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, 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.