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, EstoniaEnergy and heat load usage was primarily evaluated bystudying the dynamic differences between the forwardand return temperature of the radiator system inrelation to the flow. These readings were then verifiedby specifications from the district heating providerregarding energy consumption and momentary heatload usage.Using this set-up we scheduled different types oftemporary heat load reductions and studied theireffects on the measured data. During this study westudied three primary types of temporary heat loadreductions:system performs a controlled heat load recovery inorder to avoid unwanted heat load peaks after thereduction.The same values are shown for a long heat loadreduction in Figure 2. The heat load reduction startsslightly before the 600 minute mark and continues forseveral hours until about the 900 minute mark. Afterthat the control system performs a controlled recoveryin order to return to the original operational state.Long – Four to eight hours of continuous heatload reduction with different intensityShort – Up to one hour long heat loadreductions with different intensityRecurring – Several short subsequent heatload reductions with short pauses in betweenWhen we studied the different types of heat loadreductions we took care in allowing the buildingsthermal process to return to its original state betweeneach reduction so that the reductions would notinfluence each other. This was done in between eachreduction except in those cases when then purposewas to explicitly study the interaction betweensubsequent heat load reductions.EXPERIMENTAL METHODFigure 2: dT in radiator circuit with long heat loadreductionFigure 3 shows the same values for a series ofrecurring heat loads.Figure 1 shows the temperature difference between theforward and return temperature in the radiator circuitduring a short heat load reduction.Figure 1: dT in radiator circuit with short heat loadreductionThe heat load reduction starts at about 60 minutes andcontinues until the 120 minute mark. Between the 120minute mark and about the 160 mark the control246Figure 3: dT in radiator circuit with recurring heat loadreductionEach of the heat load reductions in Figure 3 is one hourlong intersected by one hour long recovery periods.The first reduction starts at the 60 minute mark andcontinues until the 120 minute mark.