About:

Research stay within the European Doctorate Program of the University of Zaragoza, and the work was developed within the framework of research project ENE2007-67122, funded by the Spanish Government (Energy program) and the European Union (FEDER Program).  

Title of work:

Instruction, training and investigation in environmental modeling with Umberto – Analysis of the distribution of energy and environmental impacts in trigeneration systems.

Description:

The proposed investigation is contained in the framework of a wider project, which aims at developing methodologies and procedures to synthesize and design trigeneration systems in the residential-commercial sector, contributing to improve the database of technical-scientific knowledge on the energetic efficiency in the provision of energetic systems to buildings. A global environmental evaluation of the proposed configurations will be considered, to formulate and quantify reasonable environmental criteria, to therefore identify which trigeneration systems are less aggressive to the environment. This type of study entails the necessity of using specialized tools and therefore, the objectives of the research stay were to study in depth the environmental analysis of trigeneration systems through the use of Umberto.

The research stay resulted in a very important contribution for the studies developed by the Thermal Engineering and Energetic Systems Group (GITSE), a consolidated investigation group, officially recognized by the government of Aragón, attached to the Aragón Institute of Engineering Research (I3A). Members belong to the Area of Thermal Engineering of the Mechanical Engineering Department at the University of Zaragoza, Spain.

Integrated models of energy flows made possible a better comprehension of the assignation of environmental impacts to the internal and final products of the trigeneration system. The 3-month work plan was designed in order to firstly, provide instruction and training in Umberto, and secondly, analyze environmental cost assignment criteria.

Trigeneration can be defined as the simultaneous and combined production of electricity, heat and cooling, starting from the same source (natural gas, for example), which, taking advantage of the energetic integration of the processes occurring in the equipment, extracts the maximum thermodynamic potential of the resources consumed. Recognizing the social benefits of trigeneration systems (less environmental contamination, energetic resource savings, and economic competiveness of the products) as well as the growing demands for energetic services (electricity, domestic hot water, heating, and cooling) in buildings, the proposal for the research stay was to study the incorporation of the evaluation of the consumption of energy, materials, and environmental impact in design decisions.

In recent years the analysis and design tools for energetic systems have undergone a very important development. The synthesis and design of trigeneration systems in the residential-commercial sector present a great variety of energy sources, technological options for use management and final products, offering much more possibilities and, at the same time, more difficulties when designing the system.

As the total product of trigeneration systems is constituted of several products that are obtained from common resources, a transcendental question arises: how to apportion the environmental costs among the different internal flows and final products? The thermodynamic analysis methodologies developed until now have focused on establishing criteria for the rational apportionment of energy costs to the internal flows and final products. The research stay builds upon the necessity of developing methodologies and procedures to synthesize and design trigeneration systems for the residential-commercial sector, considering appropriately the environmental loads generated.

Umberto was utilized to model and analyze a simple trigeneration system, throughout one year of operation. Based on the energy flows, the costs of materials/resources consumed and residues generated were analyzed and represented. The internal cost distribution obtained allowed for the identification of potential improvements with a consistent basis, taking into account environmental aspects. In the model, the border system was defined for each piece of equipment so instead of representing the life cycle of a product, the energy flow network represented a multiproduct system, with total transparency and that can be analyzed and managed from different perspectives.

The trigeneration system modeled with Umberto is shown is Figure 1.

Figure 1 Trigeneration system.

Different criteria were studied for the allocation of the environmental costs to the final products of the trigeneration system. The main idea is for the consumer to know the environmental cost included in the consumption of each energetic service.

Criteria analyzed for the allocation of environmental costs included: Allocation based on energy content of products, Allocation based on exergy content of products, Allocation based on economic value of products, Allocation based on incremental fuel consumption to electrical production, Allocation based on incremental fuel consumption to thermal energy production, and Allocation based on shared emission savings between electrical and thermal energy.

The exergy-based method of allocation allows for a rational and meaningful allocation of such emissions (loads, environmental impact) for trigeneration systems, and is superior to several other allocation methods. The exergy-based allocations method also provides a sensible basis for a meaningful overall approach for emissions trading. By permitting loads to be allocated more appropriately among trigeneration products, the research will likely allow the environmental benefits of trigeneration technologies to be better understood and exploited. The results should therefore allow the more beneficial among competing technologies to be identified rationally, and benefits to society through the selection and design of better energy technologies, based on environmental considerations.