Under hösten 2022 gick textgenererande AI (artificiell intelligens) överen brytpunkt för nivån på språket. Plötsligt höll texter skrivna av AI enliknande kvalitét som texter skrivna av människor. Det innebar att allastudenter plötsligt fick tillgång till teknik som kan skriva skriftligainlämningar åt dem. En sådan omvälvande förändring gör att det blirviktigt att se över syftet med att studenterna ska skriva olika texter.Med utgångspunkt i examensmålens formulering kring skriftligkommunikation presenterar den här artikeln mitt försök attstrukturera olika syften med studenternas skrivande. Två olika syftenpresenteras, skrivande för att kommunicera och skrivande för att lära.Om syftet med skrivande är att kommunicera ett innehåll så blir AI ettverktyg som i bästa fall kan göra kommunikationen tydligare. Om inteinnehållet som kommuniceras ska representera studentens kunskap,då kommer en AI-skriven text bara ge information om AIns kunskapoch inte säga något om studenten. Om det istället finns ett syfte att detegna skrivandet ska hjälpa studenten i lärandet så kommer AI iställethindra syftet, men då måste det redas ut vilka texter som bäst hjälperlärandet. Valet av syfte kommer påverka hur AI bör hanteras ochintroduceras i undervisningen. Slutligen presenteras hur jag och minakollegor på byggteknik börjat ta oss an frågan genom att vara tydligamed reglerna kring AI och genom att formalisera hur studenterna skadeklarera om de använt AI i sina texter.

Fjärrvärmerörets termiska och mekaniska prestanda minskar med tiden. I ettfjärrvärmesystem är det viktigt att den producerade värmen levereras tillkonsumenterna med minsta möjliga förluster. Detta blir ännu viktigare närbyggnader (konsumenterna) blir mer och mer energieffektiva. Många energibolaghar behov av att förnya sitt fjärrvärmenät men det finns inga metoder för attfastställa de befintliga fjärrvärmerörens prestanda under användningstiden. Det ärockså önskvärt att använda mer energieffektiva fjärrvärmerör vid en eventuellförnyelse.I detta projekt, utreds livslängden och status hos fjärrvärmenätet med hjälp avfältmätningar, laboratorieförsök och teoretiska beräkningar. Målet med projektet äratt ta fram ett effektivare fjärrvärmerör med lång livslängd, ta fram en icke-förstörande metod för bestämning av fjärrvärmerörs status under dess livslängdsamt att utveckla numeriska modeller för bedömning av fjärrvärmerörs livslängd.Livslängden för fjärrvärmerör har bestämts för rör från en provanläggning iHisings Backa. Resultaten visar att efter cirka 30 år har dessa fjärrvärmerörfortfarande goda mekaniska och termiska prestanda. Rörens värmeisoleringförändrades med cirka 10 % och de mekaniska egenskaperna uppfyller kravenenligt SS-EN253. För att bättre kunna beräkna rörens termiska livslängd med hjälpav teoretiska modeller skall modellen kompletteras med indata om den omgivandemarkens förhållanden.Hybridisolering av fjärrvärmerör minskar värmeförlusterna med nästan 50 % förett singelrör och med runt 30 % för ett dubbelrör. Mätresultaten från femfältstationer har analyserats. Prestanda för hybridisolerade fjärrvärmerör medvakuumpaneler har endast förändrats marginellt efter nära 5 år i bruk.En icke-förstörande metod baserad på avsvalning har utvecklats och testats påChalmers fjärrvärmenät. För att mäta temperaturer i fjärrvärmerören i fält användsresistansen i den befintliga koppartråden. Undersökningen visar att näsa steg förden icke-förstörande metoden bör vara tester i fält.Det finns behov av ytterligare forskning. -Mätresultaten från mätstationen i Hisings Backa har gett värdefull ny information. Det är av stort intresse att hållamätstationen igång. Framtida mätningar kan leda till att modellerna (gasdiffusion,nedbrytningsprocesser) kan förbättras. -På samma sätt samlas fortsatta mätresultati fältmätstationerna för hybridisolerade fjärrvärmerör. För hybridisolerade rörskulle det också vara av intresse att genomföra en större mätstudie där lovande panelkonfigurationer ställs mot varandra. -Icke förstörande metoden behöverundersökas på längre sträckor och i fält för att utvärdera dess potential som mätmetod.

Thermal and mechanical performance of district heating pipes decreasesthroughout its lifetime. In a district heating system it is important that theproduced heat is delivered to consumers with the least possible heat losses. Manyenergy companies face renewal of district heating networks, but there are nomethods for determining the performance of existing pipes. It is also desirable touse more energy efficient district heating pipes for any type renewal.In this project, the status of the district heating network is investigated using fieldmeasurements, laboratory tests and theoretical calculations. The outcome of theproject is a, a non-destructive method for determining the status of pipes andmodification of the theoretical model concerning lifetime assessment. Furthermoreperformance of the energy efficient district heating pipe is assessed.The lifetime of district heating pipes is investigated using naturally aged pipeslocated at a test facility in Hisings Backa. The results indicate that after about 30years, the pipes have good mechanical and thermal performance. Thermalconductivity of the pipes decreased by 10% and the mechanical properties meet therequirements of SS-EN253. In order to increase the accuracy of the lifetimeestimation, the theoretical models must be complemented with input data relatedto the surrounding soil condition.Hybrid insulation of district heating pipes reduces heat losses by almost 50% for asingle pipe and around 30% for a twin pipe. The results from five field stationshave been analyzed. The thermal performance of hybrid-insulated district heatingpipes with vacuum panels has changed marginally after almost 5 years.A non-destructive method based on a ‘cooling method’ has been developed andtested on Chalmers district heating network. To measure temperatures inside thedistrict heating pipe, the existing copper wire can be used. The results of theinvestigation indicate that the developed non-destructive method has largepotential to be tested in field measurements.Further research is needed. 1) The results from the field station in Hisings Backahave provided valuable new information. It is of great interest to keep themeasurement station running. Future measurements can lead to improved models.2) In the same way, the field measurements are essential for further developmentof hybrid-insulated pipes. For this type of pipes, it would also be of interest to conduct a large field study where panel configurations are used. 3) The non-destructive method needs to be investigated on longer distances and in the field toevaluate its potential as a measurement method for assessing the status of thepipes.

This paper presents studies on district heating pipes where a vacuum insulation panel replace the innermost layers of polyurethane around the service pipe. One of the main challenges are their long term performance. Prototypes have been tested both in field in a district heating grid and in laboratory with a constant temperatures. The results indicate that the panels are intact after four years in field. In the laboratory, the pipes have been exposed to a constant temperature of 115 degrees C for over three years without damage to the panels.

In nano-porous thermal insulation there is a strong relation between the pressure and the thermal conductivity, even at pressures close to atmospheric pressure. This thesis presents research on applications of nano-porous insulation in hybrid insulation district heating pipes and in building walls.A concept of hybrid insulation district heating pipes has been investigated where the innermost layers of insulation consists of nano-porous insulation and the outer layers consists of polyurethane foam insulation. The concept has been investigated through a mix of laboratory measurements, field measurements and simulations. The presented research indicates that vacuum insulation panels (VIPs) can be used in district heating pipes to reduce the heat losses. For the evaluated configurations the heat losses were reduced by a magnitude of 30%. The heat losses from the supply pipe in a twin pipe were reduced by 50%. The two main considerations with using vacuum panels in district heating pipes are the thermal bridges and the long term performance. It is shown that the position of the thermal bridges in the panels has a large effect on the thermal performance of the twin pipes and the results indicate a preferred configuration to minimize heat loss. The thesis presents a model to evaluate the long term performance of the VIPs through temperature measurements. After three years of field measurements on pipes connected to a district heating network with temperatures up to 90C, there is no sign of any uncontrolled deterioration of the VIPs. Results from the investigation show that the use of aerogel can reduce the thickness of a load bearing stud wall with 40% compared to the use of conventional insulation. If done wrong, this can lead to some new consideration regarding mold growth risk. The fact that the thermal conductivity of nano-porous insulation is strongly influenced by the pressure in the pore gas can be used to create variable insulation, where the thermal properties of the insulation is changed to match the current circumstances. By putting the insulation in a diffusion tight bag, connected to a vacuum pump, the pressure in the material can be changed and thereby the thermal conductivity. The pressure was varied in a fumed silica and an aerogel blanket sample between 1 kPa and atmospheric pressure, which gave a variation in the thermal conductivity of 1.5 for the aerogel blanket and 3 for the fumed silica. Transient measurements during evacuation and refilling show that the thermal performance will be influenced by some transient effects, such as influence from the temperature of the inserted air, but the time scale is too small to have any large effect on the energy performance. When the variation is used in simulations of the energy use for an office building, an interesting result is that a variable construction gave a higher optimum U-value, corresponding to thinner walls.

In Swedish district heating networks, around 10% of the supplied thermal energy is lost in the distribution system. One solution to decrease the losses is to use hybrid insulation district heating pipes, a concept where the innermost part of the thermal insulation consists of vacuum insulation panels, held in place by polyurethane foam. One problem with vacuum insulation panels are their sensitivity to high temperatures. This paper presents field measurements on a hybrid insulation district heating pipe where the temperatures have been measured continuously at various positions of a pipe section. The measurements show consistency and a large difference between hybrid insulation parts and reference parts without vacuum insulation panels. A superposition model has been used to calculate the temperature in a point and compare it to the measurement. The results are compared to the same calculation on the results from finite element simulations. The results show clearly that the vacuum panels in the pipes have not collapsed. A slow deterioration of the panels is harder to find with this model. Changes in the system, such as a return temperature which decreases over time, can give a larger impact, concealing the change in the panel performance.

In Sweden, around 10% of the energy supplied to the district heating networks are lost through heat losses from the distribution pipes. In cylindrical geometries it is preferable to improve the insulation as close to the center as possible. This has resulted in a hybrid insulation district heating pipe concept with a combination of vacuum insulation panels at the center, held in place bypolyurethane foam. In the twin pipe concept, the vacuum insulation panel cover the supply pipe. This creates a complex temperature profile over the section and measured results on single pipes might not be applicable. Therefore, there is a need for a method to evaluate the improvement of hybrid insulation twin pipes in the laboratory. This paper presents a method where two guarded hot pipe apparatuses is used, one heating rod for each pipe, to measure the heat losses from hybrid pipes and compare to a conventional polyurethane pipe. The measurements indicate an improvement in thermal performance by 12%-18% for the total losses and by 29% -39% for the supply pipe losses.

Cold climates might have a variable need for thermal insulation. When there are large heat loads a low Uvalueis preferable, and opposite when heat loads are low and it is cold outdoors. One way to adjust the Uvalueis to change the gas pressure within the insulation. This would be especially effective in nano-porousmaterials where the relation between pressure and thermal conductivity is stronger. Measurements have beenconducted on an aerogel blanket and a fumed silica material. The results show an almost linear dependencein thermal conductivity at pressures between 1 kPa and 100 kPA for both materials. In the measurements,the thermal conductivity increase by a factor between 1.5 and 2.6 (highest conductivity divided by lowestconductivity).

A variable U-value would be beneficial for a buildings thermal performance. One way to switch the U-value of a wall, insulated with nano-porous material, is to change the internal pressure of the insulation This paper present thermal conductivity measurements showing a possible variation around of 3 times for a fumed silica and less than 2 times for an aerogel blanket when the pressure was varied between 1 and 100 kPa. The variation factor of 3 was used in building energy simulation of a Swedish office showing that a U-value which can be varied within that range can give a significant reduction energy demand. Especially when energy used for cooling is weighted as worse than energy used for heating.

Apart from the higher initial cost for using vacuum insulation panels (VIPs) in buildings there is still hesitation among architects and engineers whether these materials will withstand long-term use in buildings with a service life of 80-100 years. To evaluate the long-term performance, further investigations are needed. VIPs have been used in buildings since the 1990s and there already exists experience from using them in various applications. This paper presents the experiences from two field studies of a previously non-insulated wall with VIPs and a district heating pipe with hybrid VIP/PUR insulation. Measurements of the relative humidity in the wall showed that there is low risk of condensation in the VIP layer. Temperature measurements in the wall during the period 2010 to 2015 show no signs of deterioration of the VIPs. The same conclusion was made based on the temperature profiles in the district heating pipes during the period 2012 to 2015. The measurements are on-going to determine the long-term performance of the VIPs in different applications.