An Integrated Thermal Simulation & Generative Design Decision Support Framework for the Refurbishment or Replacement of Buildings: A Life Cycle Performance Optimisation Approach
The environmental performance of existing buildings can have a major role in achieving the CO2 reduction targets, set out by the UK government. In the UK, new buildings account for around 1% of the total building stock (annually), and predictions show that around 75% of the housing stock that will still remain in 2050 has already been built. Furthermore, while current building performance improvement efforts focus mainly on the operational performance of buildings, the environmental impact of the built environment is the result of processes that occur throughout their whole life-cycle (construction, usage and demolition).
To achieve significant CO2 emission reductions in the built environment in an economically viable way, this thesis adopted the Life Cycle Carbon Footprint (LCCF) and Life Cycle Cost (LCC) analysis approaches, to enable a cross-comparison between multiple design alternatives and to identify the preferable design solution: the refurbishment of existing buildings or their replacement by new ones. In particular, this thesis has developed, tested and validated a computational framework that integrates life cycle performance protocols (EN 15978:2011 and BS ISO 15686-5), thermal simulation tools (EnergyPlus), mathematical optimisation (NSGA-II) and a designated building generative design programming (PLOOTO - Parametric Lay-Out Organisation generator) into a single computer application.
The investigation was carried out using a comparative analysis of simulated case study buildings: a terrace-house, a bungalow and a block of flats. Results show that under the considered assumptions, the optimal refurbishment case studies achieved lower LCCF and LCC values than the replacements: The LCCF of the refurbishment scenarios was between 1,100-1,500 kgCO2e/m2 and their LCC 440-680 £/m2, compared to those of the replacements scenarios, who achieved between 1,220-1,850 kgCO2e/m2 and 550-890 £/m2. Furthermore, this research has found that optimising the performance of a typical London-based terrace house using a life cycle carbon approach reached 10% more savings in CO2 throughout its life, compared to targeting operational CO2 only. This means that complying with current UK regulations – which is currently only focused on the improvement of operational efficiencies – may result in buildings with poorer performance, in terms of their overall life cycle carbon footprint. This is associated to the difference in the analysis scope: while operational efficiencies only examine emissions due to heating and lighting within the building, the Life Cycle approach accounts for emissions that occur in other stages in the building’s life, e.g., emissions that are embodied within its structure, emissions during construction, maintenance and more.
An important conclusion of this research is, therefore, that to reach significant reductions in emissions rates – a life-cycle approach should be adopted. More specifically, to achieve immediate reductions (on a 20-year scale) - refurbishments are generally preferable over replacements. It can, therefore, be concluded that there is a greater importance in incentivising re-use to achieve quicker emissions reductions.
The research has shown that the integration of the various research tools in the proposed computational framework was successful in automating the analysis process. The comparative analysis approach was found to be useful in identifying the preferable design solution – the refurbishment of existing buildings or their replacement. Finally, the research sets out an extensive discussion in regard to the proposed computational framework, life cycle performance analysis and the potential benefits of refurbishments or replacements of existing buildings, in the context of the UK
