Energy refurbishment of historic districts. A techno-economic and environmental analysis of a case study

Abstract

A techno-economic and environmental analysis of proposed energetic refurbishment measures combined with energy supply variants for a historic district in Switzerland (303 entities; 64’546 m2 energy reference area (AE)) is given. The economic evaluation is based on the Net Present Value (NPV) method and the environmental impact is quantified in “eco-points” (German: “Umweltbelastungspunkte” (UBP)) and equivalent CO2 emissions. Data for the analysis is provided by the Swiss building certification (German: “Gebäudeenergieausweis der Kantone” (GEAK)) and secondary literature. A total of three variants, V I through V III is analysed. The results show how current limit values for heating demand can be met with energetic refurbishment measures (including aerogel-super-insulation materials) which conform to requirements of the regional monument protection. It is found that a local heat distribution system based on a Brine/Water Heat Pump (B/W HP) (V I) can reduce the environmental impact for heating, hot water, ventilation, auxiliary energy (HWVA) from currently 1.8 tons CO2 eq per capita and annum (p.c.a.) (1.5 Million UBP’s p.c.a.) for the fossil fuel based system to 118 kg CO2 eq p.c.a. (325 thousand UBP’s p.c.a.). The environmental impact of a central wood chip plant (Combined heat and power (CHP)) in V II or a district heating based system in V III is slightly higher than in V I. Negative NPV (for a 30 years’ time frame) is found for all three mentioned energy supply systems in combination with energetic refurbishment measures (V I: -147.- CHF/m2 AE, V II: -125.- CHF/m2 AE, V III: -98.- CHF/m2 AE). However, it can be shown that reducing the energetic refurbishment costs by one third leads to a positive NPV for all three variants mentioned. Furthermore, the NPV-results do not differ significantly between the variants and should therefore not be the sole basis for decision-making. A sensitivity analysis shows a great impact of materials’ lifetime on the NPV. Therefore, reliable estimates for e.g. aerogel-super-insulation materials are important data for a NPV evaluation. Furthermore, the environmental impact was calculated for HWVA, only. This system boundary should be extended to domestic electricity consumption, embodied energy in insulation materials and PV in further research. Keywords: aerogel-super-insulation, historic district, energetic refurbishment, energy supply variants, sustainability assessment