This dissertation proposed a new methodology for determining the optimal operating strategies for a chilled water storage system under a Time-of-Use electricity rate structure. It is based on a new classification of operating strategies and an investigation of multiple search paths. Each operating strategy consists of a control strategy and the maximum number of chillers running during the off-peak and on-peak periods. For each month, the strategy with the lowest monthly billing cost and minimal water level higher than the setpoint is selected as the optimal operating strategy for the current month. A system model is built to simulate the tank water level at the end of each time step and the system total power during each time step. This model includes six sub-models. Specifically, the plant model is a forward model using a wire-to-water concept to simulate the plant total power. For the Thermal Energy Storage (TES) model, the tank state is described with total chilled water volume in the tank and its derivation is the tank charging or discharging flow rate. A regression model is adopted to simulate the loop supply and return temperature difference as well as the loop total flow rate demand. In the control strategy sub-model, except for three conventional control strategies and the operation without TES, a new control strategy is advanced to load the chiller optimally. The final results will be a table showing the monthly control strategy and maximal number of chillers staged on during the off-peak and on-peak periods, an approach which is easy for the operators to follow. Two project applications of this methodology are introduced in this dissertation. One is an existing TES system with state-of-the-art control and metering systems. The monthly optimal operating strategies are generated, which will achieve significant savings. The comparisons among different control strategies are also provided. The other application consists of multiple plants with little data. The purpose of the study is to evaluate the economic feasibility of designing a new chilled water storage tank and sharing it among four plants. This problem can be solved with a simplified system model, and an optimal tank size is recommended.

This thesis seeks to examine the effective convective heat exchange of sand as a heat exchange medium. The goal of this exploratory research is to quantify the heat transfer coefficient of sand in a proposed Thermal Energy Storage (TES) system which intends to complement solar thermal power generation. Standard concentrator solar thermal power plants typically employ a heat transfer fluid (HTF) that is heated in the collector field then routed to the power generators or TES unit. A fairly clear option for a TES system would be to utilize the existing HTF as the working storage medium. However, the use of conventional HTF systems may be too expensive. These fluids are quite costly as the quantity needed for storage is high and for some fluids their associated high vapor pressures require expensive highly reinforced containment vessels. The proposed storage system seeks to use sand as the storage medium; greatly reducing the expenses involved for both medium and storage costs. Most prior TES designs using sand or other solids employed them in a fixed bed for thermal exchange. The proposed TES system will instead move the sand to drive a counter flow thermal exchange. This counter flow design allows for a much closer temperature of approach when compared to a fixed bed. As cost and performance are the primary goals to tackle of the proposed system, the evaluation of the sandâ s thermal exchange effectiveness in a flowing state is necessary. Experiments will be conducted to measure the effective heat transfer coefficient between the sand and representative solid surfaces used as the heat transfer conduits. Additional experiments that will be looked at are wear caused by the sand as a consideration for long term design viability as well as angle of repose of the sand and its effect on scoop design for improved materials handling. Key investigational aspects of these experiments involve the sand grain size as well as shape of the heat exchanger surfaces. The thesis will evaluate the resulting convective heat transfer coefficient of the sand as related to these features. The data will then be compared and verified with available literature of previously studied characteristic thermal properties of sand. The measured and confirmed data will then be used to further aid in a design model for the proposed TES system.

This work considers how various integrated energy systems can be managed in order to provide economic or energetic benefits. Energy systems can gain additional degrees of freedom by incorporating some form of energy storage (in this work, thermal energy storage), and the increasing penetration of smart grid technologies provides a wealth of data for both modeling and management. Data used for the system models here come primarily from the Pecan Street Smart Grid Demonstration Project in Austin, Texas, USA. Other data are from the Austin Energy Mueller Energy Center and the University of Texas Hal C. Weaver combined heat and power plant. Systems considered in this work include thermal energy storage, chiller plants, combined heat and power plants, turbine inlet cooling, residential air conditioning, and solar photovoltaics. These systems are modeled and controlled in integrated environments in order to provide system benefits. In a district cooling system with thermal energy storage, combined heat and power, and turbine inlet cooling, model-based optimization strategies are able to reduce peak demand and decrease cooling electricity costs by 79%. Smart grid data are employed to consider a system of 900 residential homes in Austin. In order to make the system model tractable for a model predictive controller, a reduced-order home modeling strategy is developed that maps thermostat set points to air conditioner electricity consumption. When the model predictive controller is developed for the system, the system is able to reduce total peak demand by 9%. Further work with the model of 900 residential homes presents a modified dual formulation for determining the optimal prices that produce a desired result in the residential homes. By using the modified dual formulation, it is found that the optimal pricing strategy for peak demand reduction is a critical peak pricing rate structure, and that those prices can be used in place of centralized control strategies to achieve peak reduction goals. / text

Driving with the cold engine increases fuel consumption and greenhouse gases emissions. A latent heat energy storage device has been proposed to recover waste heat and reduce engine warm-up time by using phase change materials (PCMs) as an energy storage medium. Two types of paraffin waxes and 50/50 mixture of the two have been examined to characterize their behaviors under repetitive heating/freezing. From the results, the heat transfer is more effective in the case of narrower spacing distances between the cooling plates and high circulating flow rate of the heat transfer fluid. A 50/50 mixture of two paraffin waxes also provides better heat transfer due to the possible existence of both conduction and natural convection. The results of the metal block simulation experiments demonstrated the potential of latent heat TES’s for use in engine warm-up.

Driving with the cold engine increases fuel consumption and greenhouse gases emissions. A latent heat energy storage device has been proposed to recover waste heat and reduce engine warm-up time by using phase change materials (PCMs) as an energy storage medium. Two types of paraffin waxes and 50/50 mixture of the two have been examined to characterize their behaviors under repetitive heating/freezing. From the results, the heat transfer is more effective in the case of narrower spacing distances between the cooling plates and high circulating flow rate of the heat transfer fluid. A 50/50 mixture of two paraffin waxes also provides better heat transfer due to the possible existence of both conduction and natural convection. The results of the metal block simulation experiments demonstrated the potential of latent heat TES’s for use in engine warm-up.

Concentrated solar power (CSP) has the potential of fulfilling the world’s electricity needs. Parabolic-trough system using synthetic oil as the HTF with operating temperature between 300 and 400o C, is the most matured CSP technology. A thermal storage system is required for the stable and cost effective operation of CSP plants. The current storage technology is the indirect two-tank system which is expensive and has high energy consumption due to the need to prevent the storage material from freezing. Latent heat storage (LHS) systems offer higher storage density translating into smaller storage size and higher performance but suitable phase change materials (PCMs) have low thermal conductivity, thus hindering the realization of their potential. The low thermal conductivity can be solved by heat transfer enhancement in the PCM. There is also lack of suitable commercially-available PCMs to cover the operating temperature range. In this study, a hybrid cascaded storage system (HCSS) consisting of a cascaded finned LHS and a high temperature sensible or concrete tube register (CTR) stages was proposed and analysed via modelling and simulation. Fluent CFD code and the Dymola simulation environment were employed. A validated CFD phase change model was used in determining the heat transfer characteristics during charging and discharging of a finned and unfinned LHS shell-and-tube storage element. The effects of various fin configurations were investigated and heat transfer coefficients that can be used for predicting the performance of the system were obtained. A model of the HCSS was then developed in the Dymola simulation environment. Simulations were conducted considering the required boundary conditions of the system to develop the best design of a system having a capacity of 875 MWhth, equivalent to 6 hours of full load operation of a 50 MWe power plant. The cascaded finned LHS section provided ~46% of the entire HCSS capacity. The HCSS and cascaded finned LHS section have volumetric specific capacities 9.3% and 54% greater than that of the two-tank system, respectively. It has been estimated that the capital cost of the system is ~12% greater than that of the two-tank system. Considering that the passive HCSS has lower operational and maintenance costs it will be more cost effective than the twotank system considering the life cycle of the system. There is no requirement of keeping the storage material above its melting temperature always. The HCSS has also the potential of even lower capital cost at higher capacities (>6 hours of full load operation).

This research examined what mix of building types result in the most efficient use of a technology known as Aquifer Thermal Energy Storage (ATES). Hourly energy simulation models for six different building archetypes were created based on representative building characteristic and energy use data from the Toronto area. A genetic algorithm optimization tool was then created to vary scheduling and production properties of the ATES system and the relative number of different building archetypes. The tool found that a cooling season from weeks 16‐42 maximized the useful energy output of the ATES and resulted in roughly 30% reduction in heating and cooling energy use and associated GHG emissions. It was also found that creating a mix consisting of a higher percentage of larger buildings than is currently found in most neighbourhoods could reduce energy usage by an additional 10%.

This research examined what mix of building types result in the most efficient use of a technology known as Aquifer Thermal Energy Storage (ATES). Hourly energy simulation models for six different building archetypes were created based on representative building characteristic and energy use data from the Toronto area. A genetic algorithm optimization tool was then created to vary scheduling and production properties of the ATES system and the relative number of different building archetypes. The tool found that a cooling season from weeks 16‐42 maximized the useful energy output of the ATES and resulted in roughly 30% reduction in heating and cooling energy use and associated GHG emissions. It was also found that creating a mix consisting of a higher percentage of larger buildings than is currently found in most neighbourhoods could reduce energy usage by an additional 10%.

The heat flux demands for electronics cooling applications are quickly approaching the limits of conventional thermal management systems. To meet the demand of next generation electronics, a means for rejecting high heat fluxes at low temperatures in a compact system is an urgent need. To answer this challenge, in this work a gasketed chevron plate heat exchanger in conjunction with a slurry consisting of highly endothermic solid ammonium carbamate and a heat transfer fluid. A reduced-order 1-dimensional model was developed and used to solve the coupled equations for heat, mass, and momentum transfer. The feasibility of this chosen design for satisfying the heat rejection load of 2kW was also explored in this study. Also, a decomposition reaction using acetic acid and sodium bicarbonate was conducted in a plate heat exchanger (to simulate a configuration similar to the ammonium carbamate reactions). This enabled the experimental validation of the numerical predictions for the momentum transfer correlations used in this study (which in turn, are closely tied to both the heat transfer correlations and chemical kinetics models). These experiments also reveal important parameters of interest that are required for the reactor design. A numerical model was developed in this study and applied for estimating the reactor size required for achieving a power rating of 2 kW. It was found that this goal could be achieved with a plate heat exchanger weighing less than 70 kg (~100 lbs) and occupying a volume of 29 L (which is roughly the size of a typical desktop printer). Investigation of the hydrodynamic phenomena using flow visualization studies showed that the flow patterns were similar to those described in previous studies. This justified the adaptation of empirical correlations involving two-phase multipliers that were developed for air-water two-phase flows. High-speed video confirmed the absence of heterogeneous flow patterns and the prevalence of bubbly flow with bubble sizes typically less than 0.5 mm, which justifies the use of homogenous flow based correlations for vigorous gas-producing reactions inside a plate heat exchanger. Absolute pressure measurements - performed for experimental validation studies - indicate a significant rise in back pressure that are observed to be several times greater than the theoretically estimated values of frictional and gravitational pressure losses. The predictions from the numerical model were found to be consistent with the experimental measurements, with an average absolute error of ~26%

L'utilisation de la réfrigération secondaire permet de réduire l'impact environnemental des systèmes frigorifiques grâce à une réduction de l'utilisation de gaz à effet de serre, néanmoins un tel procédé abaisse l'efficacité des systèmes. Afin de rendre ce procédé plus efficace et viable, l'utilisation de fluide à forte densité énergétique ainsi qu'un couplage avec un dispositif de stockage thermique a été envisagé comme réponse à une problématique industrielle de distribution de froid (climatisation, procédés de refroidissement). Un montage expérimental constitué d'une boucle de circulation et d'un réacteur de formation a été utilisé afin d'évaluer les caractéristiques de charge et décharge d'un réseau utilisant des fluides diphasiques. Cette étude a également permis l'élaboration et la validation de modèles prédictifs (réservoir de stockage, échangeur de chaleur, écoulement) de dynamique de stockage et déstockage pour différents matériaux. Ces modèles ont ensuite été appliqués au cas d'un réseau industriel afin d'étudier l'impact du matériau de stockage choisi sur le dimensionnement du système, sur la consommation énergétique mais aussi sur sa viabilité économique. Ainsi, les résultats ont d'abord montré que l'utilisation d'un dispositif améliorait l'efficacité d'un système et que le retour sur investissement dépendait des scénarios de stockage envisagés. Enfin, une forte dépendance sur le choix du matériau a également été soulevée. / The use of secondary refrigeration can reduce cooling system impact on environment by greenhouse gas reduction, nevertheless this kind of technology reduce the system efficiency. The use of high energetic density and thermal energy storage was considered to improve system efficiency and to answer to industrial cooling process issue (air-conditioning, cooling process or temperature preservation). An experimental set-up composed by a stired tank reactor and circulation loop was used in order to evaluate the charging and discharging dynamic of a cooling district using phase change slurry. This experimental study offers the opportunity to elaborate and validate further models (stirred tank reactor, heat exchanger, flow behavior) to predict the charging and discharging behaviors for various storage materials. Then, these models were used in the case of an industrial system to observe the impact of the storage material or system sizing, energy consumption and economic sustainability. Thus, results show that the impact of the storage device on system energy efficiency and the return on investment depends on storage scenarios. Finally the impact of the chosen material on system efficiency was pointed out.