In Canada 15% of greenhouse gas (GHG) emissions are produced by the residential sector’s energy demand. The majority of the energy demand is space heating which is primarily met with natural gas combustion. Motivation exists to reduce GHG emissions due to their contribution to climate change. Integrated Community Energy Harvesting (ICE-Harvest) systems seek to integrate thermal and electrical energy production, storage, redistribution, and consumption in a way that reduces GHG emissions. Borehole thermal energy storage (BTES) is implemented in ICE-Harvest systems as seasonal thermal energy storage. This thesis presents a novel model of BTES thermal response with reduced complexity to aid in early siting, design, optimization, and control systems development work for ICE-Harvest systems. The reduced model can be used to approximate periodic steady state BTES thermal response. The model provides information on average ground storage volume temperature, outlet fluid temperature, heat exchanger fluid to storage volume heat transfer rate, storage volume top loss heat transfer rate, storage volume side and bottom loss heat transfer rate, and annual thermal energy storage efficiency which aids system modelling efforts for BTES in solar thermal and ICE-Harvest systems. The reduced model is formed from a solution of the thermal energy balance equations for the BTES ground storage volume and heat exchanger fluid with simplified operating conditions for a yearly BTES charging and discharging cycle. Ground storage volume temperature is lumped as a single value. Heat transfer rates between the storage volume and the heat exchanger fluid and the storage volume and its surroundings are modelled with periodic steady state thermal resistance values for the charging and discharging timesteps. A TRNSYS DST simulation of BTES is validated against measurements from a BTES installation and TRNSYS DST is used to generate the periodic steady state thermal resistance values the reduced model requires. The periodic steady state thermal resistance values of BTES charging and discharging are dependent on BTES design parameters (spacing between boreholes, number of boreholes, borehole depth, and storage volume size) and ground thermal properties (thermal capacity and thermal conductivity) which is presented in a series of parameter sweeps with respect to a reference simulation. The reduced model predicts periodic steady state average storage volume temperature with a RMSD of 0.96°C for charging and 1.3°C for discharging when compared to the TRNSYS DST reference simulation. The reduced model predicts the periodic steady state heat exchanger total energy transfer within 1.8% for the charging timestep and 2.8% for the discharging timestep when compared to the TRNSYS DST reference simulation. The reduced model’s periodic steady state thermal resistance values are demonstrated to be independent of heat exchanger fluid inlet temperature except for the side and bottom loss thermal resistance during discharging. The reduced model cannot replicate the change in heat transfer direction that occurs during BTES discharging when the temperature of the storage volume decreases below the temperature of the surrounding ground, however, the magnitude of the energy transfer that would occur is negligible compared to the magnitude of the BTES heat exchanger total energy transfer. / Thesis / Master of Applied Science (MASc)

Future defense, aerospace and automotive technologies involve electronic systems that release high pulsed waste heat like during high power microwave and laser diode applications in tactical and combat aircraft, and electrical and electronic systems in hybrid electric vehicles, which will require the development of an efficient thermal management system. A key design issue is the need for fast charging so as not to overheat the key components. The goal of this work is to study the fabrication and technology implementation feasibility of a novel high energy storage, high heat flux passive heat sink. Key focus is to verify by theory and experiments, the practicability of using phase change materials as a temporary storage of waste heat for heat sink applications. The reason for storing the high heat fluxes temporarily is to be able to reject the heat at the average level when the heat source is off. Accordingly, a concept of a dual latent heat sink intended for moderate to low thermal duty cycle electronic heat sink applications is presented. This heat sink design combines the features of a vapor chamber with rapid thermal energy storage employing graphite foam inside the heat storage facility along with phase change materials and is attractive owing to its passive operation unlike some of the current thermal management techniques for cooling of electronics employing forced air circulation or external heat exchangers. In addition to the concept, end-application dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance concept based design tool/model has been developed to analyze and optimize the design for experiments. The model showed that it is possible to have a dual latent heat sink design capable of handling 7 MJ of thermal load at a heat flux of 500 W/cm2 (over an area of 100 cm2) with a volume of 0.072 m3 and weighing about 57.5 kg. It was also found that with such high heat flux absorption capability, the proposed conceptual design could have a vapor-to-condenser temperature difference of less than 10 0C with a volume storage density of 97 MJ/m3 and a mass storage density of 0.122 MJ/kg. The effectiveness of this heat sink depends on the rapidness of the heat storage facility in the design during the pulse heat generation period of the duty cycle. Heat storage in this heat sink involves transient simultaneous laminar film condensation of vapor and melting of an encapsulated phase change material in graphite foam. Therefore, this conjugate heat transfer problem including the wall inertia effect is numerically analyzed and the effectiveness of the heat storage mechanism of the heat sink is verified. An effective heat capacity formulation is employed for modeling the phase change problem and is solved using finite element method. The results of the developed model showed that the concept is effective in preventing undue temperature rise of the heat source. Experiments are performed to investigate the fabrication and implementation feasibility and heat transfer performance for validating the objectives of the design i.e., to show that the VCTES heat sink is practicable and using PCM helps in arresting the vapor temperature rise in the heat sink. For this purpose, a prototype version of the VCTES heat sink is fabricated and tested for thermal performance. The volume foot-print of the vapor chamber is about 6"X5"X2.5". A custom fabricated thermal energy storage setup is incorporated inside this vapor chamber. A heat flux of 40 W/cm2 is applied at the source as a pulse and convection cooling is used on the condenser surface. Experiments are done with and without using PCM in the thermal energy storage setup. It is found that using PCM as a second latent system in the setup helps in lowering the undue temperature rise of the heat sink system. It is also found that the thermal resistance between the vapor chamber and the thermal energy storage setup, the pool boiling resistance at the heat source in the vapor chamber, the condenser resistance during heat discharging were key parameters that affect the thermal performance. Some suggestions for future improvements in the design to ease its implementation and enhance the heat transfer of this novel heat sink are also presented.

No description available.

No description available.

A desirable feature of concentrated solar power (CSP) with integrated thermal energy storage (TES) unit is to provide electricity in a dispatchable manner during cloud transient and non-daylight hours. Latent heat thermal energy storage (LHTES) offers many advantages such as higher energy storage density, wider range of operating temperature and nearly isothermal heat transfer relative to sensible heat thermal energy storage (SHTES), which is the current standard for trough and tower CSP systems. Despite the advantages mentioned above, LHTES systems performance is often limited by low thermal conductivity of commonly used, low cost phase change materials (PCMs). Research and development of passive heat transfer devices, such as heat pipes (HPs) to enhance the heat transfer in the PCM has received considerable attention. Due to its high effective thermal conductivity, heat pipe can transport large amounts of heat with relatively small temperature difference. The objective of this research is to study the charging and discharging processes of heat pipe-assisted LHTES systems using computational fluid dynamics (CFD) and experimental testing to develop a method for more efficient energy storage system design. The results revealed that the heat pipe network configurations and the quantities of heat pipes integrated in a thermal energy storage system have a profound effect on the thermal response of the system. The optimal placement of heat pipes in the system can significantly enhance the thermal performance. It was also found that the inclusion of natural convection heat transfer in the CFD simulation of the system is necessary to have a realistic prediction of a latent heat thermal storage system performance. In addition, the effects of geometrical features and quantity of fins attached to the HPs have been studied. / Mechanical Engineering

The balance of the supply of renewable energy sources with electricity demand will become increasingly difficult with further penetration of renewable energy sources. Traditionally, large stationary batteries have been used to store renewable energy in excess of electricity demand and dispatch the stored energy to meet future electricity demand. Cool thermal energy storage is a feasible renewable energy balancing solution that has economic and environmental advantages over utility scale stationary lead-acid batteries. Two technologies, ice harvesters and internal-melt ice-on-coil cool thermal energy storage, have the capability to store excess renewable energy and use the energy to displace electricity used for building cooling systems. When implemented by a utility, cool thermal energy storage can replace large utility scale batteries for renewable energy balancing in utility regions with high renewable energy penetration. The California Independent System Operator (CAISO) region and the Electric Reliability Council of Texas (ERCOT) are utility regions with large solar and wind resources, respectively, that can benefit from installation of cool thermal energy storage systems for renewable energy balancing. With proper scheduling of energy dispatched from cool thermal energy storage, these technologies can be effective in displacing peak power capacity for the region, in displacing traditional building cooling equipment, and in recovering renewable energy that would otherwise be curtailed. / Master of Science

Thesis (MScIng)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Spier Estate - a wine estate in the Western Cape Province of South Africa - is engaged in a transition towards operating according to the principles of sustainable development. Besides changes in social and other environmental aspects, the company has set itself the goal to be carbon neutral by 2017. To this end, Spier is considering the on-site generation of electricity from renewable energy sources. This study was initiated to explore the technical and economic feasibility of a concentrating solar power plant for this purpose on the estate. The investigation was carried out to identify the most appropriate solar thermal energy technology and the dimensions of a system that fulfils the carbon-offset requirements of the estate. In particular, potential to offset the annual electricity consumption of the currently 5 570 MWh needed at Spier, using a concentrating solar power (CSP) system, was investigated. Due to rising utility-provided electricity prices, and the expected initial higher cost of the generated power, it is assumed that implemented efficiency measures would lead to a reduction in demand of 50% by 2017. However, sufficient suitable land was identified to allow electricity production exceeding today’s demand. The outcome of this study is the recommendation of a linear Fresnel collector field without additional heat storage and a saturated steam Rankine cycle power block with evaporative wet cooling. This decision was based on the system’s minimal impact on the sensitive environment in combination with the highest potential for local development. A simulation model was written to evaluate the plant performance, dimension and cost. The analysis was based on a literature review of prototype system behaviour and system simulations. The direct normal irradiation (DNI) data that was used is based on calibrated satellite data. The result of the study is a levelised cost of electricity (LCOE) of R2.741 per kWh, which is cost competitive to the power provided by diesel generators, but more expensive than current and predicted near-future utility rates. The system contains a 1.8 ha aperture area and a 2.0 MWe power block. Operating the plant as a research facility would provide significant potential for LCOE reduction with R2.01 per kWh or less (favourable funding conditions would allow for LCOE of R1.49 per kWh) appearing feasible, which results in cost competitiveness in comparison a photovoltaic (PV) solution. Depending on tariff development, Eskom rates are predicted to reach a similar level between 2017, the time of commissioning, and the year 2025. The downside is that the plant would not solely serve the purpose of electricity offsetting for Spier, which may result in a reduced amount of electricity that may be generated. Further studies are proposed to refine the full potential of cost reduction by local development and manufacturing as well as external funding. This includes identification of suitable technology vendors for plant construction. An EIA is required to be triggered at an early stage to compensate for its long preparation. / AFRIKAANSE OPSOMMING: Die Spier wynlandgoed in die Wes-Kaap Provinsie van Suid-Afrika is tans in ‘n oorgangsfase tot besigheids-praktyke gebaseer op volhoubare ontwikkeling. Afgesien van die sosiale en omgewingsaspekte het die groep hom ook ten doel gestel om koolstof neutraal te wees teen 2017. Ten einde hierdie doel te bereik, moet die maatskappy sy algehele elektrisiteitsverbruik vervang met hernubare bronne. Hierdie studie is dus geloods om die tegniese en ekonomiese uitvoerbaarheid van 'n gekonsentreerde sonkragstasie op die landgoed te ondersoek. Hierdie ondersoek is gedoen om die mees toepaslike sontermiese tegnologie en die grootte van 'n termiese sonkragstelsel te bepaal, wat aan die koolstof vereistes van die landgoed voldoen. Die potensiaal om die jaarlikse elektrisiteitsverbruik van 5 570 MWh met 'n gekonsentreerde elektriese sonkragstelsel te vervang, is ondersoek. Weens die toename in die elektrisiteitsprys en die verwagte hoërkoste van opgewekte elektrisiteit word aanvaar dat die implementering van voorgestelde doeltreffendheidsverbeteringe, sal lei tot 'n afname in die aanvraag na elektrisiteit van tot 50% teen die jaar 2017. Voldoende beskikbare grond is geïdentifiseer om genoeg elektrisiteit te produseer om die huidige vraag na elektrisiteit te oorskry. Die uitkoms van die studie is die aanbeveling van 'n lineêre Fresnel kollektorveld sonder addisionele warmte storing, asook 'n versadigde stoom Rankine sikluskragblok met ‘n nat-verdamping verkoelingstelsel. Die besluit is gebaseer op die stelsel se minimale impak op die omgewing, tesame met die hoogste potensiaal vir plaaslike ontwikkeling. 'n Simulasie is ontwikkel om die aanleg se werkverrigting, grootte en koste te evalueer. Die analise is gebaseer op 'n literatuuroorsig van 'n prototipe stelsel gedrag en stelsel-simulasies. Die direkte normale sonstralings data wat gebruik is, is gebaseer op gekalibreerde satelliet data. Die bevinding van die studie is 'n gebalanseerd koste van elektrisiteit van R2.74 per kWh, wat mededingend is met die koste van elektrisiteit wat deur diesel kragopwekkers verskaf word, maar is aansienlik duurder as die huidige en toekomstige voorspellings van Eskom-tariewe. Die stelsel bevat 'n 1.8 ha son kollektor oppervlakte en 'n 2.0 MWe krag-blok. Daarbenewens, sal die gebruik van die aanleg as 'n navorsingsfasiliteit die potensiaal hê om die gebalanseerd koste van elektrisiteit te verminder na R2.01 per kWh of minder (gunstig befondsing voorwaardes sal gebalanseerd koste van elektrisiteit van R1.49 per kWh tot gevolg hê), wat mededingend is met die koste van 'n fotovoltaïese alternatief. Daar word voorspel dat Eskom-tariewe dieselfde sal bly vanaf 2017, die jaar van inbedryfstelling van die aanleg, tot en met die jaar 2025. Die nadeel is dat die aanleg nie noodwendig uitsluitlik vir die opwek van elektrisiteit vir Spier gebruik sal word nie, en daarom kan dit lei tot 'n vermindering in die hoeveelheid elektrisiteit wat deur die aanleg opgewek word. Daar word voorgestel dat verdere studies onderneem word om die moontlikheid van koste-besparings vir die aanleg te ondersoek deur gebruik te maak van plaaslike ontwikkeling en vervaardiging, asook eksterne befondsing. Dit sluit die identifisering van geskikte tegnologie verskaffers vir die aanleg-kostruksie in. 'n Omgewingsimpakstudie, volgens die EIA regulasies, moet ook so gou as moontlik gedoen word aangesien dit n langsame proses is.

Worldwide there is an increasing demand of natural resources. In future, non renewable resources get substituted by renewable resources in the energetic sector as well as in the material sector. That implies a stronger usage of renewable resources especially - wood. In 2009 there was a usage of 77 million cubic meters of wood for material applications and a quantity of 55 million cubic meters for energetic applications in Germany alone. Furthermore, there is an increasing demand on wood for energetic purposes. In 2007 this problematic development led to the first supply bottlenecks. To meet the increasing demands of the future, Short Rotation Coppices (SRC) can help to improve the wood provision. An SRC is a planting of fast growing coppice on agricultural areas, which is managed more intensively than usual forestry practices for a quicker production of wooden biomass. With a comparative LCA of conventional wood and wood from SRC the present study evaluates if wood from SRC is reasonable to cover the increasing demand of wood for material and energetic purposes in an environmental friendly way. A comprehensive literature research regarding LCAs of wood and wooden products shows that there are no previous studies comparing the two types of wood. Hence, the present study examines a particleboard production as the material scenario and the combustion of woodchips in a firing system as the energetic scenario to compare the ecological advantages and disadvantages of wood from SRC and conventional wood. The LCA is implemented with the Gabi software designed by PE International. Data is obtained from previous LCA studies evaluating the production of wood, the particleboard production and the combustion of wood. Additionally, data from the Ecoinvent database is used. Functional units are the production of 1m3 particleboard and the production of 1 MJ of thermal energy. The LCIA is implemented with the “Ecoindicator” as endpoint- and “CML 2001” as midpoint approach to cover broad range of environmental issues. Moreover a sensitivity analyses shows the impact of decisive variables on the results of “Ecoindicator” and “CML 2001”. Results reveal that outcomes of the LCIA are dependent of the assessment method and the processed part of trees from conventional forestry. The present study shows, that with an efficient land use, wood from SRC can help to cover the increasing demand of wood for material and energetic purposes in a sustainable way. However, an immediate usage of wood for energetic purposes has to be seen critical. Instead, a cascaded and sustainable utilization of wood is recommendable to counteract climate change and to improve the efficient use of the renew-able resource - “wood”.

The huge natural energy resources available in the world’s oceans are attracting increasing commercial and political interest. In order to evaluate the status and the degree of acceptability of future Ocean Energy (OE) schemes, it was considered important to develop an Integrated Assessment Methodology (IAM) for ascertaining the relative merits of the competing OE devices being proposed. Initial studies included the gathering of information on the present status of development of the ocean energy systems on wave, OTEC and tidal schemes with the challenges faced for their commercial application. In order to develop the IAM, studies were undertaken for the development and standardization of the assessment tools focussing on: • Life Cycle Assessment (LCA) on emission characteristics. • Energy Accounting (EA) studies. • Environmental Impact Assessment (EIA) over different environmental issues. • Resource captures aspects. • Defining economy evaluation indices. The IAM developed from such studies comprised of four interrelated well defined tasks and six assessment tools. The tasks included the identification of the modus operandi on data collection to be followed (from industry) for assessing respective OE devices, and also advancing relevant guidelines as to the safety standards to be followed, for their deployment at suitable sites. The IAM as developed and validated from case studies in ascertaining relative merits of competing OE devices included: suitable site selection aspects with scope for resource utilisation capability, safety factors for survivability, scope for addressing global warming & energy accounting, the environmental impact assessment both qualitatively and quantitatively on different environmental issues, and the economic benefits achievable. Some of the new ideas and concepts which were also discovered during the development of the IAM, and considered useful to both industry and researchers are given below: • Relative Product Cost (RPC) ratio concept- introduced in making an economic evaluation. This is considered helpful in sensitivity analysis and making design improvements (hybridising etc) for the cost reduction of OE devices. This index thus helps in making feasibility studies on R&D efforts, where the capital cost requirement data and life span of the device is not well defined in the primary stages of development. • Determination of the threshold limit value of the barrage constant - considered useful in determining the efficacy of the planning process. The concept ascertained the relative efficiency achieved for various barrage proposals globally. It could also be applied to suggest the revisions required for certain barrage proposals and also found useful in predicting the basin area of undefined barrage proposal for achieving economic viability. • Estimations made on the future possibility of revenue earnings from the by-products of various OTEC types, including the scope of chemical hubs from grazing type OTEC plants. • Determination of breakeven point- on cost versus life span of wave and OTEC devices studied, which is useful in designing optimum life of the concerned devices. The above stated multi-criterion assessment methodology, IAM, was extended leading to the development of a single criterion model for ascertaining sustainability percent achievable from an OE device and termed IAMs. The IAMs was developed identifying 7 Sustainability Development Indices (SDI) using some the tools of the IAM. A sustainability scale of 0-100 was also developed, attributing a Sustainability Development Load Score (SDLS) percentage distribution pattern over each SDIs, depending on their relative importance in achieving sustainability. The total sum of sustainability development (SD) gained from each SDI gave the IAMs (for the concerned device), indicating the total sustainable percentage achieved. The above IAMs developed, could be applied in ranking OE devices alongside the unsustainable coal power station. A mathematical model of estimating the IAMs was formulated, in order to ascertain the viability to the sustainable development of any energy device. The instruments of IAM and IAMs which have been developed would be helpful to the OE industry in ascertaining the degree of acceptability of their product. In addition it would also provide guidelines for their safe deployment by assessing the relative merits of competing devices. Furthermore, IAM and IAMs would be helpful to researchers undertaking feasibility studies on R&D efforts for material development research, ‘hybridization studies’ (as also new innovations), cost reduction, the performance improvement of respective devices, and any economic gains. With future advancements in OE systems and the availability of field data from large scale commercial applications, the specific values/data of the IAM & IAMs may be refined, but the logic of the models developed in this research would remain the same.

Energy related geo-systems involve a wide range of engineering solutions from energy piles to energy geo-storage facilities and waste repositories (CO₂, nuclear). The analysis and design of these systems require proper understanding of geo-materials, their properties and their response to extreme temperature and high stress excitations, the implications of mixed-fluid conditions when contrasting fluid viscosities and densities are involved, the effect of static and cyclic coupled hydro-thermo-chemo-mechanical excitations, and rate effects on the response of long design-life facilities. This study places emphasis on thermal geo-systems and associated physical properties. Uncemented soils and rocks are considered. The research approach involves data compilation, experimental studies and analytical methods. Emphasis is also placed to engineer geomaterials in order to attain enhanced performance in energy geo-systems. The thermal conductivity and stiffness of most geomaterials decrease as temperature increases but increase with effective stress. This macroscale response is intimately related to contact-scale conduction and deformation processes at interparticle contacts. Pore-filling liquids play a critical role in heat conduction as liquids provide efficient conduction paths that can diminish the effects of thermal contact resistance. Conversely, grains and fluids can be selected to attain very low thermal conductivity in order to create mechanically sound thermal barriers. In the case of rock masses, heat (and gas) recovery can be enhanced by injecting fluids at high pressure to cause hydraulic fractures. Scaled experiments reveal the physical meaning of hydraulic fractures in pre-structured rocks (e.g., shale) and highlight the extensive self-propped dilational distortion the medium experiences. This result explains the higher production rate from shale gas and fractured geothermal reservoirs that is observed in the field, contrary to theoretical predictions.