Indoor-outdoor cooling potential of nature-based solutions: an application to university campus retrofit

The combined effect of global warming and urban heat island (UHI) is leading to a sharp increase in building cooling consumption and outdoor thermal stress in cities. Building retrofits interventions using nature-based solutions (NBS) such as green facades (GF) and green roofs (GR) can reverse this vicious heat cycle. GFs and GRs reduce the radiant heat transfer from the building envelope to the interior, while also reducing the external radiant temperatures, with positive impacts on both the indoor and the outdoor environments. For district scale applications, they can mitigate the local UHI intensity, with positive returns in terms of building cooling demand. The positive effect of GF and GR on the indoor thermal conditions of buildings has been widely studied, as well as their positive effect on the urban microclimate. However, most of the studies focused on only one of the two domains, lacking a comprehensive assessment of the global indoor-outdoor cooling potential.

This work proposes a simulation framework to quantify the global cooling potential of NBS applied to building retrofits at the district scale, considering their dual impact on the indoor and outdoor thermal environment. The approach is applied to the UPC University Campus of Terrassa (Barcelona, Spain), considering a deep retrofit scenario with GF and GR applied to all buildings. ENVImet is used to simulate the outdoor microclimate conditions of the campus in the current and retrofit scenarios. The ENVImet outputs are used to morph the weather files for use in EnergyPlus simulations of a representative building, including simplified GR and GF models. The improvement in indoor operative temperature and outdoor mean radiant temperature are used as performance indicators.

The results provide an assessment of the potential for district-scale building retrofits using NBS to improve urban thermal comfort while contributing to the transition towards climate neutral cities.