Using integer Linear Programming to minimize the embodied CO2 emissions of the opaque part of a façade

[EN] Buildings are responsible for about 36% of the CO2 emissions in Europe but there is a significant potential to reduce these emissions. This paper deals with the embodied CO2 emissions of the opaque part of a facade, which include the life cycle of any material used in its construction: excavation, processing, construction, operation, maintenance, demolition and waste or recycling. With the aim of minimizing such embodied CO2 emissions, an Integer Linear Programming problem is presented, in which CO2 emissions are minimized depending on other parameters involved in the construction of the facade, like the maximal thermal transmittance allowed by current legislation, thickness of the wall, budget, availability of materials for the different layers of the wall, etc. The paper also shows a case study based on a constructive solution for the opaque part of the envelope defined by up to six layers, with more than 1.1 million possible combinations. This case study considers seventy scenarios depending on maximal allowed thermal transmittances and thickness intervals for five different technologies applied to the structural element of the wall. Results show that an adequate selection of materials can reduce the embodied CO2 emissions of the opaque part of the envelope up to 78.5% for similar values of transmittance and thickness.