Measures of Environmental Performance and Ecosystem Condition (1999) / Chapter Skim
Currently Skimming:
Life-Cycle Analysis:
Life-Cycle Analysis:
Net Energy Expenditure: A Method for Assessing the Environmental Impact of Technologies
Pages 13-28
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 13... ...
Life-Cycle Analysis
|
From page 15... ...
In other words, it is often difficult to select a valid approach to compare the environmental advantages of very different technologies, even when they are used to accomplish similar functions. Various factors such as usefulness, convenience, aesthetics, or the production of waste could be used to weigh the value of parallel technologies; however, a comparison of the net energy expenditure may be the most useful measure for judging environmental performance.
|
From page 16... ...
Multiplying this by the fractional efficiency of the gasoline-powered car produces an overall efficiency for this system of 0.17. The relatively low efficiency of thermal electricity generation coupled with losses in fuel production and delivery, and electricity lost during transmission, gives an overall efficiency for delivered electricity of about 0.24.
|
From page 17... ...
. Dotted-line boundaries encompass the fractional efficiencies restricted to automotive options, suggesting that the electric automobile, at 0.64 fractional efficiency, is more efficient than the gasoline-powered automobile.
|
From page 18... ...
However, care must be taken to select the appropriate data. For the production of glassware, for example, published sources give energy requirements ranging from 9.1 to 79.1 J/g of glass, each correct for the particular boundaries and production conditions considered (Table 1)
|
From page 19... ...
79.1 Gas–air firing, melting only aEstimated primary fuel requirement from an electrical requirement of 1 kWh per 1.18 kg of glass. bElectrical energy required is multiplied by 3, assuming a 33 percent efficiency of thermal electricity generation (see text)
|
From page 20... ...
Three reusable cup types -- ceramic, glass, and reusable polystyrene -- and two disposable cup types -- uncoated paper and molded polystyrene foam -- are considered. For the plastic cup types, the boundaries for evaluation included the total energy required -- from the extraction of crude oil to production of the final product; for the paper cup, they included the total energy required to produce a finished cup from a standing forest; and for the glass and ceramic cups, they included the energy required to process the raw materials and to produce the finished cups.
|
From page 21... ...
On this basis, the very low mass of the molded polystyrene foam cup required the least total energy to produce, 198 kJ/cup, and the ceramic cup the most, at 14,088 kJ/cup. Energy of Reuse Most of the electrical energy required for dish washing goes to heat the water, which must be hot for effective cleaning.
|
From page 22... ...
For the disposable cup types used only once before discard, the energy consumption per use is the energy required to manufacture the cup. For a single use, all three types of reusable cups consume more than 10 times the energy per use than do either of the disposable cups.
|
From page 23... ...
could any of the reusable cups be a better energy value. The 278 kJ required to wash a reusable cup with an efficient dishwasher in the United States is less than half of the energy needed to make a paper cup.
|
From page 24... ...
For this hypothetical scenario, then, recycling these materials entails energy costs equal to about one-fourth those involved in using virgin material for both plastic cup types and two-fifths of that required if virgin material is used for the paper cup. The larger fractional benefit of recycling plastic cups is due solely to the larger intrinsic energy content of polystyrene.
|
From page 25... ...
But the analysis revealed that the break-even points are not as sensitive to changes in this parameter (the fabrication energy of the reusable cup types) as they are to the energy required for washing and sanitizing the reusable cups or fabricating the disposable cups.
|
From page 26... ...
In this way, it is possible to identify the factors most important for decreasing the energy consumption of a technology. In the cup example, sensitivity tests demonstrated that the significant factors were the energy requirement for washing reusable cups and the fabrication energy for the disposable cups.
|
From page 27... ...
In Figure 5, System A, which could represent one of the reusable cups, has a high aesthetic rating but also high energy costs and emission loadings. System D, which could represent a disposable cup, has a low aesthetic rating but ecologically favorable low energy costs and low emission loadings.
|
From page 28... ...
1979. Energiebedarf bei der Herstellung und Verarbeitung von Kunststoffen.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.