Article pubs.acs.org/est
Ecological Accounting Based on Extended Exergy: A Sustainability Perspective Jing Dai,† Bin Chen,*,† and Enrico Sciubba‡ †
State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China ‡ Department of Mechanical and Aerospace Engineering, University of Roma 1, La Sapienza, via Eudossiana 18, 00184, Roma, Italy S Supporting Information *
ABSTRACT: The excessive energy consumption, environmental pollution, and ecological destruction problems have gradually become huge obstacles for the development of societal−economic−natural complex ecosystems. Regarding the national ecological−economic system, how to make explicit the resource accounting, diagnose the resource conversion, and measure the disturbance of environmental emissions to the systems are the fundamental basis of sustainable development and coordinated management. This paper presents an extended exergy (EE) accounting including the material exergy and exergy equivalent of externalities consideration in a systematic process from production to consumption, and China in 2010 is chosen as a case study to foster an in-depth understanding of the conflict between high-speed development and the available resources. The whole society is decomposed into seven sectors (i.e., Agriculture, Extraction, Conversion, Industry, Transportation, Tertiary, and Domestic sectors) according to their distinct characteristics. An adaptive EE accounting database, which incorporates traditional energy, renewable energy, mineral element, and other natural resources as well as resource-based secondary products, is constructed on the basis of the internal flows in the system. In addition, the environmental emission accounting has been adjusted to calculate the externalities-equivalent exergy. The results show that the EE value for the year 2010 in China was 1.80 × 1014 MJ, which is greatly increased. Furthermore, an EE-based sustainability indices system has been established to provide an epitomized exploration for evaluating the performance of flows and storages with the system from a sustainability perspective. The value of the EE-based sustainability indicator was calculated to be 0.23, much lower than the critical value of 1, implying that China is still developing in the stages of high energy consumption and a low sustainability level. countries and sectors;5,6 their purpose was 2-fold: to disclose the latent productive or consumptive structure of societies in a completely thermodynamic sense and to identify the priorities that should be in place during the development or restructuring of specific sectors to establish better resource management. Sciubba proposed extended exergy that was built on Wall’s approach by extending the traditional exergy analysis to consider two of the primary production factors that are included in neo-classical economics (namely, labor and capital).7 Moreover, to better understand the application of exergy in a comprehensive ecological, social, and environmental analysis, the exergy accounting boundary should be updated by taking both ecological and environmental factors into account.8 Therefore, an ecological assessment of resource depletion
1. INTRODUCTION Exergy is physically defined as the maximum work that is performed by a system in the process of reaching a state of equilibrium with its surroundings. Originally, it was developed in the field of engineering with the purpose to solve problems related to use value of the cost-optimization procedures in energy conversion systems and energy policies. Due to its functional role as a rational and rigorously founded thermodynamic quantification of the consumption of natural resources, exergy has been widely used in the fields of process optimization, resource accounting, and environmental impact assessment.1 In recent decades, society has been considered to be a particular thermodynamic system, and as such, it is analyzed with exergy analysis to gain insights into its energy/ resource utilization efficiency and its potential for improvements.2 This application of the exergy method was first introduced by Reistad3 in 1975, whereupon it was carried forward by Wall4 to analyze the useful efficiency of various energy-consuming systems and sectors in the US. Subsequently, a series of similar analyses has been performed for different © 2014 American Chemical Society
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finally, there is a brief discussion about embedded connotation of the exergy-based sustainability evaluation.
levels, social influence, environmental impact, and regional sustainability can be fulfilled by means of exergy analysis. From the beginning of exergy-based measurements, exergy, which was closely related to use value, was combined with economic analysis to quantify the costs of exergy-related destruction and losses and, hence, the costs of products. Subsequently, Lozano and Valero9 proposed the theory of “Exergetic Cost”, which is based on both economic and thermodynamical aspects and has frequently been employed, e.g., in the works of Tribus and Pezier,10 Gaggioli and Wepfer,11 and Tsatsaronis,12 and this capitalizing method has been expanded to include meaningful analyses within the human species and natural world.13 Afterward, the concept of “Exergo-ecological Cost” was proposed in the works of R.U. Ayres and L.W. Ayres,14 Cornelissen,15 and Szargut and Morris16 as a complementary tool that can be used in an exergetic life-cycle analysis to ascertain the whole process exergy of a product or service, the environmental emissions, and the technological process of replacing materials. Additionally, Szargut et al.17 recommended using “Cumulative Exergy Consumption (CEC)” as an ecological indicator to quantify those exergy losses that are connected with the fabrication process. In an attempt to bridge the gap between industrial ecology and systems ecology, Hau and Bakshi18 developed a novel network and allocation algorithm to expand the CEC analysis into “Ecological Cumulative Exergy Consumption (ECEC)”. Meanwhile, Dewulf et al.19 introduced Cumulative Exergy Extraction from the Natural Environment (CEENE) as a comprehensive life cycle impact assessment method for resource accounting, which owns some strong points in addressing the substitutability issues compared with the conventional exergy analysis method. Meanwhile, Jørgensen and Mejer20 put forward “Eco-exergy” to measure the available energy that is invested and/or the information that is coded by an ecosystem context where boundary growth, biomass growth, network growth, and information growth are involved. In general, pioneered by Reistad and improved by Wall, Szargut, Sciubba, and Jørgensen, the exergy analysis method has considered a society in its entirety to be a huge “transformer” that consumes resources from the environment and discharges waste into it via its production sectors and consumption terminals. This paper aims to gain an understanding of sustainability in a social consumption system using Extended Exergy Analysis (EEA) that is acknowledged to be a comprehensive tool for assessing the development of a socio-economic system. Herein, we present a methodological foundation by adding systematic and quantized applicabilities to the preexisting objective system. The rest of this paper is arranged as follows: the basic methods that can be used in the present work and some descriptions of the social consumption system’s boundary are introduced in Section 2. In Section 3.1, we conduct the accounting for extended exergy fluxes with an internal analysis of Chinese society in 2010 and use an ecological methodology to obtain a more comprehensive description of it. Furthermore, the adjusted models are used to calculate the externalitiesequivalent exergy. In Section 3.2, we propose the basic extended exergy-based indices with respect to the sustainability of the ecological system based on Extended Exergy Analysis. In Section 4 (the first two paragraphs) and also in Figure S5 (Supporting Information), some fundamental aspects of both exergetic analyses and sustainability studies are interpreted, and
2. MATERIALS AND METHODS 2.1. Accounting Method. Initially proposed by Sciubba, EEA is a socio-economic construct with biophysical references, with extended exergy (EE) values being assigned to labor and capital fluxes in addition to thermomechanical and chemical exergy values.8 The calculation of an EE value (in Joules) is formulated as follows: EE = CEC + EC + E W + E R (1) where CEC represents the cumulative exergy consumption, EC is the exergy equivalent of monetary fluxes, EW is the exergy equivalent of human labor, and ER represents the environmental cleanup or remediation cost in terms of exergy. In eq 1, the EE value includes two phyletic contributions, in which CEC and ER are acquired on a material basis while EC and E W originate from human dominated behavioral dedications. Specifically, the natural resources-based material exergy (namely, CEC) is defined by Szargut et al.,17,21 which expresses the cumulative exergy consumption (including both primary resources consumption and secondary manufacturingrelated material input);22 CEC is quantified by calculating the transformation factors as their lower heating values. For the evaluation of ER, EEA uses an innovative strategy to explain the treatment of pollutants. This strategy is to estimate the added equivalent exergy by calculating how much energy would be required to remove the pollutants that the studied process creates. Thus, the environmental emission-equivalent exergy can be regarded as ‘‘environmental externalities’’ or as the ‘“environmental disturbance”’. In addition, EC and EW have been modified by Sciubba23 by introducing the coefficients α and β to reflect the influences of human development level. The Human Development Index (HDI) measures a society’s or human’s basic requirements for survival, and usually, this index takes the population size, currency liquidity, and working intensity into account. The computation models are expressed in eqs 2−5: E W = α × E in
(2)
EC = β × E W
(3)
α=
β=
f × esurvival × Nh E in
(4)
M2 s × NW × W
(5)
where Ein is the primary energy that is used to sustain the total population of a society so that it can generate labor. The variable f is a correction factor that is related to the standard of living; esurvival (in units of J/(person × day)) represents the exergy consumption that is needed for human survival; Nh (in units of persons) is the system’s population. Additionally, M2 represents the supply of general capital in an economic market or business activity, and this variable is intended to reflect the social changes of the total demand and inflation pressure. Because of its low liquidity, M2 refers to a country’s money supply. Furthermore, Nw is the workers’ population (the economically active population), s (in units of RMB/(person × year)) is the total average wage for the economically active population, and W (in units of 2000 h/(person × year)) is the 9827
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average workload. Moreover, α and β are directly introduced to model the fraction of the primary exergy that is embodied in labor and labor’s overall fraction of a society’s exergy that is embodied in capital, respectively. 2.2. Accounting Decomposition and System Boundary. The societal accounting, initially proposed by Wall,4 focuses on the cross-section from the resource base to end-use sectors. This method indirectly followed the approach that was originally suggested by Szargut24 and was improved by both Ertesvåg25 and Milia and Sciubba,26 who divided the society into seven subsystems that interact with their environment and labeled all the fluxes of matter and energy in a manner like metabolism process. Furthermore, Utlu and Hepbasli 2 presented an illustration of the energy fluxes throughout the utility, natural resources, transportation, industrial, residential, commercial, and agricultural sectors. Chen and Chen27 established a pyramidal scheme that consists of seven sectors, and their goal was to reveal the exergetic consumption structure of a society. Later, Dewulf et al.28 schematically represented the exergy fluxes that occur between a society and the environment by simultaneously considering the inputs and outputs balance. In this study, we have further modified this framework to show how the extended exergetic perception of a society corresponds to its individual socio-economic characteristics. The detailed accounting decomposition and the boundary of this very large complex system are explained in the Supporting Information in Part 1 and Figure S1. 2.3. Database Construction for the EE Account. Using the previously mentioned descriptions of different compositions in EEA, we construct a database for the EE accounting based on the flow decomposition in Figure S1, Supporting Information, gathering data on energy, resources, and primary and secondary material products from subsistent studies. This attempt was made to unify or normalize the EE accounting framework that can be further used in national-scale and sectoral-scales. Table 1 is the material-based exergy database of the energy that comes from the environment and enters the social consumption system through the production sectors (the EX,
CO, and AG sectors); the detailed sector decomposition, system boundary, and the sectoral acronyms are demonstrated in the Supporting Information, Part 1. In summary, natural resources’ inputs are decomposed into three categories: first, Z1 represents the exergy that is contained in the multitudinous mineral resources and types of energy that are extracted by the production sector. This extraction provides the most available energy source in large-scale social systems. The second essential exergy flux is Z2, which is connected to both the natural environment and CO sector. This flux primarily accounts for the introduction of renewable energy and resources from the environment into the target system. Third, the food flux is labeled Z3, which is a substantial provider of humans’ physical survival and the industrial raw materials that are extracted from nature. The material-based exergy flux data are enumerated in the Supporting Information (Part 3), and the values of the specific exergy have been calculated by Szargut et al.21 as reported in Tables S1 and S2 in the Supporting Information. 2.4. Settings for Indices. Sustainability is about human values, which are sometimes simplified in the form of “desirability” determined by a subject (agent, like people or groups with various interests), object (to sustain), and the necessity or importance or cost that needs measuring or valuation by specific metrics. Via a systemic analysis of the relationships between the components of a system’s web, the flows of energy and other resources that converge to produce output (e.g., products, service, and utilities) can be evaluated on a common basis.29 Those indices and ratios that are based on exergy flows can be calculated and used to evaluate the behavior from the systematic perspective. However, although exergy is one of the pure thermodynamic measures, it is dependent upon descriptive science, which is not suitable for studying the sustainability issue as a normative science. Nevertheless, EEA is appropriate for the identification of available energy with the revisit of labor theory of value that shed light on feasibility of the unified metric in a very large complex system (namely, VLCS in the following description).30,31 In addition, when the externalities-equivalent exergy is assessed, the production factors such as labor and capital and the state of the environment are highlighted in the EEA framework, where they are linked with thermodynamics-based analyses; EEA may thereby contribute to sustainability studies. Extended exergy-based indicators offer effective sustainability metrics for evaluating the utilization of resources and energy and quantifying the side effects of the ecological and economic behaviors in VLCS. Table 2 contains the six basic extended exergy-based indices for the evaluation of VLCS with respect to a system’s performance from a sustainability perspective. 2.5. Data. The data were collected from the standard yearbooks that are compiled by the central government of China and its subordinate ministries. Detailed data from the individual sectors can be obtained from the ministry yearbooks (2011), e.g., China Agricultural Yearbook (CAY), China Food Industry Yearbook (CFIY), China Forest Statistical Yearbook (CFSY), and China Statistical Yearbook (CSY)32−35 for the AG sector; CSY, China Energy Statistical Yearbook (CESY), and China Foreign Economic Statistical Yearbook (CFESY)35−37 for most sectors; China Iron and Steel Industry Yearbook (CISIY) and China Iron and Steel Industry Yearbook (CISIY)38,39 for the IN sector; CSY and China Mining Yearbook (CMY)35,40 for the EX sector; and CSY and China Transportation Yearbook (CTY)35,41 for the TR sector; China
Table 1. Natural Resources Input Flux through Production Sectors flux symbol Z1 (to EX) input from natural resources
fuels
wind
ores
geothermal heat for electricity generation geothermal heat for direct use hydropower water coke motor gasoline gas/diesel heavy fuel oil other petroleum products electricity biofuel CHP heat geothermal heat
minerals waters output into the social system inside
Z2 (to CO)
energy raw materials
Z3 (to AG) solar energy water
food
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Table 2. Sustainability Evaluation Framework Based on Extended Exergy Accounting and Its Compositional Analysis indicator
formulation
implication
ESR
CECi/(EWi + ECi)
SECR
(EW + EC)/ΣCECi
EDE
Σf ij/CECj
EYR
CEC/Ein
ELR
(ER + CECN)/(CECR + ER)
EESI
EYR/ELR
i.e., exergy structure ratio of specific sector; it is a metric of exergy consumption structure in different sectors, calculated by the material-based exergy consumption compared with the social supporting exergy within sectoral size. i.e., social exergy conversion rate; it measures the net social exergy conversion level by intaking material-based exergy, calculated by the ratio of labor and capital equivalent exergy (EW and EC) to exergy input into the system (CEC). i.e., exergy deliver efficiency; it is a measure of the ability in production sectors to deliver exergy into the system from the environment, calculated by exergy output from production sector j divided by exergy input into production sector j from the surrounding (j refers to EX, CO, and AG sector and i refers to the other six sectors except j). i.e., environmental yield ratio; it is a measure of the ability of a process to exploit available locally renewable and nonrenewable resources by investing outsider sources. The higher the value of this index, the greater is the return obtained per unit of exergy invested. i.e., environmental loading ratio; it is a measure of the possible disturbance to the local drive from outside sources. The lower the ratio, the lower is the stress to the environment. i.e., extended exergy sustainability index; it is an aggregating index based on both interaction with the surrounding environment and renewability.
Table 3. Material-Based Exergy Fluxes Distribution Accounting Resultsa Z1 Z2 Z3
a
8.94 × 1014 2.46 × 1018 3.57 × 1022
C1 f 21 f 31 f41 f51 f61 f 71
6.52 4.07 4.41 4.74 2.45 5.51 2.54
× × × × × × ×
1012 1013 1011 1013 1011 1011 1012
f12 C2 f 32 f42 f52 f62 f 72
3.16 2.29 6.14 1.14 5.43 1.54 7.61
× × × × × × ×
1011 1011 1011 1013 1012 1011 1011
f13 f 23 C3 f43 f53 f63 f 73
2.11 × 106
1.09 × 10
13
f14 f 24 f 34 C4 f54 f64 f 74
8.26 1.30 5.90 2.81 3.19 1.61 1.52
× × × × × × ×
108 109 1010 1012 109 109 1012
f15 f 25 f 35 f45 C5 f65
3.00 2.79 2.28 3.97
× × × ×
1011 1011 1011 1012
2.25 × 1012
f16 f 26 f 36 f46 f56 C6
2.25 3.75 2.51 3.42 2.80
× × × × ×
1010 1010 1010 1011 1011
Unit, MJ.
Labor Statistical Yearbook (CLSY)42 for the labor data; China Environment Statistical Yearbook (CESY)43 for the environmental emissions. Some data were obtained from these network databases: National Bureau of Statistics of China (NBSC), The People’s Bank of China Network (PBCN), China Economic Information Network (CEIN), and China Macroeconomic Information Network (CMIN);44−47 the literature25,26,48−50 also provided data.
sector utilizes the exergy that is delivered from the products of the Production Sectors, and the outflow exergy is inset in elaborate industrial products. The exergy inputs of both the TR and TE sectors are from the Production Sectors, and the outputs of these sectors are nonmaterial services, rather than material exergy. Moreover, DO is a unique sector that plays an important role as the provider of labor and economic contributors. For these reasons, we colored the seven sectors shown in Figure S3, Supporting Information, to distinguish their functional and properties’ differences. The CEC fluxes’ accounting results are also enumerated in Table 3, where the fluxes’ numbers correspond to their exhibitions in Figure S3, Supporting Information, and Ci refers to consumption within a certain sector for self-operation. The specific calculation processes are presented in the Supporting Information (Parts 2 and 3, Tables S1 and S2). As we have mentioned previously, the TR and TE sectors are special exergy consumers and services generators. On the basis of the exergy balance equations (as shown in the Supporting Information Part 3 and Tables S3 and S4), the exergy outflows that are embodied in exergy and sent to other sectors are also evaluated and labeled in Table 3. 3.1.2. Exergy Equivalent of Externalities. In this work, the exergetic equivalents of labor and capital are calculated on the basis of two country-specific (and time-dependent) exergoeconometric factors: α and β. The detailed calculation procedure and the values of the necessary required parameters and statistics for Chinese society in 2010 are presented in the Supporting Information (Part 4). On the basis of the methodology in Section 2.1, “i” here refers to “EX, CO, AG, IN, TR, TE”, and “DO”, although EW and EC are regarded as the output of DO. EW in Sector “i” is directly determined by the CEC depletion in the ith Sector, and EC is related to the total salary of the economically active population that exists in Sector i. Therefore, the important derivations for E W and E C accounting in six sectors are deduced as follows (using Sector
3. RESULTS 3.1. EE Accounting and Analysis. On the basis of the previous compilation of data and the EE account database’s construction, which we explained in Sections 2.2 and 2.3, the EE account is primarily divided into two portions: the CEC depletion from renewable and nonrenewable energy and resources and exergy consumption, which is equivalent to the externalities within an entire social system. 3.1.1. CEC Fluxes. The database we constructed using the available data sources and statistics indicates that material-based exergy fluxes have complex flow directions among the Production Sectors and the Consumption Sectors (the IN, TR, TE, and DO sectors). To explain each distribution’s flux, a sectoral number series for each sector were constructed as follows: EX (sector 1, Extraction), CO (sector 2, Conversion), AG (sector 3, Agriculture), IN (sector 4, Industry), TR (sector 5, Transportation), TE (sector 6, Tertiary), and DO (sector 7, Domestic). The symbol “f12” means that there is an exergy flux from sector 2 to sector 1 (i.e., there is exergy that moves from the CO sector to the EX sector). Figure S3, Supporting Information, is the fluxes diagram, and the exergy input/outputdependent noumena are quite different, e.g., for the EX, CO, and AG sectors. The exergy inputs are implicated in natural energy and resources directed from the surrounding ecosystem, and the production sectors transfer raw materials into improvable exergy or primary commodities/products consumed by other sectors in addition to themselves. The IN 9829
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EX as an example), and furthermore, the final accounting results are listed in Table 4: E W (EX) =
CECEX × EW ∑ CECi
EC(EX) =
sEX × NWEX × EC ∑ si × NWi
Table 5. ER Accounting Results Based on the Decomposed Calculation Model parameter name
(i = EX, CO, AG, IN, TR, TE)
(6)
(i = EX, CO, AG, IN, TR, TE)
eC eR,W eR,G eR,S ER,W ER,G ER,S ER
(7)
Table 4. Exergy Equivalent of Externalities for EW and EC in the Sectoral Distribution EW in sector “i” EW(EX) EW(CO) EW(AG) EW(IN) EW(TR) EW(TE)
unit, MJ
EC in sector “i”
× × × × × ×
EC(EX) EC(CO) EC(AG) EC(IN) EC(TR) EC(TE)
3.36 2.01 5.19 3.03 2.79 3.47
1012 1013 1011 1013 1012 1011
unit, MJ 1.32 7.80 3.33 1.52 1.36 2.14
× × × × × ×
109 108 108 1010 109 1010
× 10−3
108 104 107 109
unit MJ/RMB RMB/ton RMB/ton RMB/ton MJ MJ MJ MJ
contributions at the sectoral level, and furthermore, the distribution map is given in Figure 1. Generally speaking, the
For the exergy equivalents of the externalities that cause environmental degradation, exergy is not a direct measure of pollution, but it provides a clear qualitative indication of the potential of a pollutant to cause environmental damage because it measures the “thermodynamic distance” of the released substance from its environmentally neutral (equilibrium) state.51 In the present analysis, the lack of sufficiently disaggregated data on the national and sectoral scales about the different types of destructive effluents made it impossible to discover the “exact” environmental remediation costs of all the pollutants. Instead, as an alternative method that has been applied in some previously published EEA analyses,49,52 the actual cost of cleanup processes was converted into an extended exergy equivalent by means of the capital eR. This capital refers to the expenditure that is required for the per-unit treatment of environmental emissions, and furthermore, eR represents the equivalent exergy that is consumed embodied per capita. To be clear, the available and reasonable data concerning environmental emissions and treatment expenditures from CSY and CESY are of three types: wastewater, waste gases, and solid waste discharges. The decomposed calculation model that is suitable for China is inferred in eq 8: ⎧ E R = E R,W + E R,G + E R,S ⎪ ⎪ = (Q × e R,W + Q G × eR,G + Q S × eR,S) W ⎪ × eC ⎪ ⎪ ⎨ C ⎪ eR,i = W,i (i = W, G, S) Q W,i ⎪ ⎪ ⎪ EC ⎪ eC = ⎩ GDP
value 1.0043 156.53 203.78 169.68 9.70 × 9.18 × 4.11 × 1.01 ×
Figure 1. Distribution map of CEC, EW, and EC contributions in the sectoral level.
CO and IN sectors are the most prolific CEC consumers and labor exergy-concentrated departments in the whole system. The capital-equivalent exergy is an important contributor for a sector to achieve its function. In general, the EX, AG, and TR sectors utilized a fairly small amount of CEC, EW, and EC, as shown in Figure 1. Finally, the EE value for the year 2010 in China was 1.80 × 1014 MJ (eq 9). In similar research by Chen and Chen,31 the EE amount in 2005 was determined to be 1.37 × 1014 MJ, which is only 76% of the value in the year 2010. This vast difference is mainly caused by multifaceted economic expansion that amplifies the exergy usage and the exergy equivalent of externalities disturbances, but another significant cause of this discrepancy is the more comprehensive derivation of our figure and the corrected decomposed calculation model for incorporating the embodied externalities-equivalent exergy. EE = CEC + EC + E W + E R = 1.23 × 1014 MJ + 5.74 × 1013 MJ + 4.05 × 1010 MJ + 1.01 × 109 MJ
(8)
= 1.80 × 1014 MJ
The detailed data collection from public statistics, the calculation procedure, and the values of the necessary required parameters are presented and explained in the Supporting Information (Part 5). Here, we present the final results, which are based on the above model, in Table 5. The entire extraenvironmental emissions-equivalent exergy, which needs an additional exergy investment before it can be reduced, was 1.01 × 109 MJ on the national scale in 2010. 3.1.3. Brief Summary of EE. We use the accounting results in Sections 3.1.1 and 3.1.2 to show the CEC, EW, and EC
(9)
3.2. Indices Analysis. Following the index-setting principles, the extended exergy-based indices with respect to an economic system’s sustainability level are summarized in Table 6, and the detailed categories of the extended exergy components or fluxes inside the system are calculated in Section 3.1. With respect to the EE accounting-based sustainability performance, the results from the sectoral efficiency show the following. (1) For the ESR value, the 9830
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accounting,6,53,54 when Sustainability Index < 1, the products and processes are not sustainable in the long term. Therefore, it is implied that China is still developing in a stage of high energy consumption and low sustainability level. Additionally, necessary supplementary information of these indices can be found in the Supporting Information (Part 6). The extended exergy efficiencies calculated for each sector of the Chinese economy are also compared to those calculated from previous studies in the Supporting Information (Table S7). The results imply that there are notable differences in the “transformation efficiencies” of energy sectors and “conversion efficiencies” of various societies.
Table 6. Extended Exergy-Based Indices for System Sustainability item
value
ESR ESREX ESRCO ESRAG ESRIN ESRTR ESRTE SECR EDE EDEEX EDECO EDEAG EYR ELR EESI
2.0347 2.0373 2.0318 2.0340 2.0349 1.9141 0.47 13.43 0.46 48.08 0.94 4.07 0.23
4. DISCUSSION To explicitly disentangle the different exergy-based indicators, we present the value coordinate graph in Figure S5, Supporting Information, to describe both the value formation during the production process and the cost for sustainability, which correspond to a society’s values in specific context. Specifically, we suggest the following classification: first, the use value is defined as the raw exergy content of a natural resource’s constituents, and this value is measured by means of a resource exergy analysis that determines its availability in a given biophysical context. Second, the existence value, which is also known as the embodied value, is equivalent to Szargut’s Cumulative Exergy Content;17 it measures the sum of the exergies of all the material and energy flux inputs that contribute to any part of the production process. Third, there are two essential production factors in addition to exergy input, labor and capital, and both of them are linked to the economic exchanges that occur in the free market and in society. Hence, we employ the exchange value to uncover the economic communication structures that vary depending on the socioeconomic texture within a society. Ultimately, if we include those end remediation and buffering activities that are essential to fit a production chain into the surrounding environment in the analysis and if we consider the overall “minimal damage” that is inflicted upon the whole biosphere, another value measure is necessary. This value measure is the f itting value, and it must be introduced because it is directly related to both the inserted system sustainability and the interference between a human-dominated social system and its supporting environment. Notice that the fitting value is closely related with the orientors, goal functions, or directionalities of ecosystems. Using exergy-based orientors and the underlying fitting values, we can adopt a forward-looking approach to explain the status and development of an ecosystem (i.e., we can describe the present interactions and behaviors of an ecosystem based on the presumed rationality and intentional stance associated with belief and desire), which is quite different from the pseudocausal explanations of all backward-looking methods. This type of approach is particularly important if the biophysical reference environment needs to be considered. In our opinion, the approach of principle therefore must be integrated into a “context”, within which the specific tenet can be fully understood and correctly described. Specifically, we argue that whereas the eco-exergy may be better suited for describing the evolution of ecosystems (Figure S5, Supporting Information), EEA is a better global tool for assessing the development of a socio-economic system. Given a system of values, the cost of sustainability can be calculated using an exergy-based quantifier, as the higher a production (develop-
average range of this index is approximately 2.03, although the TE sector has a low value of 1.9141. This low value reflects the fact that the TE sector uses less exergy per unit in the form of social externalities-equivalent exergy. TE is a service-provider sector that is dominated by human’s behaviors, e.g., the labor intensity patterns and a rapid capital turnover in flexible or small-scale management for today’s China. (2) The SECR value is 0.47, which implies that the systematic net social exergy conversion ratio from taking in material-based exergy is nearly one-half. In addition, the economic and labor-equivalent exergy performance is approximately 0.47, which is greater than the overall contributions of energy and resource exergy. Because EW is positively correlated with both the HDI and the national population and EC is stimulated by the circulation of economic capital, the SECR value will increase with the improvement of living standards and the acceleration of currency recycling. (3) For the three fundamental production sectors, the EDE index’s values are dramatically different; a higher value implies that more exergy is provided to the other sectors than selfconsumption. AG sector is a generous exergy-deliverer because it involves the extraction of a large amount of exergy in the form of food, which is obviously required to sustain any society. In contrast, the CO sector has an extremely low EDE index value, which we ascribe to the fact that a very high proportion of electricity is produced by nonrenewable depletion from thermal power stations. As a result, increasing the renewable energy conversation in the CO sector is the most effective strategy to improve the EDE index. In addition, the EX sector uses a smaller amount of CEC than it sends to other sectors. From the perspective of environmental concerned sustainability, (1) the environmental yield ratio is 0.94, from which we infer that 94% of the exergy in the locally available renewable and nonrenewable resources are extracted by the production sectors from outside the environment and one-off used or recycled by the primary and secondary consumption sectors. Furthermore, 6% of the total exergy is depleted in the process of delivering exergy to the EX, CO, and AG sectors. (2) The environmental loading ratio is 4.07, which indicates a magnifying possible disturbance to the local economy from outside sources. (3) On the basis of the environmental yield ratio and the environmental loading ratio, the sustainability index is calculated to be 0.23. On the basis of the Sustainability Index evaluations that have been made in similar environmental 9831
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ment) mode’s cost, the more unsustainable it is. Indeed, the principle struggle for existence, which was previously quantified as a struggle for available “excess” free energy55 in terms of the lowest requirement for human life to exist, can be reformulated as a struggle for the smallest extended exergy cost, containing all four of the values that are associated with sustainability issues. The levels of various exergy-based indicators are also presented in Figure S5, Supporting Information. Obviously, any aggregate quantity is going to be an indicator of weak sustainability, especially for the exergy-based orientors.56 The drawbacks of extended exergy as an energy sustainability indicator have been identified, e.g., exergy aggregations derived from various resource inputs to the system without full consideration of quality differences and cost allocations, uncertainty of calculation for nonenergy externalities of labor and capital, and difficulty in distinguishing the real environmental impact. Still, extended exergy can be regarded as a combined evaluation method that offers a worthy contribution to the assessment and estimation framework designed for sustainable development. EEA is widely acknowledged to be a useful tool for ecological accounting and analysis on a VLCS. It is founded on a combination of the exergy concept with the production factors of capital and labor. To clearly illustrate an exergy-fluxed distribution, the ecological evaluation account that was completed in this study is an omnibus collection and selection of the multiple existing EE accounts and analyses, which is also expected to be a rudiment standardized database exploitation in subsequent research. Several small but effective adjustments in the calculation models for sectoral EW and EC have been made, and in the attempt to evaluate ER with respect to the three sources of waste emission, we also direct an evaluation method due to the absence of the precise sectoral environmental emissions data in the current statistics.
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ASSOCIATED CONTENT
S Supporting Information *
More explanatory details of extended exergy accounting, full case study and data description, and calculation details. This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86−10−58807368; fax: +86−10−58807368; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Major Research plan of the National Natural Science Foundation of China (No. 91325302), Fund for Creative Research Groups of the National Natural Science Foundation of China (No. 51121003), National Natural Science Foundation of China (No. 41271543), and Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20130003110027).
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