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, Estoniaby integrating renewable heat into a district heatingnetwork. A detailed simulation for a solar thermalintegration was done by using RETscreen [14] assimulation software.MATERIAL AND METHODSEvaluation of heat demandFor planning a new heat production facility, the heatdemand of the connected consumers is necessary. Ifthose are existing households, the heat demand fromthe past can be used for calculations. For newly builthouses the heat demand should be exactly calculatedwith the standards named in DIN V 4108-6.If this is not possible, the yearly heat demand can beassumed by the given figures:Table 1: heat demand [15]Building size[housingunits]Heat demand(room heating)[kWh/m²a]heating demand(hot tap water)[kWh/m²a]1-2 72,3 20More than 3 55,3 20These figures can be realized in buildings constructedbetween 2011 and 2020. [15]Another factor for the planning of a heating grid is theoutlook into the future, because the payback period ofa renewable heat production facility is very long.The following graph shows the expected change inheat demand for Germany focusing on different factorsof influence:is not part of the simulated area and on the reductionthrough population, which has not a direct effect on onespecial housing area. The reduction through influenceof temperature has a share below 5 % within 15 yearsand is therefore not included within the simulation.Existing SystemsBetween newly built and existing heat networks thereexist some main differences which have to beconsidered. If the network is designed especially for therenewable energy source, it can be technicallyspecialized (e.g. forced low return temperature forbuilding owners; special isolation of the used pipes).Older heating grids on the other hand are normallyconstructed for the heat production with fossil fuels andare normally designed for higher temperatures.Furthermore, in some heating grids a high temperatureis necessary either for thermal cooling systems (e.g.absorption chillers) or for the heat transfer stationswithin the houses which are built for high temperatures(low flow temperatures need optimized heat transferstations [12]. In the following, the main aspects for theintegration of different sustainable heat generationtechnologies are described.Heat grid for renewable energyFor the integration of renewable energy into heat grids,different possibilities for the connection exist.Especially for the solar thermal energy production it isassumed, that more than one heat plant will beconnected.The three options are:1. Taking water from the return pipe, heat it andreturn it into the return pipe2. Taking water from the flow pipe, heat it furtherand return it into the flow pipeFig 1: development of heat demand [11]Within the following simulation this development is notfurther regarded. The major reduction within wholeGermany is based on renovation of old buildings, which1333. Taking water from the grid out of the returnpipe and rise the temperature to the necessaryflow pipe value [3]All of those options have some obstacles. The firstoption is normally not welcome by the grid operatorbecause of higher losses in the system. The secondoption is almost impossible for the use of flat plate solarcollectors; because the high flow temperature cannotbe further heated.The third option shows the best possibility forintegration but has the obstacle with high pressuredifferences between the flow pipe and the return pipe.To evaluate the necessary pump work a first estimationcan be done with equation (1). It gives the pump workW depending on the necessary heat flow ∆Q, the