn of the
twentieth century, it still cost 100-125 GJ to produce
most North American passenger cars. A medium-sized
(1.3 t) five-passenger car requiring 110 GJ to produce
would consume (at nearly 8 L/100 km) about 50 GJ of
fuel and oil annually, and hence its production cost
would be only about 16% of its ten-year lifetime energy
cost of about 680 GJ, including about 80 GJ for spares,
repairs, garaging, and road maintenance. Less fuel-
efficient cars and longer service can lower the share of
embodied energy to as low as 10% of the vehicle's life-
time energy cost.
Even small European cars have become heavier as the
average mass of a typical vehicle increased from about
0.8 t in 1970 to 1.2 t by 2003. In North America lighter
but more energy-intensive materials have been used to
