12th International Symposium on District Heating and Cooling

The values presented do of course largely depend onthe actual physical lambdas (in W/m.K) of the insulationmaterial, but the underlying measurement data suggestthat other factors come into play as well, such as thegeometry of foam in combination with the temperaturedependence of the ―physical‖ lambda of the foam.Therefore, the values in Table 1 are valid only forcalculation / prediction purposes, in exactly the samecalculation model from which they were derived (alsoaccording to EN15632). The values in Table 1 aresupported by experimental data on four samples at thetime of writing this paper.When all parameters are known, equation 1 can beused to calculate heat loss: i Where:1ln sd 2d 1 2 T probe T casing1 ln id 3d 21 ln cT probe, T casing represent probe (medium) and casingtemperatured 1 to d 4 represent inner/outer diameters of servicepipe and casingλ s , λ i , λ c = heat coefficient of service pipe,insulation and casingIn this case, λ s and λ c are known: λ s = 0.19 W/m.Kand λ c = 0.40 W/m.K. On a test rig, T probe , T casing andheat loss are measured, so for specific test samples,eq. 1 can be used backwards to calculate ―synthetic‖values for λ i in Table 1.For the Steel-PUR-PE reference, see [1], values canbe determined in a similar fashion. ―Synthetic‖ λ ivalues for PUR foam, determined frommeasurement of samples, were typically in the rangeof 0.030 to 0.032 W/m.K, with λ s for steel 50 W/m.KHeat Loss [W/m]50454035302520151050St stdPB std insulation thicknessPB extended insulation thicknessPB impr. freshd 4d 316 20 25 32 40 50 63 75 90 110Nominal diameter [mm]Fig. 7, Heat loss per pair, including improved insulationquality(1)The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estonia313The red graph in Fig. 7 represents the predicted heatloss values for the combined effect of both increasedinsulation thickness and insulation qualityimprovement. For most diameters, these are on parwith or slightly better than the reference in Steel-PUR-PE. These data are valid only for the recently producedor ―fresh‖ product. As there is no experimental dataavailable on the rate of degassing and therefore therate of ageing, it is difficult to predict heat loss over thelife time of the product.However, it is possible to speed up the process ofageing artificially, until all the foaming agent has beenreplaced by air. The predicted values for this conditionare also presented in Table 1, as lambda degassed.These are ―synthetic‖ as well, and suitable forcalculation purposes only. Calculated heat loss resultswith these values are presented in Fig. 8.Pump I, power: 16 kWHeat Loss [W/m]454035302520151050St std PB impr fresh PB impr degassed84 %14 %2 %16 20 25 32 40 50 63 75 90 110Nominal diameter [mm]Fig. 8, Heat loss per pair, including improved insulationquality, fully degassedIn Fig. 8, the purple graph represents the reference,Steel-PUR-PE as measured, see Smits et al. 2010 [1].The red graph represents the prediction of improved,fresh PB-PE-PE and green the prediction of fullydegassed PB-PE-PE. The values vary a bit, but aregenerally in the same range. During the lifetime of theproduct, heat loss is expected to increase from the redvalues to the green values.Of course, ageing is also applicable to the referenceproduct, but not included here for two reasons. First,the ageing process for rigid systems is expected to besignificantly slower than for flexible systems, andsecond, the reference samples were not fresh, as couldbe judged by the gas content. Therefore, it is not likelythat the values presented for the reference system willdeteriorate much further during lifetime.Ageing can be slowed down considerably if measuresare taken to prevent the exchange of blowing agentwith the environment. If successful, these measures