<p>  </p> <p>Thermal energy storage (TES) is used to reduce the operating costs of heating, ventilation, and air conditioning (HVAC) systems by shifting loads away from on-peak periods, to reduce the maximum heating or cooling capacity needed from the HVAC system, and to store excess energy generated by on-site solar power. The most commonly-used form of TES is ice storage with air conditioning (A/C) systems in commercial buildings. There has been extensive research into many other forms of TES for use with HVAC systems, both in commercial and residential buildings. However, this research is often limited to use with either heating or cooling systems.</p> <p>Year-round, high-density storage for both heating and cooling would yield significantly larger cost savings than existing TES systems, particularly for residential buildings, where heating loads are often larger than cooling loads. This dissertation examines the feasibility of using metal hydrides for year-round storage, as well as analyzing the potential of variable-temperature energy storage for optimizing system performance beyond allowing for year-round use.</p> <p>Metal hydrides are metals that exothermically absorb and endothermically desorb hydrogen. Since the temperature this reaction occurs at depends on the hydrogen pressure, hydrides can be used for energy storage at varying temperatures. System architecture for using metal hydrides with an HVAC system is developed. A thermodynamic model which combines a dynamic model of the hydride reactors with a static model of the HVAC system is used to calculate operating costs, compared to a conventional HVAC system, for different utility rates and locations. The payback period of the system is unacceptably high, due to the high initial cost of metal hydrides and the operating costs of compressing hydrogen to move it between hydride reactors.</p> <p>In addition to the metal hydride system model, a generalized model of a variable-temperature TES system is used to determine the potential cost savings from dynamically altering the storage temperature to achieve optimal cost savings. Dynamic tuning does result in cost savings but is most effective for storage tank sizes significantly smaller than the optimal tank size. An alternate system design where the storage tank is charged with the outlet flow from the house achieves larger cost savings even for the optimally-sized tanks. Payback periods calculated for optimal sizing show that year-round storage has a lower payback period than separate cold and heat storage if the year-round storage system is not more expensive than two separate storage tanks. </p>

<p dir="ltr">Ice thermal energy storage (ITES) systems have long been an economic way to slash cooling costs in the commercial sector since the 1980s. An ITES system generates cooling in the formation of ice within a storage tank. This occurs during periods of the day when the cost of electricity is low, normally at night. This ice is then melted to absorb the energy within the conditioned space. While ITES systems have been prosperous in the commercial sector, they have yet to take root in the residential sector.</p><p dir="ltr">The U.S. Department of Energy (DoE) has published guidelines for TES. The DoE guidelines include providing a minimum of four hours of cooling, shifting 30-50% of a space’s cooling load to non-peak hours, minimizing the weight, volume, complexity, and cost of the system, creating a system than operates for over 10,000 cycles, enacting predictive control measures, and being modular to increase scale for larger single-family and multi-family homes [1]. The purpose of this research is to develop a model that meets these guidelines.</p><p dir="ltr">After extensive research in both experimental data, technical specifications, existing models, and best practices taken from the works of others a MATLAB model was generated. The modeled ITES system is comprised of a 1m diameter tank by 1m tall. Ice was selected as the PCM. A baseline model was constructed with parameters deemed to be ideal. This model generated an ITES system that can be charged in under four hours and is capable of providing a total of 22.18 kWh of cooling for a single-family home over a four-hour time period. This model was then validated with experimental data and found to have a root mean squared error of 0.0959 for the system state of charge. During the validation both the experimental and model estimation for the water/ice within the tank converged at the HTF supply temperature of -5.2°C.</p><p dir="ltr">With the model established, a parametric analysis was conducted to learn how adjusting a few of the system parameters impact it. The first parameter, reducing the pipe radius, has the potential to lead to a 152.6-minute reduction in charge time. The second parameter, varying the heat transfer fluid (HTF) within the prescribed zone of 0.7 kg/s to 1.2 kg/s, experienced a 4.8-minute increase in charge time for the former and a decrease in charge time by 5.4 minutes for the latter. The third parameter, increasing the pipe spacing and consequently increasing the ratio of mass of water to mass of HTF, yielded a negative impact. A 7.1mm increase in pipe spacing produced a 16.6-minute increase in charge time. Meanwhile, a 14.2mm increase in pipe spacing created a 93.3-minute increase in charge time and exceeded the charging time limit of five hours.</p><p dir="ltr">This functioning model establishes the foundation of creating a residential-scale ITES system. The adjustability and scalability of the code enable it to be modified to user specifications. Thus, allowing for various prototypes to be generated based on it. The model also lays the groundwork to synthesize a code containing an ITES system and a heat pump operating as one. This will aid in the understanding of residential-scale ITES systems and their energy effects.</p>

Examining methods for controlling the electricity demand in Kuwait was the main objective and motivation of this researchp roject. The extensiveu se of air-conditioning for indoor cooling in office and large commercial buildings in Kuwait and the Gulf States represents a major part of the power and electricity consumption in such countries. The rising electricity generation cost and growing rates of consumption continuously demand the construction new power plants. Devising and enforcing Demand-SideM anagemen(t DSM) in the form of energye fficient operations trategies was the response of this research project to provide a means to rectify this situation using the demand-side management technique known as demand levelling or load shifting. State of the art demand-sidem anagementte chniquesh ave been examined through the developmenot f a model basedp redictive control optimisations trategyf or an integrateda ndm odulara pproachto the provisiono f ice thermals torage. To evaluate the potential of ice-storage assisted air-conditioning systems in flattening the demand curve at peak times during the summer months in Kuwait, a model of a Heating, Ventilation, and Air-conditioning (HVAC) plant was developed in Matlab. The model engaged the use of model based predictive control (MPQ) as an optimisation tool for the plant as a whole. The model with MPC was developed to chose and decide on which control strategy to operate the integrated ice-storage HVAC plant. The model succeeded in optimising the operation of the plant and introduced encouraging improvement of the performance of the system as a whole. The concept of the modular ice-storage system was introduced through a control zoning strategy based on zonal orientation. It is believed that such strategy could lead to the modularisation of ice-storage systems. Additionally, the model was examined and tested in relation to load flattening and demonstrated promising enhancement in the shape of the load curve and demonstrated flattened demand curves through the employed strategy. When compared with measured data from existing buildings, the model showed potential for the techniques utilised to improve the load factor for office buildings.