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, EstoniaThe annual replacement of pipes is in average about3,06 km per year, which is less than 1 percent from thelength of Tallinn DH system pipelines.Length, km87654321019851986198719881989199019911992199319941995Fig. 6 Length of replaced pipelines by years in Tallinndistrict heating networkTHE FORECASTS FOR DISTRICT HEATINGSYSTEM AGE1996One of the tasks was to assess, how big the renovationworks should be in order to stop increasing the averageage of pipes. A simulation model, which uses both realdata and also some assumptions, was created for suchestimation.199719981999200020012002200320042005200620072008The average age of pipes for each year was calculatedaccording equation (2)Aavji=b, ifwherejiiabl ( j i)l liiajbiial ( j i) ( j c) ( l ; i=c, ifi jcljl liaAav is average age of pipes in j yearli is length of pipes, constructed in i yearI – year of construction;J – current year;jbl )iiaa – year of construction of the oldest pipes, operating inthe current year.As a result of simulations, seven forecasts for pipesaverage age were calculated according differentintensity of renovation works: for current intensity ofrenovation (3,06 km/year) and for intensities when 1%,1,5%, 2%, 2,5%, 3% and 4% of total DH system lengthwould be annually renovated. The forecasts weresimulated for the 20 year long period.The results of simulation are shown in Fig. 8.(2)Assuming that the length of pipes (360,67 km) will notchange during the forecast period and that the annualscope of renovation works will remain the same duringwhole of the period means that the length of renovatedpipes also will not change. Besides it‘s was assumedthat every year just the oldest pipes would berenovated; however in reality the renovation works arebased on the pipes actual state estimation.Allocation of pipes ages for starting point (2008) isshown on Fig. 7 [5].age, years4035302520151052008200920102011201220132014201520162017201820192020202120222023202420252026202720282029203020312032203320342035203620372038203920401%2%3%4%1,50%2,50%currentlength, km2520151050494643403734312825221916131074age, yearsFig. 7 Length of DH networks by pipes age (in 2008)1Fig. 8 Pipe age forecasts for different intensity of networkrenovation worksAs it can be seen from Fig. 8 in case the renovationstays on the same level, the average age of pipes willgrow till reaching 39 years in 2040. In case the lengthof annually changed pipes is 1% or 1,5% higher, theaverage age will still rise, but in a less steep way.When the 2% of DH system length is annuallyrenovated there will be the minimal changes in ageduring first 5 years, after that the age will start risingand only after 15 years it will begin to decrease.If renovation intensity is 2,5% of the length or higher,the average age will not rise at all or will decrease. Forreducing the damages occurrence probabilityinfluenced by the networks age, the amount of repaired281