- Title
- Empirical and theoretical modelling of the effects of slab-edge-insulation in slab-on-ground housing
- Creator
- Liu, Zhang
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- To reduce the operational energy in residential buildings is an important and urgent task in relation to energy conservation and mitigating greenhouse effects. A potential way to achieve this is to install rigid insulation boards at the edges of a house slab perimeter, which could substantially reduce the operational energy loss. The saved operational energy via the house slab could be approximate 8% - 33% by using slab-edge-insulation. However, because of the complex physical mechanisms and relevant thermal parameters involved in ground-coupled heat transfer (GCHT) and the complexity of GCHT in three spatial dimensions and temporal dimensions at all timescales (from hours to years), there have been few comprehensive and in-depth studies or guidelines on the effects of slab-edge-insulation improving the thermal performance of housing by reducing energy loss via the ground floors. The primary aims of the current study are, through empirical and theoretical methods, to carry out an assessment of the effects of slab-edge-insulation (SEI) on saving operational energy, and to provide appropriate strategies to use SEI in buildings located in different climate zones of Australia, together with consideration of the different wall-ground interfaces and walling systems. In the empirical approach adopted in this study, experiments were conducted on two full-scale housing modules on the University of Newcastle campus with typical slab-on-ground footing systems. The data collected from in-situ experiments indicated that the temperature fluctuation at the slab edge surface and annual operational energy loss (or accumulated heat flow) via the ground floor in artificially controlled internal conditions (i.e., a constant room temperature condition) were effectively mitigated by employment of extruded polystyrene (XPS) boards adhered to the edges of the floor perimeter. The experimental data was then also used for validating the accuracy of the ground-coupled heat transfer model and the corresponding numerical simulation tool developed in this study. To further investigate the effects of SEI on improving the thermal performance of the slab-on-grade floor and the reduction of operational energy lost from the concrete floor, a numerical simulation tool based on the finite volume method (FVM) was developed as part of this study. The simulation program consists of approximate 10,000 lines of C++ codes. Detailed geometries and configurations of earth-contact structures, surrounding ground and SEI, a variety of physical mechanisms and parameters involved in GCHT and a range of wall-ground interfaces (walling systems) were taken into account in the numerical model and the FVM simulation tool. The developed simulation tool contains complete functions as a numerical modelling program including ‘pre-processing’ (geometries and thermal parameters setting, temporal and spatial discretization, initial and boundary conditions setting), ‘solver’ (discrete equations solving) and ‘post-processing’ (preliminary data visualization). The developed simulation program was theoretically verified through an analytical case and empirically validated by a range of experimental data collected from the in-situ experiments on the Callaghan campus of the University of Newcastle. It was shown that the simulation results compared well with the analytic solutions and provided satisfactory predictions of the temperature variations in case studies of ground-coupled heat transfer in comparison with the experimental data. According to the relevant evaluation standards, the numerical model and the simulation tool can be rated as ‘good’. In order to calculate the heat flow through the floor surface with three-dimensional (3-D) precision with a two-dimensional (2-D) computation speed, four approximate 3-D techniques were discussed and compared. In addition, a new approximate 3-D technique was also proposed in the study. From a view of accuracy and ease of use, one of these methods based on area-to-perimeter ratio (of the ground floor) was adopted in the case studies of the theoretical analysis. The energy loss through the ground floor and the effects of SEI on improving the thermal performance of housing subject to seven Australian climates in five types of housing (with different walling systems) were investigated through numerical simulations and theoretical analysis. From the numerical simulation results of the case studies, it was found that the demand for both cooling and heating loads for buildings in artificially controlled conditions located in different climate zones were effectively reduced by employing the SEI (extruded polystyrene boards vertically adhered to the edges of the floor perimeter). It was also found that more benefits can be obtained from utilization of SEI for housing located in extreme Australian climatic conditions like climate zone 1 (Darwin), 3 (Alice Springs) and 7 (Hobart) than for housing located in mild climates such as climate zone 5 (Sydney) and 2 (Brisbane). It was also found that, the effects of SEI were obviously influenced by the thermal performance of the walling system (wall-ground interface). Generally, the poorer the thermal performance of the walling system, the more benefits were obtained from employment of SEI. For example, the most benefit (i.e., the energy saving) obtained from employment of SEI was found in housing with a light weight (LW) walling system, in contrast, the least benefits were found in housing with insulated cavity brick (InsCB) walls. Furthermore, optimum strategies for saving energy and improving cost effectiveness by using SEI were investigated with consideration of the insulation position and depth, the climate, the walling system type, the embodied energy of XPS and the economic parameters. According to theoretical analysis, it was found that the optimal design of SEI from the view of energy conservation (i.e., 1.30 m depth of SEI for housing in Darwin and 0.90 m depth of SEI for housing in Sydney) was larger than the optimal design of SEI from the view of cost effectiveness (i.e., 0.40 m depth of SEI for housing in Darwin and 0.30 m depth of SEI for housing in Sydney). Besides, it was found that in areas subject to severe climates such as Darwin and Hobart, the geometry of optimal design of SEI and benefits from it were larger than their counterparts in areas subject to mild climates such as Sydney and Brisbane.
- Subject
- residential buildings; insulation; Australia; footings; slab edge surfaces
- Identifier
- http://hdl.handle.net/1959.13/1408202
- Identifier
- uon:35810
- Rights
- Copyright 2019 Zhang Liu
- Language
- eng
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