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, EstoniaAverage cell size [mm]60504030201001,81,51,20,90,60,30,0- 5.000 10.000 15.000 20.000 25.000Cross section of foam [mm²]Graph 1: Density and cell size in relation to foam crosssectionHeat loss of buried piping [W/m]40,035,030,025,020,015,03050 100 150 200Outer diameter pipesystem [mm]Graph 2: 50,calculated and calculated heat loss of buriedpipe in relation to outer pipe size8070605040Conductivity [mW/m.K]Density [kg/m³]Graph 3 shows the relationship between outer pipesystem diameter size and the percentage of foamingagent directly from production. With increasingdiameter the foaming agent increases, possibly to anasymptotic value.An additional interesting factor is the ongoing processin the foam during and after production. As describedbefore the final step in the production is a 5-day curingstage.During the curing stage the foam expands and part ofthe foaming agent releases from the foam. As the foamis locked by a hard outer shell, expansion is directedinwards. By this the gap between the foam and the PBmedium pipe, typical for our production method, isdecreased.Table 2 shows the effect of curing and degassing onboth the contents of foaming agent and the calculatedheat loss.Even when forced, degassing takes time. The numberof degassed samples manufactured in the same wayas the fresh samples is therefore limited. Table 2 isshort due to a lack of adequate and comparablesamples.Table 2: The effect of time on curing and degassingFresh6 days curing DegassedProduct AgentHeatHeatHeatAgent AgentLossLossLoss% W/m % W/m % % W/m %63 A 32 52 15 23 17,5 15 0 17,1 1275 A 40 46 18 40 16,9 -5 0 20,1 1390 A 40 64 17 53 18 5 0 18,5 8Graph 2 shows the influence of outer pipe size tocalculated conductivity 50 and heat loss of buried pipesystems.It also shows that part of the increase of the heat losswith the diameter is caused by increase of conductivity.Percentage foaming agent90807060504050 100 150 200Outer diameter pipesystem [mm]Graph 3: Foaming agent content in relation to outerdiameter sizeHeat loss of buried piping [W/m]2019181716150 10 20 30 40 50 60Percentage of foaming agentGraph 4: Relationship between heat loss and foamingagentGraph 4 shows that there is a tendency of decreasingheat loss with increasing foaming agent. This tendencyhas seems weak. The spread is large over the entiregraph.116