Towards zero-energy cities : a numerical tool to optimize retrofitting of existing urban blocks

According to the European Commission, the built environment accounts for more than 40% of the overall energy consumption and 36% of the overall CO2 emissions in Europe. The energy efficiency of both new and existing constructions is a crucial issue in winning the fight against Global Warming. While zero-energy buildings – constructions that consume only as much as can be produced onsite through renewable resources –, seem like a concept of the future, new technologies are constantly emerging that make them possible to achieve today. In practice, several examples have recently been built that prove their feasibility. Going even further, the concept of zero-energy can be applied to entire urban blocks, linking transportation and building energy consumption with local renewable energy production. It can even be achieved in existing urban environments through major retrofitting works. To enable and facilitate the implementation of such schemes, a myriad of parameters need to be taken into account, assessed, and coordinated. To this end, Dr. Modeste Kameni Nematchoua, from the Faculty of Applied Sciences, in Liege (Belgium), aims to develop, validate and apply a numerical tool for the energy optimization of renovated urban blocks. The researcher will build on two complementary case studies, located in Belgium and in Madagascar. The overall objective of the project, called ZEUS (for Zero-Energy Urban blocks: low environmental impacts and cost-efficient Solutions), is to generate a major and interdisciplinary scientific contribution towards effective and cost-efficient retrofitting of existing urban blocks in very different climate and urban contexts.

"Zero-energy buildings are attracting increasing interest internationally in policies, scientific literature and practical applications, reports the main investigator, using the example of Europe." The recasting of the European Performance of Buildings Directive requires all new buildings, built in Member States, to be “nearly zero-energy” buildings (nZEB) by 2030". Similar initiatives are emerging in the United States of America, Canada, China, India, Japan, South Korea… Until now, Dr. Nematchoua explains, "optimization methods approaches to the zero-energy concept adopt only the perspective of the individual building. Furthermore, current policies and applications concerning the zero-energy objective are focusing on new buildings, neglecting the potential for retrofitting the existing residential building stock as well as the impact of the urban form and the localization of buildings on transportation energy consumption and potential local energy production through renewable energy sources".

Expanding the scope of existing zero-energy optimization softwares at the neighborhood level

Research-wise, an appreciated body of studies have already been conducted on zero-energy building, using similar mathematical optimization methods as the one that will be developed here, "but always at the individual building level, very little at the urban block level", specifies Dr. Nematchoua. "In this research, numerical optimization of buildings will be extended to include energy aspects related to mobility and renewable energies, in order to take into account their potential interactions. Furthermore, the study will also take into account the environmental impacts of these zero-energy solutions (including the impacts on the health of inhabitants), as well as their overall costs. Several side factors will also be investigated, like modal change from individual cars to green transportation modes (ie: bicycles, walking, etc), future high-tech transportation modes (for example shared autonomous cars), as well as the influence of the urban density on the most suitable local renewable energy sources. The ultimate objective is to produce a software that will be able to select the most sustainable solutions over the entire life cycle of buildings. An other important point to notice about the present project is its particular attention to carbon emissions. Indeed, reducing energy consumption does not necessarily mean that carbon emissions will decrease. "Zero-energy and carbon neutral are two different concepts", confirms the investigator. "However, it is possible to combine both, by paying particular attention to building materials, for instance, and transportation, of course. We aim to reduce carbon emissions up to 40%".

By 2050, more than 75% of the population will live in cities. Better understanding of the interactions and energy exchanges occurring in the urban environment, between buildings, transports, and local renewable energy sources, is thus an absolutely crucial research step on the road to global sustainability. By aiming to "help stakeholders to identify new opportunities regarding the implementation of zero-energy policies and to provide community planners, traffic engineers, buildings engineers and designers with a tool, information and data aiding in the design and implementation of zero-energy renovated urban blocks", the ZEUS project will make a considerable contribution towards this goal.