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, EstoniaSystem B: From a city in Southwest of Sweden with anannual heat generation of 64 GWh.System C: From a city in the middle of Sweden with anannual heat generation of 1550 GWh.Momentary daily variation ( )The momentary daily variation is proportional to theamount of heat that needs to be fed in or out to the DHnetwork to extinguish the daily variation. This variabledescribe the heat power capacity needed for in and output from and to the heat storage. For each districtheating systems you will get 8 760 (8 784 during leapyears) values per system and year.hd1224h1P PThe total daily variation is presented in Fig. 2 for thethree example systems. The figure verifies that thevariations are more pronounced in the two smallersystems compared to the larger system. Anotherimplication is that the highest day values are very few,giving an incentive to construct heat storagessomewhat smaller than the peaks in the figure. Hence,the investment costs will be reduced more the lostbenefits from the storage, giving a more optimised heatstorage.PhadThe momentary daily variation is defined as thedifference of each hourly measured value and themean value of heat per hour of the same day dividedby the mean heat per hour of the year.54,54Total daily variationSysten ASystem BSystem CPh PdhPaThe momentary daily variation is presented in Fig. 1 forthe three example systems. The figure shows that thevariations are more pronounced in the two smallersystems compared to the larger system.Total daily variation, τd[h/day]3,532,521,510,5Momentary daily variation, τh[h/h]0,70,60,50,40,30,20,10-0,1-0,2-0,3-0,4-0,5-0,6-0,7Momentary daily variation0 1000 2000 3000 4000 5000 6000 7000 8000Hour of the yearSysten ASystem BSystem CFig. 1 Momentary daily variation sorted by size hour byhour for the three different district heating systems.Total daily variation ( d )Total daily variation is defined for each day and is avariable that is proportional to the amount of heat thatdivert from the daily mean heat load. If you want toextinguish the daily variation in a system this variabledescribe the size of the heat storage. For each DHsystems you will get 365 (366 during leap years) valuesper system and year.The total daily variation is defined as the sum over theday of the difference of each hourly measuring valueand the mean value of energy per hour of the sameday divided by two times the mean energy per hour ofthe year.0- 50 100 150 200 250 300 350Days of the yearFig. 2 Total daily variation sorted by size day by day forthe three different district heating systems.Total annual relative daily variation ( )Total annual daily variation is a variable that isproportional to the total amount of energy that at dailybasis divert from the mean value accumulated for aperiod of one year. It is used to compare differentsystems between themselves. For each DH systemsyou will get 1 value per system and year.Total annual daily variation is defined as the sum overthe year of the difference between each hourlymeasuring value and the mean value of energy perhour of the same day divided by two times the meanenergy per hour of the year. a128760,365hh1,d 1PP PThe annual daily variation is presented in Fig. 3 for 10different Swedish district heating systems. Since theannual daily load variation has a magnitude of250–500 h, only 3–6% of the annual heat load isgenerated above the daily average heat loads. Hence,it is the seasonal variations that dominate the heat loadvariations in the Swedish district heating systems.ada200