12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaTwo different methods of impact assessment had to beused in the impact assessment calculations. For theprimary energy factor, the Cumulative Energy Demand(CED) method [15] was used which is based on amethod published by Ecoinvent 1.01 and available inSimaPro 7 impact assessment methods. For thecalculation of the CO 2 emission factor, the IPCC 2007GWP 100a V1.01 [16] was used to get the CO 2equivalent total global warming potential for the chosenfunctional unit of 1 MWh electricity produced.Principles for AllocationTo allocate the impacts of the different products,electricity and heat, produced at Hellisheidi CHP plant,several methods can be used. The method usedshould reflect the physical relation between the twoproducts, such as how the different inputs and outputsof the process are dependent on the two differentproducts. Simple methods of allocation for an energyconversion process can be:Based on energy content of the productsBased on exergy content of the productsBased on the monetary value of the productsThe abovementioned methods can be used when thephysical relation between the two products is unclear.In the case of the Hellisheidi CHP plant, the physicalrelation between the two outputs (electricity and heat)is mainly the use of waste heat from condensers andthe geothermal fluid from the production wells, asshown in Figure 2. The impacts of construction caneasily be divided between the electricity and heatproduction with the detail of inventory data provided.Also, the geothermal fluid used in the heat productionis taken from steam separators in the electricitygeneration process and would otherwise be reinjectedback into the geothermal reservoir via reinjection wells.The disposed heat in the condenser is utilized topreheat the district heating water by using it as coolingwater. The condenser pressure determines thetemperature of the steam output from the turbines andthus, also the final temperature of preheating of thedistrict heating water. If the heat demand is high, thecondenser pressure must be higher than the optimumfor power production in order to supply high enoughtemperatures to the district heating water. This limitsthe electrical power production and requires that moregeothermal wells have to be drilled in order to sustainthe electrical production under high thermal loads ofthe district heating system. These limitations on theelectrical production imply that the allocation of impactsfrom the drilling of wells should be related to thenumber of wells that have to be drilled to sustain boththe electricity production and the highest thermal loaddesigned for the district heating system.Data QualityTo calculate the energy performance indicators bymethods of LCA, reliable inventory information isneeded on material and energy flows to and from thegeothermal power production facilities during theirlifetime.. The inventory in this study is constructedfrom data provided by Reykjavik Energy, the powercompany in ownership of the Hellisheidi plant. Thedata on the construction phase is retrieved from theconditions and specifications in a tender for theconstruction of the power plant, where quantitativeinformation is collected on all major material flowsrequired for the constructions and machinery. Theinventory information for the fluid collection and drillingis retrieved from a report done by Reykjavik Energy,including the power and performance of the geothermalwells drilled for the power and heat production [17].For a LCA study, the following data quality indicatorsmust be presented:Time periodRegionType of technology and representativenessAllocationSystem boundariesIn this study, the time period of the data is from 2005 to2009 and the region is Western Europe. The type oftechnology is modern and the representativeness isdata from a specific company. The allocation, asmentioned before, is by physical connections betweenthe two outputs. The system boundaries are describedby three different criteria. First, the cut-off criteria is ingeneral set to be less than 5% which means that allinventory data that does not contribute more than 5%to the overall impacts of the two products isdisregarded. Also, the system boundary is chosen tobe of the first order, only to account for the materialsused in the construction and operation of the CHP plantbut not the processing and transportation of thesematerials. The third system boundary criterion is thesystem boundary with nature, which in this study isdescribed as unspecified at this stage of the LCAstudy.RESULTS FOR THE ENERGY PERFORMANCEINDICATORSEnergy Performance Indicators for ElectricityProductionThe results for the impact assessment of the electricityproduction alone, focusing on the two energyperformance indicators, is shown in Table 2. Thehighest value of fp 6.33 MWh primary energy/MWhproduced energy, is obtained when no heat productionis present at the power plant and the effects ofreinjection of waste streams is not taken into account.189