From Convention Management, by Daniel Kellenberger, retrieved 19-05-2010
SCION, Sustainable Consumer Products, LCA Group, 89 Courtenay Place, Wellington 6011,
After a short description of each tool, an analysis was made of its assessment of a simple geometrical structure composed of concrete and reinforcing steel. The aim was to examine the variability of results from different tools when the number of construction materials was restricted. Assessments were then compared for a complete building made from wood, concrete or brick. Both studies showed variation of 10 to 25% about the mean value for greenhouse gas emissions from each material used. In a virtual exercise, a number of PRESCO recommendations were applied individually to the concrete house. The contribution of each recommendation to the total result was very small. A clear improvement was achieved when several recommendations were applied together. A list of recommendation is presented for the improvement of existing and future building related environmental assessment and design tools.
Various methods have been proposed for evaluation of the environmental quality of buildings. These attempt to integrate issues of concern such as protection of human health, protection of climate, fauna and flora and the efficient use of resources (energy, water, materials). Their precision and relevance is often questioned. The aim of the work presented here was the development of recommendations for rationalising LCA-based assessment tools for buildings. The work was performed within the European thematic network PRESCO and based on the final report of Work Package 2 (Peuportier et al. (2005)).
Assessment tools were compared in three studies. The first was an examination of assessments of a simple geometrical structure composed of concrete and steel including the use phase over 50 years. These results allowed analysis and comparison of the materials and energy datasets included in the different assessment tools. The second study was a comparison of assessments of a complete building (FUTURA house) made of one of three different structural materials: wood, concrete or brick. This study mainly helped to analyse the model used within the different assessment tools. The third study was a virtual exercise in which a number of general recommendations for sustainable construction of the concrete house were applied and the sensitivity of the assessment tools was compared.
The assessment tools studied were:
Input data included a description of the building (geometry, techniques, materials…) and its context (e.g. electricity production mix). The LCI (Life Cycle Inventory) data connected to the different models was derived from either the SimaPro database Goedkop & Oele 2001, the “Ökoinventare für Energiesysteme” from the ETH (Swiss Federal Institute of Technology) in Zürich (Frischknecht et al. 1996) or national databases. The output was a multi-indicator comparison of alternatives to support decision making. Assessment indicators among the tools were mainly CML 92 classifications. Some were aggregated indicators such as energy consumption, water consumption, waste, direct and/or external costs, etc. Some included routine calculation of annual energy consumption.
The first case study involved consideration of a simple reinforced concrete cube structure without windows and doors but with electric heating (a European electricity production mix). The service life was assumed to be 50 years. Information was obtained about the methods incorporated into the tools for assessment of the material components (reinforcing steel, concrete, electricity production and distribution) and the LCI data (building process, transport, infrastructure, demolition process, etc.).
Two of the results are shown in Fig. 1 and 2:
For 1 kg of concrete (Fig. 1) variation of +/- 20% around the mean emission value for all tools was related to the type of concrete, amount and type of cement, different production processes and the nature of energy production and allocation process.
The heat loss calculation was based on the location “Switzerland”, a thermostat set point 20°C (constant), a ventilation rate of 0.6 ach (air change per hour), a conductivity of concrete of 1.28 W/mK and of steel of 46 W/m/K, absorption factor of the surfaces of 0.6 and emission factor of 0.9, a north and south orientation of the larger facades and a ventilated crawl space under the floor. This resulted in a total heating load of 38,900kWh or 700kWh/m2/a. This high amount is mainly due to the uninsulated concrete external walls and the requirement of 24 hour heating on 20°C. This fictive example has been used to identify differences due to different heat loss calculation tools.
Figure 2 shows predicted greenhouse gas emissions associated with the construction and operation of the entire cube. Two tools (BeCost and ENVEST) assumed a national electricity mix instead of the European mix. This accounted for the large difference between BeCost and the other tools because Finnish electricity is modelled as heat and electricity co-generation and was probably included in energy allocation. If allocation is expressed as exergy or economic revenue instead of energy, greenhouse gas emissions for electricity increase. The electricity mix used by ENVEST seemed to correspond to the European mix. Excluding BeCost, the overall variation was +/- 10% of the mean value. Analysis of the construction phase showed that the structural materials (concrete and reinforcing steel) had the greatest effect. Discrepancies between the tools were related to:
The second case was based on a low energy building, prefabricated in Switzerland and known as FUTURA (Fig. 3). It is a single-family house with two levels (210 m2 heated area), well insulated, with a high solar aperture. Gas is used for space heating and domestic hot water, demand being related to the Swiss climate. A European electricity mix is used. A detailed description of the building was provided to all tool developers, who performed a life cycle assessment based on 80 year operation period. Three different construction materials (wood, brick, concrete) were considered separately.
The impact of the whole building is influenced by different parameters (see Appendix). This made it difficult to come up with specific recommendations on the building level. Therefore a comparison on the “lowest” building level has been added. The impact on the basis of the greenhouse gas emission (expressed as a weight of equivalent CO2 emission) which is the only common indicator between all tools (except OGIP) from the same materials (e.g. brick) and from the used heating system has been analysed .The results are summarised in following Table 1.
Comparing the huge variation on the level of one material and the smaller variation on the level of the whole building shows that the differences cancel each other out. This shows how difficult it is to make recommendations on the building level.
Wood as a building material was assumed differently by different tools. Some considered carbon dioxide uptake in the forest during timber growth as well as carbon dioxide and methane release to the atmosphere at the end of life. Disposal of wood always ends in releasing the stored amount of CO2 through rotting (sooner or later), processing (e.g. fermentation and burning of the ethanol) or just burning. Other tools took neutrality as the starting point and ignored uptake and release of biogenic carbon dioxide. Over the whole life cycle the result was the same but problems arose when an assessment did not take the disposal phase into account (from cradle to gate).
All assessment tools except ENVEST showed that wood construction produced the lowest greenhouse gas emissions. Results for brick and concrete were similar to each other. During the operation phase, emissions were similar for all three construction types (results not illustrated). Tools including negative carbon dioxide values for wooden parts during the construction phase (e.g. EQUER) accounted separately for release at the end of life. Looking at the results for the EQUER tool it shows a very small amount of CO2 emitted by the whole timber frame building. This is mainly due to the high amount of timber with biogenic, stored “negative” CO2. As this value does not represent the demolition phase and therefore the CO2 realease from disposed wood it has to be shown separatly (see Fig. 4, EQUER). Emissions from the operation phase of the timber framed house were similar for all 7 tools (+/- 5% about the mean value). All tools indicated that the operation phase produced greater greenhouse gas emissions than the construction or demolition phases (results not illustrated)
The result of another work package within the PRESCO Network came up with a list of about 350 recommendations to improve houses to a higher level of sustainability. Some of these recommendations have been adapted to the model of the concrete based FUTURA house. In general LCA-based building assessment tools mainly deal with environmentally relevant recommendations and therefore unfortunately only a small part of the overall PRESCO recommendations towards more sustainable constructions were applicable. Furthermore the fact that most of these recommendations are described qualitatively reduced the number of applicable recommendations additionally.
Following examples have been applied and its impact on the overall result presented:
In general there was good agreement that each of the recommendations had a limited or marginal individual effect on greenhouse gas emissions. Combining several recommendations within a certain project is likely to improve the ecological quality of a building.
Results of the three studies have suggested a long list of recommendations for improving existing assessment tools and for designing new tools. Important examples are:
Further work is needed to harmonise and facilitate the development of environmental assessment and design tools for buildings. End-users of these tools (architects, civil engineers, etc.) must be trained to interpret results. There is a need for tools to be easier to use and for their relevance to be more transparent.
There will be a strong future need for New Zealand to develop its own building assessment tool. The main driver will be the new building Code which plans to publish requirements for energy and Gobal Warming Potential for the construction, operation and disposal. It is recommended to build up its own assessment tool with focus on timber framed residential houses. The knowledge of this comparison helps Scion to work out a NZ specific building assessment tool.
|Frischknecht et al. (1996)||
Frischknecht R., Suter P., Bollens U., Bosshart S., Ciot M., Ciseri L., Doka G., Hischier R., Martin A., Dones R. and Gantner U. (1996)
Ökoinventare von Energiesystemen, 3. Aufl. Edition. Bundesamt für Energiewirtschaft (BEW/PSEL), Bern.
|Goedkop & Oele (2001)||User Manual. Introduction into LCA methodology and practice with SimaPro 5. Pré Consultants, Amersfoort, http://www.pre.nl/simapro/|
|Peuportier et al. (2005)||
Peuportier B, Putzeys K, Anerson J, Anink A, Hendriks N, Kellenberger D, Moetzl H, Nibel S, Vares S, Final Report of Work
Package 2 of the PRESCO Network, Inter-Comparison and Benchmarking of LCA-based Environmental Assessment and Design Tools, downloadable from http://www.etn-presco.net
Table 2: First part of the materials and parameters used for the calculation of the impact of the FUTURA house
Table 3: Second part of the materials and other parameters used for the calculation of the impact of the FUTURA house