12th International Symposium on District Heating and Cooling

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The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estoniaheat and electric power as well as the parameters theoptimization problem is defined automatically. FreeOptcalculates the minimal costs to satisfy the demand. Fortesting purpose there is no limitation of the values.The mathematical model belongs to the mixed integerproblems. So the objective function and all constraintsare linear, all variables are continuous or discrete. It iswritten in the mathematical modelling language GMPL[2] and solved with the COIN-OR brunch-and-cut solverCBC [3]. Both GMPL and CBC are open-sourcesoftware under GNU GLP license [4]. An intuitive userinterface enables to enter all input data like variableboundaries, cost coefficients, starting values, demandvalues or figure lines in a very easy way. The internaldata flow between user interface, optimization modeland solver is realised with help of txt-files (Fig. 2).The most important ones are the two balanceequations for power (2) and heat (3).stands for the generated electric power,power transferred in or out the grid via contracts,for the electric power demand andconsumption of electric power.stands for the generated thermal power,the heat demand,cooler andheat storage.(2)forfor the own(3)forthe heat disposed in the auxiliaryfor the heat transferred in or out of theExampleAs an example the following heat network of a localenergy supply company is given in Fig. .Fig. 2 FreeOpt user interfaceElectricity networkRunning the generators cause costs. Therefore themain aim is to minimize the total costHeat boiler plantCHP 1CHP 2 CHP 3Heatstoragestorage(1)in whichproceeds):are the following operating costs (andcosts for fuelcosts or proceeds for transferredelectricitycosts for start-up procedurescosts for network accesscosts for maintenancecosts for CO 2 -cerfiticatesCHP-refundEEG-refundproceeds for avoiding network accesscosts for electricity taxpenal costs for balance violation(virtual costs)As already noted several variables exist for every timestep limited by some boundaries and connected byparameters in lots of equations and inequations.319Fig. 3 Flow scheme of a local heat networkThe heat demand of the customer is provided by3 CHPs (Block Heat & Power Plants) – baseloadHeat plant (natural gas) – peak loadHeat storage – used for optimizationand is given for every hour of one year.The electricity demand is not directly consideredbecause of intern clearings inside the energy supplycompany. The whole generated power is transferred inthe grid and refunded as well as used to satisfied theown consumption. It is also possible to transferelectrical power out the grid when all CHPs areswitched off.
The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaTab.1 gives an overview on the design parameters of allheat and power generation units as well as on the costassumptions for fuel and the refund of the energy tax.Tab. 1 Design parameters of generation unitsGenerationunitCHP 1 CHP 2 CHP 3 HeatPlant/ kW 911 774 911 -/ kW 911 774 911 -/ kW 1200 1020 1200 200/ kW 1200 1020 1200 2000/ % 0.35OwnconsumptionCosts fuel /€/kWhRefundenergy tax /€/kWhStart upcost /€/start up( )0.35( )0.35( )0.87( )0.76 0.76 0.76 -2.0 %(of )2.0 %(of )2.0 %(of )0.04444 0.04444 0.044440.0055 0.0055 0.00550.5 %One specific characteristic of the energy system is thatall three CHP cannot be operated in part load, so thevalue of the maximum and the minimum power have tobe equal.The base own consumption of the whole energysystem is 50 kW. In the 100 m 3 heat storage it ispossible to store 4000 kWh. Tab.2 gives an overview ofall intern electricity contracts.(of)0.045740.002212 12 12 6Analysis operation modeFirst the real operation mode of whole year 2008 isanalysed retrospectively (case I) and the optimaloperation mode is determined with the help of FreeOpt(case II). Following the annual operation costs arecalculated for both cases (Tab. 3).The calculations in Tab.3 show that the costs for fuelincrease but so the proceeds through electricity saleand CHP-refund increase too.Tab. 3 Comparison annual operating costs and proceeds(case I and case II)Annual operationcosts andproceeds / 10 3 €Real operationmode(case I)Optimaloperationmode(case II)Costs fuel 1326.12 1331.13Proceedselectricitycontracts468.48 473.65CHP-refund 58.17 58.67Start up costs 10.01 6.62Costs networkaccess2.83 2.47Total costs 812.30 807.90Furthermore costs for start ups and network accesscan be reduced. But altogether the total annualoperating costs for case I and case II are nearly equal.In this particular example savings are under 1% of theoperation costs. So the energy system is operatednearly in an optimal way.System configuration changesThe energy supply company considers to replace theCHP 2 through a new one. Of course the new CHP hasnew parameters (Tab. 4).Tab. 4 System configuration changes CHP 2Tab. 2 Electricity contractsCosts /€/kWhElectricity purchase6am – 22pm22pm – 6 amElectricitysale0.08150 0.05700 0.04735The CHP-refund is 0.0056 €/kWh and costs for networkaccess are 0.0386 €/kWh.320Generation unit Old CHP New CHP/ kW 774 404/ kW 774 404/ kW 1020 535/ kW 1020 535/ % 0.35 0.36Start up cost /€/start up12 9.5
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P-1P-4P-9P-7E-5P-14P-8The 1
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to heating costs of 14,5 ct/kWh. Th
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academic access is facilitated as t
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1. CHP system operation in A2. Ther
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is covered by operating HOB. In oth
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produce heat and electricity. Fluct
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To assure that the temperatures mea
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production and provide for marginal
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In addition, it can also be observe
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owner is normally only interested i
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12th International Symposium on District Heating and Cooling

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