Jens Tønnesen
2 THE BUILDING
The case office building concept has a total of 1980 m2 heated floor area and the office area consists of a mix of office cells and open landscape. The area also contains meeting rooms and common spaces.
The cellar, used for technical rooms and parking, is unheated and not included in the heated floor area, although included in the material emission analysis. The general design of the building does not impose restrictions on the floor plan in having the possibility of frequent changes over time (Arge, K., 2003). The structure and fittings are designed with regard to a high level of flexibility. Dismantling, removal and installations of partitions are easy to manage without extensive demolition and construction work and without having to make large electrical and/or mechanical reconstructions. The office areas are suitable both for open floor plans and/or office cells, or a combination thereof. The model presented here is composed with objects containing designated information used in the calculations.
The building physics and energy concept for the office building model are described in the Technical report on the Office concept by Dokka et. al. (2013). However, a short review of the concept is presented here. The Norwegian passive house standard NS3701:2010 has been used to develop an energy efficient building envelope (Standard Norway, 2010). The total windows and doors area is 456 m², which gives a windows/doors to floor area ratio of 23 %. The building has a high performance building envelope achieved by using materials and solutions already available on the market. The U-values and levels of insulation of the envelope are given in Table 1. Furthermore, the building envelope has an air tightness of < 0.3 arc@50 Pa, and the air flow rate is 7,0m3/h·m2 during hours of operation and 0.7 outside.
Table 1. U-values of different parts of the envelope Construction part U-value
The energy supply system is based on a heat pump, solar thermal panels and solar electric panels.
Simulations of the annual energy performance of the building have been carried out using SIMIEN version 5.011 (SIMIEN, 2012). The performance of solar collector system and the heat pump system have been done by simulation in PolySun (Polysun, 2012) and performance of the PV-systems have been simulated with the solar energy simulation program PV-syst (PV-syst, 2012).
3 METHODOLOGY
The overall methodology is shown in Figure 1. This paper is concentrated around step 1 of the embodied emission calculations, shown on the right side of figure. TEK10 refers to the Norwegian regulation ontechnicalrequirements for construction (KRD, 2010). The approach regarding the energy concept is described in Dokka et. al.,(2013).
Figure 1 A step wise methodology on calculation towards a ZEB.
The following subsections describe the embodied emission calculations performed in step 1.
3.1 Scope, aims and ambition level
The goal of these calculations is to estimate the embodied emissions in the materials and components and emissions from the operational energy, and then calculate the GHG emission balance with the offset on site renewable energy production.
3.2 Life cycle emissions
In 2011 a new standard was launched; EN15978:2011 that gives the calculation framework for conducting a life cycle assessment of an entire building (Standards Norway, 2011). This study seeks to follow the basic framework of this standard. The focus has been on the GHG emission and not a full environmental assessment. The SimaPro version 7.3 has been used for the emission analysis (SimaPro, 2012) where the Global Warming Potential with a 100 year scenario is used. This method is developed by the Intergovernmental panel on climate change (IPCC, 2007).
3.3 Functional unit
The functional unit used in the analysis is 1 m2 of heated floor area in the office building over an estimated life time of 60 years.
3.4 Boundaries
The analysis focuses on module A1-A3 from EN15978 which is material inputs to gate and the use phase replacements B4. The emissions from energy use in operation are connected to the use phase B1 (Standard Norway, 2011). The expected service lifetime used for the different materials and components is mainly based on product category rules for different materials and components. The product category rules for different building materials and construction parts are available from the Norwegian EPD foundation (EPD-Norway, 2012). The life time of the solar cells is set to 30 years with reference to recommendation from (IEA, 2011). The end of life phase is not included at this stage.
3.5 Inventory
The follow section describe the methodology applied in the inventory phase, the complete inventory for the analysis is available in the Technical report by Dokka,et. al.,(2013).
3.5.1 BIM and embodied emissions
The study on the embodied emissions is based on quantities derived on the material take off from the Building Information Model. The detailed dimensions of the material inputs has simplified the life cycle inventory phase and improved the level of detail of the material inputs. Both the lists from the BIM (Excel sheets) and the modeling in SimaPro have used the structure of the table of building elements from NS 3451:2009 (Standards Norway, 2009) which has simplified traceability and flexibility of the calculations.
3.5.2 Encountered challengesusing BIM in LCA
The level of details in the model, reflect the levels of details extracted in terms of material inputs.
Different types of BIM tools allow for different levels of details when drawing the constructions. In the example of the slab structures the concrete amounts from BIM are based on a full concrete slab, but in reality the building is dimensioned to use hollow core elements. At this stage hollow core elements have not been drawn into the model, and a reduction of 20 % of the total volume compared to compact concrete has been estimated. Another example is the use of steel in inner walls, where there usually are used steel studs in the inner wall concepts based on gypsum. The amounts of steel used in inner walls are based on estimates from handbooks from producers and on the SINTEF Building Research Design Guides(SINTEF, 2012).By applying more refined modeling the detailing of the model can increase and finally become as detailed as the building is as built.
3.5.3 Environmental data
Wiberg, et. al. (2011) emphasizes the need for a transparent robust calculation method for GHG emission calculations from materials in Zero emission buildings. The current status in Norway is that there is a continuously increasing availability of environmental product declarations (EPDs) for building materials and components. Furthermore Statsbygg, the Norwegian government's key advisor in construction and a partner in ZEB has developed version 4 of a GHG accounting tool called Klimagassregnskap(Selvig, 2012). The tool can assist in early decision making enabling the developmentof more climate friendly buildings. However, seen in a research perspectiveKlimagassregnskap is not considered appropriatein this study, due to limited transparency and control of the input data. Neither is the use of environmental product declarationssince the methodologies used arenon consistent and transparency is still limited. The standard EN15804:2012 (Standards Norway, 2012) gives guidelines on for how to perform a life cycle assessment of building products and current work in the Norwegian EPD foundation is expected to make the EPDs more transparent and robust for comparison. Due to the lack of information and current inconsistency, it was decided to use data from the Ecoinvent v. 2.2 database, (Ecoinvent, 2010) in the first step of the concept calculations. The Ecoinvent is a Swiss based European life cycle inventory database. The methodology used in the inventories is presented in Frischknecht et al., (2007).
The calculations presented here are not based on a single emission factor for electricity. Processes from theEcoinvent database are applied with no adjustments regarding source of electricityused. Mono crystalline solar panels with an efficiency of 15,4 % are used as the data for the solar panels. It is estimated that solar cells will be 50 % more effectively produced in 30 years, when it is time for them to be replaced. This decision is influenced by Alsema, 2006. However this kind of adjustment is not in accordance to the standard EN15978 where future scenarios are not included. The material inputs of the technical units are based on experiences from ZEB pilot buildings (Kristjansdottir et al., 2012).
3.6 Simplification and uncertainty
Calculations for GHG emissions for technical units, such as the ventilation system components are based on estimations of raw materials. In the next step of this research these estimates have to be further studied and refined, especially on gathering environmental data for the different components used. The service lifetime for solar cells is also uncertain but the consensus, on using 30 years as the
assumed to be the best available approach (IEA, 2011). The service life time of the different materials and components used is also an uncertainty factor and needs further attention.Building material losses on site are not included in this analysis. Neither are chemical substances such as glue and paint for surface treatment.
4 RESULTS
4.1 Emissions from operation
In the case of a ZEB-OM, the renewable energy produced at site needs to compensate for the emissions that are embodied in all the materials and due to operational energy use. Total annual net energy demand is simulated to be 57 kWh/m2 per year, and the total annual electricity delivered to the building is 33 kWh/m2per year; which has to be compensated by local electricity production. The emissions related to operational energy (electricity) are approximately 4.3 kg CO2eq /m² (Dokka, et.
al. 2013). The operational emissions are based on conversion from energy to emissions through the ZEB average factor for GHG emissions electricity production of 0.132 kg CO2eq/kWh. The ZEB emission factor is based on best case scenario calculations for electricity production in Europe in the period 2010-2070 made by Graabak&Feilberg, (2011).
4.2 Emissions from materials
The results of the first step of the embodied emission analysis are summed up in Table 2. The results are mainly presented for emissions on an annual basis, where the functional unit of 1m2 is divided by 60 years. The total embodied emissions for the office building at this stage are approximately 8.5 kg CO2eq/m2 annually.
Table 2. Results embodied emissions.
Phase Amount [kg CO2eq /m2] Amount [kg CO2eq/m2per year]
Initial material use 384 6,4
Replacements 126 2,1
Total 510 8,5
In Figure 2 the results of the embodied emissions are presented according to the table of building elements. From the figure, it is clear that the emissions related to the power producing solar cells have the highest emissions. If the solar cells are not estimated to be produced in a 50 % more efficient way in 30 years, and the same Ecoinvent process is used the total emissions will be approximately 9,2 kg CO2eq /m2 per year or approximately 0,7 kg higher. The PV system alone account for between 2.1-2.8 kg CO2eq /m2per year depend on the replacement scenario. Results also show that concrete, steel, inner walls, and exterior walls all contribute to high GHG missions. The total emissions from concrete are around 1,9 kg CO2eq /m2per year (around 875 m3 of concrete).
Figure 2
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