Assessment of energy and cost effectiveness in retrofitting existing buildings

Abstract

The construction of buildings and their operation contribute to a large proportion of total energy end-use worldwide; indeed, buildings account for 40% of the total energy consumption and for 36% of CO2 emissions in the European Union. The sector is expanding, which is bound to increase its energy consumption. In order to reduce the growing energy expenditure, the European Directive imposes the adoption of measures to improve the energy efficiency in buildings. The recast of the Directive on the Energy Performance of Buildings defined all new buildings will be nearly zero-energy buildings by the end of 2020. However, the transformation of the EU's building stock will not be completed until well after 2020 and this target can only constitute an intermediate step. Indeed, the recent Commission Roadmap for moving towards a competitive, low-carbon economy showed that emissions in the building sector could be reduced by around 90% by 2050. While new buildings should be designed as intelligent low or zero-energy buildings, refurbishment of existing building stock has many challenges and opportunities because, in the building sector, most energy is consumed by existing buildings. Since the replacement rate of existing buildings by the new-build is only around 1-3% per annum, a rapid enhancement of taking up retrofit measures on a large scale is essential for a timely reduction in global energy use and promotion of environmental sustainability. Consequently, defining minimum energy performance requirements for new and, in particular, for existing buildings represent a key element in European building codes. For this reason, EPBD recast has set out Member States must ensure that minimum energy performance requirements are set with a view to achieve cost-optimal levels for buildings, building units and buildings elements. A cost-optimal level is defined as the energy performance level which leads to the lowest cost during the estimated economic lifecycle. It must be calculated in accordance with a comparative methodology framework that is based on the global cost method. To apply this methodology Member States are expected to define a series of Reference Buildings as baseline and representative models of the national building stock. Additionally, they must define energy efficiency measures to be applied to Reference Building; these ones can be a single measure or constitute a package of measures. Reference Buildings can be exploited as a basis for analysing national building stock and the potential impacts of energy efficiency measures in order to select effective strategies for upgrading existing buildings. Finally, once estimated the Reference Building energy consumptions and the impact of the different energy efficiency measures, the costs of the different packages are estimated in order to establish which of them has the lowest global cost and, consequently, represents the cost-optimal level. Global cost method considers the initial investment, the sum of the annual costs for every year and the final value, all with reference to the starting year of the calculation period. A measure or package of measures is cost-effective when the cost of implementation is lower than the value of the benefits that result, taken over the expected life of the measure. The cost-optimal result represents that retrofit action or combination of actions that minimized the global cost. From the variety of specific results, a cost curve can be derived; the lowest part of this curve represents the economic optimum for the specific set of the analyzed energy efficiency measures. This PhD study deals with complex scenario above described. Its main objective is to examine cost-optimal analysis in order to establish if this methodology can be an appropriate tool to guide and support decisions related with buildings energy performances. In detail, a critical review of the methodology has been developed and some sensitivity analyses have been exploited in order to testing the robustness of the cost-optimal analysis results. Considering the influence that similar outcomes could have on the European energy policies and on the roadmap towards 2050, it is fundamental to evaluate, even before the same outcomes, how these are reliable. Cost-optimality as a theoretical concept is well and clearly established. However, its application is far from easy and straightforward. Indeed, cost-optimal analysis is a complex methodology characterized by an inherent degree of uncertainty in the final outputs; choices of methodology, procedural decision and complexity of much of the input data significantly affect outcomes. In addition, the research highlights that often although a cost-optimal calculation is being developed and some energy efficiency retrofit measures are individualized, there are no effective instruments, in term of energy policies and financial tools, to drive the market to increase the rate of deep renovations