How cost-efficient is energy efficiency in buildings? A comparison of building shell efficiency and heating system change in the European building stock

Abstract

Mitigating CO₂ emissions for space heat- ing (SH) and hot water (HW) preparation in buildings is key to reaching climate protection targets. In this context, it is important to understand meaningful bal- ances between CO₂ reduction through thermal reno- vation activities and the change of heating systems. In this work, we develop cost-optimal balances for dif- ferent system settings with the Invert/Opt model. This model optimises the measures applied in each build- ing so that the system costs for SH and HW prepara- tion are minimised under given constraints for a given country. About 500–1000 options are considered for each building. We calculate scenarios and sensi- tivities for all countries of EU-27, reflecting a 95% reduction in CO₂ emissions for SH and HW with a mix of direct and indirect RES technologies. These differ in the settings related to the applicability and costs of building-shell-related measures and the costs and availability of resource potentials. The results show that probably a high share of thermal renovation on total upcoming refurbishment activities until 2050 is cost-efficient to reach a 95% CO₂ reduction in the EU-27 building stocks. Assuming that up to 90% of the buildings in each EU-27 country is applicable for a thermal renovation in case a refurbishment activity is needed leads to around 4% lower system costs by 2050 (13 billion EUR/year) compared to assuming a maximum share of 35%. Energy needs are reduced on average more in older buildings than in newer build- ings. Nonetheless, a combination of thermal renova- tion and heating system change is often the most cost- effective option to reduce system-wide CO₂ emissions also in more recent buildings. The calculations lead to cost-optimal savings in final energy demand in the range of 29–47% between 2019 and 2050. Assum- ing less favourable conditions for thermal renovation (high capital recovery expectations, additional techni- cal barriers and high availability of cheap fuels) the cost-optimal level of heat savings in buildings for overall EU-27 could be suspected at around 1/3 down to 1/4 of current final energy demand.