Analysis of the concept of sustainability: definition of conditions for using exergy as a uniform environmental metric

Transcription

1 Analysis of the concept of sustainability: efinition of conitions for using exergy as a uniform environmental metric Eric Coatanéa 1, Markku Kuuva 1,Petri E. Makkonnen 1, Tanja Saarelainen 1, María O. Castillón-Solano 1 1 Helsinki University of Technology, Machine Design, Finlan Abstract The concept of sustainability has evolve over recent years partly because sustainability is ifficult to characterize an because environment interactions are ifficult to moel quantitatively. Consequently, the viewpoints about sustainability are numerous an unlike mature sciences, it has not yet been establishe reliable moes of investigation or a uniform framework for ialogue. When questions relate to sustainability, what is sustainability? how to conuct a sustainability analysis?, have been thoroughly investigate. The funamental hypothesis, which constitutes the basis of the concept, has been rarely iscusse. The funamental hypothesis states that society will not reaily accept limits to growth. This paper concentrates at first on the analysis of this funamental hypothesis an show that a paraox exists when comparing the infinite growth hypothesis, the limite natural resources an the limitation of the environmental pump capable of recycling the resiues create by inustrial activities. In secon part, the paper argues that a esign approach base on some environmental principles is a way to ecouple the ifferent metrics, which often makes the esign problems intractable. The funamental principles of an environmentally conscious esign regulation consist of: - avoiing irect release of exogenous resiues in the actual ecosystem, consiering a systematic use of renewable resources or recycle resources an limiting exploitation of renewable resources uner the recovery rates of these resources. It is argue in the paper that the traitional shortcoming of Life Cycle Assessment an systems analysis, the lack of a uniform basis for comparison or expression of isparate material an energy requirements, emissions or environmental impacts, is surmounte using such type of approach. The authors argue that using exergy as a uniform metric makes sense if a strong regulation integrating the previous principles can enter into force in the future. The paper ens with the presentation of the practical framework for conceptual esign evelope by the research team an applie to the environmental analysis of two manufacturing processes, a san casting process an a machining process. Keywors Exergy, metric, open system, imensional analysis 1 INTRODUCTION The hypothesis motivating this article is the mathematically efensible position that efficiency gains in the esign activity can be realize by shifting from a position consiering separate perspectives of a prouct or service, which have to be inepenently optimize to a holistic approach taking into account simultaneously ifferent perspectives of a prouct or a service. A generic framework has been evelope by the author in orer to unify the esign perspectives from a life cycle viewpoint. Nevertheless, to be practically applicable the approach requires that we can obtain measurable attributes. This aspect can quickly become an intractable problem especially when analyzing environmental aspects in esign from ifferent viewpoints. This is the case because no stanarize quantitative scientific measures of environmental efficiency are available. This is ue to the fact that managing environmental systems an impacts is complex when various metrics exist. These metrics have been evelope in orer to analyze environmental issues from ifferent perspectives. These metrics an the ifferent perspectives are require because the concept of sustainability itself expect to combine economical growth an protection of the environment. For example, how shoul the environmental impact of a cast part be consiere? Base on the energy efficiency, material efficiency, financial cost estimating the environmental impact or toxics release, socio-economic impact. This paper iscusses at first the basis of the concept of sustainability. Then into secon part, the metrics families evelope in the context of sustainability are presente an iscusse. Base on the results of the iscussion, the concept of exergy is introuce an efine. A uniform metric base on exergy associate with a moeling approach evelope by the authors is presente in the thir part in orer to analyze a practical case stuy. This part focuses on the analysis uring the early phase of a esign process of a manufacturing problem. The problem is simply analyze from an environmental viewpoint in this article. This paper s framework represents an application of an existing generic conceptual esign approach to environmental problems. The framework has been evelope by the main author of this article in his PhD thesis [9]. 2 CONCEPT OF SUSTAINABILITY The concept of sustainability is seen by many researchers as a solution in orer to attack the possible limitation of the economical growth ue to the increasing environmental loa cause by the human community on the nature [10]. Interesting ieas have been evelope by researchers in the fiel of engineering esign recently, in orer to shift from quantitative sufficiency to qualitative satisfaction [10] [11]. Their funamental goal is to ecouple the economic growth from the material an energy consumption [10] an to integrate esign in a broaer manner in the society [11]. These ieas are tempting. Nevertheless, other authors argue that the principle of an infinite economical growth, which unerlies the leaing economical theories an the sustainability theory, is highly questionable. Inee, the valiation of this hypothesis requires the availability of unlimite 81

2 resources. However, isposing of an increasing number of artifacts an inustry generate waste seems to lea to the evient limitation of the environment. Scientific proofs emonstrating ifferent aspects of the environmental limitation accumulate. Consequently, the attempt to ecouple the economic growth from the material an energy consumption can perhaps slightly improve the environment situation. However, nothing proves that intensification of services guarantees less environmental impacts. Inee, intensification of services can en up with more physical use; therefore more energy an material consumption. Consequently, the valiity of the concept of continuous growth is most certainly oubtful in the context of limitation of resources an limitation of the environmental pump [12]. As a result, we argue in this article that the entire concept of sustainability requires profoun revisions. The scope of this article is not to provie such type of funamental analysis. The goal of the article is more moest. Our iea is to emonstrate that moification of initial conitions can lea to rastic simplification of the environmental impact moeling. We argue that a uniform environmental metric can be efine an use uring the early phase of the esign process. The following part escribes first the existing metric families use in the sustainability framework, secon iscusses the sustainable framework an its metric system. 3 EXISTING METRICS FOR ENVIRONMENTAL ANALYSIS IN A SUSTAINABILITY PERSPECTIVE 3.1 Taxonomy an analysis of the sustainability metrics The increasing environmental buren cause by our inustrial activities an services is clearly the funamental anger for our species. A raical reuction or the elimination of the environmental loa in orer to stabilize ecosystems is require if we woul like to expect a positive future for human species on earth. In our viewpoint, It is necessary to be able to evaluate, to measure the ifferent aspects of the environmental impact an to evelop tools for analyzing the environmental impact before eveloping new approaches an solutions to tackle the environmental buren issue. This issue has alreay guie the creation of numerous metrics an methos in engineering esign. These metrics can be interprete as an attempt to better manage this complex problem involving various kins of interactions. The first part of the section escribes the existing families of metrics. The authors of this article have retaine the classification use by Seager [6]. The secon part of the section iscusses the limitations of a multi-metric approach from the engineering esigners viewpoint. Finally, the final part of the article proposes a raical approach in orer to solve the previously highlighte restrictions. Accoring to Seager [6] all of the sustainable metrics may be characterize in a classification that inclues six broa categories: Financial metrics estimate environmental impacts or ecosystem services in terms of currency so that they may be compare with monetary transactions or inustrial accounts. In practice, monetization may lea to the erroneous assumption that environmental exploitation can be reversible in a manner analogous to pecuniary transactions, even if in many cases ecological systems are amage beyon recovery. Nevertheless, emission traing alreay exists. For example, the European Union Greenhouse Gas Emission Traing Scheme is involving all the 25-member states of the European Union participate in the scheme. Nevertheless, it can be argue that emissions traing o little to solve pollution problems, as groups that o not pollute sell their conservation to the highest polluters. Thermoynamic metrics inicate the resource requirements of inustrial activities or services, usually thermoynamic metrics o not inicate the specific environmental impacts associate with resource consumption. Only a few, such as the concept of exergy attempt to inicate whether the resources consume were use wisely an efficiently. Nevertheless, it has been argue that thermoynamic metrics o not consier the potential coupling existing with environmental impact metrics ue to the export of exogenous material into the environment. It can be argue that no single metric can capture environmental impact per se. Nevertheless, it is evelope in the following sections that exergy may be a goo basis for the evelopment of a uniform metric especially if the funamental approach leas to the ecoupling of the thermoynamic metrics an environmental metrics. Environmental (incluing health an safety) metrics estimate the potential for creating chemical changes or hazarous conitions in the environment. They may be simple measures of what is release to the environment, without consiering chemical consierations such as pollutant egraation, catalysis, or recombination to form new pollutants; or they may inclue potency factors, such as toxicity, reactivity, or rarity. Most are irecte at specific biological or ecological en points, such as eath, cancer, or mutation, while others may inicate a loss of environmental quality without suggesting any particular ecological manifestation, such as ozone formation [5]. It is possible for environmental metrics to be expresse in chemical or thermoynamic units; but, environmental metrics are istinguishe from thermoynamic by the fact that they are intene to measure environmental loas or changes, rather than resource emans. They are generally measures of the waste create by inustrial processes, rather than raw materials use. Nevertheless, if some environmental metrics are expresse via thermoynamic quantities, it can be argue that the conceptual framework of the thermoynamic metrics can be extene in orer to combine environmental an thermoynamic metrics. This is the goal of this paper. Ecological metrics attempt to estimate the effects of human intervention on natural systems in ways that are relate to living things an ecosystem functions. The rates of species extinction an loss of bioiversity are examples, an may be incorporate in the concept of ecosystem health. Ecological metrics relate to biological processes, but environmental relate to chemical or other hazarous conitions. For example, a pollution free environment may not lea to recovery of eplete bear population if there is a total absence of quality sites because of the human pressure. It is also argue in this paper that ecoupling between effect of environmental metrics an ecological metrics can be obtaine if an aministrative approach can make obligatory the very long-term storage of exogenous substances. This type of regulation will oblige to efine the nature of a reference ecosystem. Socio-political metrics evaluate whether inustrial activities are consistent with political or ethical goals. 82 PROCEEDINGS OF LCE2006

3 Aggregate metrics may combine features or metrics belonging to a variety of other categories, or they may group a number of metrics that belong to a single category. 3.2 Discussion about the sustainability metrics The lack of uniform metric basis for comparison or expression of ifferent types of impacts or requirements has been clearly pointe out as a shortcoming of the Life Cycle Assessment (LCA) an systems analysis approaches [7]. The previous section has given a summarize classification of the metrics use in the sustainability framework, which integrate both LCA an systems analysis approaches. It has been sai above that the valiity of the infinite growth hypothesis is questionable. In aition, this hypothesis leas to a tremenous optimization problem complexity involving all the metrics classifie in the previous section. Moreover, this complexity limits the practical use of the methoologies. As a final result, pollution or estruction of the ecosystems is most certainly unavoiable in the long term if this type of ogma remains the funament of our economic system. Nevertheless, without efining an entire new framework, it can be easily imagine that avoiing issipation of exogenous substances in the external environment, using preferably renewable resources at a lower level than the recovery rate an privilege recycle resources will require the use of a limite number of metrics. It can be argue that the use of thermoynamic metrics can be sufficient. To be vali, this scheme requires that economical an esign practices follow basic funamental rules, which can be liste below: - Dissipation of exogenous substances shoul be forbien in the external ecosystem, - When necessary exogenous substances, resulting from irreversible processes, shoul be store, - The choice of the resources shoul privilege renewable resources or recycle resources. These goo practices are now wiely accepte. Nevertheless, strong regulations are necessary in orer to guie everyay practices in this irection. We argue in this article that if these funamental conitions are impose by regulation, a uniform environmental accounting base on thermoynamic approach is aequate. In aition, this article states that the thermoynamic concept of exergy is an interesting basis for the evelopment of a simple uniform metric of environmental pollution at the early stage of the esign process. The following sections evelop the concept of exergy an show that the use of imensional analysis can lea to further simplification of the analysis. 4 EXERGY 4.1 Definition an calculation Engineering is an activity where choices have to be mae continuously. Choices mae uring the initial stages of the esign process have an important impact. The scope of this paper is limite to the evaluation of some environmental aspects of manufacturing approaches at the early stage of the esign process. The analysis mae in the previous sections shows that it is possible uner certain conitions to focus on thermoynamic metrics. The conition for valiating that type of choice is a legislation avoiing irect liberation of inustrial waste in the actual ecosystem to enter into force in the near future. The goal of this section is to efine the thermoynamic concept of exergy an to show in practice how to compute it. The concept of exergy or available work can help to answer to questions such as: - Does the prouction of one prouct or service by metho A utilize more of a resource's exergy than by metho B? - Does the prouction of the artifact C utilize more of a resource's exergy than the prouction of the artifact D? - Does the prouction of the artifact C utilize a resource's exergy more efficiently than the prouction of the artifact D? Then, it is consiere that the principal avantage of exergy compare with two other thermoynamic metrics, the entropy an the Gibbs free energy respectively, is a system of environmental reference states. There exists a general relationship between exergy, entropy an a material life cycle. In the case of woo use for cooking, we extract woo with high exergy (low entropy) from the environment an return to the environment a low exergy (high entropy) waste. Energy is a conserve quantity. The first law of thermoynamics says that the total energy in an isolate system, incluing the universe itself, cannot change. Only its form can change. There is energy available for performing useful work an energy not available. For example, the higher the temperature of a heat source relative to the ambient temperature is, the greater the proportion of heat that can be converte into mechanical work. In the same manner, the refine material or energy use for human activities iffer raically from the average values of the components that are common in the nature. The capacity for oing work is accepte as a measure of the quality of energy [2]. Consequently, in orer to unerstan the most efficient manner these processes can be carrie out within the environment; the exergy or available energy has been introuce The selection of this ambient temperature will efine the reference level for calculating this quality. In a more extene manner when comparing conjointly the natural resources an the inustry prouce energy, the efinition of the reference level is important. Accoring to Szargut [2]: Exergy is efine as the maximum amount of work that can be one by a subsystem as it approaches thermoynamic equilibrium with its surrounings by a sequence of reversible processes. Equilibrium is a homogeneous unchanging state in which there are no graients of any kin, incluing the time imension. Szargut says that the equilibrium state is also one in which no part of the system can be istinguishe from any other part of the system. Thus, the exergy of a subsystem is also a measure of its ifference from its surrounings, which is a measure of its istance from equilibrium. Consequently, in orer to calculate exergy, the environment must be specifie. Because of the lack of thermoynamic equilibrium in the environment, only the common components of nature can be use to efine the environment, for example, the atmosphere, the ocean an the earth s crust. Exergy is expresse in Joules (J) unit or ML 2 T -2 using the international system of funamental quantities with (M) Mass, (L) Length an (T) Time respectively. 13 th CIRP INTERNATIONAL CONFERENCE ON LIFE CYCLE ENGINEERING 83

4 Exergy can be foun in four basic forms, kinetic, potential, chemical an physical (i.e. pressure-volume an heat exchange type of work). Form of energy such as gravitational, electric an kinetic energy can be completely recovere as mechanical work. Therefore, accoring to the above efinition of Szargut, exergy an energy are equal for these types of energy. The reference state for such type of form of energy must be establishe relative to a reference state, such as motionless at sea level. Nevertheless, even if energy an exergy are expresse in similar unit, there exist significant ifferences between the concepts. Szargut [2] has presente these ifferences. The most important of these ifferences in the context of this article is liste below. Energy Is subject to the law of conservation Exergy Is exempt from the law of conservation Table1: Energy versus Exergy [2] Consequently, a balance of exergy shoul be close by the introuction of a term representing the exergy loss in the system. The exergy loss takes the following form: δ B T Σ S (1) = 0 where T 0 = Temperature of the environment δq S is the variation of entropy accoring to T the secon law of thermoynamic (J/K). In practice, the entropy can be calculate by using the heat capacity via the following formula: C S = X T (2) T where C x is the heat capacity of a flui at constant pressure (C P ) or constant temperature (C T ) in (J/kgK). The exergy balance takes the following form accoring to Szargut [2]: B = B + B + Σ B + W + δb (3) S a q where B, B a = Exergy of the input an output matters B S = Increase of exergy in the system B q = Increase of exergy in the heat source in contact with the system W= Work performe by the system δb= Internal exergy loss, ue to irreversibilities insie the system The increase of exergy in the heat source in contact with the system, B q, can be expresse by a reversible Carnot machine, which use the environment, as a heat source or sink. For example, san mol just poure with liqui cast iron will export heat into its external environment. B q, takes the following form: T T B q = Q 0 (4) T The temperature of the heat source T 0 shoul be measure insie the plant. The system can be consiere to be at a steay state when the analysis is conucte over complete cycles, for example over a complete casting process. Then the quantity B S = 0 because all the parameters are constant. The exergy balance equation on time base unit is: B = B + Σ B + W + δb (5) a q Most of the above quantities are combination of useful part an a waste part. B + waste = Ba waste + Σ Bq Wwaste (6) B + useful = Ba useful Wuseful (7) It is then possible to rewrite (5) as B waste = B B δb (8) useful It is now possible to imagine an accounting of the environmental impact by iviing a system as a combination of basic organs as presente below: B Figure 1 Π waste is a imensionless number obtaine via the imensional analysis approach [9]. This approach is consistent with the generic approach evelope by the main author in his PhD thesis. Each process can consequently be ecompose in elementary organs belonging to a preefine list [9]. For each organ, it is possible to efine a imensionless number, which etermines the egree of its pollution. The accounting process is cumulative. We also can imagine creating a more precise account of the pollution by iviing the imensionless groups in subgroups relate to the chemical part an thermal part of the pollution for example. An approach to calculate B q has been given in (4). The calculation of the exergy loss ue to irreversible phenomenon can be complex. Another approach consists of calculating this term using the exergy balance of equation 8. The following section presents the general elements for calculating a stanar chemical exergy. The reference levels are given in existing tables [4] [2]. 4.2 Reference level for calculation of exergy For efining the reference level, rules have been efine base on convention. We have retaine the proposal of Szargut [2]. Rules: Elementary organ of a process δb waste = π B waste B useful B a waste + Bq + W B waste 1- If the processes uner consieration are chemical, the reference level shoul be aopte separately for each chemical element taking part in chemical reactions. 2- As reference species for the calculation of exergy, the common components of the environment shoul be aopte. 84 PROCEEDINGS OF LCE2006

5 3- The mean parameters of the ambient temperature, the partial pressure in the air, the concentration in seawater or in the external layer of the earth s crust shoul be taken as the zero level for the calculation of chemical exergy 4- If exact calculation is not possible for chemical exergy, calculation shoul be mae with currently available ata. For chemical exergy, the approach recommene by Seager [4] consists of approximating the net chemical exergy ue to the mechanism of heat transfer using the Gibbs free energy as presente in the following equation. The chemical connections an the release uring reactions are emonstrations of this heat transfer. Bch heat = G = H T S (9) Stanar methos for calculating the Gibbs free energy an efining the elements use for computing the stanar reference states have been presente in text book [8]. The secon mechanism is the mass transfer, which is evient in the ilution or issipation of reaction of en - proucts throughout the environment. The calculation of the part of the exergy ue to the mass transfer consists of calculating the composition-epenant component of the chemical exergy [2]. Consequently, the activity of the species is a measure of the potential chemical change attributable to introuction of any pollutant into the environment [4]. The following equation shows how to compute this exergy. comparison an the analysis of ifferent concepts of solutions. Figure 2: A pressure regulator The set of funamental rules of the approach can be summarize below: Stuie part - A function is seen as an interface between an initial situation an a final situation, - A situation represents the states of the elements of the environment that the concept of solution shoul moify, - Different concepts of solutions are comparable if they exhibit similar initial an final situations. - A situation is escribe by efining the obtaine state of the manufacture part at each stage (e.g. Ingot, part outline, part finishe) an by comparing this stage with the final state requirements neee at the en of the process, for example: the material requirements (MR), the macro-geometrical requirements (MGR) an the microgeometrical requirements (mgr). Accoring to the following rules, the Table 2 highlights two comparable moules.. Situations an functions Manufacturing process 1 (Casting) Manufacturing process 2 (Machining) m = 0 ln y B i i nirt 0 (10) y i Initial situation Scrap an Ingot MR: No Ingot MR: No where m B i is the exergy of the composition-epenent component in joules (J), the species, y i uner consieration, n i the total number of moles of the activity in the thermoynamic system 0 y i the reference activity in the appropriate environment (sea, earth crust or atmosphere), R=8,314 J/mol/K is the universal gas constant an To=298,15 K is the stanar temperature. Practical information useful for the calculation of this exergy is available in many stuy books [8] [2]. Comparable moules 1 Place: Casting company Place: Smelter Function 1 To shape To outline To convert Intermeiate situation 1 Part outline Normalize shape Casting company Place: Smelter 5 PROPOSAL OF A COMPARATIVE APPROACH: SAND CASTING-MILLING VERSUS MILLING FOR A PRESSURE REGULATOR PART This section presents healines of a metho evelope in the PhD of Eric Coatanéa [9]. The iea is only here to show how such type of environmental approach can be use using the type of framework escribe below. For example, if the goal is to evaluate possible manufacturing concepts from an environmental perspective, at the early esign stage, for the part inicate in Figure 2. The environmental analysis requires evaluation of some attributes of the stuie part to manufacture. For example, its mass (M), its volume (L 3 ), an possible manufacturing material. Base on this type of initial information, the approach can be applie. The approach is base on a set of rules an classifications. Several classifications have been establishe [9]: -a normalize functional vocabulary, normalize set of generic organs, mapping between functions an organs, generic laws for organs, generic rules for solving esign trae-off. In aition, algorithms have been establishe in orer to facilitate the Comparable moules 2 Function 2 To remove To shape Intermeiate situation 2 Function 3 Final situation Part Outline Place: Casting company To shape Part finishe MGR: Yes mgr:yes To finish Place: Casting company Part outline To outline Place: Machining company To shape Part finishe MGR: Yes mgr:yes To finish Place: Machining company Table 2: Overall functional escription an efinition of the comparable moules The next step of the analysis consists of efining a functional moel of the manufacturing approaches. The 13 th CIRP INTERNATIONAL CONFERENCE ON LIFE CYCLE ENGINEERING 85

6 Figures 3 an 4 present a simplifie functional moel of the two manufacturing concepts. This stage is then refine using the basic organs of the metho. The Figure 5 presents this SADT iagram for the machining solution. Base on this SADT iagrams, it is easy to make an accounting of the environmental impacts for each comparable moules. The accounting can be mae at overall level an at the organ level Figure 3: San casting Figure 4: Machining Figure 5: SADT moel of the machining process 6 SUMMARY This article has analyze funamental hypothesis about sustainability. In aition, the authors have efine a simplifie environmental accounting approach an the necessary hypotheses necessary to valiate the scientific scheme. The framework is extensive an can integrate the entire esign process. The compilation of the numerical values necessary to complete the accounting requires a supplementary work. Another complementary approach can consists of creating an ieal process, which can be compare with existing ones. It is also the goal of a future work to evelop further the example use in this article. ACKNOWLEDGMENTS Eric Coatanéa has performe this work within the research projects COMODE an KITARA. The COMODE project has receive research funing from the EIF Marie Curie Action, which is part of the European Community s Sixth Framework Program. Petri E. Makkonen, María O. Castillón an Tanja Saarelainen have performe the work within the research project KITARA. The KITARA project has receive research funing from the Acaemy of Finlan. REFERENCES [1] Brezet, J.C., A.S. Bijma, J. Ehrenfel, an S. Silvester, The Design of Eco-Efficient Services: Metho, Tools An Review of the Case Stuy Base Designing Eco-Efficient Services Project,Design for Sustainability Program, Delft University of Technology, Delft, The Netherlans, [2] Szargut J, Morris DR, Stewar FR. Exergy analysis of thermal, chemical an metallurgical processes. New York, NY: Hemisphere Publishing; [3] Ayres RU, Ayres LW, Martinas K. Exergy, waste accounting an life cycle analysis. Energy; 23:355 63, [4] Seager TP, Theis TL., A uniform efinition an quantitative basis for inustrial ecology. Journal of Cleaner Prouction;10: , [5] Pré Consultants, The Eco-Inicators 99- A amage oriente metho for Life Cycle Impact Assessment, methoology Report, Pré Consultants b.v., Amersfoort, The Netherlans, [6] Seager TP, Theis TL., A taxonomy of metrics for testing the inustrial ecology hypotheses an application to esign of freezer insulation. Journal of Cleaner Prouction 2004; 12: [7] Raymer S, Klimisch R. Macro workshop. In: Eisenberger P, eitor.basic research nees for environmentally responsive technologies of the future. Princeton (NJ): Princeton University, [8] Stumm W, Morgan JJ. Aquatic chemistry: chemical equilibria an rates in natural waters. 3r e. New York (NY): Wiley, [9] Coatanea, E, Conceptual Design of Life Cycle Design: A moelling an evaluation metho base on analogies an imensionless numbers, ISBN , Doctoral issertation, Helsinki University of Technology, 2005 [10] Tomiyama, T, Service Engineering to Intensify Service Contents in Prouct Life Cycles, Proceeings of EcoDesign 2001: 2 n International Symposium On Environmentally Conscious Design An Inverse Manufacturing, Tokyo International Exhibition Center,, Tokyo, Japan, 2001 [11] McAloone T.C., Anreasen, M.M., Design for utility, sustainability an societal virtues: Developping prouct service systems, International Design Conference-Design 2004, Dubrovnik, [12] Svirezhev Y. M., Thermoynamics an ecology, Ecological Moelling, 132: 11 22, 2000 CONTACT Eric Coatanéa Researcher Department of Mechanical Engineering Helsinki University of technology P.O. Box 4100, FIN TKK, Finlan Telephone: Telefax: eric.coatanea@tkk.fi URL: 86 PROCEEDINGS OF LCE2006