• Energy Research

Peer reviewed

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.

Shallow ground-source heat pumps (GSHPs) are a promising technology for contributing to the decarbonisation of the energy sector. In heating-dominated climates, the combined use of GSHPs for both heating and cooling increases their technical potential, defined as the maximum energy that can be exchanged with the ground, as the re-injection of excess heat from space cooling leads to a seasonal regeneration of the ground. This paper proposes a new approach to quantify the technical potential of GSHPs, accounting for effects of seasonal regeneration, and to estimate the useful energy to supply building energy demands at regional scale. The useful energy is obtained for direct heat exchange and for district heating and cooling (DHC) under several scenarios for climate change and market penetration levels of cooling systems. The case study in western Switzerland suggests that seasonal regeneration allows for annual maximum heat extraction densities above 300 kWh/m$^2$ at heat injection densities above 330 kWh/m$^2$. Results also show that GSHPs may cover up to 55% of heating demand while covering 57% of service-sector cooling demand for individual GSHPs in 2050, which increases to around 85% with DHC. The regional-scale results may serve to inform decision making on strategic areas for installing GSHPs. Walch and Li contributed equally. Revision submitted to Energy

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 Typically, 70% of the total final energy demand in the industry sector is used for process heat. A substantial share of this energy could be provided by excess heat recovery. This study evaluates the techno-economic excess heat recovery potential in the Swiss industry through exergy and energy analysis and provides an overview of the spatial distribution of the potential by temperature level. The specific costs and payback periods of excess heat recovery are analyzed by conventional and new measures, as well as the overall costs of sector-wide excess heat recovery. The overall mean energy and exergy efficiencies of the Swiss industry sector are estimated to be 61% and 27%, respectively. The total amount of potentially recoverable excess heat is estimated at 14 PJ per year, i.e. 12% of the total final energy and 24% of the total process heat demand of Swiss industry in 2016. However, the economic potential amounts to only 5% and 10% if a payback period of 3 and 4 years is assumed, respectively. Long payback times of heat recovery measures and a high percentage of low-quality and small heat streams were the most important barriers to energy efficiency improvement in Swiss industry. Furthermore, 30–40% of the steam demand in Swiss industry could be provided from excess heat in an economically viable manner, if all excess heat available at temperatures below 80 °C was utilized for steam generation using low pressure evaporation, vapor compression, and high temperature heat pump techniques. The results and the data provided in this study can be adapted to other regions of the world and can serve as a base for conducting more comprehensive analyses and formulating more effective policies.