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In order to meet the ambitious emission-reduction targets of the Paris Agreement, energy efficient transition of the building sector requires building retrofit methodologies as a critical part of a greenhouse-gas (GHG) emissions mitigation plan, since in 2050 a high proportion of the current global building stock will still be in use. This paper reviews current retrofit methodologies with a focus on the contrast between data-driven approaches that utilize measured building data, acquired through either 1) on-site sensor deployment or 2) from pre-aggregated national repositories of building data. Differentiating between 1) bottom-up approaches that can be divided into white-, grey- and black-box modelling, and 2) top-down approaches that utilize analytical methods of clustering and regression, this paper presents the state-of-the-art in current building retrofit methodologies; outlines their strengths and weaknesses; briefly highlights the challenges in their implementation and concludes by identifying a hybrid approach - of lean in-situ measurements supplemented by modelling for verification - as a potential strategy to develop and implement more robust retrofit methodologies for the building stock., Renewable and Sustainable Energy Reviews, 144, ISSN:1364-0321

Applied Energy, 294, ISSN:0306-2619, ISSN:1872-9118

The current retrofit rate in Switzerland is very low. Among other reasons this is attributed to a lack of knowledge about cost-optimal retrofit strategies. In this work we carry out a holistic cost-optimal retrofit analysis for a Swiss single-family house. First, currently popular retrofit measures including all incurring lifecycle costs are identified and collected. Thereby, building systems as well as building envelope retrofit measures are considered. The retrofit measures are then combined to form a wide range of applicable retrofit strategies which are assessed in terms of cost-effectiveness and environmental impact. The calculation methodology considers the impact of building envelope retrofit measures on the design and efficiency of the heating system. For the case study building, the most cost-optimal retrofit strategy is to combine a geothermal heat pump with inter-rafter roof insulation and cellar ceiling insulation. The results indicate that the choice of heating system is much more crucial in terms of cost-effectiveness than building envelope measures. With respect to reducing primary energy consumption, building envelope measures are indispensable, however, when aiming for reducing greenhouse gas emissions, the choice of heating system becomes dominant., Journal of Physics: Conference Series, 1343 (1), ISSN:1742-6588, ISSN:1742-6596