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close this bookUnited Nations University - Work in Progress Newsletter - Volume 12, Number 1, 1989 (UNU, 1989, 12 pages)
View the document(introductory text...)
View the documentSustaining the Earth
View the documentAnticipating global trends: Aspects of UNU work for the period 1990-1995
View the document'An uncontrolled global experiment...'
View the document'A little breathing space': Report from the Budapest
View the documentEnergy savings: Sooner much better than later
View the document'The rich get richer...'
View the documentOld wine in new bottles?
View the documentTectonics of the desert cities
View the documentMan in the mangroves
View the documentDiverting the Nile
View the documentLosing the soils of Africa
View the documentIn fairness to the future

Energy savings: Sooner much better than later

By Robert U. Ayres

Conventional development wisdom has it that energy input is essential to economic growth. Not so, says Robert U. Ayres in taking issue with what he calls this "important misconception. " The basic services needed by most people, he argues in this excerpt from the paper he presented at the Tokyo symposium on the Human Response to Global Change, could be delivered with only "a very small fraction" of the energy now commonly used in the industrialized nations. He feels that innovative ways to conserve on energy use are therefore extremely important to consider. He bolsters his case with examples from the United States, one of the globe's most voracious energy consumers. Dr. Ayres is a member of the Department of Engineering and Public Policy at Carnegie-Mellon University, Pittsburgh, Pennsylvania, USA. - Editor

To address realistically the question of energy efficiency in the US economy, it is helpful to view the economic system as a sequence of energy conversions: beginning with raw materials extracted from the environment and ending as wastes returned to it. At each stage of the production process, energy is dissipated - as materials are identified, separated, purified, alloyed, shaped, assembled into products or systems, and operated to deliver services.

Some amount of energy dissipation - or entropy - is associated with each stage of conversion or transformation. Two questions need to be considered: first, how much energy is utilized at each stage as the system functions today? And, second, what is the minimum amount of energy that would be required to accomplish the same transformation or conversion in an ideal no-energy-loss world?

Unfortunately, many estimates consider only the initial energy conversions stages: (1) fuel combustion and (2) electricity generation. In addition, they often use inconsistent and misleading measures of efficiency. As, for example, when claimed "heating energy efficiency" really refers to the chemical energy converted into heat and delivered to the walls of the furnace. The purpose of heating is not to heat the furnace walls, but to heat the room. The fact that a high degree of the energy available is delivered to the furnace walls at 1,000°F. is essentially irrelevant. The question is not which is the most efficient technical scheme, but, rather, what is the least amount of chemical energy in the form of fuel? If one cares about using as little fuel as possible to deliver a given amount of warm air to a given point of use, then efficiency has to be measured differently.

Space Heating

Consider the heating of homes, working places and other areas - space heating - which accounts for 20 per cent of energy use in the United States. It exemplifies the subtlety of problems in estimating the efficiency of providing services to the final consumer.

It appears to be technically feasible - by taking advantage of the principles of co-generation and using heat pumps - to build central heating systems up to 10 times more efficient than current ones. But this is only half the story: we also must consider the heat actually delivered to rooms versus the minimum amount needed to make people comfortable. That amount depends on the efficiency with which heat is retained in the room - on insulation and ventilation. The major US energy savings in space heating over the past 15 years have resulted almost entirely from improved insulation, not from more efficient furnaces.


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From a number of studies and demonstrations in many countries, it is now clear that virtually all use of fossil fuels for energy for space heating could be eliminated in a properly designed and insulated house - simply by making use of the solar heating available through windows and the waste heat generated by the electrical appliances such as the refrigerator. Obviously, such a house would cost more to build than a "conventional" house - but it would also cost much less to operate. The trade-off between capital and operating costs is one that public policy can influence.

Cooling and Refrigeration

Cooling and refrigeration account for 2.5 per cent and 2 per cent respectively of total energy consumed in the US, both uses at very low energy efficiencies (4 to 5 per cent). Again the amount of cooling required is a function of insulation and system design. In a new, well-insulated building, through use of overhangs, reflective windows, shades and other devices to minimize heat in hot weather, the need for air-conditioning can be drastically reduced. Obviously, fixing existing buildings is much harder, but substantial improvements are still possible.

Refrigerators are becoming considerably more efficient, but are still designed more for convenience and appearance than for efficiency. The need for refrigeration to preserve food is unlikely to be eliminated completely, but - In principle - it can be sharply reduced over time by gradually increased use of new technologies such as sterile packaging. The fact that fluorocarbons, which are used as refrigerants, are now known to be a responsible factor for the ozone depletion problem in the stratosphere may eventually result in regulatory pressures that will work in favour of alternatives.

Does Hotter Water Clean Better?

Cooking and washing account for 1.3 per cent and 4 per cent respectively of total energy consumption. Again, studies have produced often irrelevant data. The thermodynamic efficiency of converting cold water into warm water at the spigot does not reflect the efficiency of hot water use. The latter is extremely low in most washing machines and dish-washers due to repeated rinses with hot water, which appears to be attributable to a popular prejudice that hotter water "cleans better." In fact, there is probably no physical reason to use hot water at all for dish-washing and laundry purposes, given the availability of effective "cold water" detergents. Lavish use of hot water for personal baths and showers can also be sharply reduced by means of water-conserving shower nozzles, already standard in Europe.

The Heat in the Kitchen

Conventional cooking with open gas burners or in ovens uses heat very inefficiently. A great deal of the cooking involves heating metal pots, which later reradiate the heat to the room. Kitchens, as we all know, do get hot! In addition, most foods are overcooked, at least in a technical sense. Microwave ovens that heat only the food are a remarkable advance, though probably no better than 10 per cent overall. Their greatest benefit may be controllability and reduced overcooking.

Automobiles: The Great Energy Guzzlers

Automobiles account for 13 per cent of national energy consumption. Trucks, buses, railways, barges and aircraft add, perhaps, another 10 per cent. The energy efficiency of the US transport sector has been estimated by a number of studies at about 25 per cent. This is based, roughly, on the average thermal efficiency of internal combustion engines - common to all these means of transportation.

Since the early 1970s, there have been useful savings in several areas of transport. The average mileage for US cars in 1972, for example, was about 14 miles per gallon (mpg); it is over 28 mpg today. A number of factors contributed to this. Radial tires "flex" much less than the tires used in the 1960s with measurable fuel savings. Better aerodynamic design has reduced air resistance.


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Microprocessor controls help the engine run closer to optimal speeds and help the transmission to change gears at the optimal points. Much of the improvement so far is due simply to removing excess weight from the vehicles - average vehicle weight is down about 1,000 lbs since 1970. Nonetheless, there is still plenty of room for improvement.

Several manufacturers now produce cars capable of getting better than 50 miles per gallon, and some now regard 100 mpg as within reach, making more use of light metals and stronger plastics. An average of 100 mpg would constitute a seven-fold improvement for the US auto fleet over 1970. Yet the overall efficiency of personal transportation would still only be something like 7 per cent! There can be little doubt that automobile transportation, as is true with most other areas of energy use in the US, remains extremely inefficient and that there is still enormous scope for further savings.

More Active Conservation

All of which, I believe, support the case for a more active approach to energy conservation, based on deliberate development of new technologies, as a viable alternative to policies aimed at increasing the domestic supply of energy.

Domestic considerations apart, there are three powerful reasons for adopting this approach. The first relates to national security. A policy of active conservation is the best way, and may be the only way, of avoiding another and more severe "oil crunch," and becoming entangled ever more deeply with incompatible political and military commitments in the volatile Middle East.

The second reasons for US policy-makers to be concerned is that conservation offers the best hope for economic development in the non-OPEC Third World, which will otherwise be competing with the industrialized West for limited supplies of petroleum.

The third reasons for adopting the active conservation approach is that cutting back sharply on the global combustion of fossil fuels is the only way to reduce the severity of the projected "greenhouse effect." Another, but far from negligible, environment problem is acid rain, also attributable to fossil fuel combustion.

I believe that gross energy consumption in the US need never in the future be larger than it is now. The energy/GNP ratio has been declining for many years now - and, provided we adopt sensible policies, it will continue to decline even as GNP continues to grow. To achieve this, the energy supply will have to gradually shift away from the present mix, which is roughly 90 per cent based on fossil hydrocarbons, to a future mix of renewable sources, including hydroelectric, wind, geothermal, biomass and solar power. The shift away from fossil fuels - and toward less energy use generally - will probably occur sooner or later, no matter what actions the government takes. But, for a number of reasons cited in this paper, sooner is obviously a lot better than later.