Putting It Together Total Primary And Secondary Work

Considering both primary and secondary work, we have arrived at something like Table 4.1. This table incorporates numerous assumptions, of course. The most surprising conclusion is that the exergy efficiency of transportation probably peaked around 1960, when gasoline engines (in the US automobile fleet) operated at higher compression ratios, and wasted much less power on accessories than is true today. Increased fleet average fuel economy since 1970 (discussed later) is not attributable to thermodynamic efficiency improvements at the conversion/transfer level, but to systems optimization. Much the same can be said of improvements in the utilization of heat. Improved performance in domestic and commercial space heating has been due mainly to better insulation and better design. However, since insulation is a normal method of improving heat economy in thermo-dynamic systems of all kinds, we take it into account here.

The end-use allocation by type of work by fossil fuels for the US and Japan were shown above in Figures 4.4a and 4.4b. We can calculate the total work done in each economy by multiplying the exergy consumed by each major category of end-use (work) by the average efficiency with which each type of work, both primary and secondary (electrical), is produced (for example, Table 4.1). Source data are too extensive to reproduce in this book, but they can be found in an earlier publication (Ayres et al. 2003). The estimated efficiencies by type of work are depicted in Figures 4.21a and 4.21b for the US and Japan, respectively. Major differences between the two countries are (1) that biomass plays a greater role in the US than Japan and (2) that hydro-electricity - which is very efficient - dominated Japanese electric-power generation during the first half of the 20th century, whereas it was never the dominant source of electric power in the US.

The total useful work done by the two countries is shown in Figure 4.22. Comparing total work output with total exergy input (including phyto-mass), we obtain the aggregate technical efficiency of exergy (resource) conversion to work in the US and Japanese economies, since 1900 as shown in Figure 4.23. In both countries, the curves are almost monotonically increasing, as one would expect. The overall thermodynamic efficiency of the Japanese economy, as estimated by the same method, is higher than the US case.

Table 4.1 Average exergy efficiency of primary work (percent)

Year

Electric power

Other

High

Medium

Low

Total secondary

generation and

mechanical

temperature

temperature

temperature

electrical efficiency

distribution

work, e.g. auto transport

industrial heat (steel)

industrial heat (steam)

space heat

1900

3.8

3

7

5

0.25

0.52

1910

5.7

4.4

0.505

1920

9.2

7

0.55

1930

17.3

8

0.55

1940

20.8

9

0.56

1950

24.3

9

0.54

1960

31.3

9

0.53

1970

32.5

8

20

14

2

0.54

1980

32.9

10.5

0.56

1990

33.3

13.9

25

20

3

0.575

Year

Figure4.21a Energy (exergy) conversion efficiencies (USA, 1900-2004)

Year

Figure4.21a Energy (exergy) conversion efficiencies (USA, 1900-2004)

Year

Figure 4.21b Energy (exergy) conversion efficiencies (Japan, 1900-2004)

Figure 4.22 Useful work (U) for the USA and Japan, 1900-2004
Figure 4.23 Aggregate efficiencies for the USA and Japan, 1900-2004

Primary work to GDP ratio (eJ/$)

Primary work to GDP ratio (eJ/$)

Figure 4.24 a Primary work and primary work/GDP ratio (USA, 1900-2005)

Primary work to GDP ratio (eJ/$)

Primary work to GDP ratio (eJ/$)

Figure 4.24b Primary work and primary work/GDP ratio (Japan, 1900-2005)

The work/GDP ratio for the US and Japan are also shown in Figures 4.24a and 4.24b, for the case in which biomass exergy is included. We note with interest that, whereas the exergy/GDP ratio does not exhibit a pronounced 'inverted-U' shape, when biomass is taken into account (as noted in Chapter 3), the work/GDP ratio does exhibit such a pattern, a sharp change of slope, with a peak in the years 1973-4. It is tempting to seek an economic interpretation of this peak, although it would lead us astray from the subject of this book.

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