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, Estonia50 % solar fraction of the total heating demand withouta thermal storage system [scenario 3].For the thermal storage a hot water system isassumed, because those are state of the art and canbe used in most applications. Other systems havemore specific requirements to the geological situationof the area. A geothermal heat storage for exampledoes not work in an area with a flow of the groundwater. For the simulation of scenario 2 a smallerthermal storage compared to scenario 1 was assumed,because there is no necessity for a seasonal heatstorage system.For the simulation model a commercial solar collectorwas taken (s. Table 3). It is a flat plate collector with aanti-reflection glass and a gross area of about 2,6 m².Its efficiency is 84,4 % (calculated according to EN12975). The simulation uses specific given parameters.Those are shown in Table 3.Table 3: used input parameters for solar simulationAnnual heating energy(calculated with givenmethod)Flow temperature 67 °CReturn temperature 45 °CSlope of collector 55°Azimuth of buildingType of collectorStorage capacityHeat exchangerefficiencyMiscellaneous lossesPump efficiency(for grid integration)Time periodScenario 1: 1076 MWhScenario 2: 493 MWhScenario 3: 1071 MWhScenario 4: 11,6 MWhScenario 5: 11,6 MWh-45° (southeast)WagnerSolar L20 ARScenario 1: 1000 l/m²Scenario 2: 100 l/m²Scenario 3: 1 l/m²Scenario 4: 100 l/m²Scenario 5: 10 l/m²80 %5 % if storage is used(smaller grid)8 % if integrated intolarge grid40 %20 yearInternal rate of return Scenario 1: 8,5 %Scenario 2: 8,5 %Scenario 3: 8,5 %Scenario 4: 5,0 %Scenario 5: 5,0 %Increase of heat price per 2 %yearFinancial support 30 %For a comparison of the different scenarios the heatcost per kWh were calculated.The calculation of the emissions is based on theoperation of the system and not on its total life cycle.For solar thermal heat the CO 2 emissions only arisefrom the used electricity for the necessary pumps.Included in the calculation is only the pump energy forthe solar thermal collectors and, if necessary, toincrease the pressure for the integration into theheating grid flow pipe. The CO 2 emissions for theGerman electricity grid are given with 506 g/kWh.For the calculation without a thermal storage system[scenario 3] it was assumed that the produced solarheat can directly be distributed throughout a districtheating network. This would make it possible to savethe investments of a seasonal heat storage system andalso reduce the losses within the thermal storagesystem.For those calculations the same heat amount was usedthan in scenario 2. But in this case it is not possible tocover 50 % of the heat demand of the total grid. Just asmall amount, for example the losses of the grid andthe base load, can be produced with solar thermaltechnologies without a thermal storage.Another option would be to integrate small systems intothe district heating grid. In this case the operator of thegrid would not run the facility by itself. The heatproducer could use a solar thermal collector for its ownheat demand but without a thermal storage system.Instead of using an in-house thermal storage (what isgetting very large if a seasonal heat storage system isused) the heating grid could be used. For the singlehouse technology an internal rate of return of 5 % wasused for the economic calculation (average percentageof building credit [4]). Furthermore the financial supportis a little different because of different regulations forlarge and small systems. In the following those twocalculations are named ―scenario 4‖ for the heatproduction of a single-family house with a thermalstorage and ―scenario 5‖ for the calculation without athermal storage.Summary of different scenarios:Scenario 1 Solar fraction of 50%Seasonal thermal storage includedScenario 2100% heat production of hot tap waterBuffer heat storage included, but no seasonalthermal storage135