Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by browse.metadata.advisor "De Villiers, Wibke"

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    Phase Change Material and Recycled Brick Aggregate in Thermal Energy Storage 3D Printed Concrete
    (Stellenbosch : Stellenbosch University, 2022-12) Christen, Heidi; Van Zijl, Gideon P. A. G.; De Villiers, Wibke; Stellenbosch University. Faculty of Engineering. Department of Civil Engineering.
    ENGLISH ABSTRACT: The building sector accounts for the highest share of anthropogenic greenhouse gas emissions from electricity and heat production, mostly due to the high energy requirement of heating, ventilation, and air conditioning systems in buildings. Passive design solutions are gaining popularity as a means to reduce the energy requirement of buildings while still providing thermal comfort in buildings. 3D printed concrete represents the next phase of automation in the construction industry with potential to allow for more complex structural geometries, with higher labour productivity, lower energy requirements, reduced waste, and a positive resulting impact on the environment. This research combines a thermal energy storage passive design solution in the form of phase change material, with 3D printed concrete, using recycled brick aggregate as a vessel for the phase change material in the concrete. This research therefore analyses a novel material with aspects of energy saving, automation and recycling. This research is original in its characterisation of a 3D printable concrete containing recycled brick aggregate, and its investigation of leakage of phase change material from recycled brick aggregate in 3D printed concrete. Two mix designs are developed, the first replacing a large portion of the natural aggregate in a 3D printed concrete mix with recycled brick aggregate, and the second adding phase change material to the pores of the recycled brick aggregate to create phase change material 3D printed concrete. Rheological and mechanical characterisations are performed on both developed mixes and compared to a reference 3D printed concrete mix. Mass-loss tests, scanning electron microscopy analysis and 90-day strength tests are used to analyse the internal and external phase change material leakage. Two façade sections are printed with the two mix designs and used in thermal tests to analyse the effectiveness of the chosen phase change material in the façade geometry during different months of early spring to late summer in Stellenbosch, South Africa. The effectiveness of the phase change material after several months of exposure to outdoor ambient conditions proved a successful vacuum impregnation technique of phase change material in recycled brick aggregate. A model of the phase change material 3D printed façade section was created in ABAQUS and validated by the experimental thermal tests, with the material thermal properties being determined by a sensitivity study. The validated model was used to determine two phase change material melting temperatures which could potentially be incorporated into the façade section for saving both cooling and heating energy in summer and winter respectively, due to their activation at separate temperature ranges.
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    South African building envelope thermal performance simulation: parameters and the role of moisture content
    (2022-04) Meyer, Edmund Stanhope; Van Zijl, Gideon P. A. G.; De Villiers, Wibke; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Literature tells of a connected, yet not well harmonised, narrative between building sustainability, building performance, building simulation and building regulations. Building simulation is actively used in industry to achieve targeted building ratings, but the targets do not always match reality due to the associated complexity and uncertainty associated with building simulation. This is further complicated by how the target is set for building performance, as many require an improvement over a benchmark value. For South Africa, the benchmark is provided by building standards. The need to investigate hygrothermal analysis for South African buildings is based on three observations. First, there is a lack of hygrothermal studies in South Africa. Second, conclusions drawn in the literature that focus on the thermal performance of South African low-income housing are based on 'what' environmental conditions are experienced and not 'why' specific environmental conditions are experienced. Third, although climate may be similar when comparing studies that focus on building performance, differences in results exist due to differences in the assumptions used for building simulation. The purpose of this study is to establish the case for improved building simulation and the regulation thereof in South Africa. To do so, four building models were adapted or created and modelled under specific conditions. The first two building models provide insight into how design choices influence the heating and cooling loads of two South African Green Star buildings when only considering heat-only analysis. Results indicate that providing high performance thermal insulation in combination with a large window-to- wall ratio will put additional strain on the air conditioning systems of the Green Star buildings. Furthermore, increasing the window-to-wall ratio of all glazed surfaces during analysis provides limited insight into the effect of the window-to-wall ratio of the Green Star buildings, unless considered alongside the changes to heat transfer through opaque building components, or considering specific surfaces. The third building model highlights the influence of moisture buffering materials on the environmental conditions of the building environment for a typical summer and winter week in South Africa. Results indicate that hygric materials directly influence the building environment. Furthermore, the sorption isotherm and initial moisture content of the material appear to influence simulation results significantly. Results indicate that if sufficient hygroscopic building materials are exposed (in terms of surface area and volume) to the South African environmental conditions, expected simulated results will be different, depending on the inclusion of moisture in heat transfer through building materials. The final building model serves as validation for the conclusions made regarding the importance of hygrothermal analysis. The model also highlights the need for improved modelling guidelines for South African buildings and additional requirements regarding buildings' material properties. The accuracy of the hygrothermal analysis, compared to heat-only analysis, confirms that hygrothermal analysis is required to accurately simulate the environmental conditions in South African buildings with moisture buffering components. Although results show the influence of moisture buffering materials on simulated temperature and relative humidity, further research is still required in South Africa to allow for independent hygrothermal analysis, i.e. hygrothermal analysis using South Africa specific data. Future research towards improved building simulation in South Africa should focus on expanding simulation input data provided for South African building performance simulation, as well as when hygrothermal modelling is needed.