Investigating steam turbine feasibility to improve the sustainability of a biomass boiler using TRNSYSPublished: 01 November 2018 by Elsevier BV in Sustainable Cities and Society
Adding a turbine to a steam generator plant of a district energy system increases the efficiency of the plant by generating some electricity. This is the method of turning a heating and cooling plant into a combined heating, cooling, and power plant. The district energy plant at University of Idaho, Moscow, Idaho, USA is modeled by using TRNSYS modeling software. Simulation of different models is made to compare the current system configuration to the current plus a small backpressure steam turbine, and adding a double effect absorption chiller. Operating costs, energy, and exergy efficiencies are evaluated at current and maximum steam pressure levels through the boiler and turbine. Primary components in the system include a wood chip fired boiler, steam turbine, 2100 kW single effect and 4100 kW double effect absorption chillers, and campus with associated pumping needs. Results show that installing a turbine and increasing pressure to maximum possible levels improve energy and exergy efficiency by 3–4% and 5%, respectively over current levels. Bringing a double effect chiller in addition to the turbine increases energy and exergy efficiencies further to 20% and 7%. Economic savings are substantial if power can be sold back to the utility at a higher rate.
The food processing industry is one of the largest consumers of energy and water in the manufacturing sector. It is vital that conservation measures are taken to reduce the use of electricity, fuel, and water for producers to have long-term, sustainable growth. The Pacific Northwest (PNW) region includes some the largest food processers in the United States, particularly with products such as fruit and vegetable preserves, apples products, potato products, and milk. Energy and water consumption in PNW food processing facilities are quantified as well as techniques to increase efficiency and reduce waste. Mechanical drive systems and refrigeration consumes the most electricity in the industry and the implementation of energy management plans has the largest potential to save electricity in PNW facilities. Heating and cooling process needs are the largest consumers of energy in the food processing industry. Implementing cogeneration/trigeneration technology, replacing of older equipment, capturing waste heat, and reusing wastewater can have significant impacts on both energy and water consumption. Novel, emerging technologies such as membrane separation, high-pressure processing, microwave assist, ultrasound, pulsed high electric fields, ozone, and hydrogen/electricity generation have significant potential to benefit the food processing industry by increasing efficiency and allowing companies to stay competitive in an industry where sustainable practices are becoming increasingly important to the public.
<p>Investigations on exergy resources are important from the point of energy sustainability. In the presented study an energy and exergy analysis of the operating biomass and natural gas boilers at the University of Idaho (UI) district energy plant is conducted. Exergy flows through the components of the steam cycle associated with the biomass boiler are quantified to identify major sources of exergy destruction in the district heating system. It is found that the biomass boiler has reduced energy and exergy efficiency compared to the natural gas boilers. Thermal efficiency varies from 76% to 85%, while exergy efficiency is significantly lower at 24% to 27% for all the boilers. Exergy accounting reveals that the biomass boiler and furnace account for the greatest exergy destruction, at approximately 68% of the exergy provided by the fuel. Steam use on campus represents about 6% of exergy losses while the pressure reducer is responsible for 3.5%.</p>
Performance analysis of single glazed solar PVT air collector in the climatic condition NE India: An analytical studyPublished: 20 November 2017 by MDPI AG in Proceedings
<p>With the rapid depletion of fossils fuels, scope for renewable energy like solar energy is huge. The efficiency of photovoltaic cells to convert the solar energy into electricity drops with the rise in temperature due to increased resistance. Thus improving the efficiency by lowering the thermal resistance and allowing the cooling fluid (air/water) to flow through photovoltaic thermal (PVT) system is an attractive engineering problem. In the present study, performance analysis of single glazed solar PVT air collector on the basis of energy and exergy has been analyzed for the climatic conditions of Silchar, India for the month of May, 2017. An analytical model is developed to evaluate the hourly variation of PV cell temperature, cell efficiency, useful thermal heat gain, useful electrical heat gain, energy efficiency and exergy efficiency PVT system. Results depict that efficiency of PV cell decreases with the increase in temperature, and a maximum efficiency of 14.6% for the PV module is found. Out of total useful heat output, electrical heat output contributes 67% while the rest is thermal heat output. Further, magnitude of both the heat output is found to increase with the solar radiation and the maximum is observed at around 1230 hrs. Trend of both energy and exergy efficiency is similar except the magnitude. Maximum efficiency observed to be 69% and 16.5% for energy and exergy respectively.</p>
The thermal energy storage (TES) of an actual district energy (DE) system is analyzed thermodynamically, using energy and exergy approaches. With a case study, the results for the TES of the DE system are verified with previous studies. The actual case considered is the Friedrichshafen DE system in Germany. This system is solar assisted, uses natural gas as a backup, and is equipped with a TES. The TES stores the surplus solar energy until is needed by thermal energy users of the system. Using solar energy allows the DE system to use significantly less fossil fuel than would otherwise be the case. Seasonal TES, which normally requires significant thermal insulation to adequately reduce thermal losses, is used in the DE system. The use and role of thermal storage in a district energy system is assessed considering the Friedrichshafen DE system. The results show the significant influence of the return temperature of the circulating media (water) from the DE system thermal network. Furthermore, the financial impact of the TES is not limited to a reduction of the operational cost of the DE system but also to an increase in the initial costs for the DE system.
Use of Exergy Analysis to Quantify the Effect of Lithium Bromide Concentration in an Absorption ChillerPublished: 01 April 2017 by MDPI in Entropy
Absorption chillers present opportunities to utilize sustainable fuels in the production of chilled water. An assessment of the steam driven absorption chiller at the University of Idaho, was performed to quantify the current exergy destruction rates. Measurements of external processes and flows were used to create a mathematical model. Using engineering equation solver to analyze and identify the major sources of exergy destruction within the chiller. It was determined that the absorber, generator and condenser are the largest contribution to the exergy destruction at 30%, 31% and 28% of the respectively. The exergetic efficiency is found to be 16% with a Coefficient of performance (COP) of 0.65. Impacts of weak solution concentration of lithium bromide on the exergy destruction rates were evaluated using parametric studies. The studies reveled an optimum concentration that could be obtained by increasing the weak solution concentration from 56% to 58.8% a net decrease in 0.4% of the exergy destruction caused by the absorption chiller can be obtained. The 2.8% increase in lithium-bromide concentration decreases the exergy destruction primarily within the absorber with a decrease of 5.1%. This increase in concentration is shown to also decrease the maximum cooling capacity by 3% and increase the exergy destruction of the generator by 4.9%. The study also shows that the increase in concentration will change the internal temperatures by 3 to 7 °C. Conversely, reducing the weak solution concentration results is also shown to increase the exergetic destruction rates while also potentially increasing the cooling capacity.
Thermal energy storage (TES) is an important technology for effective and efficient energy management. The proper design and operation of a TES require an understanding of its behavior and characteristics. Here, the transient behavior during charging and discharging of a fully mixed, open TES is modeled and analyzed. Included are developments and analyses of the charging temperature function and the maximum charging temperature of the TES, the charging energy flow function and the maximum heat flow capacity of the TES, the discharging temperature function and the minimum charging temperature of the TES, the discharging energy flow function and the maximum heat flow capacity of the TES, and the expression for one cycle of the TES. The impact of various factors on charging and discharging are investigated. The results show that, by increasing the input energy flow rate, the charging temperature of the TES is raised, and that an increase in the input energy flow rate raises the discharging temperature of the TES in the early stage of discharging, while a decrease in the outlet energy flow rate increases the discharging temperature of the TES in the late stage of discharging. Copyright © 2016 John Wiley & Sons, Ltd.
The role of thermal energy storage (TES) in district energy (DE) system is assessed. The Friedrichshafen DE system is considered as a case study and exergy analysis is utilized. The TES is designed to complement and to increase the effectiveness of the solar panels included in the district energy system. The TES stores the surplus solar energy until is needed by thermal energy users of the Friedrichshafen DE system. The results quantify the positive impact of the TES on the performance of the Friedrichshafen DE system, and demonstrate that the overall energy and exergy efficiencies of the TES are 60% and 19%, respectively. It is also shown over an annual period that the temperature, energy, exergy and energy efficiency of the TES exhibit similar trends and that the TES exergy accumulation and exergy efficiency exhibit similar trends.
District energy (DE) and thermal energy storage (TES) are two energy technologies that can enhance the efficiency of energy systems. Also, DE and TES can help address global warming and other environmental problems. In this study, a stratified TES is assessed using exergy analysis, to improve understanding of the thermodynamic performance of the stratified TES, and to identify energy and exergy behavioural trends. The analysis is based on the Friedrichshafen DE system, which incorporates seasonal TES, and which uses solar energy and fossil fuel. The overall energy and exergy efficiencies for the Friedrichshafen TES are found to be 60 and 19 % respectively, when accounting for thermal stratification. It is also found that stratification does not improve the performance of the TES notably. Considering the TES as stratified and fully mixed does not significantly affect the overall performance of the Friedrichshafen TES because, for this particular case, temperatures are very close whether the TES is treated as stratified or fully mixed.
The building sector, as the major energy consumers, demands most of the energy research to assess different energy suppliers from various aspects. In this study, two non-residential buildings, one being commercial and the other industrial, are chosen as case studies. For these case studies, two different renewable energy technologies and one hybrid system are considered for a specified size. The environmental impact indices, renewable energy indices, and the renewable exergy indices have been evaluated for every energy options. The results obtained indicate that the hybrid system (without considering the economics factors) is superior since having top indices. The importance of the energy consumption patterns in buildings were proven by the indices. Utilization of the non-fossil fuels is one part of the solution to environmental hazards while energy conservation being the other. It is shown that the re-design of the energy resources would be achievable for buildings.
District energy (DE) systems provide an important means of mitigating greenhouse gas emissions and the significant related concerns associated with global climate change. DE systems can use fossil fuels, renewable energy and waste heat as energy sources, and facilitate intelligent integration of energy systems. In this study, an enviro-economic function is developed for assessing various energy sources for a district energy system. The DE system is assessed for the considered energy resources by considering two main factors: CO2 emissions and economics. Using renewable energy resources and associated technologies as the energy suppliers for a DE system yields environmental benefits which can lead to financial advantages through such instruments as tax breaks; while fossil fuels are increasingly penalized by a carbon tax. Considering these factors as well as the financial value of the technology, an analysis approach is developed for energy suppliers of the DE system. In addition, the proposed approach is modified for the case when thermal energy storage is integrated into a DE system.
In some thermal networks like district energy systems, there can exist conditions, depending on space availability, economics, project requirements, insulation, storing media type and other issues, for which it may be advantageous to utilize several thermal energy storages (TESs) instead of one. Here, various configurations for multiple TESs are proposed and investigated. Significant parameters for a TES, or a set of TESs, include discharging temperature and recovered energy. First, one TES is modeled to determine the final temperature, energy recovery, and energy efficiency. Next, characteristics for various grid configurations of multiple TESs are developed as functions of TES characteristics (e.g., charging and discharging temperatures and energy quantities). Series, parallel and comprehensive grid TES configurations are considered. In the parallel configuration, the TESs behave independently. This suggests that the TES can consist of different storage media types and sizes, and that there is no restriction on initial temperature of the TES. In the series configuration, the situation is different because the TESs are connected directly or indirectly through a heat exchanger. If there is no heat exchanger between the TESs, the TES storage media should be the same, because the outlet of one TES in the series is the inlet to the next. The initial temperature of the second TES must be smaller than the discharge temperature of the first. There is no restriction on the TES size for series configurations. The general grid configuration is observed to exhibit characteristics of both series and parallel configurations.
Economic and CO2 Emissions Comparison of District Energy System Using Geothermal and Solar Energy ResourcesPublished: 31 October 2013 by MDPI AG in Proceedings of The 3rd World Sustainability Forum
District energy (DE) systems provide an important means of mitigating greenhouse gas (GHG) emissions and the significant related concerns associated with global climate change. DE systems can use fossil fuel, renewable energy and waste heat as energy sources, and facilitate intelligent integration of energy systems. In this paper, solar thermal and geothermal energy are compared as energy sources for a district energy system which serves a community including commercial and educational buildings. The DE system is assessed for the considered energy resources in two main ways, by considering CO<sub>2</sub> emissions and economic aspects. The results obtained for the solar and geothermal energy sources are compared to detect trends. The results indicate that solar thermal energy is the most advantageous energy technology for a DE system from an environmental perspective, while geothermal energy is more beneficial from a financial point of view. An examination of the cost distribution for the technologies shows that when solar thermal energy is the main energy supply for a DE system, the system exhibits the highest loan payments and the lowest fuel costs (FCs) and insurance and maintenance (I&M) payments. With geothermal systems, loan payments are lower while the total cost over the life of the technology is higher for the DE system. Using solar thermal and geothermal technologies as the energy supply for a DE system also yields environmental benefits which can lead to financial advantages through such instruments as tax breaks. The research reported here is intended to allow energy technology suppliers to work with communities while accounting appropriately for economic issues and CO<sub>2</sub> emissions associated with these energy technologies.
In practice, there are some conditions, depending on space availability, economics, project requirements, insulation, storing media type and other issues, for which it may be advantageous to utilize several thermal energy storages (TESs) instead of one in thermal networks like district energy systems. Here, various configurations for multiple TESs are proposed and investigated. Significant parameters for a TES, or a set of TESs, include discharging temperature and recovered energy. First, one TES is investigated to determine the final temperature and energy recovery. Next, characteristics for various configurations of multiple TESs are developed as functions of TES characteristics (e.g., charging and discharging temperatures and energy quantities). Series, parallel and general grid (simultaneous series and parallel) TES configurations are considered. In the parallel configuration, the TESs behave independently. This suggests that with the TES can consist of different storage media types and sizes, and that there is no restriction on initial temperature of the TES. In the series configuration, the situation is different because the TESs are connected directly or indirectly through a heat exchanger. If there is no heat exchanger between the TESs, the TES storage media should be the same, because the outlet of one TES is the inlet to the next one in the series. The initial temperature of the second TES must be smaller than the discharge temperature of the first. There is no restriction on the TES size for series configurations. The general grid configuration is observed to exhibit characteristics of both series and parallel configurations.
The building sector, as one of the major energy consumers, demands most of the energy research to assess different energy options from various aspects. In this paper, two similar residential buildings, with either low or high energy consumption patterns, are chosen as case studies. For these case studies, three different renewable energy technology and three different hybrid systems are designed for a specified size. Then, the environmental impact indices, renewable energy indices, and the renewable exergy indices have been estimated for every energy options. Results obtained show that the hybrid systems (without considering the economics factors) are superior and having top indices. The importance of the energy consumption patterns in buildings are proven by the indices. By cutting the energy consumption to about 40% the environment index would increase by more than twice (2.1). Utilization of the non-fossil fuels is one part of the solution to environmental problems while energy conservation being the other. It has been shown that the re-design of the energy consumption model is less complex but more achievable for buildings.
District energy systems are reviewed and possible future enhancements involving expanded thermal networks are considered. Various definitions, classifications and applications of district cooling and heating are discussed and elements of a district energy system are described. Also, the integration of combined heat and power (CHP) with district energy, permitting the cogeneration of electricity and heat, is examined from several points of view and for various locations and applications. One of the main advantages of district heating and cooling systems is their environmental benefits, which are explained in detail. The economics of a thermal network system, as a major factor in the justification for any project, is elaborated upon from industrial, governmental and societal perspectives. Furthermore, related regulations at government levels are suggested based on various investigations. The efficiency of district energy is discussed and exergy analysis, as an effective method for calculating the efficiency of a thermal network, is explained. Finally, other advantages of the district energy technology for communities are pointed out. This review of district heating and cooling considers technical, economic and environmental aspects and helps identify possibilities for future study on district energy systems.
This paper deals with a novel approach to study renewable energy options for buildings to make them more efficient, more cost effective, more environmentally benign, and more technologically attractive. To demonstrate the application of this study, four buildings are chosen as case studies with two from the residential sector, one commercial/institutional building, and one industrial building. A ground source heat pump for heating and cooling, a solar water heater for space heating and/or hot water, and a photovoltaic panel to generate electricity are designed for these case studies. Attempt is made to design projects under hybrid systems combined from two technologies are developed for the above-mentioned four cases. Results obtained indicate that solar thermal option for hot water and space heating becomes the most cost effective one for all cases (e.g., $4956 for Cases 1 and 2 and $70,652 for Case 3, and $91,361 for Case 4). In addition, solar electricity through PVs is technologically the most suitable one to meet the electricity demand. The ground source heat pump option is quite attractive from the efficiency and environmental impact point of views although it requires installation and maintenance, etc. Finally, hybrid systems provide better advantages, such as higher efficiency, reduced cost, reduced emissions, etc.