Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Analysis of a Trigeneration System Through Transient Simulations(2013) Hartsog, John; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis develops a transient computer model of a trigeneration system using TRNSYS software. This simulation model can accurately reproduce the results from a real world experiment of a trigeneration system conducted over five days. This model is then applied to an entire cooling season to show the primary energy usage of a trigeneration system using an adsorption chiller to meet the cooling load. These results can then be compared to the primary energy usage of a residence with a traditional grid-powered Vapor Compression System (VCS) air conditioner. In order to evaluate the geographic feasibility of this trigeneration system, four different cities were selected for analysis. The chosen cities had various climate conditions to aid in comparison. An analysis was performed on the primary energy usage, environmental impact, and economic cost of the trigeneration system to demonstrate the feasibility and likely implementation of one form of trigeneration technology.Item Development and analysis of micro polygeneration systems and adsorption chillers(2012) Gluesenkamp, Kyle; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)About a fifth of all primary energy in the US is consumed by residential buildings, mostly for cooling, heating and to provide electricity. Furthermore, retrofits are essential to reducing this consumption, since the buildings that exist today will comprise over half of those in use in 2050. Residential combined heat and power (or micro CHP, defined by <5 kW electrical generation capacity) has been identified as a retrofit technology which can reduce energy consumption in existing homes during the heating season by 5-30%. This thesis investigates the addition of a thermally-driven chiller/heat pump to a CHP system (to form a trigeneration system) to additionally provide savings during the cooling season, and enhance heating season savings. Scenarios are identified in which adding thermally-driven equipment to a micro CHP system reduces primary energy consumption, through analytical and experimental investigations. The experimental focus is on adsorption heat pump systems, which are capable of being used with the CHP engines (prime movers) that are already widely deployed. The analytical analysis identifies energy saving potential off-grid for today's prime movers, with potential on-grid for various fuel cell technologies. A novel dynamic test facility was developed to measure real-world residential trigeneration system performance using a prototype adsorption chiller. The chiller was designed and constructed for this thesis and was driven by waste heat from a commercially available natural gas-fueled 4 kW (electric) CHP engine. A control strategy for the chiller was developed, enabling a 5-day experiment to be run using a thermal load profile based on moderate Maryland summer air conditioning loads and typical single-family domestic hot water demand, with experimental results in agreement with models. In this summer mode, depending on electrical loads, the trigeneration system used up to 36% less fuel than off-grid separate generation and up to 29% less fuel than off-grid CHP without thermally driven cooling. However, compared to on-grid separate generation, the experimental facility used 16% more primary energy. Despite high chiller performance relative to its thermodynamic limit, this result is primarily due to the electrical efficiency of the prime mover being lower than the grid. A residential trigeneration system utilizing a high temperature fuel cell is predicted to save up to 42% primary energy relative to the grid.Item COMPARISON OF WASTE HEAT DRIVEN AND ELECTRICALLY DRIVEN COOLING SYSTEMS FOR A HIGH AMBIENT TEMPERATURE, OFF-GRID APPLICATION(2012) Horvath, Christopher Philip; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forward army bases in off-grid locations with high temperatures require power and cooling capacity. Each gallon of fuel providing electrical power passes through a complex network, introducing issues of safety and reliability if this network is interrupted. Instead of using an engine and an electrically powered cooling system, a more efficient combined heat and power (CHP) configuration with a smaller engine and LiBr/Water absorption system (AS) powered by waste heat could be used. These two configurations were simulated in both steady state and transient conditions, in ambient temperatures up to 52°C, providing up to 3 kW of non-cooling electricity, and 5.3 kW of cooling. Unlike conventional AS's which crystallize at high temperatures and use bulky cooling towers, the proposed AS's avoid crystallization and have air-cooled HXs for portability. For the hottest transient week, the results showed fuel savings of 34-37%, weight reduction of 11-19%, and a volumetric footprint 3-10% smaller.Item MODELING OF A COMBINED HEAT AND POWER UNIT AND EVALUATION OF SYSTEM PERFORMANCE IN BUILDING APPLICATIONS(2010) Bush, John; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a validated model of a 4 kilowatt combined heat and power (CHP) system derived from laboratory experiments. The model is tuned to match steady state experimental tests, and validated with transient experimental results. Further simulations are performed using a modeled thermal storage system, and implementing the CHP system into a building model to evaluate the feasibility of CHP in the mid-Atlantic region, as well as the Great Lakes region. The transient simulation outputs are within 4.8% of experimental results for identical load profiles for a simulated summer week, and within 2.2% for a spring or autumn week. When integrated with a building model, the results show 23.5% cost savings on energy in the mid-Atlantic region, and 29.7% savings in the Great Lakes region.Item Experimental and Theoretical Investigation of Integrated Engine Generator - Liquid Desiccant System(2005-11-30) Nayak, Sandeep M; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Combined heat and power (CHP) involves on-site generation of electricity by using gas-fired equipment along with utilization of waste heat available from the power generation process. This research focuses on the design, installation and analysis of integration options of a modular CHP system involving the integration of a natural gas fired reciprocating engine generator with a liquid desiccant dehumidification system in a medium sized commercial office building. The engine generator provides 75 kW of electrical power fed parallel to the grid while the combined waste heat from the exhaust gases and jacket water from the engine is used to regenerate the liquid desiccant. The liquid desiccant unit dehumidifies the outdoor air and supplies it to the mixed air section of the roof top unit of the building. The experimental part of the research discusses the various aspects involved in the design and installation of the system such as the mechanical design of the structure, the heat recovery loop design and the electrical interconnection with the grid. Extensive testing and data analysis was conducted to characterize the performance of the integrated system and compare the performance with a traditional power plant as well as conventional HVAC systems. A comprehensive steady state thermodynamic model of the integrated CHP system was coded in Visual Basic .Net. After validation with experimental results, an economic and climate model was integrated into the thermodynamic model with actual electricity and gas prices as well as the climate data for different representative states in the United States to demonstrate the feasibility of the system under different scenarios. This research addresses and assesses the different integration opportunities and issues encountered during the integration of the engine generator - liquid desiccant system with the existing electrical grid and the roof top unit. Based on the hands-on experience gained during the design, installation, operation and maintenance of the integrated system as well as the results obtained from extensive simulation of the system, this research develops valuable design guidelines on the integration and operation of the packaged engine generator-liquid desiccant system in commercial office buildings for future designers and system integrators.Item Performance Investigation of CHP Equipment(2005-11-03) Bian, Ji; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Cooling Heating & Power systems for Buildings (BCHP) are attracting more attention due to their advantages as compared to conventional energy systems. As a developing technology, there are still problems to be solved. Fuel flexibility and dynamic response between different machines in the system are two of the main issues to be investigated. This study presents research conducted on a BCHP system that is composed of a microturbine, an absorption chiller and a solid desiccant unit that are driven by the microturbine's exhaust gas to provide cooling and dehumidification. It demonstrates the feasibility of operating the microturbine that is originally designed for natural gas on propane and analyzes the reasons for the efficiency reduction when operating on propane. It further presents a model that describes the transient behavior of the absorption chiller, which requires a much longer period to reach its steady state compared with the microturbine.Item THE DEVELOPMENT OF AN AIR-COOLED ABSORPTION CHILLER CONCEPT AND ITS INTEGRATION IN CHP SYSTEMS(2004) Liao, Xiaohong; Radermacher, Reinhard K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on the feasibility, crystallization issues, and the integration of LiBr-H2O air-cooled absorption chillers into Cooling, Heating and Power (CHP) systems. The concept of an air-cooled system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr-H2O solution then becomes the main issue in the operation of the unit, since the air-cooled absorber tends to operate hotter than the water-cooled absorber due to the relative heat transfer characteristics of the coolant leading to crystallization of the working fluid. Differently from the conventional approaches to air-cooled absorption chillers, novel temperature control strategies in conjunction with a specialized application is proposed. This prevents crystallization but presents unique system integration challenges and opportunities. A model to accurately reflect the thermodynamic characteristics of air-cooled absorption chillers and to facilitate control is developed as part of this research, and field experiments that simulate air-cooled conditions with a water-cooled absorption chiller, which was driven by the waste heat of a microturbine, were conducted to validate the feasibility of the air-cooled concept and the accuracy of computer model. While CHP provides a good opportunity for the application of air-cooled absorption chillers, system integration issues need to be investigated. The capital cost of CHP equipment and the load fluctuation of a commercial building restrict the advantage of designing a unit sized for peak load. Therefore, the conventional Heating Ventilation and Air Conditioning (HVAC) system is needed to pick up the residual loads. Thus, the result of an extensive system integration analysis is that CHP should be arranged in series with the HVAC system to ensure obtaining more operating hours at its full capacity, so that the cost savings achieved through the recovery of waste heat are fully realized to repay its higher initial capital cost. The primary energy savings are presented for all potential configurations. As a part of this research a fully integrated CHP system has been installed and instrumented at the Chesapeake Building. It is a commercial office building on the University of Maryland campus. The experimental setup, data processing, and experience gained are detailed here. Based on the computer simulation, extensive experiments, first hand installation, operation and maintenance experience, valuable guidelines on the integration of an air-cooled absorption chiller in CHP are developed. All the guidelines are also applicable to water-cooled absorption chillers.