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, EstoniaTotal annual daily variation, τa[h/year]50045040035030025020015010050Total annual daily variationSYSTEM B01 10 100 1 000 10 000Annual heat supply [GWh]SYSTEM ASYSTEM CFig. 3 Total annual daily variation for 10 different districtheating systems in Sweden.RESULTSTo characterize daily heat load variations in districtheating systems three variables have been defined.h= Momentary daily variationd= Total daily variationa= Total annual daily variationTogether with the mean annual heat per hour (P a ) andthe energy transfer capacity in and out of the heatstorage, size of storage to extinguish the systems dailyvariation and the total daily variation and can bedetermined according to the expressions below.Energy transfer capacity:S h = ·P a [MWh/h]hSize of heat storage:S d = ·P a [MWh/day]dCONCLUSIONSAn expected conclusion would be that large districtheating systems have smaller relative daily variations ) than small district heating systems. There are two(areasons for that:1. In a large district heating system, the use of heatpower is spread on different distances from the heatplant, i e the chilled water in the return pipe return backto the heat generation at different time compared towhen the return water left ach substation (geographicaldiversity)2. In large district heating networks, you would expectthat the operators have more active operation of theheat distribution network with respect to temporary heatstorage.But as can be observed in the Fig. 3 there does notseem to be such a trend. One explanation could be thatthe heat users differ in different systems. e.g. in thesystem in Fig 3 with an annual heat supply of 9 GWh,mostly single and multi family houses are connectedand very few industry or office buildings are connected.Since there is a large diversity among the annual dailyvariation more data need to be collected to be able tomake any further conclusions.REFERENCES[1] Olsson L, Werner S: ―Building mass used as shortterm heat storage‖, The 11th <strong>International</strong><strong>Symposium</strong> on District Heating and CoolingReykjavik 2008.Total annual daily heat load variation:S a = ·P a [MWh/year]a201