Multi-criteria analysis of building assessment regarding energy performance using a life-cycle approach

Buildings are associated with large environmental impacts over a long duration. They consume an enormous amount of energy and other resources, and they contribute to carbon emissions at each stage of the building project, from design and construction through operation and finally to demolition [1, 2]. The identification of the building sector as one of the key consumers of energy led to the creation of some rules targeted at improving the energy performance of buildings down to nearly zero through the reduction of energy consumption during the occupation phase [3]. This energy consumption for a building is considered to be the energy used to maintain the occupants’ comfort inside the building (energy for heating, cooling, lighting, etc.). When taking the entire building life cycle into account, total energy used includes operational and embodied energy [4]. The assessment of energy performance of buildings is very important for achieving sustainable development. The aim of the building environmental assessment tools is to provide a sustainable building design, construction, operation, maintenance and renovation, which require cooperation between civil engineers, architects, designers, environmentalists and other experts from different areas of building performance. The relatively new approach of making a sustainability assessment of buildings requires the quantification of impacts and aspects of the environmental, social and economic performance of buildings using quantitative and qualitative indicators. These indicators are included in systems and tools used in various countries for the integrated assessment of buildings. The Slovak building environmental assessment system (BEAS) involves the evaluation of the following fields: site selection and project planning, building construction, the indoor environment, energy performance, water management and waste management [5]. Life-cycle assessment (LCA) belongs to a broadly used methodology which helps with decision-making on sustainable building design. The significance of LCA lies in the fact that it equips policy makers and decision makers for the adoption of suitable and sustainable energy supply systems. Increasing global concern about air pollution and limited oil reserves has generated a great deal of interest in environmentally friendly alternatives [6, 7]. Many works studied problems of life-cycle assessment of concrete through a variety of environmental indicators [8, 9]. The goals of energy performance are: to reduce total building energy consumption and peak electrical demand; to reduce air pollution, contributions to global warming and ozone depletion caused by energy production; to slow down the depletion of fossil fuel reserves; and to lower energy costs and gain related savings due to upgrades to infrastructure. Energy consumption in buildings takes place in two different ways: energy capital that goes into the production and transportation of building materials and the assembling of the building itself (embodied energy), and the energy needed to maintain the building during its useful life. This paper deals with the proposal of a building environmental assessment system, especially one dealing with the assessment and weighting of the energy performance of buildings in Slovakia.

Within the European Union (EU) energy use by the built environment represents more than 40 % of total energy consumption [10, 11], with attention paid to energy and the environment currently growing in the everyday political agenda, even at a local level. As pointed out in the Agenda 21 document approved at the Rio Conference in 1992, local administrations can play a fundamental role in increasing sustainability by acting according to the well-known motto “think globally, act locally”; the inspiring principles of the Local A21 process are a suitable tool for designing a strategic road map to sustainability [12]. In line with the European Union’s Energy Performance of Buildings Directive (EPBD), all new buildings within the union must be nearly zero-energy by the end of 2020 [10]. To quantify the effect of energy-saving measures in the built environment, different methodologies with accompanying indicators have been, and still are being developed. Because of the European EPBD [13], many indicators have been developed to express the energy performance of European buildings through use of an energy label with a classification system with grades from A to G. Now that Energy Performance Certification is compulsory within the European Union, it might be useful to relate the value of real estate objects to the life-cycle costs of energy-saving measures [12]. Promotion of energy efficiency is one of the main goals of energy policies since it improves resource management and reduces energy use and environmental impacts. Today most developed nations include a section on energy efficiency within their energy planning policies, usually implemented through a series of laws, codes, strategies, regulations and certification schemes [14].

Table 1 shows the most significant and globally used building environmental assessment systems [15‐23] and main fields related to energy assessment.

In recent years, the evaluation of building performance in terms of environmental, social and economic aspects has become a topic of discussion in the Slovak Republic. A new Building Environmental Assessment System (BEAS) has been developed at the Institute of Environmental Engineering, Technical University of Košice. Systems and tools used in many other countries were the foundation of this new system developed for application in Slovak conditions. The main fields and relevant indicators of BEAS were proposed on the basis of available information from particular fields of building performance in Slovakia and also according to our own experimental experience. BEAS as a multi-criteria system includes environmental, social and cultural aspects. The proposed fields and indicators respect and adhere to Slovak standards, rules, studies and experiments. The presented system was developed for use during the design stage of office buildings. This system for Slovakia contains 6 main fields and 52 indicators. For the purpose of system weighting, the analytical hierarchy process (AHP) was used [5]. The hierarchy structure of BEAS is shown in Table 2.

The proposed main fields are: A—site selection and project planning, B—building construction, C—indoor environment, D—energy performance, E—water management, and F—waste management.

The methodology for the derivation of the assessment indicators in BEAS was elaborated according to a study [24] and the list of indicators derived through a three-step process. To establish a comprehensive set of indicators for this method of building environmental assessment for office buildings, existing methods of building environmental assessment used worldwide were combined with valid Slovak standards and codes and an academic research paper. A three-step process was carried out. In the first step, a full range of indicators relating to sustainable building efficiency were collected through an extensive review of the literature. In step two, a draft indicator list was selected from the full indicator list based on an in-depth analysis, and in step three, a survey was conducted to gather comments from experts to refine the selected draft indicators. As a result, a final indicator list was then proposed. This list is presented for the field of energy performance in the following sections of this paper.

Multi-criteria decision analysis (MCDA) through mathematical methods can help clarify choices between alternative solutions based on many, often conflicting, criteria and aspects. It seeks to integrate several goals to arrive at the most suitable solution, considering along the way the relative importance of each goal, and offers the possibility of developing a deeper understanding of the problem. If necessary, a section is dedicated to the experimental part, where the teams and means used to develop the work are briefly described [25, 26].

The significance weights of the energy performance field and indicators were determined using the mathematical analytic hierarchy process (AHP), the Saaty method and the pairwise comparison method (the Fuller method). Determined weights of significance were analysed and compared with weights of significance determined in various other systems used around the world. On the basis of comparison and consistent analysis of several variants, the most suitable variant was determined by the Saaty method. In Table 3, an example of field D—energy performance weighting by Saaty—is presented. The criteria weights were determined using the Saaty matrix, a concrete example of which is in the first part of the table with rows and columns marked D1, D2, D3. Di means the ith criterion of D—energy performance weighting for i = 1, 2, 3. The values of the Table 2 in columns P(i), R(i), v(i) were computed using the following Eqs. (1–3). In the last column of the table are percentage weights of assessment criteria. The weights of all assessment criteria in main field D—energy performance—were determined using the same method and all computed values are given in Tables 3, 4, 5, and 6. where n is the dimension of the Saaty matrix, a(i,j) the element of the Saaty matrix of ith row and jth column, P(i) the product of all elements of the Saaty matrix ith row, R(i) the quadratic average of the Saaty matrix ith row and v(i) the weight of ith criterion

In Tables 4, 5, and 6, the weighting of indicators in the subfields are presented:

The criteria weights were assigned using the Saaty matrix.

The significant weights of the criteria were determined using various methods presented in Table 7. The determined weights of significance were analysed and compared with weights of significance determined in various systems used around the world. On the basis of comparison and consistent analysis of four variants, the most suitable variant is that determined by the MCA—the Saaty method.

According to the presented methodology for derivation of indicators for assessment and significance weighting, the percentage weights and the means of the assessment of indicators related to energy performance of buildings are presented in Table 8.

In this paper, the indicators related to the field of energy performance and method for determining the significance weight of this field in BEAS are presented. The percentage weights for energy performance field in the significant environmental assessment systems vary from 19 to 41.3 %, the lowest significant weight of 19 % for BREEAM and the highest of 41.3 % for BEAM. Energy performance in BEAS has a percentage weight of 26.45 %, which corresponds with the mean percentage weight of 28.33 % determined for selected significant systems used in the world (Table 1). The field of energy performance in BEAS consists of 3 subfields and 11 indicators. Within this field the subfield, D1—operational energy has a weight of 56.25 %, the second subfield, D2—active systems using renewable energy sources has 25 % and the third subfield, D3—energy management has 18.75 %.

Building environmental assessment systems and tools has been developed for various types of buildings and for each stage of their life cycle, comparison of the methods and tools developed in different countries showing that these systems are quite diverse. At the same time, however, we can see that the approaches of assessment are essentially not that different. Several differences are found in the terminology, but different indicators in the systems are often evaluated under similar headings. Classification and certification of buildings differ from one country to another in accordance with national conditions and requirements. The sensitivity of methods and independence of indicators are progressively ensured with continuous modification and specification of methods and tools. It, therefore, follows that good building environmental assessment requires a multidisciplinary and multi-criteria approach.

The developed building environmental assessment system applicable in the conditions of Slovakia consists of 6 main fields and 52 indicators and incorporates systems and methods used in many other countries. The main fields are building site and project planning, building constructions, the indoor environment, energy performance, water management and waste management.

The main features of the system include the following:

Based on the comparison of the main fields in BEAS, it is possible to assert that the field of energy performance has the highest percentage weight significance (26.45 %). The percentage weights of others fields are 14.71 %—site selection and project planning, 20.59 %—building construction, 23.49 %—indoor environment, 8.88 %—water management and 5.88 %—waste management.

The theoretical level of existing knowledge about building environmental assessment has been thoroughly analysed and applied, making it necessary to implement this knowledge in construction practice. For the purpose of system verification, a statistically significant set of buildings needs to be evaluated, the outcome of which will be modification of the fields and indicators weighting. Our future research work will be an implementation of aspects and indicators given in European standards for the sustainability assessment of buildings to the BEAS applicable in Slovakia and a comparison of BEAS with significant and globally used building environmental assessment systems.