Now showing 1 - 10 of 14
- PublicationNumerical and finite element analysis of heat transfer in a closed loop geothermal systemAnalysis of the thermal regime created by a geothermal borehole heat exchanger is performed using a closed form radial heat flow equation, a geothermal borehole heat exchanger design tool and a finite element model. Climatic, heat exchanger construction and building load data are entered into the heat exchanger design tool in order to create a theoretical model along with thermal parameters from a number of geological formations. Output data from the design tool model are used in conjunction with the closed form radial heat flow equation to calculate the predicted temperature with respect to time and distance from the heat exchanger for the modelled ground formations. The output data from the design tool is also used to create a number of finite element method models against which the predictions calculated using the closed form radial heat flow equation can be compared. A good correlation between the temperatures predicted by the finite element models and the closed form equation calculations is observed. However when used within its recommended limiting conditions, the closed form equation is shown to slightly underestimate the temperature of the ground when compared to the finite element model predictions. The limiting conditions associated with the closed form equation are discussed in the context of the output from the finite element method models.
- PublicationGeothermal energy in small countries - laying the foundations for innovative developmentCreation of an environment in which shallow geothermal energy can thrive will require a coherent approach and a high level of collaboration with professionals from countries that have developed technical expertise in the area. Implementation of regulations, standards and guidelines adapted from best practice in countries such as Switzerland, Germany and Sweden, in addition to understanding the mistakes and successes made by these countries, with respect to the development of their geothermal industries, will help small countries such as Ireland to develop a well-regulated market for the technology. This paper outlines and addresses some of the technical, regulatory and certification issues faced particularly by small countries in their efforts to develop a shallow geothermal energy industry, provides examples of best practice with regard to development in countries with established geothermal energy industries and presents proposed solutions to these issues / barriers using the existing situation in Ireland by way of example.
- PublicationDesign and development of a low-cost thermal response rigA thermal response test (TRT) is a controlled insitu test during which a known quantity of heat energy is injected into a closed loop heat-exchanger pipe while the heat dissipation rate into the surrounding ground is monitored. Results from a test can be interpreted to determine a number of ground thermal parameters with are vital design requirements for any medium to large scale ground source energy system. This paper describes the design and construction of a low cost TRT rig and compares the results obtained from a test using the constructed rig and a commercially built rig in order to evaluate the accuracy of the constructed equipment. The TRT rig is designed in accordance with the following principles: keep construction costs low, improve the cost-efficiency of TRT testing by incorporating remote data transmission capability and ensure attainment of sufficient accuracy to satisfy the design requirements of ground source energy systems. Analysis of data collected by the TRT rigs result in a calculated thermal conductivity of 1.9 W/mK in both cases. This value falls within the range expected for the tested geological formation and confirms the accuracy of both test rigs.
Scopus© Citations 5 2060
- PublicationBubbling fluidised bed gasification of wheat straw-gasifier performance using mullite as bed materialThe adoption of wheat straw as a fuel for gasification processes has been hindered due to a lack of experience and its propensity to cause bed agglomeration in fluidised bed gasifiers. In this study wheat straw was gasified in a small scale, air blown bubbling fluidised bed using mullite as bed material. The gasifier was successfully operated and isothermal bed conditions maintained at temperatures up to 750 ◦C. Below this temperature, the gasifier was operated at equivalence ratios from 0.1 to 0.26. The maximum lower heating value of the producer gas was approximately 3.6 MJm−3 at standard temperature and pressure (STP) conditions and was obtained at an equivalence ratio of 0.165. In general, a producer gas with a lower heating value of approximately 3 MJm−3 at STP could be obtained across the entire range of equivalence ratios operated. The lower heating value tended to fluctuate, however, and it was considered more appropriate for use in heat applications than as a fuel for internal combustion engines. The concentration of combustibles in the producer gas was lower than that obtained from the gasification of wheat straw in a dual distributor type gasifier and a circulating fluidised bed. These differences were associated with reactor design and, in the case of the circulating fluidised bed, with higher temperatures. Equilibrium modelling at adiabatic conditions, which provides the maximum performance of the system, showed that the gasifier was operating at suboptimal equivalence ratios to achieve greatest efficiencies. The maximum calculated theoretical cold gas efficiency of 73% was obtained at an equivalence ratio of 0.35.
Scopus© Citations 8 946
- PublicationDesign and development of a low-cost divided bar apparatusA divided bar apparatus is deemed to be the most accurate method of measuring the thermal conductivity, λ, (W/mK) of intact rock cores in the laboratory. The divided bar is a steady-state comparative method in which the temperature drop across a disk of rock is compared with that across a disk of standard material of known conductivity. Thermal conductivity test results obtained from rock cores can be used in software programs to determine the design requirements for any medium to large-scale ground-source energy system. This paper describes the design and development of a low-cost divided bar apparatus and compares the values obtained to those achieved by previous researchers and those recommended by EED, a commonly used borehole heat exchanger design software program. The divided bar was designed in accordance with the following principles: keep construction costs low by using readily available materials, develop a simplistic operating procedure to promote continuity of use and cater for the testing of different sized rock cores. As there are currently no recognised testing standards available for operation of a divided bar apparatus, the sample preparation procedure for samples tested on the UCD divided bar apparatus was developed as a proposed standard testing procedure. The proposed procedure amalgamates the developments and suggestions of previous researchers in addition to published test procedures in Ulusay and Hudson (2007), and could possibly contribute towards the development of a standardised procedure for testing on a divided bar apparatus. The test results presented in this paper demonstrate a strong relationship between thermal conductivity and mineral composition with the effects of porosity also having a notable influence on the thermal conductivity of the tested rocks.
Scopus© Citations 8 907
- PublicationEnergy piles: site investigation and analysisDespite an increasing worldwide use of geothermal energy foundations, there is a lack of published guidelines and results from thermal response testing of such installations. In this paper the results are presented from thermal response, thermal recovery and laboratory thermal testing performed at two sites in Ireland. Some practical issues concerned with the use of thermal response testing rigs, designed for use with deep boreholes, on relatively short piles are discussed and addressed. Given the relatively short geothermally active depth of the energy foundations tested, and the fact that the University College Dublin thermal response testing rig has been designed primarily for testing on medium and deep geothermal boreholes, thermal response tests of shorter durations than are normally used for deep boreholes were performed. The techniques used to analyse the various test results are outlined, and the resulting values of thermal conductivity obtained are within the range of those expected for the prevailing geology of the sites.
Scopus© Citations 17 1310
- PublicationGeothermal energy : settlement and water chemistry in Cork, IrelandDetailed analysis of potential water chemistry and settlement issues associated with the installation of open-loop geothermal systems is infrequently carried out. This has led to the failure of several previously installed systems. Chemical analysis of water extracted from beneath the Cork docklands, Ireland has been performed by the authors in order to assess the suitability of the area for the exploitation of open-loop geothermal energy. The possibility of settlement induced by pumping of groundwater for open-loop systems has also been examined. Current market penetration of ground source heat pumps in Ireland is discussed to illustrate the infancy of the technology in Ireland relative to other European countries and to highlight the necessity of approaching the possible installation of such systems with the care required. Water extracted from beneath the docklands shows that significant water chemistry issues exist. Laboratory and field tests confirm that optimal concentration levels of several water chemistry characteristics are significantly exceeded; leading to the conclusion that open-loop exploitation in the area may not be suitable. In addition, settlement induced by pumping of water could potentially lead to a consolidation settlement in excess of 30 mm due primarily to the existence of highly compressible alluvium.
Scopus© Citations 5 1468
- PublicationAnalysis of bed agglomeration during gasification of wheat straw in a bubbling fluidised bed gasifier using mullite as bed materialThe quantity and composition of the ash content of straw poses technical challenges to its thermal conversion and have been widely reported to cause severe ash sintering and bed agglomeration during fluidised bed gasification. Literature indicates that a combination of reactor design and bed material measures is required to avoid defluidisation at temperatures above 800 °C. Using scanning electron microscopy and energy dispersive X-ray spectroscopy this study investigated the initial agglomeration of a mullite bed during the gasification of wheat straw in a small scale, air blown bubbling fluidised bed. The results show that the temperatures along the height of the bed converge prior to any marked drop in pressure or heating of the lower freeboard. This convergence was seen to occur at temperatures close to 750 °C in repeated gasification experiments. Energy dispersive X-ray spectroscopy indicates coating-induced agglomeration caused by the reaction of alkali metals with silica. Scanning electron microscopy under high magnification revealed a layered structure to the agglomerates, where ash particles are subsumed into a fused material. This suggests the formation of agglomerates by the three step agglomeration process postulated by other authors. Analysis of indices used to predict agglomeration on the basis of a fuel's ash content and composition indicates that the Alkali Index is the most accurate, successfully predicting agglomeration for 7 of the 9 fuels where agglomeration was observed.
Scopus© Citations 30 985
- PublicationMonitoring environmental parameters in poultry production facilitiesIncreases in fuel and feed prices are placing a significant burden on the poultry industry in Ireland and worldwide. For producers to meet their financial targets, increased performance and output is a key issue, now more than ever. To optimise performance in broiler production houses, the effect of environmental and air quality parameters on bird performance and energy consumption must be known to allow farmers make informed management decisions. This paper concentrates on the application precision livestock farming sensors to develop recommendations for improved bird performance and energy consumption in broiler production farms in Ireland. Air temperature, relative humidity, light, air speed and air quality (in particular CO2 and NH3 concentrations) are identified as important parameters for improving bird performance and energy consumption in broiler production houses. Several of these parameters (temperature, relative humidity, CO2 and NH3) were monitored on two farms during the study over the initial 2 weeks of the production cycle. Air quality was often overlooked during the production process, as farmers struggled to limit high heating and feed costs. However, elevated levels of CO2 (>3000 ppm) did not appear to affect broiler growth rates. Additionally, a strong correlation was observed between relative humidity and NH3 (R2 = 0.86 - 0.92). Producers tend to use relative humidity as an indication for NH3 levels and the research shown in this study confirms the close relationship between the two parameters. It is recommended that further data should be gathered from producing units and novel performance technologies should also be investigated.
- PublicationDeveloping Geothermal Energy Research Capabilities at University College DublinIreland has one of the highest energy dependencies in Europe and as such must adapt quickly to increase renewable energy exploitation levels in order to secure its energy future. A mix of renewable energy technology types (wind, solar, biomass, wave, tidal, geothermal) will be required in order to achieve Ireland’s national renewable energy generation targets. Geothermal (or ground source) energy can have a part to play in this mix. Over the last number of years the School of Civil, Structural & Environmental Engineering in University College Dublin has begun to develop shallow geothermal energy research capabilities in several areas of interest. Early studies involved the investigation of water chemistry and settlement issues at several sites on the Cork docklands. It was concluded that the chemical characteristics of the water contained in the aquifer could hinder the development of open loop geothermal systems in the area, and that settlement may be a potential concern in cases where open loop systems are installed due to the presence of highly compressible alluvium deposits. Subsequent work has involved the development, construction & performance validation of a thermal response testing rig for site thermal characterisation, installation of both domestic and commercial sized energy piles for research purposes and investigation of soil, rock and grout thermal properties using both steady-state and non-steady-state laboratory testing techniques. This paper gives a brief overview of the completed and ongoing work in the School of Civil, Structural & Environmental Engineering.