Latent Heat Thermal Energy Storage for Indoor Comfort Control

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Equating Earth’s existence to 24 hours, we, the Homo sapiens, came about in the last four seconds. Fossil fuel came to our knowledge with mass extraction dating from the Industrial Revolution two centuries ago, in other words 4 milliseconds out of Earth’s 24-hour equivalent lifetime. With the unruly use of fossil fuel based resources, global temperature increase due to anthropogenic emission is projected by the Intergovernmental Panel on Climate Change (IPCC) to increase between 2 °C and 6 °C by 2100. The expected results are unprecedented climatic phenomena, such as intense tropical cyclones, extreme heat waves, and heavy precipitation among others. Limiting climate change has become one of the most discerning issues in our highly energy dependent society.Ever-increasing energy demand goes in hand with improved living standard due to technologic and economic progress. Behavioral change is one of the ultimate solutions to reduce energy demand through adequate life style change; however such approach requires societal paradigm shift. In this thesis, we look into using energy storage technology to peak shave and to load shift energy so as to attain increased renewable energy source utilization, improved system’s energy efficiency, and reduced Greenhouse Gas (GHG) emission without compromising living comfort.High energy density thermal energy storage (TES) systems utilize phase change materials as storage mediums where thermal energy is principally stored in the form of latent heat (LH). Advantages of such systems are compact components and small storage temperature swing. However, challenges remain in implementing LHTES to the built environment, namely lack of understanding of system dynamics, uncertainty in component design, and non-documented material property are to be addressed.The goal of this thesis is to address the issues on material property characterization, on component heat transfer study and on system integration. A methodology in measuring material’s thermo physical property through T-History setup is defined. Caveats of existing methodology are presented and improvements are proposed. The second part of this thesis consists of establishing valid numerical models of LHTES component for both shape stabilized and free flowing PCMs. Experimental verifications were performed and models were validated. Improvement to the thermal power performance was studied and was reached with multistage multi-PCM storage design. Techno-economic optimization and parametric study were carried out for transient TES integrated system study. Finally, an estimation of the Swedish peak energy demand reduction was performed through study of TES implementation to the existing energy systems. The peak energy shave attained through TES implementation determines the amount of fossil fuel based marginal energy that can be reduced for a greener environment.

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