It is important to remember that labeling and MEPS programs aim to influence the selection of products by consumers at the point of sale by making higher efficiency units more attractive (through labeling) or by making less efficient ones unavailable (through MEPS). Labeling or MEPS cannot be expected to have any significant ongoing influence on consumers’ use of products once they have been purchased and installed. (more…)

The commercialization prospects for fuel cell vehicles depend not only on their performance and cost, but also on how well they can compete with other technology options that address similar market and policy needs. While market forces have not traditionally motivated design change for reasons of environmental performance, customer values and expectations can evolve and such characteristics could grow in importance. However, inherent market conservatism will favor less disruptive ways to address evolving needs, which might be met by improved gasoline and diesel vehicles, including hybrid-electric versions. Yet looking over the long run, particularly the need to substantially reducing greenhouse gas emissions, hydrogen fuel cells may well provide a solution that is superior to other alternatives. (more…)

The outlook for reductions in future energy use is necessarily based on the potential for increased technological and operational efficiencies. In this section, the outlook for such improvements in large commercial aircraft over the next quarter century is examined.

Engine efficiencies may be improved by between 10 and 30% with further emphasis on moving more mass through engines that operate at higher temperatures and higher pressures. A continuation of the historical trend would lead to a 10% increase in L/D by 2025, and further improvements in the reduction of parasitic drag may extend these savings to perhaps 25%. However, the technologies associated with these improvements have weight and noise constraints that may make their use difficult. (more…)

Energy performance ratings tell what the energy performance of a building is, but if the energy performance of a building is to be improved, the causes of lower than desired performance must be understood, and methods of achieving improved performance must be determined. Causes of variation in energy performance among commercial buildings are understood to a degree, but much remains to be learned. (more…)

Interest in rating the real-life energy performance of buildings has increased in recent years, and the real life efficiency performance rating of buildings is important for any sustainable energy future. (more…)

As the need for energy efficiency becomes more pronounced, the drive toward efficiency in the commercial sector will be impeded by its complicated mix of building sizes and uses, the complicated systems often used in commercial buildings, and the relative lack of understanding of operations factors impacting energy use and how to achieve efficiency. (more…)

ISO document 14040 identifies four areas for using life cycle analysis (LCA) results:

(1) identifying opportunities to improve the environmental aspects of products,
(2) helping industry, governments, and nongovernmental organizations make sound environmental decisions,
(3) selecting relevant environmental indicators for measuring the environmental performance of products, and (more…)

The issues of hydrogen storage run through the hydrogen production, hydrogen transport, supply and demand for end use of hydrogen as an energy sources. (more…)

Current forecasts call for solid growth in world energy use over the next 20 years, potentially increasing 60% above current energy use. With the forces in place to keep energy use patterns the same, a safe, conservative assumption would be that the commercial sector will contribute about 12% to final total energy consumption in the year 2020. (more…)

Fuel efficiency gains due to technological and operational change can mitigate the influence of growth on total emissions. Increased demand has historically outpaced these gains, resulting in an overall increase in emissions over the history of commercial aviation. The figure of merit relative to total energy use and emissions in aviation is the energy intensity (EI).

When discussing energy intensity, the most convenient unit of technology is the system represented by a complete aircraft. In this section, trends in energy use and energy intensity are elaborated. In the following section, the discussion focuses on the relation of energy intensity to the technological and operational characteristics of an aircraft.

Reviews of trends in technology and aircraft operations undertaken by Lee et al. and Babikian et al. indicate that continuation of historical precedents would result in a future decline in energy intensity for the large commercial aircraft fleet of 1.2–2.2%/year when averaged over the next 25 years, and perhaps an increase in energy intensity for regional aircraft, because regional jets use larger engines and replace turbo- props in the regional fleet. When compared with trends in traffic growth, expected improvements in aircraft technologies and operational measures alone are not likely to offset more than one-third of total emissions growth. Therefore, effects on the global atmosphere are expected to increase in the future in the absence of additional measures. Industry and government projections, which are based on more sophisticated technology and operations forecasting, are in general agreement with the historical trend.

Compared with the early 1990s, global aviation fuel consumption and subsequent CO2 emissions level could increase three-to sevenfold by 2050, equivalent to a 1.8–3.2% annual rate of change. In addition to the different demand growth projections entailed in such forecasts, variability in projected emissions also originates from different assumptions about aircraft technology, fleet mix, and operational evolution in air traffic management and scheduling.

We shows historical trends in energy intensity for the U.S. large commercial and regional fleets. Year-to-year variations in energy intensity for each aircraft type, due to different operating conditions, such as load factor, flight speed, altitude, and routing, controlled by different operators, can be 730%, as represented by the vertical extent of the data symbols. For large commercial aircraft, a combination of technological and operational improvements led to a reduction in energy intensity of the entire U.S. fleet of more than 60% between 1971 and 1998, averaging about 3.3%/year. In contrast, total RPK has grown by 330%, or 5.5%/year over the same period.

Long- range aircraft are B5% more fuel efficient than are short-range aircraft because they carry more passengers over a flight spent primarily at the cruise condition. Regional aircraft are 40–60% less fuel efficient than are their larger narrow- and wide-body counterparts, and regional jets are 10–60% less fuel efficient compared to turboprops. Importantly, fuel efficiency differences between large and regional aircraft can be explained mostly by differences in aircraft operations, not technology.

Reductions in energy intensity do not always directly imply lower environmental impact. For example, the prevalence of contrails is enhanced by greater engine efficiency. NOx emissions also become increasingly difficult to limit as engine temperatures and pressures are increased—a common method for improving engine efficiency. These conflicting influences make it difficult to translate the expected changes in overall system performance into air quality impacts. Historical trends suggest that feet-averaged NOx emissions per unit thrust during landing and takeoff (LTO) cycles have seen little improvement, and total NOx emissions have slightly increased. However, HC and CO emissions have been reduced drastically since the 1950s.