Toward Industrialized Retrofitting Accelerating the Transformation of the Residential Building Stock in Sweden

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Energy utilization issues are becoming increasingly important around the world. Existing residential and building service sectors represent a large part of total energy utilization, and the corresponding operational costs and environmental impacts are high. Retrofitting is considered an effective way to accelerate the sustainable transformation of the existing building stock. In Sweden, 1945–1975 was a boom period for the construction of residential buildings. After 40–70 years of use, large contingents of buildings need to be systematically retrofitted. In the past, most Swedish buildings were retrofitted individually, and occasionally in small clusters. Cost-effective retrofitting for large-scale implementation has not yet been substantially attained. Standardizing and industrializing the retrofitting process is expected to produce the following benefits: availability of standardized toolkits based on building typologies; simplified and more efficient decision-making process; lower retrofitting costs; shorter project durations; greater resource-efficiency; lower environmental impact; and higher profitability.The overall aim of the present study is to contribute to the knowledge regarding industrialized retrofitting toolkits in Swedish residential buildings and evaluate the various toolkits. More specifically, the study aims to analyze the energy demand saving potential of different retrofitting measures and long-term profits based on the typology of residential buildings. Based on a systematic set of building properties and classification of existing residential types in Sweden, four slab houses (lamellhus) were selected as the major sub-types of building stock for the demonstration cases. The case buildings were constructed between 1945 and 1975 and are currently used as single-family houses, multi-family houses, or apartment blocks. The main approaches applied to model the retrofitting profits were Consolis Energy +, parametric-based sensitivity analysis, and life-cycle-based economic assessment.Based on the theoretical modeling and analytical results from the case studies, it was found that the energy-saving potential is strongly dominated by the building type, which affects the design of retrofitting toolkits and defines life cycle costs. The results show that improving the efficiency of heat recovery in exhaust ventilation systems is an effective retrofitting measure for energy demand savings in the studied building types. However, the efficiency of other measures is highly dependent on the typology of the buildings. From an economic perspective, toolkits that include all of the possible retrofitting measures may not lead to larger expected reduction in LCC compared to standard retrofits that only include the most sensitive parameters. In addition, the impacts of energy price changes to the LCC in the future are highly diverse in different types of residential buildings. Developing systematic retrofitting guidelines for Swedish residential buildings requires both further research and a close collaboration between all stakeholders involved in the retrofitting process.