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, EstoniaTHE OVERALL ENERGY SYSTEMThe energy system of a country is complex, and it isimportant to understand how changes in sub systemsmay affect the whole system. Sub optimizations mighteasily occur. A simplified example of a situation wherea more energy efficient building through suboptimization of the total system gives a larger overallprimary energy need is illustrated in Fig. 3. Obviously itis possible to create a system with higherenvironmental impacts with energy efficient buildingscompared to a system with less energy efficientbuildings. It is not enough that the individual parts of asystem are good and efficient to give a lowenvironmental impact; the parts must be connected intothe system in a good way.Thus it is important to identify system solutions thatavoids sub optimization and gives us energy efficientbuildings and an efficient energy system with a goodenvironmental performance.IMPLICATIONS OF NEW TYPES HEAT LOADTo better understand implications of different new typesof heat load (as illustrated in the right hand side ofFigure 1) a life cycle assessment (LCA) has beenperformed regarding the use of heat instead ofelectricity for the three examples of house holdappliances: dish washer, washing machine and tumbledrier. Basic data regarding the appliances areexemplified with those in the ―district heating villa‖ inGöteborg, Sweden. The LCA model includes energyproduction (electricity or/and heat) for an average useof each machine and the materials needed to produceit. Different types of energy mixes for electricity anddistrict heat generation were studied. Details of thesystem boundaries and data can be found in the fullreport of the study [2].The results indicate that the total energy systeminfluences the results greatly. If we consider electricityproduction with large environmental impacts, to utilizedistrict heating is a good alternative, even in caseswhere the district heating generation in itself is notoptimally environmentally friendly. This is exemplified inFig. 4 where we consider Swedish average districtheating fuel mix (bio and residue heat, but also fossilfuels and some peat [5]) and European averageelectricity generation. If we for the long termdevelopment consider electricity generation that ismuch less fossil carbon intensive and compare it withdistrict heating based on forest bio fuels the results aremuch more narrow, and it become important whatenvironmental impact category is considered. In Fig. 5this is exemplified with climate impact and acidificationimpact.If district heating should continue to be seen in generalas an environmentally preferable option it is importantthat district heating companies continue to developdistrict heating production in a favourable direction.Heat for district heating should originate from resourcesthat are otherwise wasted. In the long term that willmean that bio fuelled district heating is not enough, butheat from other primary production like bio energy orbiomaterial combines producing transport fuels and/orbio based materials.CONCLUSIONSFrom environmental perspective energy efficientbuildings and district heating don‘t oppose each other– good parts connected in a good system will give anoptimal. It is not enough that the individual parts of asystem are good and efficient to give a lowenvironmental impact; the parts must be connected intothe system in a good way. The results from the study ofthe three items of household equipment showpossibilities for district heating to be an alternative withgood environmental performance, but not under allheat generation regimes. Heat generation mustcontinuously be considered.Fig. 4 Environmental impact from using district heat fordishwasher, drier and washer. Case: Swedish av. districtheating and European av. electricity.204