Energy, Emergy, and the City1

Ecotechnology working paper 2016-1c Energy, emergy, and the city1 Erik Grönlund, Morgan Fröling, Torbjörn Skytt Ecotechnology and Sustainable Building Engineering, Mid Sweden University, 83125 Östersund Corresponding Author e-mail: [email protected] Abstract In his book “Environment, Power, and Society” (1971) H.T. Odum introduced a picture of the energy metabolism of a city based on Wolman's paper from 1965 (Sci. Am., 213: 179-190). With the development of the emergy analysis--a branch of energy systems accounting--several authors have contributed to develop quantitative measures of HT Odum’s picture, which from many perspectives are diverging from traditional energy studies. In this paper, studies using emergy analysis to study cities are reviewed. The research regarding emergy and cities had during the period 1975-1995 its focus on cities in the United States, e.g. Miami, Jacksonville, San Francisco and Chicago. The research during 1995-2005 was almost exclusively focused on Taipei. From approximately 2006 up till 2015 the research focus has been on Chinese cities; Macao, Beijing and 37 other Chinese cities have been investigated. But there are resent also studies made on Rome (Italy) and Montreal (Canada). Studies up to about 2007/2008 were generally concerned with understanding spatial aspects of the cities investigated. After that, evaluating the sustainability of cities has become a main research focus. Keywords: Emergy assessment, Spatial distribution, Sustainable city 1 Introduction With half of the world population living in cities, such anthropogenic structures are important to understand. One approach is to extend a more traditional thinking on ecosystems to incorporate also the human society and its technical systems. A central research theme for the systems ecologist H.T. Odum was how ecosystems and general systems can be described from an energy perspective. This was his approach in the seminal research on food webs in Silver Springs, Florida – a cornerstone study in many textbooks on ecology – and in the work with his brother, E.P. Odum, on the coral reefs at the Eniwetok Atoll (Cleveland, 2008). In his book “Environment, Power, and Society” (Odum, 1971) he continued and extended his work applying the energy hierarchies found for food webs of natural systems to systems also including humans. Working with this approach, Odum found systems properties of energy hierarchies of systems including many living organisms that were difficult to deal with using only traditional thermodynamic descriptions of energy flows, developed for describing heat engines and later chemical processes (Giannantoni, 2002). H.T. Odum thus started to develop new concepts to describe the situation he observed, that would later be grouped under the heading Emergy. The latest previous overview of this topic is more than 20 years old (Odum et al., 1995). During the 1 Version 3, 14 April 2016, (version 1 from 30 March 2015 is available in the conference proceedings of the 9th BIWAES conference Energy and Urban Systems, held in Stockholm 4-7 May 2015) 2 Grönlund et al. / Ecotechnology working paper 2016-1c last decade an increasing amount of emergy papers have addressed cities, especially in China. This paper gives a review of how the emergy concept has been used in the context of cities during the whole period of 1971-2015. In section 2 is explained how energy and emergy are related to each other. Section 3 contains the review of the use of emergy in the context of cities, spatial focus, what quantitative emergy related parameters that has been used and underlying research motivation is analyzed. The section is divided into two periods: 1971-1995, earlier described by Odum et al (1995), and 1996-2015. Section 4 contains the discussion. 2 Methods and concepts This study is based on a literature search in the databases ScienceDirect and Springer Link, and on publica- tion lists available at the web site Emergy Systems2. Search terms have been “emergy”, “city”, “cities”, and “urban”. All publications found are reported in Table 3 of this paper, except for a few very short conference papers. 2.1 Energy and emergy Emergy is a concept developed in systems ecology (Odum, 1994, 1996), and is in some ways similar to the concept of primary energy, sometimes used for understanding human constructed technical systems (Arvidsson et al., 2012). In H.T. Odum’s many studies of natural and human ecosystems he had found that describing energy flows by the mass flows and their heating values did not capture all qualitative aspects of the energy hierarchies of the nutrient webs that he could observe. He therefore started to express energy units in terms of the type of energy that generated it. An example used by Odum (1996) was to express coal power plant electricity in terms of how much coal energy was needed to produce it. On average, for the existing technology at that time, it took 4 joules of coal to produce 1 joule of electricity. The electricity from the coal could then be expressed as 4 coal emergy joules (cej). So far this practice is the same as for a primary energy calculation. However, any hard coal or brown coal that can be mined from the ground are in themselves results of complex biogeochemical processes over long time, and originates ultimately from solar energy captured by photosynthesis creating the biomass that eventually has been converted into coal. Thus the hard coal could in turn be expressed in how many joules of solar energy it took to produce it, solar emergy joules (sej). Solar emergy joules is today the dominating unit to express emergy, but in principle any type of energy carrier can be chosen. The calculation is also here similar to a primary energy calculation, with a main difference in that primary energy seldom is calculated further back than through the man made technical systems, whereas emergy generally takes the calculation back through the bio-geo-chemical transformation in nature to the energy inputs to the biosphere, with the main input being the influx of solar radiation (but also gravitational energy generating tidal flows and geothermal heat). A significant conceptual difference to the conventional primary energy calculations (see Arvidsson et al 2012) emerge from its roots in system ecology, though; if an ecosystem converts solar radiation into different types of energy carriers, the whole biological system is con- sidered needed for each of the output, it is not allocated to different outputs (Odum, 1996). H.T. Odum (1996) described emergy as the previous energy it took to generate the actual type of joule, and all of them expressed in one type of energy, almost always solar energy, giving the sej unit. Emergy is often said to be an abbreviation of “energy memory”. This view is relevant in many cases, but sometimes it can be useful to think of the concept as a steady state equilibrium measure where everything is produced in average amounts within the time frame chosen (Grönlund, 2009). In modeling terms this means that no stocks are changed. This is of course almost never the real situation, where stocks of for example wood, or body fat, are used in cyclic or fluctuating patterns, and stocks sometimes built up, sometimes used up. However, the 2 www.emergysystems.org Grönlund et al. / Ecotechnology working paper 2016-1c 3 simplified description of ‘no change in stocks’ can still be helpful to grasp the concept of emergy, since it to some extent diverts from our everyday use of the word energy (where we happily add up different kinds of energies). Odum also introduced the concept Empower, which is the flow of emergy per time unit. Emergy can be used to understand structures of ecosystems - the different form of energy that flows through an ecosystem, and to describe hierarchical patterns created by the living ecosystems channeling energy flows in different ways. Since humans and the human society can be seen as part of ecosystems, or emerg- ing from ecosystems, emergy studies can potentially reveal similar information on human societal artifacts, like cities. Such application of emery studies, especially when applied to cities, is the focus of this paper. 3 Emergy and the city 3.1 The period 1971-1995 Regarding emergy and the city it was addressed already in H.T. Odum’s book “Environment, Power, and So- ciety” from 1971. In a picture (Figure 1-3 in that book, based on Wolman's paper from 1965 the similarities between the energy metabolism of an oyster reef and a city were pointed out. No more explicit discussion on cities was presented in “Environment, Power, and Society”, other than that cities were natural centers, or nodes, higher up in the energy hierarchies of the world. This had not changed in Odum’s second book from 1976, the more popular written “Energy basis for man and nature” (co-authored with Elisabeth C. Odum). Cities was not further described in emergy terms except that the internal internal structure of the city was sketched in Figure 10-2 in that book. However, during these years several references reveal that cities were in focus in H.T. Odum’s research. A young Mark Brown – Odum’s long time coworker for the coming 30 years - wrote a Master's thesis on the subject 1973 (Brown, 1973), and James Zucchetto was also already working on the subject, and his disserta- tion with an urban focus was presented in 1975 “Energy basis for Miami, Florida, and other urban systems” (Zucchetto, 1975a; Zucchetto, 1975b). Mark Brown, during the second half of the 1970s, wrote his doctoral thesis about "Energy hierarchies in urban and regional landscapes", presented 1980 (Brown, 1980).

Load more