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, EstoniaTHERMAFLEX HEAT LOSS EQUIPMENT 600The Thermaflex heat loss equipment is speciallydesigned for the Thermaflex Flexalen 600 series. Oneof the major design goals was to develop a fast andeasy to use test rig with the precision of a laboratorialtest. These goals have resulted in a test rig that is ableto measure heat loss in a few hours, allowing directoptimization during the production process, and isoperable by the production staff without the loss ofaccuracyPhysical test facilityThe physical part of the Thermaflex heat lossequipment consists of three segments.The first is the water cooled compartment in which alltests are performed. This compartment is kept at aconstant temperature, (23 °C), during eachmeasurement.The second is a heat source, for which heating probesare used. These heating probes are custom made byequipping a two meter Thermaflex piping segment, ofall available diameters, with three heating coils.The third part of the heat loss equipment is the controlunit. Here the heating probe is powered and all thermalreadings are done. By applying custom made softwareall desired readings can be done. The final output is theactual heat loss in W/m through the entire pre-insulatedFlexalen pipe, consisting of the service pipe, insulationand outer casing.section. With this method it is possible to measure theheat loss by measuring the power needed to maintain aconstant temperature of the test sample. Incontradiction to the measurements at the test institutes,the Thermaflex heating probes temperature isregulated by PID controlled power supplies. In the testresults Graph 2 the power consumption versus testtime is shown. This variable power supply makes itpossible to pre-heat the probes in a short period oftime, shortening waiting times considerably.Furthermore the use of the actual pipe material as aheating probe increases the accuracy. Moreover iteliminates all additional heat loss by convection thatwill be present with the use of smaller, not inner servicepipe connecting heating probes.For testing competitive products with differentdiameters these advantages are lost. However by theuse of thermal compartments in the service pipe thetest results can be guaranteed.Thermaflex method of testingFor testing, the heating probe with the appropriatediameter is inserted in the insulation covered with outercasing, and inserted in the cooled test section. Afterconnecting the probe to the control unit themeasurement can be started. Different testingconditions can be entered at this point such as theinner pipe temperature, representing the internalmedium. When the test is started the heating coils heatthe inner side of the probe until the desiredtemperature is reached. When the inner temperature isconsidered constant and uniform throughout the threeheating coils, the actual measurement is started. Toensure a constant temperature in the probe, a waitingtime is built in the software that will reset themeasurement if temperature exceeds presettemperature values.Fig 3, Thermaflex heat loss equipment 600.Measurement principle ThermaflexThe Thermaflex test rig is designed in compliance withthe European standard [1] and also the tests arecarried out according to ISO 8497 and EN 15632. Inthe design of the heating probes the most realisticmethod, the guarded end method, is used. Accordingto this method the heating probes are equipped withthree heating coils with separate power supply. Asshown in Figure 2, two 400 mm heating coils located ateach end of the 1000 mm test section. These twosections provide a thermal insulation at both ends ofthe test section since all three are kept under uniformtemperature, eliminating axial heat loss of the test252The heat loss measurement is done by measuring theenergy required to keep the probe at a constanttemperature, by measuring the current at constantvoltage in the heating coils, and calculating the powerconsumption. Since the middle/testing coil is exactlyone meter in length the required energy represents theexact heat loss through one meter of piping andinsulation in W/m. Since the actual piping material isused during the measurement, there are no otherlosses, nor advantages, than there will be in practise,ensuring an objective measurement. Furthermore arealistic fit of the insulation material is guaranteed. Asstated in the foregoing paragraph these advantagesare lost for divergent diameters. However during thisinvestigation the probes have proven suitable fortesting, as both testing institutes also use smallerheating probes.