Sustainable construction is at the heart of modern construction, and refers to all aspects of this branch of industry: the environmental aspect, which includes energy efficiency, the financial aspect, and the sociological aspect, while not forgetting the technical aspects of sustainable construction. Sustainable construction is also concerned with safety issues such as the effect of earthquakes and fires, and the adverse effects of radon. It is, in fact, ZAG's very ability to treat such problems in an integrated way that defines us, both in Slovenia and on a European scale, as one of the most highly-valued competence centres for life cycle assessments in the fields of both buildings and construction products.
In the case of the environmental aspects of construction, the focus is on the use of different kinds of materials. These include both mineral resources and biogenic raw materials (wood, sheep's wool, cellulose fibres, hemp fibres, and poplar fibres), as well as on recycled waste materials. Materials and products are first evaluated through life-cycle assessments (LCA). In performing this work, ZAG's researchers make use of databases containing a large number of individual analytical units, thus making it possible to carry out high-quality analyses, including, if necessary, the modelling of many sub-processes. ZAG's researchers have, within the framework of numerous programs, coordinated or cooperated in the implementation of life cycle assessments, or in tasks of directly related to environmental sustainability. Such programs are the TIGR Competence Centre, the SMARTRAIL and HEROMAT projects, which were part of the 7th Framework Program, and the Unisash and RusaLCA projects, which belong to the Life+ Program.
ZAG also manages its own system of environmental product declarations (EPD) in accordance with the provisions of the standard EN 15804 (this system is known asZAG EPD) and is also a member of the ECO Platform organization. Within EOTA, the European Organisation for Technical Assessment, ZAG coordinates the work of the group which is concerned with the different aspects of the sustainability of construction products. With its wide range of activities ZAG can offer both Slovenian industry and industry in other countries mechanisms for the environmental optimization of products, as well as a reliable and credible system for the exploitation of available market advantage.
Research and development work ZAG level includes analyses performed at the level of individual buildings, with calculations of their environmental. As and when necessary, in-depth knowledge of building physics, including numerical simulations, is combined with knowledge about the environmental properties of materials. The results of such analyses frequently indicate interesting relationships between the impact of the selection of materials, the regime of use of the building, and the effect of its occupants. It has been shown that the share of emissions from the production of materials can makea very large contribution to the total emissions. For this reason it is important that, when buildings or civil engineering works are being designed, the aspect of embedded emissions is properly taken into account.
Example of the analysis of the environmental footprint of a building
The results of an analysis of an actual building were the following:
- the calculated embedded emissions amounted to 5.6 kg of CO2 equivalent/m2 per year, or 335 kg of CO2 equivalent/m2 over the building's full life expectancy,
- the CO2 emissions associated with the heat necessary to heat the building (assuming a space heating demand of 15 kWh/m2 per year, the use of an electrically powered heating pump, and a seasonal COP value of 2.5) were 2.8 kg of CO2 equivalent/m2 per year, and
- the CO2 emissions associated with the use of primary energy (assuming a space heating demand of 45 kWh/m2 per year) were 8.4 kg CO2 equivalent/m2 per year.
The shares of the individual contributions to the emissions can be seen in the two diagrams shown below:
Comparison of the embedded emissions, the emissions due to heating (using a heat pump), and the emissions due to the use of primary energy (without heating)
Comparison of the embedded emissions, the emissions due to heating (using a heat pump), the emissions due to the use of primary energy (without heating), and emissions due to daily commuting
The basic data used in the above calculations are as follows: average life expectancy of the building: 60 years, an internal space of 150 m2, energy efficiency class A2 (the level achieved by passive houses), and the use of an electrically powered air/water heat pump. The presented building is quite energy efficien. The impact of commuting is taken into account by assuming a distance of 30 km (one way 15 km, on weekdays), with the release of 100 g of CO2 per km.
The results of the above analysis show, interestingly, that the primary energy consumption for heating is quite low, due to the use of a renewable source of energy (the heat of the air inside the building), but at the same time the electricity which is used has a higher emission rate in CO2/kWh than that obtained in the case of other fuels, so that the positive impact on the reduction of emissions is practically cancelled out. Of course, if the source of the electricity is changed, and if the share of OVE is increased, then this undesirable effect can be reduced. The presented data were obtained from the 2008 version of PURES, i.e. the Code about the Efficient Use of Energy in Buildings.
The results of the analysis can also be normalized, from the point of view of the emission of greenhouse gasses, with respect to the release corresponding to average inhabitant of Europe. This amounts to almost 10 tonnes of CO2 equivalent /m2 per year. If it is assumed that 5 people live in the above-described house (i.e. 30 m2 of floor area per person), then calculated total(?) emissions amount to about 250 kg of CO2 equivalent /m2 per year, which makes up just 2.5% of the total emmissions which could be ascribed to a single person. If we realize that the buildings which make up most of today's building stock cause approximately 35% of all greenhouse gas emissions, then it should be technically possible to reduce these emissions by as much as 90%. Of course, this figure would only be achievable if the entire building stock were to be renovated to a passive level of energy consumption.
The second segment of sustainable construction with which ZAG's researchers are concerned involves LCC (Life-Cycle Cost) analyses, in which the effects of various factors on the payback return period are investigated. The LCC method is still used only infrequently at the level of buildings, although it can provide good comparisons of the advantages and disadvantages of different designs. Within the scope of the SMARTRAIL project, which was part of FP7, and in co-operation with our partners, a tool for the implementation of LCC analyses in the case of a structure belonging to the infrastructure was developed.
Example of the cost analysis of a building
Analysis of the effect of the discount rate "r", as shown in the diagrams below, shows shows that the LCC method is quite sensitive to the selection of this rate, so that it should be used with discretion, on the basis of reliable data.
The effect of the discount rate on the payback return period (a hypothetical comparison of two variants of the construction of a building taking into account different discount rates).