Building Design Optimization: Integration of Thermal and Fire Performance

The main objective pursued by a fire safety strategy defined for a building design is to achieve an appropriate safe egress time required by the occupants under any fire scenario. This time must be shorter than the fire growth rate, profoundly influenced by the material flammability characteristics of building components. As witnessed in recent fire scenarios, this egress time can be severely compromised by the flammability of innovative building assemblies that include light and combustible materials which are suitable for thermal insulation and provide an easy and affordable way to comply with strict energy efficiency building code requirements. This study analysed the potential conflict between the assessment of thermal insulation and flammability characteristics such as the onset of ignition through heat transfer fundamentals. It was concluded that material properties like the density needed to control flammability characteristics are not evaluated by the current energy efficiency approach adopted by most building policies. By addressing this issue, this study focussed on the development of an integrated assessment method to attain optimised design solutions from where the best insulating properties for a particular geographical location is achieved together with adequate fire safety performance. The first task to address an integrated assessment approach was to identify sharing quantitative parameters relevant to both thermal efficiency and fire performance disciplines by analysing the theoretical thermal models available commonly applied to each field. A fire scenario is a temporal event, and thus its physics is based on a transient thermal approach where the thermal conductivity, the density and the specific heat are significant material properties for evaluation. However, most building components are designed on a thermal steady state approach according to prescriptive thermal design parameters like the thermal transmittance “U-value” derived from a steady state thermal model where thermal conductivity is the only relevant material property. A steady-state thermal model is most precise when daily temperature fluctuations remain within a narrow range allowing for detail associated with large seasonal temperature variation, such as north Europe. In geographical locations, such Australian regions with potentially larger daily (smaller seasonal) temperature variations, a steady state approach can introduce significant errors when assessing building thermal performance. This study analysed Australian weather data and evaluated both steady and transient state model’s parameters on case study Australian prefabricated building component systems. It was concluded that introducing transient model thermal parameters like the cyclic transmittance “u-value”, and the surface admittance “y-value” a more precise thermal performance evaluation is achieved. Furthermore, the definition of these parameters includes all relevant material properties combined in the form of the thermal inertia needed for material flammability assessment allowing for an integrated assessment approach. By using this approach, a quantitative procedure was developed to characterise insulating properties under both steady and transient approaches to building assembly’s designs using numerical models. A small-scale thermal test procedure was defined to analyse both transient and steady-state heat flow processes, allowing for effective numerical fitting of parameters that describe all internal heat flow processes. By using this simple experimental thermal test set-up, the contribution of each element of an assembly design alternative can be evaluated on its overall insulating capabilities including the effect of structural elements acting as thermal bridges and construction imperfections, thereby allowing optimised assessment. As a result, the quantification of the steady state U-value and the transient state u-value and y-value is achieved delivering average values. Also, information can be obtained from specific points in the building assembly to quantify the interaction amongst the components for a more detailed insulating capabilities assessment. Both u-value and y-value analytical definitions include material properties combined in the form of thermal inertia as the material flammability analytical expressions do. The integrated assessment method continues by including in these analytical expressions the numerical outputs at specific points of the building assembly. Thus, it is established a system of non-linear equations that delivers apparent thermal inertia values of these points that include the influence of the whole assembly. From these parameters, a flammability analysis can be performed for different fire scenarios. It was observed that higher energy efficiency u-values and y-values are linked to better material flammability characteristics that effectively contribute to the fire safety strategy. Similarly to the thermal performance analysis, a small scale fire test approach was defined to support this study where the building assembly tested is exposed to higher heat loads. This study analysed and tested two real-life prefab building assemblies supplied by industry partners that challenged the method due to their design complexity. The outcome is presented in this study for illustration and procedural validation. Also, conclusions delivered vital information to assist in their ongoing design improvement. From the analysis of building design alternatives by using the proposed integrated approach and the definition of particular design criteria for thermal efficiency and flammability characteristics, an optimal and balanced solution can be achieved. Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my higher degree by research candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co-authors for any jointly authored works included in the thesis. Publications during candidature Peer-reviewed papers. • Soret, G. M., Lázaro, D., Carrascal, J., Alvear, D., Aitchison, M., & Torero, J. L. (2017). Thermal characterization of building assemblies by means of transient data assimilation. Energy and Buildings, Vol. 155, p. 128-142. Conference publications: • Soret, G. M., Tonino, J., Torero, J. L., & Aitchison, M. (2015). Towards optimizing thermal performance of prefabricated houses in Australian climates. In 3rd Annual International Conference Architecture and Civil Engineering (ACE 2015) (Vol. 1, pp. 186-193). Global Science and Technology Forum (GSTF). Publications included in this thesis Soret, G. M., Tonino, J., Torero, J. L., & Aitchison, M. (2015). Towards optimizing thermal performance of prefabricated houses in Australian climates. In 3rd Annual International Conference Architecture and Civil Engineering (ACE 2015) (Vol. 1, pp. 186-193). Global Science and Technology Forum (GSTF) – incorporated in Chapter 2 and 3. Contributor Statement of contribution Author Soret, G. M. (Candidate) Conception and design (80%) Analysis and interpretation (80%) Drafting and production (80%) Author Tonino, J. Conception and design (5%) Analysis and interpretation (5%) Drafting and production (5%) Author Aitchison, M. Conception and design (5%) Analysis and interpretation (5%) Drafting and production (5%) Author Torero, J. L. Conception and design (10%) Analysis and interpretation (10%) Drafting and production (10%) Soret, G. M., Lázaro, D., Carrascal, J., Alvear, D., Aitchison, M., & Torero, J. L. (2017). Thermal characterization of building assemblies by means of transient data assimilation. Energy and Buildings, Vol. 155, p. 128-142. – incorporated in Chapter 2, 4 and 5. Contributor Statement of contribution Author Soret, G. M. (Candidate) Conception and design (75%) Analysis and interpretation (75%) Drafting and production (75%) Author Lázaro, D. Conception and design (13%) Analysis and interpretation (13%) Drafting and production (13%) Author Carrascal, J. Conception and design (4%) Analysis and interpretation (4%) Drafting and production (4%) Author Alvear, D. Conception and design (2%) Analysis and interpretation (2%) Drafting and production (2%) Author Aitchison, M. Conception and design (1%) Analysis and interpretation (1%) Drafting and production (1%) Author Torero, J. L. Conception and design (5%) Analysis and interpretation (5%) Drafting and production (5%) Contributions by others to the thesis Professor Jose Torero advised on all engineering aspects of the thesis approach and cr