Energy Retrofit Cost-Optimal Design Solutions in Social Housing: The Case of Three Tower Buildings of the 1980s

This paper focuses on the energy retrofit cost-optimal analysis in the usual and deep building renovation scenarios, considering the importance of non-energy-related aspect in an integrated design approach. This objective is developed within the Italian regulation framework on energy efficiency and building renovation. Nowadays, the great part of tax incentives is given to retrofits merely based on technologies existing in the market, without any balanced design approach that may lead to the optimal solution. Moreover, three-quarters of the residential stock are expected to remain in use in 2050. In this framework, we present as a case study a tower building of the 1980s located in a social housing district of Rome (Italy). This kind of districts represents most of the urban expansions built during the second half of the twentieth century. Therefore, they are today one of the most relevant parts of the residential stock, suffering users’ discomfort, unhealthy conditions, typological obsolescence and structural and technological deficiency. Two integrated design options are proposed and analyzed both in terms of energy performance and in terms of related energy and construction costs. Focusing on the case of a tower building, the study attempts at including non-energy and economic factor in the definition of the optimal design solution and at establishing to what extent deep renovation is competitive with respect to usual renovation. The current situation, as reference case, has been compared both with nowadays usual retrofit solutions (envelope thermal insulation, high-performing windows, oil-condensing boiler, LED lights) both with advanced ones (superinsulation, ventilated façade, high-efficiency heat pump). The building has been modelled with Revit applying the well-known H-BIM method in order to accurately control architectural, typological, technological, economic and energy aspects in one single platform. Energy simulations have been performed with EnergyPlus using Insight plug-in and Green Building Studio. Results demonstrate a significant variation in terms of energy consumption and costs (heating, DHW, equipment and lightings) as well as construction costs and payback period of the initial investments. Compared to the reference case, on one side, the proposed usual renovation scenario reduces the former of about 52% and needs a 9-year payback period; on the other side, deep renovation scenario through a 22% additional investment leads to a decrease of 69% in energy consumption and 51% in energy costs, needing an 8-year payback period. The proposed approach in the assessment of renovation scenario allows public and private real estate companies to create energy-conscious design solutions and make cost-optimal investments. These solutions will result in a promotion of sustainable design perspectives taking advantages of the actual Italian incentive regulatory system and increasing substantially the real estate value of this kind of buildings and districts.