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Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 3, 2007) Includes bibliographical references.

Space heating is one of the simplest and most appealing applications of solar energy. The Roof Integrated Solar Heating System (RISHS) initiated by the Sustainable Energy Centre (SEC) of the University of South Australia offers a practical solution for this application. The main objective of this project is to study the technical viability of this system for domestic applications in Australia. / The research work carried out and reported in this thesis brings together the pioneering work on RISHS, namely: modelling and analysis of both the roof integrated heating system and the phase change material (PCM) thermal storage. The work accomplished includes: developing an improved model for the PCM thermal storage unit (TSU), the development of a comprehensive collector model, the development of control strategy of the total system, the development of TRNSYS-based simulation tool for analysing individual component as well the total system, and analysis of the thermal performance of the system. / The new phase change thermal storage model allows for the inclusion of sensible heat both prior to and after the phase change is complete. It relies on the newly developed phase change processor (PCP) algorithm for accurately predicting the outlet temperature and heat transfer rate. The PCP algorithm facilitates the iterative process required to simulate the phase change process, a phenomenon which cannot be dealt with using the general conduction heat transfer equations. The work has also identified that a melting or freezing process of PCM can be divided into three stages; (a) the sensible heat exchange stage characterised by very high heat transfer rates, (b) predominant latent heat transfer stage with much reduced but relatively constant heat transfer rate, and (c) the stage of combined sensible and latent heat exchange with much a further reduced rate. Two temperature differences governing the melting and freezing processes have been introduced. It has been found that these two quantities affect melting and freezing significantly. Given the clear significance of these two newly introduced quantities, the research work questions some previous claims about the effects of natural convection in certain PCM TSU geometries. / The work on the roof integrated solar collector includes the development of a comprehensive solar collector model where the collector dimensions, construction and material properties become inputs or parameters. Using this model, thermal performance of the collector can be evaluated and the collector standard thermal parameters such as collector heat removal factor and collector heat loss coefficient can be evaluated. / The development of a control strategy of the total system which includes the house being heated, the collector, the PCM, the fan and the auxiliary heater, has been carried out. In the control strategy, the characteristics of each component are taken into account and the schedule of energy flow from the heat source and / or thermal storage are designed to maximise the solar contribution and minimise the auxiliary heating required throughout the heating period. To achieve this, an integrated control strategy of auxiliary and solar heating / thermal storage unit has been proposed. Using this approach, the optimum solar contribution for a specified RISIS can be established. The air mass flow rate and the room space temperature difference are the key parameters which influence the system thermal performance. / The subroutines for modelling the PCM thermal storage and the roof integrated solar collector and the system control strategy have been incorporated into the TRSNSYS simulation package to analyse the total system. The analysis carried out indicates that the RISHS is a technically viable system which can provide significant heating contribution for house heating in Adelaide and Melbourne. The introduction of the PCM thermal storage in the system is a technically viable option; it is in fact the main factor which improves RISHS overall performance. The analyses on three PCMs have revealed that the main factors which dictate their thermal performance are the charge temperature and the melting point (which affect the chargeability), mass flow rate and charge and discharge temperature differences. / The TRNSYS-based simulation tool developed during the research project is expected to become a reliable tool for designing any real system for any location and applications. / Thesis (PhDMechanicalEng)--University of South Australia, 2005.

Thesis (Ph. D.)--University of Melbourne, 1996. / Typescript (photocopy). Includes bibliographical references (leaves 190-195).

Thesis (Ph. D.)--University of Florida, 1982. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 140-143).

Thermal energy storage via the latent heat of suitable phase change materials has the advantages of higher energy storage density and relatively isothermal behaviour compared to sensible heat storage systems. Glauber's salt (Na₂S0₄∙10H₂0) is one of the most extensively studied phase change materials for solar energy systems because of its low price, suitable phase change temperature and high latent heat. However, segregation due to incongruent melting behaviour leading to loss in the heat storage efficiency upon repeated melting-freezing cycling is a serious problem which has severely limited application of Glauber's salt. In this study Glauber's salt was encapsulated in 25 mm diameter hollow spheres and agitated in different systems including a liquid fluidized bed, rotating drum and rotating tube to reduce or eliminate the Toss in its heat storage efficiency. The encapsulated mixture consisted of 96% Glauber's salt and 4% borax by weight with 5% by volume air space in the capsules. Some capsules containing 25%, 15% and 5% by weight excess sodium sulfate and 10% by weight excess water were also prepared, to test the effect of sodium sulfate concentration under different agitation conditions. The heat storage capacity of 5756 capsules, agitated by fluidizing with water in a pilot plant size (0.34 m diameter) column, showed a decrease over the first three cycles to about 60% of that theoretically possible, but there was no further decrease over the next 93 cycles under fluidization conditions. The heat storage efficiency was found to be improved by increasing the superficial water velocity and by decreasing the cooling rate. Heating rate had little or no effect. The fluidized capsules provide enhanced heat transfer rates to or from the heat storage medium, enabling the energy to be charged or discharged in about one hour with realistic inlet and outlet temperatures. The high heat transfer rates are an important advantage for the system and may open new areas of applications for thermal energy storage by encapsulated phase change material. Economic analysis of the liquid fluidized bed heat storage system shows that operating costs are almost negligible compared to fixed capital costs. The heat storage efficiency of capsules decreased to 38.4% of the theoretical capacity or 67% of the corresponding agitated (fluidized) system in only 7 cycles under fixed bed conditions, and the efficiency decreased with further cycling. 97.5% of the original heat storage-capacity was recovered within three cycles when these capsules were refluidized. Performances of the regular and different composition capsules were tested in the rotating tube, with rotation around a fixed horizontal axis passing through the capsules' centers, and in the rotating drum, with impact due to collisions in addition to rotation. The results showed that full rotation of a capsule around a horizontal axis improves the heat storage efficiency. However, full recovery of the theoretical capacity was not possible, even under vigorous mixing conditions. The efficiencies in the rotating tube were similar to those in the rotating drum for capsules subject to the same number of rotations around a horizontal axis. At high rotation speeds centrifugal force had a negative influence, especially in the rotating tube. On the basis of heat storage capacity per unit volume or weight of phase change material, 47% by weight sodium sulfate concentration was found to be optimal for the rotating drum and the rotating tube cases. Some small scale experiments were performed to determine the relative importance of different factors in the loss of heat storage capacity. Sodium sulfate concentration gradients in the capsules with different thermal cycling histories were found by thermogravimetric analysis. The results showed that bulk segregation of anhydrous sodium sulfate is not the only reason for the loss of heat storage capacity in systems using Glauber's salt. Microencapsulation of anhydrous sodium sulfate beneath a layer of Glauber's salt crystals is at least as important. Experiments to determine the degree of subcooling, believed to be another factor in the loss of heat storage capacity, showed that a mixture of 96% Glauber's salt and 4% borax by weight undergoes subcooling of about 5 K in gently agitated capsules. Nucleation and crystallization temperatures both increase with increased agitation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

M.Ing. / Ice storage systems are used to store thermal energy in the form of ice build-up inside storage tanks. During off peak hours, the chiller is used to charge up the storage tank until it is full. During on peak hours, the storage is discharged to meet a certain fraction of the building cooling load. The control strategy employed determines the extent to which the storage compensates the chiller and visa versa. Given the way in which electricity rates are structured, ice storage systems become an effective energy management strategy. The objective of the study is to compare energy savings derived by using conventional control strategies versus optimal control. Conventional control strategies can be classified as chiller priority control, constant proportion control and storage priority control. In chiller priority control, the chiller meets the cooling load subject to a pre-set limit not being exceeded. Should the limit be exceeded, the remaining cooling load (at each time horizon) is compensated for by the storage. In constant proportion control, both the storage and chiller meets a constant proportion of the cooling load. Storage priority control attempts to discharge as much of the storage as possible, such that at the end of the planning horizon, the ice build up in the storage tank is just depleted. Optimal control employs dynamic programming to ensure that the integrated cost of energy, during the entire planning horizon, is minimal. A steady state ice storage plant model for analysing the performance of the control strategies is presented. The model computes the inlet and outlet temperatures into the various components of the air-conditioning plant, being the air-handling units, heat exchanger, ice storage tanks and chiller. The maximal possible discharge and charging rate at each time period (for the different control strategies) is determined using the model. Given the state of charge of the ice storage tank at each time period, it is then possible to calculate chiller power consumption. The power consumed by fans, fan coil units and pumps (in the air-conditioning plant) has not been calculated in the present analysis, however, the model can easily be extended to include such calculations. The ice storage plant model, enabled simulations of the different control strategies to be carried out over building cooling load profiles for summer and winter. Based on a 24-hour planning horizon, optimal control is found to be optimal and the only consistently performing strategy for all seasons. For the 5000 kWh ice storage plant investigated, optimal control yielded 25% energy savings in June and 12% in January, amounting to a potential of R 11 000 per month. Chiller priority control was near optimal in January but consumed 25% more energy than the base case (without storage) in June. Constant proportion control was optimal in January but poorer in June. Storage priority control is found to be optimal in June but the lowest performer in January. The drawback of optimal control and storage priority control, however, is that they require prediction of future cooling loads. The variance when using auto-regressive neural network to predict the load is expected to be in the region of 2% and thus considered acceptable. Chiller priority control and constant proportion control are instantaneous and simple to implement hence their popularity.

Thesis (Ph.D.)--University of Central Florida, 2008. / Advisers: Louis Chow, Jay Kapat. Includes bibliographical references (p. 111-118).

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on February 12, 2010). Thesis advisor: Dr. Galen J. Suppes. Includes bibliographical references.

Large percentages of the South African population have no access to grid power and are located at distances that make provision for such facility uneconomical. Also traditional fuels are under pressure. Most areas in South Africa receive 300 days of sunshine per year. The proposed solar system addresses the needs of such communities. A solar thermal energy storage system utilizing phase change material has been proposed that can overcome the time mismatch between solar availability and demand. The system consists of two types of thermal heat storage. The latent heat storage used Phase Change Materials (PCM) which melts at a sufficiently high temperature for cooking a variety of food types. By choosing a suitable PCM to take advantage of the latent heat absorbed during phase changes. Heat losses from both the latent heat storage and condenser are captured in the surrounding sensible heat store. The objective of this project to develop a prototype modules which together as a system could provide the essential domestic power requirements of the target groups. This includes power for cooking, hot water and in addition a limited electrical power supply for the system itself as well as for other minor loads. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.