Energy Renovation of an Historic Town Using Life Cycle Cost Optimization : An Assessment of Primary Energy Use and CO₂ Emissions

Abstract:

Historic buildings, buildings built before 1945, represent a third of the total building stock in Sweden. While implementing energy efficiency measures (EEMs) on historic buildings it is important to consider heritage values. This thesis aims to investigate impacts on primary energy use and CO₂ emissions while using life cycle cost (LCC) optimization on historic buildings in three studied cases: reference case with no implemented EEMs (case 1), lowest possible LCC (case 2) and a decrease by 50% in energy use (case 3). As a case study 920 historic buildings divided into twelve typical buildings (6 wood buildings, 1w-6w, and 6 stone buildings, 1s-6s) in the downtown area of Visby, Sweden, are used. Within the scope of the thesis, how to achieve the most profitable EEMs and how the profitability of energy renovation varies between the typical buildings in the studied cases will be analyzed also.

An interdisciplinary method is applied in the thesis that considers both heritage values and energy savings. However, the keystone of the thesis is the use of the program Optimal Energy Retrofit Advisory-Mixed Integer Linear Programming (OPERA-MILP), which is a part of the interdisciplinary method. With the use of OPERA-MILP, the cost-optimal energy renovation strategy is obtained for a building. The program takes into account all energy-related investment costs, as well as the investment and operation costs for the heating system, during a set time period.

The results show unique packages of EEMs for each of the twelve typical buildings with a potential to lower the total LCC by between 4-11% in the building stock and simultaneously decrease the energy use by more than 50%. The thesis also shows a possible decrease in primary energy use from 24%-57%. The CO₂ emissions vary significantly depending on what assumptions are made related to electricity production and biomass use; the results show increases up to 224% in CO₂ emissions but also decreases up to 85%. All typical buildings are economically viable to energy renovate. The LCC savings are between 1.4-11.8 SEK with a life cycle set to 50 years for every annually saved kWh, except for case 3 where cost is incurred for every annually saved kWh, 10.0-17.2 SEK, for a number of the typical buildings.