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 calculated end method states the ends of theservice pipe shall be insulated with a known thermalconductivity as shown in Fig 2.X, L: distance to next measuring point from the middle,sample lengthT 0m ,T 0X ,∆T 0m ,T 2 : pipe temperature at the middle of thetest section, temperature at distance X of the middle,temperature correction, temperature at insulationsurface.Fig 2, Configuration calculated end cap.The service pipe is heated, using a heating elementwith only one section. During the tests a thermal profileis made of the outer casing of the sample, showinglower values at the ends. After testing the heat loss iscompensated for the end loss with the van Rinsum orNukiyama theory. For this investigation only the vanRinsum theory is used and therefore described.According to the van Rinsum theory, the axial heat losscauses a decrease in temperature not only towards theends of the service pipe, but in the test section as well.With the use of the equations (1), (2), (3) thistemperature decrease in the test section can becalculated and added to the measured value,compensating the end loss. This corrected temperatureis used in equation (4) to calculate the overall thermalconductivity. This method is used by one of theGerman institutes. calcc D 2 lnD 0 2LT 0m T 2 2 calc DA 1 1 A 2 2 2 lnD 0 T 0m T 0XT 0m cosh Xc 2 D 2 lnD 0 LT 0m T 0m T 2 λ calc : approximate value of thermal conductivity(1)(2)(3)(4)D 2 /D 0 : outer/inner diameters of casing and service pipeA 1 , A 2 : areas of the heating probe, inner service pipeλ 1 , λ 2 , λ: thermal conductivity of heating probe, thermalconductivity of medium in the service pipe, thermalconductivity total sample.251VERIFICATION OF SAMPLESTo verify the outcome of the Thermaflex heat lossequipment and the laboratory tests, three samples ofthe Flexalen 600 piping system are tested on theiroverall heat loss. These samples consist of 2 or 3 m ofthe pre-insulated piping system. More informationabout the Flexalen 600 system can be found in “Heatloss of flexible plastic pipe systems analysis andoptimization” (E. van der Ven et Al.) [4]. Furthermore,method comparison tests are performed on competitivepre-insulated piping systems, a comparison of theproducts themselves is given in “Performance of preinsulated pipes” (I. Smits et Al.) [6].The tests on the Flexalen 600 products are performedby Thermaflex and by one of the acknowledgedinstitutes, using the different methods. To ensure theeffect of ageing in the Flexalen 600 system is the sameduring all tests, the Flexalen 600 samples are testedsimultaneously. To exclude effects of the productionprocess both tested samples are half of a 6 meter stick.An alternative method is used for Flexalen 50A25 andcompetitive products. Here the same sample is testedat the different test facilities.The comparison of the results is based on the outcomeof heat loss per meter, calculated as described in theEuropean standard [1]. This loss per meter is onlyconclusive on a very small part of the entire system.Therefore the complete Flexalen 600 system will becovered in paper “Heat loss system optimisation” (J.Korsman et Al.) [3] and ‗‟New economical connectionsolutions for flexible piping systems” (C. Engel et Al.)[5].In this report the following diameters of the Flexalen600 piping systems are used for comparison of themeasurements: Flexalen 600: 50A25, two guarded end tests* and calculated endtest. 160A90, one guarded end test* and calculated endtest. 200A110, one guarded end test* and calculatedend test.Competitive products: Sample 1 two guarded end tests Sample 2 two guarded end tests**At the time of writing the second test results were notyet available.