The public defense of the doctoral thesis presented by Sergi Aguacil Moreno took place on May 15th, 2019, at Ecole polytechnique fédérale de Lausanne (EPFL). Conducted under the supervision of Prof. Emmanuel Rey, Laboratory of Architecture and Sustainable Technologies (LAST-EPFL), his work was carried out in the framework of the ACTIVE INTERFACES interdisciplinary resarch project, part of the National Research Programme "Energy Turnaround" (NRP 70) of the Swiss National Science Foundation (SNSF). It focuses on architectural design strategies for building-integrated photovoltaics (BIPV) in residential building renovation.
Tomorrow's cities are already largely built, as much of the existing building stock – with a low level of energy performance – will still be standing in 2050. Urban renewal processes therefore play an essential role towards the sustainable transition of European cities. In this context, Building-integrated photovoltaic (BIPV) systems can potentially provide a crucial response to achieve current energy and mid- to long-term carbon targets based on the 2’000-Watt society concept in Switzerland, and to fulfil the objectives of the energy turnaround for 2050.
Functioning both as envelope material and electricity generator, BIPV systems can simultaneously reduce the use of fossil fuels and greenhouse gases (GHG) emissions, while providing savings in materials and electricity costs. These are precisely the objectives of most European energy directives, from zero- to positive-energy buildings. However, despite continuous technological progress and increasingly favorable economic conditions, the significant assets of BIPV remain broadly undervalued in the current practice. Various obstacles related among others to technology choice, low demand (which induces small volume production of BIPV products), and lack of information and of aesthetically convincing renovation examples, tend to increase the costs and prevent the acceptance of BIPV solutions.
Considering that BIPV can be integrated into the design process, but in a case-specific rather than in a systematic way, this thesis aims at offering support to stakeholders – especially architects – involved in the design process of renovation projects.
Focusing on an integrated architectural design process for addressing renovation projects of residential buildings, the approach involves four main phases: (1) building stock analysis to identify representative (archetypal) situations, (2) detailed analysis of real case studies, (3) development of architectural renewal design scenarios using BIPV strategies, and (4) multi-criteria assessment of each scenario.
The concrete contributions of this thesis are twofold. First, a set of architectural design strategies – illustrated through real case studies – is defined to promote the integration of BIPV in urban renewal processes. It integrates: (i) passive strategies, to improve the envelope through low embodied-energy materials and construction systems, (ii) BIPV strategies, using innovative photovoltaic products as a new material for façades and roofs, and (iii) active strategies, adapting heating, ventilation, and air conditioning (HVAC) systems to improve the efficiency of the BIPV installation and reduce the dependence on feed-in-tariffs to ensure the profitability of investments.
Second, a multi-criteria assessment methodology is developed to compare the different intervention scenarios, based on a qualitative and quantitative approach. The proposed workflow thus allows comparing different design solutions in terms of BIPV performance, final energy balance, Life-Cycle Analysis (LCA) and Cost (LCC) of the whole renovation process. This approach shall provide architects and engineers with advanced BIPV renovation strategies that depend on the building typology, the architectural design goals, and the level of intervention, thus supporting them towards a low-carbon built environment.