Cost-effective and energy-efficient renovation measures of multi-family apartment buildings constructed during the million program - Where carbon dioxide emissions minimization is a key issue

Sammanfattning: The Swedish construction and real estate sector has a significant impact on the total national carbon dioxide emissions and energy consumption. Thus, energy efficient and environmentally friendly renovation measures of existing buildings in Sweden plays an important role in the attempt to mitigate the climate changes. By applying the methodology developed by the IEA EBC Annex 56, this study focused on optimization of renovation measures to define energy, environmentally and cost-efficient renovation measures of multi-family apartment buildings located in southern Sweden. The analyzed reference building presented in this study is a high-energy consuming multi-family apartment building constructed during the mid 60’s in the city of Malmö. The present study includes an investigation of the current energy need of the building and compares it with different renovation alternatives with different intervention levels. The renovation measures studied within this project includes modifications to the building envelope, the ventilation system as well as an implementation of an individual metering and price charging system of the domestic hot water. The main aim of this project was to analyze different renovation alternatives in order to determine their effects on the energy consumption in the building, their financial profitability and their effects on the overall environmental impact of the building. Moreover, an additional analysis was conducted in order to study the potential co-benefits that may arise from the implementation of the renovation measures. The secondary aim of the project was to try to find renovation measures that would successfully reduce the annual energy consumption of the studied reference building down to a level where the current energy requirements established by the Swedish building sector was fulfilled. The annual energy consumption of the studied reference building was assessed by the use of a dynamic energy simulation software. The effects of the linear thermal bridges were calculated separately under steady-state conditions. Moreover, the cost-efficiency of the studied renovation measures were evaluated by several conducted life cycle cost analyzes. In order to assess the environmental impacts related to the implementation of the studied renovation measures, a life cycle impact assessment, LCA, was conducted. The resulting co-benefits that arise from the implementation of the renovation measures were evaluated by using an assessment matrix provided by IEA EBC Annex 56. The results of the study showed that it is possible to reduce the annual energy consumption of the building down to a level where the current energy requirements established by the Swedish building sector are fulfilled by implementing comprehensive renovation measures. The results of the life cycle cost analyzes indicates that the financial profitability of the renovation measures is mostly dependent of the balance between the initial investment costs, the saved energy costs that the measures entails and the assessed evaluation period. However, the life cycle cost analyzes conducted within this project shows that by combining the renovation measures with a number of legal aids, such as governmental subventions and increased monthly housing rent will radically affect the cost-effectiveness of the renovation measures in a positive way. The results of the life cycle assessments conducted within this project indicates that renovation measures that significantly reduces the dependence of district heating will also significantly reduce the annual CO2 emissions and primary energy consumption of the building over time. Although the results showed that the comprehensive renovation measures contributes to a rather high environmental impact in the upstream and core process, their implementation will still reduce the environmental impact of the building from a long-term perspective. Thus, the general conclusion is that the energy carrier and the quantity of the overall energy use in the building is the two biggest determining factors of how environmentally friendly the building will be from a long-term perspective. The general conclusion of this research is that comprehensive renovation measures including modifications to the building envelope combined with ventilation and domestic hot water measures are preferable when retrofitting buildings with features similar to the studied reference building from a long-term financial and environmental perspective.