Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on September 23, 2009. Major professor: Craig Baltimore, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Architecture with a Specialization in Architectural Engineering." "June 2009." Includes bibliographical references (p. 65-67). Also available on microfiche.

Solar thermal energy harvesting is a promising solution to offset the electricity demands of a growing population. The use of the technology is however still limited and this can most likely be attributed to the capital cost and also the intermittent nature of solar energy which requires incorporation of a storage system. To make the technology more attractive and effective, cheap means of harvesting solar energy and the development of efficient and inexpensive thermal energy storage devices will improve the performance of solar energy systems and the widespread use of solar energy. Heat storage in a packed-bed rock with air as the working fluid presents an attractive and simple solution for storing solar thermal energy and it is recommended for solar air heaters. A packed-bed rock storage system consists of rocks of good heat capacity packed in a storage tank. The working fluid (air) flows through the bed to transfer its energy. The major concern of the design for a packed-bed rock thermal storage system is to maximize the heat transfer and minimise the pressure drop across the storage tank and hence the pumping power. The time duration the stored energy can be preserved and the air flow wall effect through the bed are the common complications encountered in this system. This study presents an experimental and analytical analysis of a vacuum storage tank with the use of expanded perlite for high temperature thermal energy storage in a packed-bed of rocks. Dolerite rocks are used as the storage medium due to their high heat capacity and as they are locally available. To minimise the pressure drop across the tank, moderate rock sizes are used. The tank contains baffles, allowing an even spread of air to rock contact through the entire tank, therefore improving heat transfer. There is a good correlation between the predicted and the actual results (4 percent) which implies that the baffles incorporated inside the vacuum tank forces the air through the entire tank, thereby resulting in an even lateral temperature distribution across the tank. The investigation of heat loss showed that a vacuum with expanded perlite is a viable solution to high temperature heat storage for an extended period. The research also focuses on the investigation of a proposed low cost parabolic trough solar collector for an air heating system as shown in Figure (1.3). The use of a standard solar geyser evacuated tube (@R130 each) has cost benefits over the industry standard solar tubes normally used in concentrating solar power systems. A mathematical was developed to predict the thermal performance of proposed PTC and it was found that the measured results compared well with the predictions. The solar energy conversion efficiency of this collector is up to 70 percent. This research could impact positively on remote rural communities by providing a source of clean energy, especially for off-grid applications for schools, clinics and communication equipment. It could lead to a significant improvement in the cost performance, ease of installation and technical performance of storage systems for solar heating applications.

As fossil fuel usage has been proven to have a negative impact on human health and the environment, the world has embraced the usage of renewable energy sources, mainly for energy production. In Cyprus, solar energy is the most potent renewable source and this can be seen by the vast majority of the population using solar water heaters in their households. This thesis explores the usage of solar energy for electricity and domestic hot water production at a residential level by presenting the designs of three solar-thermal concept systems for achieving this task; the first being the basic design of all three without any form of storage, the second is fitted with thermal latent heat storage and the third is fitted with a natural gas boiler instead. The optimal solution is the second concept system that is capable of storing thermal energy around the year thus having a nearly uninterrupted operation, reducing the dependency on fossil fuel produced electricity and emissions. The thesis also explored the usage of siloxane organic compounds as working fluids for a low temperature Rankine cycle, which had a significant impact in the increase of the thermal-to-electrical efficiency of the cycle, raising it to nearly 25%, greater than the efficiency of best acclaimed photovoltaic collector currently available. Lastly, taking into account a typical household’s demand profile and by allowing the optimal system to operate as part of the national electrical network continuously, the size of the system’s components could be reduced significantly making it more feasible for installing in a typical household’s premises. However, due to the non-existence of these components in the within the project’s specifications, the thesis could not include a useful economic analysis for a more realistic comparison with a similar sized photovoltaic system.

M.Ing. / The research in this thesis focuses on the theoretical thermal modelling and design of a Latent Heat Storage system (LHS) for an absorption refrigeration machine. A shell-and-tube latent heat storage exchanger retaining any excess solar thermal energy is selected. Here, solar thermal energy supplied by a collector is transferred to and stored by the LHS. During low insolation, stored thermal energy is transferred by a Heat Transfer Fluid (HTF) into the generator, a component of an Ammonia Absorption Refrigerator (AAAR), to ensure efficiency of the cooling cycle. The shell-and-tube LHS contains Phase Change Material (PCM) which fills space outside the tube heat exchangers. The HTF flowing through the tubes exchanges thermal energy with the PCM. The selection of a suitable PCM for a LHS is based on several factors. A primary criterion for an efficient, reliable storage unit is the correct melting point of the PCM at a desired operating temperature of the heating application. An analytical model describing both the freezing process in the PCM and increased HTF temperature in the tube heat exchangers is investigated. The model is developed using energy balance equations. It is solved in terms of dimensionless parameters. The thermal resistance of the tube heat exchangers is considered for this model. From the result of the analytical model, the design approach to size the LHS is provided and the different steps are given in order to determine the volume, mass, number of tube heat exchangers, inner and outer radius of the tube heat exchangers and other parameters of the LHS. The dimensions of LHS are given as a function of a storage period, PCM properties, HTF properties, inner and outer radius of the tube heat exchangers, material of construction of the tube heat exchangers and the nature of load on the heating process. Simulations from the analytical model developed are provided for the output thermal parameters of the storage system. These thermal parameters of the shell-and-tube latent exchanger are given in terms of the HTF outlet temperature, the front solidification of the PCM and the heat transfer rate during the solidification process of the PCM. A case study to demonstrate the application of the design approach with respect to the size shell-and-tube latent heat exchanger is provided.The integration of the tube heat exchangers thermal conductivity in the modelling of the LHS resulted in an increase of 2% in mass of the storage material compared to an analytical model neglecting the thermal conductivity of the tube heat exchangers. The results of the model developed compared well with the results obtained from other analytical models at similar operating conditions.

This pilot study aims to evaluate the thermal performance of different types of solar thermal collectors and their long-term economic benefits for Obbola school, located within the Umeå municipality. The goal of this project is to investigate how much thermal and electrical energy can be generated annually and even during summertime by using only solar collectors for heating purposes of an outdoor pool at Obbola school. The solar thermal collectors that are selected for this project are Solar Keymark-certified flat plate, evacuated tube, and photovoltaic hybrid solar collectors. This study will include designing and simulation roof-integrated and ground-based collectors in Polysun software and determine their thermal performance at European Standards of 45° and collectors facing true south. The simulations in Polysun were conducted on the main site roof area of 65 m2 and a steep grass area of 66 m2 behind the main roof.This pilot study shows that only during the summertime, between the 1st of May and the 31st of August, flat and evacuated tube solar collectors can generate between 4.5 - 5.1% of the school's annual average thermal energy needs. The total average generated thermal energy by these collectors during a year is about 20800 kWh. A hybrid solar collector's thermal energy generated during the summertime covers only 0.6% of 400215 kWh, the annual average thermal energy the school needs. At the same time, the generated electricity will cover only 1.2% of the average electricity the Obbola school needs, which is 539600 kWh.Some economic analyses were conducted to evaluate the long-term economic benefits of installing solar thermal collectors for Umeå municipality, including payback period, life cycle profit, annuity, and life cycle costs. The payback period results show that these collectors have between 9 to 20 years of returning their initial investment. This economic analysis was based on the collector's service life between 25 to 40 years, depending on the brands and manufacturers. These collectors' average life cycle profit revenue is between 178816 SEK and 294415 SEK after 25 and 40 years, respectively. This profit margin makes it very attractive for Umeå municipality, and this model can be used for further implementation at other schools within the municipality. The annual annuity revenue from these collectors is 10269 SEK to 12737 SEK after 25 and 40 years of service, respectively. The results from the return-on-investment show that the installation will give about a percentage profit of 2.8% to 3.5% between 25 and 40 years, respectively. These collectors' average life cycle costs over 25 and 40 years are 358094 SEK and 677231 SEK, respectively. According to the economic analyses, the results show that this pilot study will be a very profitable investment for the Umeå municipality.

No description available.

The integrated solar roof collector system can bring the house year-round energy saving benefit. In heating season, part of the space heating and preheating domestic hot water demand can be met by this integrated system. In the cooling season, cooling load reduction and preheating domestic hot water can be achieved by operating this system. The traditional solar thermal system is an add-on system rather than integrated, which increases the cost-benefit ratio. The current system is integrated with the roof structure. Except for the energy collecting benefit, it will reduce the material cost, labor cost and construction period. The objectives of this research is to estimate the energy performance of three collector configurations including space heating saving, and preheat hot water saving. This study also compares energy performance for the three collectors on two types of evaluated houses in Roanoke, Virginia. / Master of Science

This thesis presents the thermodynamic and economic assessment of gas power cycles for 100 MW solar thermal power generation systems. A gas power cycle for solar power generation is a totally different technology from the current state of the art solar power generation systems. As a result, this thesis provides an assessment of the solar power generation systems with gas power cycles and provides guidance in the selection of design and operating parameters for gas power cycle based solar power generation system. The gas power cycle based power generation systems are assessed by means of thermodynamic and economic models developed and simulated using commercial thermodynamic analysis software. The gas cycle based power generation systems considered in this study are Cold Gas Turbine, High Temperature Solar Gas Turbine and Lorentz Cycle Gas Turbine. The system models are assessed for their thermodynamic performance using theory based turbo-machinery models with practical performance and loss data. In addition, extensive cost models have been developed for assessing the economic performance of the system models to determine their practical feasibility. The results from this study indicate that the most economical power generation system is the HTSGT system for a high peak cycle temperature utilizing the central receiver power tower solar collector system. The LCGT system also has a comparable performance at the same operating temperature. The CGT system assessed for operating with parabolic trough solar collector system at a lower peak cycle temperature had an inferior performance compared to the current state of the art technology for the power generation using parabolic troughs.

Thermodynamic and thermoeconomic aspects of 12.5 kW residential solar-thermal power generating systems suitable for distributed, decentralized power generation paradigm are presented in this thesis. The design of a meso-scale power system greatly differs from centralized power generation. As a result, this thesis provides guidance in the selection of the power cycle and operating parameters suitable for meso-scale power generation. Development of standard thermodynamic power cycle computer simulations provides means for evaluation of the feasibility of meso-scale solar-thermal power generation. The thermodynamic power cycles considered in this study are the Rankine cycle, the organic Rankine cycle with toluene, R123, and ethylbenzene as working fluids, the Kalina cycle, and the Maloney-Robertson cycle. From a strictly thermodynamic perspective, the cycles are evaluated based on first- and second-law efficiencies. Additionally, the study includes economic feasibility through thermoeconomic characterization that encompasses a meso-scale cost model for solar-thermal power generation systems. Key results from this study indicate that a R123 organic Rankine cycle is the most cost-effective cycle implementation for operating conditions in which the maximum temperature is limited below 240C. For temperatures greater than 240C and less than 375C, the toluene and ethylbenzne organic Rankine cycles outperform the other cycles. The highest first law efficiency of 28% of the Kalina cycle exceeds all other cycles at temperatures between 375C and 500C. However, when considering cycle cost and overall feasibility, including thermodynamic and thermoeconomic performance, the Maloney-Robertson and Kalina cycles have poor performance on a cost-to-efficiency basis.

abstract: Nanoparticle suspensions, popularly termed “nanofluids,” have been extensively investigated for their thermal and radiative properties. Such work has generated great controversy, although it is arguably accepted today that the presence of nanoparticles rarely leads to useful enhancements in either thermal conductivity or convective heat transfer. On the other hand, there are still examples of unanticipated enhancements to some properties, such as the reported specific heat of molten salt-based nanofluids and the critical heat flux. Another largely overlooked example is the apparent effect of nanoparticles on the effective latent heat of vaporization (hfg) of aqueous nanofluids. A previous study focused on molecular dynamics (MD) modeling supplemented with limited experimental data to suggest that hfg increases with increasing nanoparticle concentration. Here, this research extends that exploratory work in an effort to determine if hfg of aqueous nanofluids can be manipulated, i.e., increased or decreased, by the addition of graphite or silver nanoparticles. Our results to date indicate that hfg can be substantially impacted, by up to ± 30% depending on the type of nanoparticle. Moreover, this dissertation reports further experiments with changing surface area based on volume fraction (0.005% to 2%) and various nanoparticle sizes to investigate the mechanisms for hfg modification in aqueous graphite and silver nanofluids. This research also investigates thermophysical properties, i.e., density and surface tension in aqueous nanofluids to support the experimental results of hfg based on the Clausius - Clapeyron equation. This theoretical investigation agrees well with the experimental results. Furthermore, this research investigates the hfg change of aqueous nanofluids with nanoscale studies in terms of melting of silver nanoparticles and hydrophobic interactions of graphite nanofluid. As a result, the entropy change due to those mechanisms could be a main cause of the changes of hfg in silver and graphite nanofluids. Finally, applying the latent heat results of graphite and silver nanofluids to an actual solar thermal system to identify enhanced performance with a Rankine cycle is suggested to show that the tunable latent heat of vaporization in nanofluilds could be beneficial for real-world solar thermal applications with improved efficiency. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2015