EMERGY SIMULATOR, AN OPEN SOURCE SIMULATION PLATFORM DEDICATED TO SYSTEMS ECOLOGY AND EMERGY STUDIES Raphaël Valyi a,1, Enrique Ortega b, 2 a Candidate for Master of Science and Master of Materials at the Ecole Centrale de Lyon, 36 Av Guy de Collongue 69134 Ecully, France; b Professor at the Food Engineering Faculty of the Unicamp University 6121 CEP 13.083-862 Campinas - SP - Brazil ABSTRACT To develop more objective and more efficient criteria for judging sustainable development, the interactions between human activities and the environment are being simulated more often using various forms of systemic modeling. H.T. Odum was a pioneer in applying modeling concepts from electrical circuitry and irreversible thermodynamics to systems ecologyusually dedicated to electronics andor chemistry. The Emergy Simulator (EmSim) project is a computer implementation of the main concepts of Odum’s Energy Systems Language a.k.a. the Energy Circuit Language. First, with EmSim you can share models through the Internet or export them as drawings. Second, EmSim is able to translate Odum’s Energy Systems diagrams directly into a set of ordinary differential equations that it can then integrate and plot. Finally, EmSim can correctly compute emergies and transformities. If we admit that the emergy of a product is the sum, on a common basis, of all the available energy (eg. exergy) contributions required to make that product (from sun light for solar emergy or from fertile soil for ecological footprint) then EmSim is able propagate the emergy in very complex production networks involving recycling loops and co-productions. If you are able to enter an exergy weigthed causal diagram, then EmSim can compute the emergy of the various products and also infer their transformity! You are welcome to try it on line, learn more and participate at: h ttp://emsim.sourceforge.net a democratic project open for unlimited improvement by otherss. See also: http://emsim.sourceforge.net. 1 Phone : 00 334 72 85 94 11 ; e-mail adress: [email protected] 2 Phone : 00 5519 37 88 40 35; Fax: 00 5519 37 88 40 27 e-mail address: [email protected] 1. INTRODUCTION Why we created Emergy Simulator [1] the way it is because we wish it could overcome the following current systems ecology limitations in the future: 1. We think that systems ecology models can only make consensus if they are widely discussed and taught. But sharing models requires standards. In every scientific field, the trend is that standard exchange formats closely stick with informatics file formats. Odum's energy diagrams is already a powerful standard but no suitable informatics implementation was available so far. A specific drawing tool was also required to communicate about models without depending on commercial softwares. 2. Moreover, when Odum's energy diagrams stands for dynamical systems, researchers are always compelled to translate themselves graphs into differential systems (not always with the same rules!) and program themselves the temporal integration using commercial software like Matlab or Excell. Others simply don't know how to do the conversion because of a lack of communication about the methodology. 3. When dealing with the emergy, very few researchers are able compute themselves the transformity of a product within a complex production process. That's because people is used to abuse of precomputed transformity tables and thus miss the original definition of emergy as well as the real power of this concept. Let's highlight briefly the problem: abusing of transformities tables can lead to questionable accuracy of emergy indicators! Indeed, a transformity is always dependent of the specific system you are speaking. Picking a transformity from one system and injecting it in an other implicitly assumes that the products you are speaking are made and exactly the same way and that they are independent. If not then you will start forgetting or double accounting some emergy. Remember the rules stated by H.T. Odum in [5] chapter 6. A simple example is that 1 Kg of Brazilian bananas will have a much more greater emergy if transported in Europa than it has in Brazil because of the transportation energy. If you miss this concept then emergy won't defend anymore the need of economy re-localization. If you would account for the transportation, then you would make a step in the right direction. But is that always sufficient and credible as such? Imagine that you have to compute the emergy of a cake made of those bananas and the emergy of Brazilian soy. But let's imagine you can to it fully because emergy data are correctly collected: imagine that you can deeply investigate at the specificity of your case study because models of many products or services are available on the Internet. Transporting 1 Kg of bananas require a very small part of the boat technology. When you'll later add the emergy of that banana to make a cake, you could have to add the emergy of the bananas with that one of the Also the basis of the the most relevant algorithms used by the pioneer H.T. Odum for systems simulations have already been coded during the 10 months of intensive programming in 2004 as it will be discussed later. But in order the project to keep improving using others academic research projects (you are very welcome to contact the authors to participate), we created EmSim as an extensible democratic project: so it's very modular and which includesing the most relevant algorithms used by the pioneer H.T. Odum for systems ecology simulations. Because the task is huge and poorly funded, EmSim has been created as a democratic project: its source code is open (GNU GPL license) and accessible on the Internet through a Concurrent Version System (CVS) while providing all the communication facilities of modern software development like forums mailing lists and bug tracking... Moreover, it is programmed in Java [2] so that it can run on line and be easily coded on any computer under any operating system; for free. This article deals with the main features of EmSim. To explain the algorithms, we will often refer to the traditional modeling done in systems ecology. However, we are unable to teach all the basics in a short paper. Also for further details, we advise the reader to look at [3] and [4] for causal modeling, energy language and its dynamical meaning, and at [5], chapter 6 for the basics of emergy algebra. EmSim allows different levels of use ecosystem:that directly reflects the main steps of ecological/economical modeling. Those steps can be summed up as: searching laws, representing the model, mapping available information into the model, simulating the kinetic of the model, qualifying the thermodynamical efficiency of the model. So this means respectively:first, in order to deduce laws in phenomena, you have to tell the spatial and temporal boundaries of your system as well as stating the granularity level at which you start accounting things (eg. accuracy). You should also find a pertinent basis of parameters qualifying the state of your system (eg. state vector). better perform inferential statistics Then, you can investigate both qualitatively (what resource is required to make what resource) and quantitatively (the steady state energy intensity or the dynamic) the causal links between phenomena by means of intuition, observation and even inferential statistics.he domain limits as well as the degree of aggregation to be used for system structures and functions.level. Of course EmSim can't help yet there since this analysis work is quite subjective and intuitive remains the responsibility of the user job. 1. Then it becomes possible to draw a causal network as an energy systems diagram that explicitly documents qualitatively and also possibly quantitatively (using classical thermodynamics) the causal pathways so that specialists from various fields can discuss it. EmSim is a diagram editor that performs this function, see part 2. 2. Models should be easy to share and remain open for further modifications, improvements and review to make it possible to achieve consensus within the scientific change so that they are catch credibleility.community. This can only be achieved by means of standardized data, that's why EmSim store every model as XMLexchange models efficiently, we needs useful standards. To learn know how EmSim structures the systemic knowledge and stores it as XML, , read the part 3. 3. Once the network of causality is established, you can study both the kinetic and the thermodynamics of the model. The kinetic of such a system is well defined by a set exactly closely the system under variable conditions and try to detail the functioning of the causality by means of detailed mathematical expressions within a set of simultaneous differential equations. In [3] and [4] Odum gives various examples of how the “energy systems language” can be translated into a system of differential equations. EmSim automates this translation and makes it possible to plot the evolution of the system given an initial state, see part 4. 4. Concerning the thermodynamics, the idea is quite simple: at any given time, whether at steady state or not, it can be interesting to check how much emergy a resource requires to be maintained in a given system, what's its transformity in that system or even what is the structural quality (the level of organization might be qualified by the empower) of the system emergy storages and flows.analysis. For instance, you can compute the empower flux through the network or the energetic cost of maintaining an emergy storage of aone resource.. EmSim is able to propagate the emergy in large and complex networks, see part 5.