Abstract

The building sector accounts for approximately 40% of the world’s total use of primary energy, and the majority of this energy is used to maintain satisfactory indoor climate conditions by heating, cooling and ventilation.

Further on, traditional energy sources are irretrievably decreasing and the price of energy and fuel is gradually increasing. On top of that, the gas emissions to the atmosphere cause long-term and hazardous changes to the global climate. As a response to that, countries started to enforce new, more demanding legislations and standards for the newly constructed and renovated buildings. For example, in Denmark the new energy frames assume a reduction of primary energy use for buildings of respectively 25% in 2010, 50% in 2015 and 75% in 2020 compared to year 2006 figures. As a consequence, the building sector has to be equipped with the new technologies that would enable fulfillment of the new requirements regarding the new energy frames.

The concept presented and developed in the thesis focuses on the energy optimization and potential of the new product that could utilize the high thermal energy storage (TES) and thermally activated building system (TABS). The work investigates the potential of combining the microencapsulated phase change material (PCM) in the hollow core concrete deck element in order to increase the dynamic heat storage capacity of the internal envelope of the multi-storey buildings. Moreover, the study investigates the cooling capacity and performance of the concrete deck with PCM and integrated TABS and highlights limitations and challenges of the new technology.

The presented work utilizes numerical methods to study the dynamic performance of the new product developed. Consequently, the experimental set-ups and methodologies are developed firstly to determine the thermal properties of the new material, such as combined PCM concrete, and secondly to investigate the performance of the developed decks in 1:1 scale.

The research is scheduled in an iterative manner, where the initial numerical study of the deck with PCM is performed with use of the theoretically determined thermal properties of the PCM concrete material. The reason for the iterative research is due to the lack of experimentally determined thermal properties of this relatively new material. In the second step of the research, the thermal properties of the PCM concrete are determined by experimental manner and afterwards, the initial numerical models are updated with the measured thermal properties of the new composite material. Finally, the results from numerical analysis are validated by the full-scale experiments performed in a specially developed and modified hot box apparatus. The full-scale experiments are also conducted for the specially constructed perforated decks in which heat exchange surface increases compared to the standard flat decks. The decks with perforations are examined with regards to the amount of heat that could be stored during the typical day-night cycle of an office building with specially designed ventilation inlet slot diffuser.

Firstly, it was observed that the assumptions regarding the theoretical thermal properties stand out from the experimentally determined thermal properties of the PCM concrete. Consequently, the results obtained from the initial (theoretical) and updated (experimental) numerical models reflect significant discrepancy of the dynamic heat storage and cooling capacity of the developed decks. The experimentally determined thermal conductivity and specific heat capacity of PCM concrete are significantly lower than ones from the theoretical calculations, what in both cases result in poorer heat storage and cooling power performances than initially expected.

Results from the full-scale investigation of dynamic heat storage capacity of decks indicated that there is no substantial difference between decks with extended heat transfer surface and one with an ordinary flat surface. Moreover, no significant improvement was observed for decks with PCM with regards to their reference deck cast with ordinary mortar. On the other hand, an improvement in the heat storage was observed for all deck casts with specially designed tiles on the bottom with regards to standard concrete deck element. These results, however, were unexpected since the material properties of mortar used to cast tiles were determined to be worse than those of concrete material used to cast standard decks.
Original languageEnglish
Place of PublicationAalborg
PublisherDepartment of Civil Engineering, Aalborg University
Number of pages156
Publication statusPublished - 2012
SeriesDCE Thesis
Number41
ISSN1901-7294

Keywords

  • Phase Change Material
  • Thermal Analysis
  • Concrete Composite
  • Specific Heat Capacity
  • Thermal Mass Activation
  • Dynamic Heat Storage
  • Latent Heat
  • Heat Transfer Enhancement

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