Abstract
The cost-optimal level of energy performance for buildings shall be identified according to the European directive of 2010. The Swedish building stock needs comprehensive knowledge and an overall strategy for the cost-optimal level of renovation. This paper studies the contribution of Swedish climate zones to the cost-optimal level of renovation on a multi-story residential building in Sweden from the building owner perspective. The building space heat demand is simulated for four Swedish climate zones. The net present profit (NPP) method is defined and used in this study in order to analyze the cost-optimal level and the cost-effective renovation of building envelope components (e.g., attic floor, basement walls, exterior walls and windows). The implication of different discount rates is studied, as well. The results show that the optimum renovation of the building envelope offers 51% more energy savings for space heating when the building is in a northern climate zone compared to a southern zone. The study suggests that different renovation strategies for the building stock renovation need to be identified, separately, for each climate zone. The NPP analysis identifies the minimum required investment and maximum achievable energy savings that are needed to have a cost-effective renovation. The broad range of studied climate zones provides the opportunity to apply the obtained results to other climate zones by either interpolation or extrapolation of NPPs for the buildings with similar characteristics.
Highlights
40% of the existing apartment blocks in Sweden were built in the period between 1961 and 1975 when the requirements for energy use for heating of buildings were less strict than present national standards
The implications of four different Swedish climate zones on the cost-optimal level and the renovation cost-effectiveness of the building envelope have been analyzed in this study
The method is denoted as net present profit (NPP)
Summary
40% of the existing apartment blocks in Sweden were built in the period between 1961 and 1975 when the requirements for energy use for heating of buildings were less strict than present national standards. Given the good serviceability condition of these buildings [2], well-developed maintenance routines, e.g., compulsory ventilation control [3], as well as a low turnover in the entire building stock (0.5% for single-family [4]), it is estimated that the majority of multi-family buildings from this period will undergo deep energy renovation during the 20 years [5]. Besides requirements on low overall thermal transmittance and specific fan power, as well as mandatory energy-related provisions (e.g., minimum air velocity in occupied zones of 0.15 m/s during heating seasons and 0.25 m/s at other times of the year and a minimum surface temperature of 16 ◦ C for the floor of occupied zone), the Swedish building regulations encompass performance requirements for buildings undergoing renovation [6]. As a result of these measures, total energy use in residential buildings has been reduced by 11% between
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