• Energy Research

Abstract Reducing space heating demand from the residential building stock has been established as a crucial element of the energy transition across Europe. Focusing on Switzerland, this paper presents a bottom-up model (SwissRes) which allows to analyse the demand for space heating by building element and by building archetype (54 archetypes in total). The model is based on detailed data on the building envelope and heating systems of over 25,000 Cantonal Building Energy Performance Certificates (CECB PLUS). We identify three building characteristics which result in above-average final energy demand: rural typology (18% higher than urban), single-family houses (41% higher than multi-family) and in particular age of buildings (525% higher from newest to oldest). In combination, these three factors can lead to up to seven times higher demand per m2 and year in extreme cases compared to the most efficient archetype. Among buildings constructed before 1970, single-family houses (SFH) show very high specific final energy demand for space heating ranging between 170 and 200 kWh/m². On the national level, SFHs and multi-family houses (MFH) are featuring almost identical shares of total final energy demand. Buildings in suburban areas account for almost 50% of the total final energy demand. In total, the buildings constructed before 1980 account for 70% of the national final energy demand for space heating, with buildings constructed before 1920 contributing 22%. Most heat is lost through walls (40%) followed by windows (25%), roofs (17%) and the floor (18%). Losses from walls are particular high (73 kWh/m²) for buildings constructed between 1920 and 1945. Given the scalability of the model, it is readily applicable not only for the country as a whole but also for a province (canton), a city or a larger neighbourhood. The energy demand by archetype and building element identified with the SwissRes model can be used to assess the techno-economic potential of large-scale energy retrofit scenarios.

Abstract A statistical analysis of more than 6,000 energy performance certificates including retrofit options proposed by experts for different building elements is performed. This provides an overview of the most commonly suggested renovation measures and their estimated investment costs and U-Values. Based on an energy model of the Swiss residential building stock (SwissRes), the theoretical energy savings are estimated. Together with the estimated investment costs, the levelized costs of each renovation measure is then determined in order to identify the most cost-effective measures. It is shown that a large-scale energy retrofit of the residential building stock would result in theoretical energy savings of up to 84% regarding the current simulated energy demand. Yet, existing technical and social constraints would lower the expected energy savings significantly. None of the selected measures is cost-effective, but under a more optimistic scenario, the cost-effective share reaches up to 85% of the total potential energy savings.

Abstract Decarbonisation and a transition towards sustainable energy systems in cities are key elements of the United Nations sustainability goal. Large-scale district heating networks sourced by excess heat or renewable energy allow to effectively transform building-related energy systems. This study proposes two different approaches for modelling load curves in large-scale district heating networks: 1) physics-based static energy balance model 2) data-driven regression model trained and adjusted on measured load curves. The load curves generated by application of these two approaches are compared with the actual load of an urban district heating network in Geneva, Switzerland. Both models allow to recreate the actual load curve of the district heating network, however with lower accuracy for higher time resolution in the case of the physics-based model. The physics-based static model can be used to simulate the demand and generate load curves of sufficient quality at monthly and daily resolution. For an hourly load curve, it is recommended to use the data-driven regression model if consumption data of the network is available.

Abstract Deep energy retrofit across the European building stock would require decades during which boundary conditions will change. This study identifies a range of retrofit pathways, using a dynamic stock model, a bottom-up energy model and an optimization model for different climate scenarios. We consider 1.1 million different retrofit options in the Swiss residential building stock for different economic/environmental objectives until 2060. Despite the replacement of old by new buildings, energy demand and greenhouse gas (GHG) emissions in the reference scenario without deep energy retrofitting are likely to decrease by only about 25%, while accounting for investments of 2–3 billion CHF/a. Partial energy retrofitting or an investment-minimized pathway are neither cost-effective nor sufficient to get close to the net zero targets. In contrast, the highest GHG-saving pathway leads to very high emission reduction of 90%, but requires investment cost of 9 billion CHF/a, which leads to specific cost of 180 CHF/t CO2eq. The cost-optimal pathway shows moderate trade-offs for investment cost and could reach GHG savings of 77% with specific cost of −140 CHF/t CO2eq. Hence, early and deep energy retrofit is cost-effective and allows deep GHG emission reductions by making full use of the synergies between GHG and cost savings.

Abstract This paper analyses optimal electricity investments (PV and battery storage) to decarbonise heat supply in residential buildings under different heat pump and energy retrofitting scenarios in a detailed representation of the Swiss power and heating system. The sensitivity of PV and storage deployment, including lithium-ion (LiB) and vanadium redox flow batteries (VRFB), with respect to distribution network capacity is also investigated. We propose an open-source dispatch sector coupling model (GRIMSEL-AH) to minimise energy system costs (social planner perspective) for heating and electricity supply in Switzerland with hourly and daily time resolution for electricity and heating respectively. Moreover, our representation of the Swiss energy system includes various types of consumers and urban settings which are represented with monitored electricity demand data for each sector and simulated heat demand data at the building level for the residential sector. We find that under a “business as usual” heat pump deployment and retrofitting rate, the optimal electricity investments correspond to 27.8 GWp of PV combined with 16.9 GW (33.8 GWh) for LiB and 1.9 GW (7.6 GWh) for VRFB. For this case, 57% (13.3 TWth/year) of the residential heat demand is covered by heat pumps with a total installed capacity of 19.7 GWth by 2050 (capacity exogenously set with its operation optimised). With increasing heat pump deployment, retrofitting rates are found to have a large impact on the investment in storage and a 100% heat pump scenario for the residential sector appears to be feasible. Our results show that heat pumps do not only decarbonise heat but also provide extra flexibility to the power system, since they increase local PV self-consumption, resulting in higher PV deployment. The model and the methodology presented in this study can be applied to other countries.

Abstract Heating and cooling contributed to about 50% of the final energy consumption in EU 28 countries. In Switzerland, about 295 PJ of heat was consumed in buildings in 2016 which emitted about 17 million tonnes CO2. However, if the Swiss nationally determined contributions (NDCs) have to be met, the country's aggregate CO2 emissions should be between 8 and 16 million tonnes in 2050. Reduction of specific space heating demand in buildings; integrating renewable energy and increased heat distribution by district heating networks (DHNs); and use of heat pumps are three strategies which have been examined for decarbonising the Swiss heating system. It is estimated that an annual reduction of 1.5%–2.5% in the aggregate heating demand for different categories of buildings would be required. DHNs would have to be expanded from 53 networks in 2016 to about 159–212 networks in 2050 to enable integration of 53–70 PJ of ambient heat. This would require 390–520 heat pumps of 2–50 MW capacity with a coefficient of performance between 3 and 4. If these strategies are implemented, it is estimated that the aggregate CO2 emissions from heating would be between 1.25 and 3.06 million tonnes by 2050 thereby significantly decarbonising the heating system.

Abstract Decarbonising energy used for space heating and hot water is critical for reaching emission targets. Modelling of thermal energy decarbonisation becomes increasingly complex as additional technology options are included. Spatial aspects become increasingly important when considering heat transport, for example using district heating. This study develops a model for heating energy decarbonisation that makes use of a techno-economic model applied to a large geographic area (Western Switzerland) at high spatial resolution. Global sensitivity analysis is applied to quantify the variance characteristics of the model. Heating energy services provided by retrofits, decentralised heat pumps, and thermal networks are considered. Final energy demand reductions ranges of 70–80% and emissions reductions of 90% were found with levelized costs of providing the heat service of 0.14–0.22CHF/kWh. High sensitivities were found with respect to efficiency parameters (retrofit potentials and seasonal performance factors). The spatial distribution of costs and sensitivities was shown to be highly variable, with a strong correlation with building density. This raises important questions, notably on equitable distribution of energy transition costs.

Abstract In this study we present a method for the assessment of the economic potential of deep energy retrofit packages for a national building stock, based on three main economic assessment approaches: 1) full investment cost and energy savings (approach FULL), 2) an approach only considering the cost of energy efficiency improvement and the related energy savings (approach IMPROVEMENT) and 3) an approach which is in line with the IMPROVEMENT approach but additionally assigns a residual value to each building element (approach DEPRECIATION). These three economic assessment approaches allow to assess the cost-effectiveness of large-scale retrofit packages according to different strategies, i.e. profit-oriented in the case of FULL, retrofitting only at end of lifetime in the case of IMPROVEMENT and pursuing a balance between environmental/energy and economic aspects in the case of DEPRECIATION. A case study for Switzerland shows that deep energy retrofit packages offer a technical energy saving potential of 55–86% and a technical greenhouse gas abatement potential of 50% to 80% (compared to current levels). The different approaches result in economic energy saving potentials of 3% (FULL), 14% (DEPRECIATION) and 50% (IMPROVEMENT). The respective marginal levelized costs for reaching a 50% reduction in final energy demand amount to 120 CHF/MWh (FULL), 40 CHF/MWh (DEPRECIATION) and 1 CHF/MWh (IMPROVEMENT). The results show an economic greenhouse gas saving potential of 1% (FULL), 13% (DEPRECIATION) and 65% (IMPROVEMENT) with respective marginal levelized costs for a 50% reduction of 350 CHF/t CO2eq., 90 CHF/t CO2eq. and −40 CHF/t CO2eq. The findings indicate that, without subsidies or with rather low subsidies, large-scale deep energy retrofit is economically viable only if it is part of the regular refurbishment cycle (IMPROVEMENT approach). Since full alignment with regular refurbishment cycle is not practically possible across the building stock, policy design is recommended to rather follow the DEPRECIATION approach according to which a subsidy of 40 CHF/MWhsaved (or 90 CHF/ t CO2, avoided) would be needed in order to achieve a 50% final energy and greenhouse gas emission reduction in the building stock.

Abstract The reduction of energy consumption in the existing building stock is a crucial element of the Swiss Energy Strategy 2050 in view of the fact that the built environment accounts for more than 44% of the final energy use in Switzerland. It is therefore necessary to characterise the Swiss building stock and in particular the residential sector at an appropriate degree of detail, distinguishing between various types of buildings (archetypes) and building elements in order to identify the untapped potential for energy retrofit. In this paper, the current thermal performance and retrofit state of the Swiss residential building stock is examined based on approximately 10,400 Cantonal Building Energy Certificates issued for individual buildings across the country. The statistical analysis of the certificates allows to estimate a thermal performance level of archetype buildings and their respective building elements as well as of the heating systems. For this purpose, we develop a method allowing to obtain typical U-Values for original and retrofitted buildings from the total U-Value distributions. Our results indicate that approximately 75% of all building elements do not yet reach the thermal performance of buildings constructed in the last 15 years. In order to reach current low-energy building standards (MINERGIE P), the U-Values of building elements constructed prior to 1990 would have to be reduced by a factor of three to more than six, from 0.5–1 W/(m²K) to 0.15 W/(m²K); windows would require an improvement by at least a factor of two, from 2.5–2 to 0.9 W/(m²K). With regard to heat supply, 50% of the surface area is still heated by inefficient and CO2-intensive oil-fired boilers. The results of this study hence confirm the high potential for thermal retrofit in the Swiss residential building stock.