Monica Carvalho

Synthesis of Trigeneration Systems: Sensitivity Analyses and Resilience

This paper presents sensitivity and resilience analyses for a trigeneration system designed for a hospital. The following information is utilized to formulate an integer linear programming model: (1) energy service demands of the hospital, (2) technical and economical characteristics of the potential technologies for installation, (3) prices of the available utilities interchanged, and (4) financial parameters of the project. The solution of the model, minimizing the annual total cost, provides the optimal configuration of the system (technologies installed and number of pieces of equipment) and the optimal operation mode (operational load of equipment, interchange of utilities with the environment, convenience of wasting cogenerated heat, etc.) at each temporal interval defining the demand. The broad range of technical, economic, and institutional uncertainties throughout the life cycle of energy supply systems for buildings makes it necessary to delve more deeply into the fundamental properties of resilient systems: feasibility, flexibility and robustness. The resilience of the obtained solution is tested by varying, within reasonable limits, selected parameters: energy demand, amortization and maintenance factor, natural gas price, self-consumption of electricity, and time-of-delivery feed-in tariffs.

Tackling environmental impacts in simple trigeneration systems operating under variable conditions

PurposeEnvironmental concerns have been a growing issue when planning energy supply systems for buildings, as the energy demands (presenting seasonal and daily variations) represent one of the most energy-intensive consumptions in industrialized societies. The optimal operation corresponding to different energy demands of a trigeneration system was analyzed by an integrated methodology combining Thermoeconomic analysis and life cycle assessment, in order to adequately allocate the energy resources and the generated environmental loads to the different energy services produced.MethodsThermoeconomic analysis, which is usually used to allocate energy and economic costs, is herein applied to the evaluation of environmental costs and distribution of resources throughout the trigeneration system. Attention is focused on the correct allocation of energy resources and environmental loads to internal flows and final products. Appropriate rules were established to calculate energy and environmental costs.Results and discussionOperation of the system considered the possibilities that surplus electricity could be exported to the national grid and part of the cogenerated heat could be wasted if this resulted in a decrease of operation costs and/or environmental loads. The results obtained show a low-cost and low-emission production with respect to the separate production in different operation modes. It was observed that, in specific periods, the trigeneration system operates wasting part of the cogenerated heat, and, in other periods, part of the electricity produced is exported to the electric grid. The trigeneration system operates in these modes because it results beneficial from environmental or economic viewpoints, achieving a lower economic cost or fewer CO2 emissions.ConclusionsThe methodology presented as well as the allocation method proposal were congruent with the objectives of installing trigeneration systems that supplied energy services with fewer emissions than those of separate production and of equally benefitting the consumers of heat, coolth (“coolth” is used as the noun form of “cool”; opposite of warmth. Not to be confused with cooling, which is the opposite of heating.) (alias cooling energy), and electricity.

Erratum to: Tackling environmental impacts in simple trigeneration systems operating under variable conditions

Purpose Environmental concerns have been a growing issue when planning energy supply systems for buildings, as the energy demands (presenting seasonal and daily variations) represent one of the most energy-intensive consumptions in industrialized societies. The optimal operation corresponding to different energy demands of a trigeneration system was analyzed by an integrated methodology combining Thermoeconomic analysis and life cycle assessment, in order to adequately allocate the energy resources and the generated environmental loads to the different energy services produced. Methods Thermoeconomic analysis, which is usually used to allocate energy and economic costs, is herein applied to the evaluation of environmental costs and distribution of resources throughout the trigeneration system. Attention is focused on the correct allocation of energy resources and environmental loads to internal flows and final products. Appropriate rules were established to calculate energy and environmental costs. Results and discussion Operation of the system considered the possibilities that surplus electricity could be exported to the national grid and part of the cogenerated heat could be wasted if this resulted in a decrease of operation costs and/or environmental loads. The results obtained show a low-cost and low-emission production with respect to the separate production in different operation modes. It was observed that, in specific periods, the trigeneration system operates wasting part of the cogenerated heat, and, in other periods, part of the electricity produced is exported to the electric grid. The trigeneration system operates in these modes because it results beneficial from environmental or economic viewpoints, achieving a lower economic cost or fewer CO2 emissions. Conclusions The methodology presented as well as the allocation method proposal were congruent with the objectives of installing trigeneration systems that supplied energy services with fewer emissions than those of separate production and of equally benefitting the consumers of heat, coolth (“coolth” is used as the noun form of “cool”; opposite of warmth. Not to be confused with cooling, which is the opposite of heating.) (alias cooling energy), and electricity.

Evaluation of Environmental Loads for the Synthesis of a Trigeneration System

This paper details the calculation of the environmental loads associated with the construction of each piece of equipment (considering that the materials were not reused at the end of the equipment’s lifetime, which is the worst case scenario) and operation of a trigeneration system. The purpose of a trigeneration system is to meet the demands of a consumer center — in this case, a medium-sized hospital located in Zaragoza, Spain. The evaluation extended over a period of one year, considering previously specified energy service demands (electricity, heat - sanitary hot water and heating -, and cooling). The system interacted with the economic environment (market) through the purchase of natural gas and electricity from the grid, and also through the sale of autogenerated electricity to the grid, according to Spanish regulations. Therefore, the environmental loads regarding the operation of the system were associated with the consumption of natural gas and electricity purchased/sold from/to the grid. Technical information on each piece of equipment was obtained from catalogs and from consultation with manufacturers. Regarding natural gas, special care was taken to correctly identify the natural gas supplied to a user in Spain (it was considered that the gas comes from Algeria, transported in Liquefied Natural Gas (LNG) carriers, including pipeline transportation to the user and controlled burning). The electricity supplied by the Spanish electric grid was also properly specified and characterized. The environmental loads were calculated utilizing SimaPro, a specialized Life Cycle Assessment tool, and then incorporated into a linear programming model, solved by LINGO optimization software. Environmental criteria were used to obtain the optimal configuration and operation of the system simultaneously.Copyright

The influence of microwave radiation on the behaviour of Rattus norvegicus

The use of mobile phones has been the target of a great controversy due to possible biological and behavioural effects. This research presents a preliminary evaluation, regarding the learning and stress levels in subjects of the species Rattus norvegicus, submitted to microwave radiation. The psychological analysis was based on laboratory tests using the aquatic maze (tank of Morris), to determine the capacity of learning and memorisation and the elevated cross maze, designed to evaluate the levels of anxiety and stress. The consumption of water and food was monitored as well as the weight of the animals. The experiments were accomplished using irradiated rats (Experimental Group), and non-irradiated rats (Control Group). No significant differences were observed in the learning or performance of the groups in the aquatic maze experiment. For the elevated cross maze tests, the subjects of the Experimental Group manifested lower stress levels.

Behavioral effects of microwave radiation on Rattus norvegicus

This paper presents a preliminary analysis of the behavioral effects, specially the learning difficulties, verified in rats of the species Rattus norvegicus, submitted to microwave radiation. Throughout the tests, an analog transmitter was used operating in the frequency of 850 MHz during a daily period of one hour. The choice of that frequency, in particular, links to the fact that in Brazil, the cellular phones use radiofrequency carriers between 800 and 900 MHz for the mobile phone service (cellular mobile service). The analysis, based on experiments with the Skinner Cage, had as main objective to verify the possible alterations on the learning ability in adult rats subjected to the influence of non-ionizing radiation and to compare their answer ratio with the control group, exempt of the influence of radiation.

Evaluation of the level of stress in rats of the species Rattus norvegicus submitted to microwave radiation

This paper presents a preliminary analysis of the behavioral effects verified in rats of the species Rattus norvegicus, submitted to microwave radiation. The analysis, based on the elevated cross form maze experiment, had as main objective to verify the stress level in adult and young rats that suffered the influence of non-ionizing radiation (Experimental Group) and to compare the answer ratio (number of entrances in the open arms/total number of entrances in the arms) with the Control Group, exempt of the influence of the radiation. Throughout the tests, a microwave generator was used operating in the frequency of 2.45 GHz during a daily period of one hour. The results obtained with the experiment showed that, for the older rats, no significant variation in the anxiety and stress levels was observed between the Experimental and Control Groups. On the other hand, for the younger rats there was a considerable increase of those levels in the Experimental Group in relation to the Control Group.