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This thesis aims to provide experimental insights on the transient phenomena of ignition light-around and lean blowoff dynamics of turbulent flames in annular combustors. Numerous ignition experiments have been performed in single flame setups but are unable to replicate the physics of flame spreading and propagation from one injector to the next in an annular geometry. Similarly, lean blowoff studies of a single flame fail to account for any flame interaction present in multi-injector configurations which is known to affect the eventual lean blowoff limit. The present work aims to contribute to the existing limited data concerning these transient flame dynamics through various experiments conducted on three different laboratory-scale annular combustors. The first of such designs is the Cambridge/NTNU annular combustor which has a greatly simplified geometry to facilitate fundamental studies. Ignition studies using hydrocarbons corroborated past findings that the ignition speed is positively correlated to a lumped parameter of laminar flame speed and thermal expansion (quantified using dilatation ratio). Mixture blends of hydrogen and ammonia were used to isolate effect of the dilatation ratio and the laminar flame speed. The use of these non-carbon fuel blends strongly suggests the dominant role of thermo-diffusivity in influencing flame propagation speed. Notably, a decrease in the volumetric expansion effect (lower dilatation ratio) leads to an unexpected increase in flame speed which is contrary to behaviour of hydrocarbon fuels and highlights that due consideration is needed when generalising existing findings to non-carbon fuels which often have drastically different flame properties. In collaboration with SAFRAN Helicopter Engines and CERFACS, two new laboratory-scale combustors were conceived to replicate the design principles of a SAFRAN spinning combustion technology (SCT) engine: (i) strong azimuthal swirl, (ii) Rich-Quench-Lean (RQL) combustion mode, and (iii) azimuthal fuel staging. These setups are named SCT V1 and SCT V2. SCT V1 was used to assess effect of strong azimuthal swirl on light-around and lean blowoff in premixed flames. SCT V2 explored these effects in a RQL configuration with and without azimuthal fuel staging. The presence of strong azimuthal swirl in SCT V1 and V2 was shown to promote higher injector-to-injector propagation speeds, and improve ignition and lean blowoff limits. Under a RQL combustion mode in SCT V2, non-premixed flame ignition behaviour was observed in that no clear correlation could be established between propagation speed and bulk flow velocity. Careful design of azimuthal fuel staging may lead to substantial improvements in the ignition limits, increasing the operating envelope of an engine. Lean blowoff limits of the three annular combustors and setups representative of their single flame equivalent were also mapped. It is found that in all three annular configurations, multiple interacting flames may extend the global extinction limits. Notably, in the case of SCT V1 and V2, there are indications that under the influence of strong azimuthal swirl, flames from an injector often have a piloting (and stabilising) effect on adjacent injectors. This finding is substantiated with Large Eddy Simulation work performed by CERFACS. Efforts are currently underway to further characterise and elucidate the various findings reported in this dissertation which have sought to (i) explore the ignition dynamics of ammonia and hydrogen in anticipation of the transition to a carbon-free future, and (ii) evaluate the ignition and lean blowoff physics of various combustor designs closely mimicking that of a Spinning Combustion Technology (SCT) engine.

PhD in cotutelle between NTNU (Norway) and INSA Lyon (France) The 21st century presents numerous challenges to urban stormwater management, including the impacts of changes in both climate and city morphology. These challenges necessitate rethinking the stormwater management paradigm, particularly in the context of existing and ageing infrastructure. This thesis deals with green infrastructures (GI) considered as decentralized multifunctional infrastructures that utilize evapotranspiration and/or horizontal and vertical infiltration to achieve a hydrological function. This study evaluates the potential of GI to manage day-to-day rainfall events, attenuate major events, and contribute to the management of extreme events in the context of climate change adaptation. It also aims to provide a framework and tools to realign current GI modelling and design methods with the principles of robust decision-making. The thesis investigates how to use climate and hydrological present and future data with hydrological GI models to extract relevant information for decision-making under deep uncertainty. The results provide guidelines for i) designing experiments to calibrate reliable hydrological models and ii) using available climate projections together with weather generators for GI performance evaluation. The proposed framework HIDES demonstrates how future downscaled time series can be used to evaluate annual retention distribution and frequency of exceedance, while sampling extreme events allows for estimating both a probability of failure and an indication of the behaviour of GI under failure. The thesis suggests rethinking the methods for implementing GI at the city scale. The study shows that system-based design outperforms site-scale design through modelling at the roof scale of a neighbourhood, and that lumping GI models at a neighbourhood scale may neglect interactions and fail to estimate performance. The thesis highlights the need to couple GI to achieve challenges in stormwater management.

Sammendrag Økende kø på vegnettet skaper utfordringer i form av økt lokal og global forurensing, og øker kostnadene på grunn av tid tapt på overbelastede veinett. Regjeringer over hele verden har tatt disse problemene forårsaket av veitrafikk på alvor og har begynt å iverksette tiltak for å omgå dem de siste tiårene. Tiltak iverksatt av myndigheter for å redusere de ovennevnte problemene inkluderer, men er ikke begrenset til (i) rushtidsavgifter for å redusere trafikken inn i byområder, (ii) økte parkeringsavgifter for å begrense biltrafikken og parkering i urbane områder, (iii) opprettelse av miljøvennlige soner som forbyr bilbruk i visse områder innenfor et urbant område og (iv) oppmuntre til bruk av elektriske batterikjøretøyer, spesielt gjennom økonomiske insentiver som fritak fra visse kjøretøyavgifter og fritak fra å betale veiavgifter. Hvordan disse statlige tiltakene fungerer eller har fungert i praksis har blitt behandlet og behandles kontinuerlig i litteraturen. Selv om litteraturen har tatt for seg hvordan myndighetenes innsats i praksis fungerer for å redusere problemene forårsaket av økende trafikkmengder, er det fortsatt flere forskningsbaserte spørsmål som ikke har blitt behandlet i litteraturen og som kan styrke beslutningstaking i myndighetene. Forskningsspørsmålene er som følger: (i) Hvordan opplever folk kø? (ii) Gitt at det allerede eksisterer en bomring med flate takster for å samle inn midler til veibygging og offentlig transport, hva er trafikantens holdninger til en omlegging til en tids og miljø differensiert avgiftsordning? (iii) Gitt at regjeringer innfører økonomiske insentiver for å motivere kjøp og bruk av elbiler, hva er de negative effektene? (iv) Gitt (iii) ovenfor, hva er trafikantenes holdninger til slike insentiver flere år etter implementeringen? Svar på disse spørsmålene vil tilføre kunnskap for beslutningstakere og til transportlitteraturen. For eksempel kan beslutningstakere ønske å vite om de negative effektene av elbilinsentiver for å hjelpe dem med å utforme eller forbedre slike insentiver. Denne avhandlingen tilfører forståelse av trafikantenes holdninger og opplevelser i forhold til kø, tids og miljø- differensierte takster og uheldige effekter av insentiver for elbiler som ikke er kjent for beslutningstakere ved utformingen av insentivene. Denne forståelsen er viktig for beslutningstakere for å sikre effektive veitransportsystemer som tar hensyn til bymiljøet i tillegg til globale klimaendringer. Oppgaven bruker Oslo, Norge som en casestudie der bompengeavgifter og elbilinsentiver er praktisert i årevis og Norge er i front på verdensbasis Tilnærmingen som er brukt i studien er omfattende spørreskjemaundersøkelser i Oslo omegn for å måle holdninger og opplevelser til trafikantene. Metodene som er brukt for å vurdere svarene fra spørreskjemaundersøkelsene er velkjente statistiske LOGIT modeller. En enkel statistisk metode er brukt for å måle de negative effektene av elbil insentiver. Hovedfunnene fra avhandlingen er som følger. 1. Faktorer som ble funnet å påvirke trafikantenes erfaringer med kø var som følger: om de opplevde kø på referanseturen, hvor ofte trafikantene foretar turer med kø, i hvilken grad trafikantene hadde andre transportmiddelvalg, utdanning, om respondentene hadde tidsforpliktelser på destinasjonene sine, reisetid brukt under reisen, hvor ofte de opplever kø som et problem, alder og når deltakerne begynner å oppleve ubehag med kø. 2. Faktorene som ble funnet å påvirke holdninger til rushtidsavgift var som følger: betalingsvillighet, om respondenten liker å kjøre bil, hvor mange biler de de disponerer, om de har liker å kjøre tog, alder, utdanningsnivå, om de hadde negativ opplevelse av kø forrige tur, om de er enige om at de opplever mindre kø med variabel takst i bomringen, drivstofftype brukt og geografi. 3. Blant de negative effektene av elbilinsentiver, er kanskje det mest problematiske det betydelige tapet av bompengeinntekter. 4. Folk som bor i Stor-Oslo har økende tendens til å være uenige i fordelaktige elbilinsentiver som bompengefritak, tilgang til bussfelt uten passasjerer og gratis offentlig parkering. I tillegg til hovedfunnene ovenfor, vektlegger denne oppgaven faktorer som er viktige for beslutningstakere å være klar over når de tar beslutninger. Et eksempel er trafikantenes holdninger til upopulær politikk som rushtidsavgift eller endringer i elbil insentiver. Et potensielt område for videre forskning på temaene som dekkes i denne oppgaven er en mer dyptgående studie av psykologiske faktorers innvirkning på holdninger og erfaringer med køproblemer. Våre spørreskjemaundersøkelser redegjorde ikke fullt ut for psykologiske faktorer, for eksempel i hvilken grad frustrasjon, irritasjon eller ubehag påvirker holdninger og opplevelser. Et annet mulig forskningsområde vil være å se på holdningen til Oslobomringen over tid, for eksempel fem år før og fem år innføringen av de variable takstene i bomringen i Oslo. ABSTRACT Increasing road traffic volumes in urban areas worldwide pose challenges to the lives and livelihoods of humans living in urban areas from pollution that is detrimental to the health of urban populations, increases costs to industries due to time lost on congested road networks, and increases global warming due to emissions from internal combustion engine vehicles (ICEVs), e.g., CO2 emissions. Governments across the globe have taken these problems caused by road traffic seriously and have started to implement measures to circumvent them in recent decades. Measures taken by governments to reduce the abovementioned problems include but are not limited to (i) congestion charging to reduce traffic entering urban areas, (ii) increased parking charges to deter people from driving and parking in urban areas, (iii) creation of environmental zones that prohibit car use in certain areas within an urban area and (iv) encouraging the use of battery electric vehicles (BEVs), particularly through economic incentives such as exemptions from certain vehicle taxes and exemptions from paying road tolls. How these government measures work or have worked in practice has been addressed and is continuously being addressed in the literature on transportation economics and planning. Although the literature has addressed how government efforts work in practice to reduce the problems caused by increasing traffic volumes, there are still several research-based questions that have not been addressed in the literature and that may enhance decision-making by governments. Among the gaps in the literature are questions such as (i) How do road transport users experience congestion? (ii) Given that there is an already existing flat rate toll in an urban area to collect funds for road building, what are the road user’s attitudes towards a transformation to a congestion charging scheme? (iii) Given that governments implement financial incentives to motivate the purchase and use of BEVs, what are the adverse economic effects? (iv) Given (iii) above, what are road users’ attitudes toward such incentives several years after their implementation? Answers to these questions will add to the knowledge available to decision-makers and to the transportation literature. For instance, decision-makers may want to know about the adverse effects of BEV incentives to help them better design or improve such incentives. This thesis henceforth seeks to provide an understanding of road user attitudes and experiences towards congestion, congestion charging, and adverse effects of electric vehicle incentives not known to decision-makers at the time of their decision making. This understanding is important for decision-makers in devising effective management to ensure effective road transport systems that account for the urban environment in addition to global climate change. The thesis uses Oslo, Norway as a case study where toll charging, congestion charging, and BEV incentives have been in practice for years, and Norway is a front-runner worldwide in those respects. The approach used in the study is extensive questionnaire surveys in the larger Oslo area to measure the attitudes and experiences of road users. The methods used to assess the responses from the questionnaire surveys are well-known statistical logit models. A simple statistical method is used to measure the adverse effects of BEV incentives. The main findings from the thesis are as follows. Factors found to influence road users' experiences with congestion were as follows: whether they experienced congestion on their reference trip, how often road users undertake trips during congestion, the extent to which road users had potential alternative modes of transport other than car use, education, whether respondents had time commitments at their destinations, travel time used during their journey, how often they experience congestion as a problem during their journey, and when participants begin to experience discomfort with congestion and age. The factors found to influence attitudes towards congestion charging were as follows: willingness to pay, whether the respondent is likely to drive a car, whether they have a positive view of train transport, age, educational level, whether they have had a negative experience with congestion, whether they agree that they experience less congestion with congestion charging in place, fuel type used and geographic location. Among the adverse effects of BEV incentives, perhaps the most problematic is the sizeable loss of toll revenue. People living in greater Oslo are starting to disapprove of beneficial BEV incentives such as toll exemptions, access to bus lanes without passengers and free public parking. In addition to the main findings above, this thesis emphasizes factors that are important for decision makers to be aware of at the time of their decision-making. An example is road user attitudes toward unpopular policies such as congestion charging or changes in BEV economic incentives. A potential area for further research on the topics covered in this thesis is a more in-depth study on the impact of psychological factors on attitudes and experiences with congestion. Our questionnaire surveys did not fully account for psychological factors, e.g., the extent to which frustration, annoyance or discomfort influence attitudes and experience. Another potential area of research will be to examine the attitude to the Oslo cordon toll scheme in a longitudinal perspective, for example five years before and five years after the introduction of the congestion charging scheme.

Refrigeration and heat-pumping systems are shifting to natural, environmentallyfriendly refrigerants like CO2 to combat global warming. Ejectors are often used in these systems for expansion work recovery to enhance efficiency. However, ejector design is complex due to interdependent parameters and flow complexity, necessitating advanced models and tools. This thesis aims to improve CO2 ejector modeling for robust design optimization and a better understanding of system operation. To create a fundamental background for this work, key knowledge gaps on this topic are reported in an exhaustive review of CO2 two-phase ejector flow modeling. An overview of different available ejector models is reported and highlights the strengths and weaknesses of the different approaches. Other aspects, such as turbulence, non-equilibrium conditions, experimental data, and model applications are thoroughly reviewed. Different models are implemented into the ANSYS Fluent computational fluid dynamics(CFD) framework, and a comparative study of these models is performed. An experimental test campaign is conducted to validate models implemented in this work. To explore novel ejector concepts and develop improved ejector design methodologies, an algorithm for automated CFD model setup was developed to generate a database of CFD results. The Gaussian Process Regression (GPR) machine learning model is applied for modeling ejector performance trained on this database. Additionally, a numerical investigation of a novel swirl bypass concept for performance improvements of ejectors at off-design conditions is conducted. Based on the review of current CO2 ejector models, it is found that significant discrepancies between experiments and model prediction are still found. These are typically attributed to non-equilibrium thermodynamics and turbulence modeling. Based on CFD model comparisons, it was found that stable and accurate modeling of CO2 ejectors with a numerically efficient CFD method is challenging and requires further development, especially for low motive-pressure conditions. The novel two-fluid model presented in this work can predict CO2 ejector performance with appropriate parameter selection, but potential challenges for further studies include the complexity of experimental tuning and numerical instabilities. The homogeneous equilibrium CFD model was experimentally validated and reproduced mass flow rates within 2-12% and 3-50% error for the motive and suction flow rates, respectively. The GPR machine learning model algorithm was applied for modeling ejector performance with various ejector geometries and at various operating conditions with mean errors in entrainment ratio below 0.1 [-]. The algorithm was able to map ejector performance for off-design conditions, explore and optimize ejector designs, and predict local flow structures. The numerical investigation of the swirl bypass ejector indicated that designing such a concept is sensitive to the specific ejector design and operating conditions. A reduction in entrainment ratio of 2-20% is obtained when operating with a swirl bypass inlet. The flow structure inside the ejector with a swirl bypass is also investigated in detail. In conclusion, it is found that CO2 ejector modeling using CFD is a valuable tool for their design. These models in combination with machine learning have been shown to be applicable for ejector design algorithms and performance mapping. Exploration of the novel ejector concepts using CFD is considered a key way to discover novel ejector improvements. Improved modeling approaches have a direct impact on design tool accuracy, and further experimental studies and numerical developments are valuable to enhance CO2 ejector models in terms of accuracy, speed, and stability.

Digitalization requires significant changes in organizational and project structures. Human factors are critical to the success of both small and large digital initiatives. Construction project design teams are highly interdisciplinary environments with rapidly evolving subject knowledge, and digitalization constantly changes their work processes. The existing research on construction management is insufficient in explaining how people in design teams think about these changes and how this impacts collaboration. This thesis aims to bring the construction industry one step closer to understanding what is needed to accelerate digitalization by focusing on human factors in the design phase. I assess team climates that may support human responses to technology changes. I do this by bridging the theories of psychological safety and digital mindsets from the organizational behavior field to enrich the construction management literature. Using the critical realism research paradigm, I have employed in-depth case studies, relying primarily on empirical research using retroductive reasoning as a method for analysis. I also created frameworks based on existing literature, which I used as lenses for data collection and comparison in the analysis. In the following paragraphs, I present the findings on what impacted psychological safety, how psychological safety and digital mindsets were connected, and how psychological safety and digital mindsets may be a foundation for purposeful digital industrial transformation. First, I found that distinct workplace characteristics in construction design teams impact psychological safety. For example, tight collaboration can lead to conflict and harm psychological safety due to intergroup tension. Also, speaking up was found to be more vulnerable in virtual environments than in physical ones due to a lack of social cues. Second, to develop high levels of psychological safety, I found structural elements such as task design, team composition, and context supports such as adequate resources and information to be essential. In virtual environments, accountability and accessibility were critical to guarantee that work was progressing and that they were included in the workplace. The main barrier to psychological safety in temporary design teams was found to be variety and separation diversity because it caused intergroup tension and thus caused knowledge barriers. Third, positive digital mindsets and psychological safety are interlinked and influenced by team composition, leadership, and context. Importantly, I found that psychological safety impacts team members’ beliefs about their ability to learn and that collaboration expands success. In other words, psychological safety provides the climate where positive digital mindsets may grow. Furthermore, I found the relation between the two phenomena to be reciprocal. I argue that implicit theories about learning and perceptions about resources support psychological safety in explaining why individuals behave as they do toward digitalization. Lastly, viewing the findings through socio-technical system theory strengthened the arguments for psychological safety and digital mindsets as essential conditions of the social aspect of digitalization. A climate of psychological safety cultivates positive digital mindsets, which motivate employees and team members to adjust their behavior. The loose and tight couplings theory helped explain how industry characteristics complicate the development of psychological safety within project boundaries. Also, I found that loose couplings of firms limit the benefits of learning environments in projects for a future digital industrial transformation. Related to the findings of this thesis, I consider the following to be the top contributions. - A strengthening of psychological safety as a team climate construct - Knowledge of the unique challenges that may arise in design teams in establishing learning team climates - Guidance for leaders on how to focus on what matters most in framing learning environments - Knowledge of how digitalization impacts team members, how it directs their behavior, and how mindsets may be facilitated to achieve support for digitalization strategies

This thesis treats the subject of increased energy efficiency in buildings. Swimming facilities, a building type designed for improving public health and well-being, are documented in the literature as having considerable potential for reducing energy consumption. Considering the building type as a complex building category, with all their inherently connected variables and processes, it is important to focus on both the design and the operational phases. This thesis is proposing a continuous rating system, as an operating tool. This can prevent costly operational flaws by quickly disclosing incidents and making the operation staff aware. In the context of energy use an energy prediction model was developed in this work that represents the baseline for the energy use in a swimming facility. The baseline represented the expected energy use for the considered time period. The model was found to be a powerful tool for continuous supervision of the energy performance of the facility. By applying this model, an operator can quickly reveal possible operational disruptions/irregularities. The energy prediction model produced in this work can easily be deployed either in a spreadsheet or in the building automation reporting system. It is therefore applicable for existing and new buildings which are equipped with thermal and electric energy meters. Regarding the design phase, this research addressed the paradox in the complexity of the building. While complex buildings such as swimming facilities should be analyzed by dynamic simulation tools in the planning phase, this is seldom done due to the demanding and time-consuming task of modeling such complex systems and phenomena. Therefore, a simplified model for simulation-based design of swimming facilities was developed and compared with a validated detailed model of a swimming pool air handling unit (AHU), which is the most complex device in a swimming facility. In conclusion, the results of this PhD project can contribute to more sustainable swimming facilities in existing and new buildings.

In the last decades, increasing global energy demand, a foreseen reduction of available fossil fuels and increasing evidence for global warming have shown the urgency to rethink the built environment and promote energy transition. Indeed, in most industrialised nations, the building sector accounts for about 40% of the total energy consumption (space heating and cooling, domestic hot water, ventilation, lighting and appliance use). A significant share of this energy is used to thermal control buildings and provide thermally comfortable indoor environments. However, technical building systems are typically designed and operated considering fixed set-point temperatures based on the ‘one-size-fits-all’ principle – which has been questioned in the last fifty years – assuming universal thermal comfort requirements. Furthermore, the indoor environment frequently changes abruptly across buildings or between various parts within a single building. For instance, manually operating thermostats, windows and solar shades can result in considerable and not systematic changes in the indoor environment. Also, automatic controllers exhibit, to a lesser degree, a similar behaviour. Moreover, individual activity modifies the basal metabolic rate over time, and the addition or removal of clothes affects the heat balance of the human body as well. In other words, the steady-state temperature settings are the exception rather than the rule. Building temperature ranges should instead be based on real-time empirical evidence regarding the needs of its occupants, which is obtained through their feedback (usually on a rating scale). This thesis investigates these topics and relies upon an experimental study to explore the human reaction to dynamic thermal environments. The general approach utilised in this thesis encompasses a technical/methodological aspect, namely a newer controlled experimental procedure and a robust and replicable methodology for human feedback acquisition, and a statistical aspect, namely an original statistics-enabled occupant-centric modelling. The technical/methodological aspect refers to how thermal comfort data are collected; that is, the specific approach and experimental set-up utilised. The statistical aspect refers to how thermal comfort data are analysed, namely, the specific statistical technique to be adopted and the needed modelling steps. It was found that the human reaction to dynamic thermal stimuli is asymmetric with respect to heating and cooling processes, and two distinct mechanisms cause discomfort due to overheating and overcooling. Compared to the recommendations regarding temperature cycles, drifts and ramps included in the ASHRAE Standard 55, this result showed that current recommendations underestimate the risk of thermal discomfort during a cooling process while overestimating it during a heating one. Concerning the subjective thermal comfort data analysis, the choice of the statistical method affects the conclusions. While it may seem a trivial consideration, till now, it is common in the thermal comfort field to find studies that use, for example, linear regression on ordinal data following an old approximation used to overcome the lack of statistical tools and computational power (which are not anymore limiting aspects in statistical analysis). Particularly, we showed that applying a linear regression model to ordinal data suggested that there is no difference in means and effect size between genders (female/male). In contrast, an ordinal regression model leaded to the opposite conclusion. This is considered one of the reasons why there is no consensus in the scientific literature on whether gender is an influential factor when assessing the perception of the thermal environment. This result points out that greater attention should be paid to the choice of the statistical method used to analyse subjective data, which should consider the level of measurement used during the data gathering. Furthermore, two different procedures were proposed to facilitate the integration of the occupants and their actual needs into the design and operation of buildings: the former is suitable for a better-informed design phase, where the target is the optimal thermal comfort conditions expressed for an ‘average’ occupant; the other is appropriate for including the human-in-the-control-loop of a building, where satisfying the needs of a specific occupant is the primary goal. Through this thesis work, new knowledge concerning the human reactions to a dynamic thermal environment was created, which can improve the understanding of the extent to which the indoor environmental conditions can vary both naturally and artificially. Designing and implementing thermally comfortable set-point modulations that consider the occupant feedback capabilities would be beneficial to increase perceived thermal comfort and productivity, potentially reduce energy consumption and significantly support the clean energy transition. In addition, several recommendations for future research are presented.

Refrigeration technology is a vital part of modern society, covering multiple applications from comfort cooling and process cooling of servers in data centres, to domestic, commercial, and industrial refrigeration systems. The market for refrigeration systems is continuously expanding, and space cooling is the fastest-growing end user of electricity in buildings today. Furthermore, refrigeration is essential in the food cold chain to preserve fresh and frozen goods and to prevent the important challenge of food loss. Refrigeration technology is crucial in every link of the cold chain, all the way from the processing plants, in transport, in retail and during the final stage at the consumer. Refrigeration systems are large electricity consumers, and some of these systems face high peak refrigeration loads and the associated high electricity consumption. Some examples of applications that experience large variations in the refrigeration load during the day are process cooling for the dairy industry and industrial freezing processes in food processing plants. Thermal energy storage (TES) technology can be applied to refrigeration systems to decouple the supply of cooling from the refrigeration system and the demand for cooling from the consumer. When TES technology is applied to store thermal energy at sub-ambient temperatures, it is often called cold TES (CTES). The two methods of achieving CTES are sensible heat storage and latent heat storage. In the former method, CTES is achieved due to the change of temperature of a storage medium, such as water. In the latter method, CTES is achieved in the phase transition of a storage medium, often by melting and solidification. A substance capable of storing large quantities of thermal energy in the solid-liquid transition is often denoted as a phase change material (PCM). Common PCM for CTES application are paraffins and various salt-water solutions. An in-depth review of applications of CTES using PCMs in refrigeration systems was carried out to identify the current research gaps and establish the state-of-the art. It was found that the interest in PCMs for the temperature range relevant to CTES applications has been increasing in the last few years, and commercial PCMs have become available on the market. It was found that research on the implementation of CTES technology in refrigeration has been carried out for multiple applications, including food transport and packaging, commercial refrigeration and various other refrigeration systems. Common to many of these applications is the pressing need to conduct experimental investigations of promising concepts studied theoretically in the past, such as for large-scale CTES systems for industrial cooling and freezing processes using ammonia or CO2 as the refrigerant. Common ways to implement CTES in refrigeration systems in the past have consisted of using ice/water as the latent storage medium, particularly for space cooling and process cooling applications. These CTES systems are connected to the refrigeration plant by an intermediate heat transfer circuit with glycol. This concept reduces the efficiency of the refrigeration plant because the evaporation temperature must be reduced considerably compared to supplying the cooling directly at the consumer temperature. The cooling must be cascaded through the intermediate circuit and then to the consumer, while the charging process of the storage requires even lower supply temperatures. To improve the efficiency of CTES systems for refrigeration plants, it can be beneficial to integrate CTES units directly into the primary refrigerant circuit, effectively avoiding the secondary heat transfer circuit. However, the review revealed a research gap for CTES solutions suitable for industrial scale that can handle the operating pressure of refrigeration systems. In the present research work, a novel concept for a CTES unit suitable for integration into the primary refrigerant circuit of a CO2 refrigeration system has been developed. A lab-scale demonstration unit and an experimental test facility using CO2 as the refrigerant was constructed. The novel concept is based on a special type of welded heat exchanger (HEX) plate called pillow plate (PP). The PPs are constructed of stainless steel and are stacked together to form a PP-HEX placed into a container. The container is filled with the PCM, immersing the PP-HEX into the storage medium. The PPs have flow channels inside for the refrigerant to exchange heat with the PCM outside the PPs. During the charging process of the CTES unit, the refrigerant evaporates due to heat extraction from the PCM, which solidifies on the PP surface. During the discharging process, the heat transfer direction is reversed so that the refrigerant condenses while the PCM is melting. The CTES unit is flexible by accepting various types of PCMs and refrigerants at multiple temperature levels. The novel CTES unit has been tested experimentally by applying two types of storage media. Water/ice was first used as the PCM to provide the proof of concept, show the feasibility of operating the CTES unit in charging and discharging cycles and provide a benchmark for future PCMs. Then, a low-temperature commercial PCM with a melting temperature of - 9.6 C, suitable for the temperature requirement in food processing plants, was experimentally characterised using established methods before being tested in the CTES unit. Various refrigerant parameters and various PP-HEX geometries were tested. The experimental test campaigns on using water/ice and the commercial PCM have shown that the evaporation and condensation temperatures of the refrigerant are the most critical parameters influencing the performance of the charging and discharging cycles of the CTES unit, respectively. It was found that the charging time was mainly affected by the refrigerant evaporation temperature, while the discharging rate and discharged energy over the cycle increased with higher refrigerant condensing temperature. Furthermore, it was found that the distance between the PPs in the PP-HEX (plate pitch) influences the discharging characteristics of the CTES unit. A smaller plate pitch resulted in high discharge rates at the cost of lower thermal storage capacity. Increasing the plate pitch improved the thermal storage capacity, but the discharging cycle length increased. Hence, the average discharge rate was reduced. In summary, the flexible design of the CTES unit allows the designer to select a discharge characteristic of the CTES unit that matches the refrigeration load curve of the refrigeration plant by changing the plate pitch. The present research work establishes the foundation for further improvement of the concept and considerations for up-scaling and industrial implementation in the future.

Decarbonization of the industrial sector is one of the most important measures to tackling global warming. Energy demand and associated greenhouse gas (GHG) emissions are continuously increasing in various industrial processes. The increasing demand in the industry for energy efficient, cost-effective, and environmentally friendly energy systems results in a growing interest in using heat pumps. Integrating high temperature heat pumps (HTHPs) for waste heat recovery and supply temperatures of more than 100 °C is a sustainable solution for many industrial high temperature applications. This study investigates the absorption-compression heat pump (ACHP) using the zeotropic ammonia-water mixture as working fluid. The ACHP system combines the technologies of an absorption and vapor compression heat pump with the ability of achieving high supply temperatures above 120 °C with large temperature lifts (> 60 𝐾) and non-isothermal heat transfer (𝑇𝑔𝑙𝑖𝑑𝑒 > 30 𝐾). The working principle and characteristics of different ACHP cycles were discussed and an overview of the current state-of-the-art was elaborated with respect to experimental investigations available in the literature. The existing solutions and challenges for the realization of ACHP systems with focus on the application at high temperature operation were identified: the compressor design with respect to discharge temperature and lubrication; the design and operation of the absorber and desorber; the establishment of efficient liquid-vapor mixing and distribution; and the selection and cavitation protection of the solution pump. It was concluded that the oil-free operation of the ACHP system can lead to improved efficiency and reduced costs by saving on the required oil infrastructure. This can further improve the competitiveness of ACHP systems for the usage in industrial high temperature applications compared to conventional energy supply systems. The analysis of an existing dairy plant, which uses heat pumps for heating and cooling at multiple temperature levels, revealed that the process efficiency can be significantly improved with a waste heat recovery rate of more than 95%. This reduced the primary energy demand by 37.9% and emitted GHG emissions by 91.7%. The ACHP system supplied a temperature of 95 °C and a temperature lift of 33.5 K. An average COP of 5.8 was achieved with a Carnot efficiency of more than 50%. The results demonstrated that ACHP systems are reliable and efficient in commercial high temperature applications up to 100 °C. The potential application area can be further expanded by increasing the achievable heat sink supply temperature above 120 °C. Based on the identified challenges and demands, the task description of the experimental ACHP prototype was specified, and a simulation model of the ACHP cycle with single-stage solution circuit was developed using Engineering Equation Solver. This model was used to investigate the system behaviour of the ACHP system and to determine the design parameters of the ACHP prototype. The energy and exergy analysis revealed that the use of liquid injection during the vapor compression process is a sufficient measure to decrease the discharge temperature and to provide lubrication. The determined design parameters were the basis for the design of applicable and feasible component section solutions. The main component sections for the defined research areas were designed to meet the specifications, considering existing limitations for available components on the market and their potential for modifications. A numerical simulation model of an oil-free liquid-injected twin-screw compressor was developed and used to reduce the limiting compressor discharge temperature and achieve the desired oil-free system operation. The investigation revealed that it is preferable to inject the lean solution with a low NH3 mass fraction (40%), and an injection ratio of 10% of the compressor’s suction mass flow rate is required. The distribution of the lean solution over multiple injection ports located at the beginning (360°) and in the middle of the compression phase (450° or 495°) can ensure a continuous liquid film. The liquid film is utilized for sealing, lubrication, and decreasing of the discharge temperature. The obtained findings are considered as a kind of best-case analysis and were used to determine modifications to an existing compressor and to design the required injection line. The outcome of the conducted research work is the ACHP prototype with a maximum heat capacity of up to 200 kW and a maximum operating pressure and temperature of 40 bar and 190 °C, respectively. Together with the pressurized water heat source and sink circuits, the test facility allows the investigation of different component sections and application cases with heat sink outlet temperatures up to 140 °C. The ACHP prototype is an important tool for the validation of numerical models, testing new elements and optimization of the control strategy. This thesis has successfully completed the aim of the development of an ammonia-water absorption-compression heat pump at high temperature operation. The results were disseminated in the context of three published journal articles, several peer-reviewed conference papers, and other presentations. This project was done in collaboration with industrial partners and generated spin-off projects.

As one of the most significant components of asphalt concrete, bitumen is crucial to the durability and lifespan of asphalt pavement. The asphalt pavement is exposed to different external conditions, such as traffic loading, temperature, ultraviolet radiation and chemicals. These external factors can significantly reduce the durability and longevity of asphalt pavement and are accompanied by high maintenance and reparation cost. Therefore, knowledge about how these factors affect bitumen performance is of significance for pavement design and precaution measures. Many of these external factors have been investigated in several research projects in the past. However, researchers have paid less attention to the influence of external chemicals on bitumen. This research simulates the practical situation of asphalt pavement under chemical conditions in the laboratory to study the chemical effect on bitumen performance and the resultant mechanisms. To do this, three common chemical solutions were prepared in the laboratory based on Norwegian or European situation: Sodium chloride (10 wt%), calcium chloride (10 wt%) and acid rain (pH 4); Five variations of bitumen were selected: neat bitumen, short-term aged bitumen, long-term aged bitumen, polymer modified bitumen and rejuvenated bitumen; Three immersion time were applied: seven, twenty-eight and ninety days. After the immersion process, the pH value test was conducted to investigate the hydrogen ion concentration in the residual solution. Scanning electron microscopy with energy dispersive spectrometer test was applied to analyse the morphology and element content of bitumen. Penetration, softening point and viscosity tests were carried out to characterise the physical properties of bitumen. Attenuated total reflectance Fourier transform infrared radiation spectroscopy was used to analyse the chemical structure of bitumen and the reaction between bitumen and chemicals. Besides, the rheological properties of bitumen were evaluated by temperature and frequency sweep modes of dynamic shear rheometer and bending beam rheometer tests. The mechanical properties of bitumen were characterised by multiple stress creep recovery test and linear amplitude sweep test. The experimental results show that three chemicals have similar effects on the physical, rheological and mechanical properties of neat and short-term aged bitumen as conventional thermal-oxidative ageing, resulting in a stiffer and aged bitumen. The hardening and oxidative degrees were accentuated over immersion time. However, different observations on the morphology, element content and chemical structure of bitumen were found because of the distinct deterioration mechanisms caused by various chemicals. Furthermore, various bitumen responded differently to chemicals due to various reaction mechanisms, especially in surface characterisation, softening point, dynamic viscosity, non-recoverable creep compliance and recovery percent. It is concluded that polymer modified bitumen has the best resistance to chemicals, neat bitumen has the worst resistance to chemicals, rejuvenated bitumen and short-term aged bitumen show moderate resistance to chemicals. Besides, NaCl, CaCl2 and acid exert the most significant impacts on neat bitumen and aged bitumen, polymer modified bitumen, and rejuvenated bitumen, respectively. The experimental results suggest that chemical immersion should be paid the same attention to thermal-oxidative ageing. Calcium chloride is a better option for de-icing strategy compared to sodium chloride during winter maintenance from the perspective of damage (but much more expensive). Moreover, polymer modified bitumen could be the best choice for pavement design in acid rain and snowy regions where a “bare road strategy” is applied for the winter maintenance. It is hoped that this study can contribute to understanding the effect of environmental chemicals on asphalt pavement and establish a standard for the solution ageing of bitumen.

The Global Navigation Satellite Systems (GNSS) signals have shown great potential for remote sensing applications. The ubiquitous GNSS signals in direct or reflected geometry can be processed to retrieve different geophysical parameters of the Earth system’s components. This thesis presents several studies on the performance assessment and enhancement of GNSS-derived remote sensing data products and investigating possible new applications. Exemplary datasets from three classes of GNSS data products are used. The first dataset belongs to GNSS meteorology, which is derived from the processing of direct GNSS signals. The data is among the established GNSS data products with about three decades of data archive. The thesis also presents studies based on reflected signals of Medium Earth Orbiting (MEO) GNSS satellites in bistatic radar configuration. The reflected signals can be received by groundbased receivers or spaceborne receivers onboard Low Earth Orbiting (LEOs) satellites. In this sense, the second part of the thesis focuses on ground-based GNSS-Reflectometry (GNSS-R) measurements with demonstrated applications for environmental monitoring. Finally, a new generation of observations from spaceborne GNSS-R technique is investigated. The first study of this thesis focuses on Precipitable Water Vapor (PWV) time series. Although this data product has been produced for decades, its usage in climate applications depends on its homogeneity verification. This demand stems from the fact that the GNSS-derived PWV time series can have change points due to instrumentation upgrades or new settings in GNSS stations. Therefore, a data homogenization method is developed and tested on real and simulated PWV datasets. The method can identify and correct inhomogeneities in the GNSS tropospheric time series without affecting climate or meteorological signals within the time series. A GNSS-R dataset from a coastal experiment has been used in four studies of this thesis to investigate possible quality improvements of sea surface characterization measurements. The dataset includes polarimetric observations recorded using a dedicated reflectometry receiver with multiple input antennas. The antennas have Right- and Left-Handed Circular Polarizations (RHCP and LHCP) and are installed at zenith and sea-looking orientations. The studies show that polarimetric observations can significantly improve the quality of the GNSS-R measurements. A clear improvement in the sensitivity and performance of GNSS-R sea surface roughness estimates is observed for combined polarimetric observations from the RHCP and LHCP links. The sensitivity is even high-enough to discern the roughness change due to rainfall over a calm sea. The dataset is also used to assess GNSS-R sea-level monitoring under different scenarios. The effects of sea surface roughness, polarization and orientation of the antenna, and the frequency of the GNSS signal are studied. The results show that the roughness can degrade the accuracy of the GNSS-R sea-level measurements. The best GNSS-R altimetric performance is observed when combined multi-frequency measurements are used from a sea-looking antenna with an LHCP design. Finally, two datasets from the new generation spaceborne GNSS-R observations are evaluated for novel applications of the GNSS remote sensing technique. In one of the studies, the feasibility of sensing mesoscale ocean eddies using spaceborne GNSS-R is demonstrated for the first time. A long dataset investigation in this thesis reveals the evidence of changes in GNSS-R Normalized Bistatic Radar Cross-Section (NBRCS) over the ocean eddies. The detected signatures are justified using different properties of the eddies, including the eddy-induced changes in Sea Surface Temperature (SST), the interaction of the eddy surface currents with overpass wind field, and accumulated surfactants brought to the surface by the turbulence associated with the eddies. The last study of the thesis evaluates the spaceborne GNSS-R observations for flood detection and mapping during heavy rainfalls. The study is conducted over an area with a high risk of flooding, requiring constant monitoring with timely observations. The results highlight the potential of the spaceborne GNSS-R for providing the observations with the required sensitivity and short revisit time to detect and map the inundated areas.

The transition from a conventional energy system to a decarbonized energy system requires an increasing penetration of intermittent renewable energy sources, which brings more fluctuations to the electricity grid. Therefore, increased flexibility is required on the demand side. This thesis focuses on the energy flexibility of residential buildings by activating their thermal mass. Model predictive control (MPC) is acknowledged to be an appropriate control method for this purpose. The thesis addresses MPC using grey-box linear models of the building thermal dynamics. The research is split into two main parts, namely modeling and control. The modeling part can also be further split into data collection and model identification subsections. In the data collection part, the experiments for collecting the data are designed for both virtual and field experiments. The experimental design includes the selection of the excitation signal, the training period, and for field experiments, the influence of the sensor location and dynamics. Thus, different experiments with various excitation signals and training periods have been executed. The results show that the identified parameters are strongly dependent on the types of excitation and the training period for deterministic grey-box models. On the contrary, the identified parameters are less dependent on the excitation signal for stochastic grey-box models. Furthermore, there is no specific period of the space-heating season that is more suited to train a linear time invariant (LTI) grey-box model since weather conditions including solar radiation vary significantly during the entire space-heating season. In the model identification part, a suitable model structure is first investigated using different resistance-capacitance (RC) networks based on existing standards for building energy modeling (like the EN13790 and VDI 6007 standards) and the knowledge of building physics. The model selection is based on the structural and practical identifiability, the physical plausibility and the prediction performance of the grey-box model. The results show that for a mono-zone grey-box model, the second-order model is an appropriate trade-off between overfitting or poor model fidelity. The optimizer for the training of the model parameters is also investigated by comparing the parameters identified using traditional gradient-based optimization routines and global optimization routines. Results reveal that global optimization performs better than gradient-based optimization. The influence of data preprocessing on the grey-box modeling is investigated by using a low-pass filter as well as the influence of input data alignment using anti-causal shift (ACS). Results show that the pre-processing of data does not have a large influence on deterministic models. However, for stochastic models, the parameter values are significantly influenced by the data pre-processing. The identified parameters are strongly correlated with the sampling time (Ts). ACS can prevent the parameter value and variance from getting non-physical for large Ts. Pre-filtering only has a limited influence with ACS, while the pre-filtering influence without ACS does not have a clear trend. Some research is done in this thesis to compare the performance between grey-box and black-box models in the case of deterministic models. Results show that the second-order black-box model shows a similar performance to the second-order grey-box model. However, the physical interpretation of the hidden states and parameters is unknown for black-box models. In the control part, the performance of conventional MPC based on LTI models and adaptive MPC that are able to recalibrate the model parameters during operation is compared. The adaptive MPC is designed to overcome the influence of varying weather conditions during the heating season. Two different candidates for this adaptive control are investigated. Partially Adaptive MPC only updates the effective window area of the grey-box model. The Fully Adaptive MPC updates all the parameters of the grey-box model. Results show that the Partially Adaptive MPC is not able to deliver satisfactory prediction performance due to the limited number ofparameters updated. The Fully Adaptive MPC outperforms the conventional MPC based on LTI models, especially in avoiding thermal discomfort. Different types of models (e.g., ARX, NARX, SVM) are also compared in an MPC experiment in a supporting paper of this thesis. Results show that the seven states black-box statespace model has the best performance among the MPCs in the study. Using multistep ahead prediction error as the objective function when training the model is beneficial for guaranteeing its prediction performance.

In recent years, resilience has become a relevant issue in the context of building performance, owing to the diverse future events, which includes climate change, extreme weather events, energy supply disturbances, and pandemics. In traditional building designs, building performance is typically estimated under a fixed set of assumptions. However, significant external factors can impact building performance during its operational phase but have not been considered by designers. Failure to protect building performance against these changes can lead to serious short- and long-term challenges, such as fails in meeting the demands of building occupants. Therefore, the resilience of building performance needs to be investigated such that its sensitivity to external factors, like climate change, is reduced. In this thesis, a building is defined as resilient if it is able to prepare for, absorb, adapt to, and recover from disruptive events. Despite the potential of resilient building designs and their growing interest, an agreed-upon definition for resilience in the context of building performance requires further research, along with the development of methodologies for resilience quantification. This situation is partly due to the polysemic background of the resilience definition that is interpreted differently in various fields. This thesis investigates resilience in the context of building performance and develops methodologies, frameworks, and metrics for the quantification of resilience on the building scale. This paper-based thesis first focuses on adapting the existing resilience definitions to the context of building performance. This procedure begins with four questions related to the concept of resilience, which are resilience of what? resilience to what, resilience in what state, and resilience based on what? The answers to these questions allow designers to establish the key parameters for a resilient design. Resilient systems usually have a combination of attributes that influence resilience and contribute to the quantification of resilience level through the derivation and validation of a function form in regard to functionality and time. The second research activity identifies robustness and flexibility as two important attributes of resilient building design and develops methodologies for their quantification. As the final step, a methodology is developed, focusing on a framework for the quantification of resilience itself. This step introduces a single metric for thermal resilience quantification in the scale of buildings. The metric is implemented for resilience labelling. In the quantification methodologies, IDA Indoor Climate and Energy software (IDA-ICE) is used as a building performance simulation tool, and MATLAB is used as a numerical analysis tool. The developed quantification methodologies were tested on a case study of a Norwegian single-family house. The results of this research led to seven peer-reviewed papers, in which four comprise the core of the thesis and are listed as primary papers. The other three papers, which are from collaborations with other researchers, are listed as supporting papers in this thesis. The results highlight the suitability of the proposed methodologies and metrics for the quantification of resilience and its attributes. For example, for the considered case study building in Norway, it has been shown that upgrading building design from the current minimum design to a passive design has a significant impact (71% improvement) on the thermal resilience against power failure during winter. Furthermore, the results of the case study implied that various building designs with the same energy consumption can behave differently when facing uncertainties in the future, such as changes in weather conditions, occupant behaviour, and energy prices. Uncertainties of the future highlight that the evaluation of energy performance by itself will not be enough in the energy performance certificates in the near future. Therefore, the evaluation of other concepts, such as building resilience (robustness and flexibility), is also needed. This thesis takes one step forward in this regard by developing metrics, quantification frameworks, and methodologies for the evaluation of robustness, flexibility, and resilience that can be easily used by architects, building designers, decisionmakers, etc. to benchmark different building designs and technologies from these perspectives.

This thesis investigates conversion of solid fuel particles from different perspectives. In particular, two aspects of the conversion process are studied: 1) the effect of turbulence on the conversion rate and 2) the combustion behaviour of a single carbon particle. Direct Numerical Simulations of polydisperse particle systems in a periodic box of isotropic and homogeneous turbulence were performed in order to analyse how turbulence affects the mass transfer rate in such configuration. The effect of turbulence was found to be identical qualitatively and very similar quantitatively to what was observed for monodisperse particle systems, i.e. there exist two opposing mechanisms through which turbulence can affect the reactant transfer to surfaces of particles. The first mechanism leads to formation of particle clusters, which are responsible for decreased mass transfer rate, while the other is associated with the mass transfer being enhanced by turbulent motions. The model which accounts for the combined effect of turbulence was shown to be applicable to polydisperse particle systems. The effect of particle back-reaction was also studied, the results revealed its importance especially in cases characterized by high Stokes numbers. A sensitivity of the effect of turbulence to selected parameters was investigated through theoretical analysis and using simple numerical examples. Several parameters (mixture composition, particle material, turbulence intensity, particle size, mass flow rate) were demonstrated to have a meaningful influence on how strong the effect is. Finally, the effect of turbulence on the conversion rate in practical systems was examined. For this purpose, an industrial-scale boiler was simulated in ANSYS Fluent. The results showed that regions of very different conditions can simultaneously occur in different parts of the boiler, which rules out the possibility to predict the net effect of turbulence a priori. Moreover, it was shown that the conversion rate might be affected by turbulence much less than expected based on theoretical predictions as the reaction rate is often controlled by kinetics, i.e. it is independent on the rate of reactant transfer. A simple model for the resolved carbon particle conversion was implemented in the Pencil Code. Efficiency of the model was achieved by pre-adjustment of diffusion coefficients, reduction of the speed of sound and employment of a semi-global mechanism. Despite numerous simplifications, an ability of the model to predict main characteristics of the char particle conversion and formation of a flame zone was demonstrated by validating the model against experimental and numerical results. Sensitivity of the conversion rate to kinetic parameters and transport coefficients was studied. A strong sensitivity to the oxygen diffusivity was registered, especially at higher temperatures.

The need for advanced biofuels produced from sustainable sources is stressed, both on national and international level due to a global agreement to limit the Earth’s global warming. The major goals in the Norwegian agreement on climate policy are to become climate neutral by 2030 and to become a net-zero emission society by 2050. One of the priority areas for action is to reduce the sources of greenhouse gases by speeding up the introduction of low-emission alternative transport fuels, such as liquid transport biofuels. A well-known process for converting biomass resources into liquid transport biofuels involves gasification, a thermochemical process that converts the biomass into a gaseous mixture of syngas in the presence of heat and a gasifying agent. The syngas consists of mainly hydrogen (H2) and carbon monoxide (CO), and can be further processed into biofuels. Among the different technologies applied for biomass gasification, fluidized beds have industrial advantages due to the ability to process a wide range of biomass under controlled operating conditions. The fluidized bed gasifiers also offer several other advantages, including good mixing, high heat and mass transfer and high productivity at a relatively low process temperature. However, processing biomass-derived fuels in fluidized beds suffers from ash related problems. The major challenge is associated with molten biomass ash and the formation of agglomerates that cause fluid dynamic disturbances in the bed. If not counteracted, the bed disturbances lead to operational problems that might result in decreased efficiency, high maintenance costs and unscheduled shutdowns. Bed agglomeration and de-fluidization are closely linked to the ash melting behaviour, and has been reported as one of the problematic issue prohibiting an economical and trouble-free operation. Hence, the key to unlocking fluidized bed biomass gasification as a viable route for biofuels production is by solving the challenges related to the ash. This PhD thesis addresses the key issues related to bed agglomeration and de-fluidization in fluidized bed gasifiers. Experimental work and computational modelling were combined in order to achieve a fundamental understanding, and insight into the underlying mechanisms of the ash melting behavior and the bed agglomeration processes. The main objective was to develop effective and accurate methods and models to be used in prediction of the agglomeration tendency of different types of biomass during gasification in fluidized beds. The overall approach was divided into three sections: (i) CPFD simulations combined with fluidization and gasification experiments to gain necessary knowledge on the fluidization characteristics, (ii) fluidization experiments to generate new sets of data that could form the basis for (iii) a mathematical model for prediction of the critical amount of accumulated ash/bed material in the gasifier. The experiments were carried out in three different fluidized bed systems: (i) a cold flow model, (ii) a 20 kW laboratory scale model, and (iii) a micro-scale model. The commercial CPFD software package Barracuda Virtual Reactor was used for the computational part. The investigated biomass samples were grass, wood, straw and bark. The results point out that the operating temperature and the composition of the major ash forming, in particular Si, K and Ca, are significant factors leading to ash melting problems in fluidized bed processes. Additionally, the findings show that the ratios between the major ash forming elements, K, Si and Ca, in the biomass play an important role in the agglomeration process, and that different combination of those elements are especially problematic when processing biomass fuels in fluidized bed systems. The results also indicate that bark tended to have the highest tolerance limit of accumulated ash in the bed for all the investigated temperatures. For example, the ash/bed material was measured to 7% by weight at 900°C, compared to grass (3%), straw (1%) and wood (1%). A multiple regression was calculated to predict the mass ratio of accumulated ash/bed material based on the operation temperature (T) and the mass ratios of (Si/K) and (K/Ca). The final model expresses the amount of accumulated ash/bed material at the onset of bed agglomeration and de-fluidization: Accumulated ash/bed material (wt %) = 17.06 – 0.02·T + 4.04·(Si/K) + 1.05·(K/Ca) The overall regression was statistically significant (R2 = 0.81, F (3, 30) = 38, p

Metal cycles form the backbone of our modern societies but are also responsible for a large part of the anthropogenic greenhouse gas (GHG) emissions. The transition towards a more sustainable socio-economic metabolism will require large quantities of metals. Aluminium, thanks to its use in transport, buildings, electronics and energy systems, is a key element to realise this transformation. This thesis is proposing the use of new tools for monitoring and simulating the future of metal cycles and their emissions at different scales, using the aluminium cycle as the main example for applications. The approach developed for monitoring material cycles and is based on two main components: (1) a framework for designing maps of the physical economy at the societal scale, with the aim to better inform sustainability strategies, and (2) a physical accounting framework to monitor material use and emissions of industrial plants based on the application of multilayer material flow analysis at the plant-level. The dynamic MFA tools developed in this thesis increase the granularity of models used for the simulation of metal cycles. The four major methodological contributions are (1) a general framework and classification for models studying the dynamics of stocks within systems, which enables the creation of a common language to foster the cross-field dissemination of models; (2) a framework for modelling the stock dynamics of product-component systems to allow modelers to better study circular economy strategies, such as reuse and replacement; (3) a combined lifetime-leaching approach that enables the simulation of radical transformation strategies, such as the early demolition of old buildings to accelerate the penetration of energy-efficient ones; (4) a new scenario-rich approach based on multilayer MFA that allows modellers to better capture the transformation of products and technologies over time and to analyse how these changes in characteristics influence primary material demand and the potential for recycling. These tools where applied to different case studies: the monitoring of emissions in an aluminium smelter, scenarios for the future demand of materials for lithium-ion batteries, scenarios for the future demand of aluminium in cars, and scenarios for the future energy use and emissions for the Swiss building stock. Our main results show that the demand for aluminium and other battery materials in transport applications will considerably increase within the next decades. For aluminium, the changes in alloy requirements driven by electrification make the occurrence of a significant scrap surplus very likely, which would severely limit the contribution of recycling to climate change mitigation in the absence of alloy-sorting technologies or increased dismantling of car components. Even if options to decarbonise primary production exist, both for direct emissions at plant-level and for the electricity supply, most of them would take time to implement and a rapid surge in primary aluminium demand will a result in a large increase of GHG emissions. To reduce emissions from metal production during this transition phase, a comprehensive approach is necessary. Policies and measures that would only target the carbon footprint of cars and batteries do not consider systemic effects, such as the recycling challenges created by the possible occurrence of a scrap surplus in the future. They might also result in burden shifting to other sectors, which does not help in reducing the overall GHG emissions. Solving these issues and optimising the whole system would require better coordination between the different actors in the supply chain, both in primary and secondary production, product manufacturing and end-oflife management. Robust monitoring tools and large-scale simulation models can facilitate this cooperation and help decision makers quantify and target the investments needed for decarbonising material cycles.

Unwanted hydrogen releases in confined spaces can be significantly more dangerous compared to open-air scenarios. The transmission towards a zero-emission system results in a growth of hydrogen-driven vehicles which increases hazards and risk of accidents. Implementing hydrogen technologies into applications that are available to the public needs investigations of the many possible accidental scenarios. The knowledge should be disseminated to specialists, first responders and end-users. The experimental campaigns presented in this study are part of a pre-normative research project to develop a recommendation for Regulation, Codes, and Standards (RCS) and an engineering tool for hydrogen safety engineers. Four experimental campaigns were conducted during this work to investigate the results from hydrogen releases in the worse case scenarios. The large and full-scale experimental setups were designed to investigate ignited and unignited hydrogen releases. The 15 m3 explosive chamber was used to investigate overpressures – from Pressure Peaking Phenomena in an enclosure similar to private garages. The 40 ft ISO container was used for the investigation of hydrogen dispersion and thermal effects from hydrogen jet fires in enclosures similar to carparks. The hydrogen releases were performed with mass flow rates from 1.4 g/s to 13 g/s from reservoir pressures from 27 bar to 700 bar through nozzle diameters 0.5 mm – 4.0 mm, depending on the experiments and experimental campaign. The first two campaigns investigated the Pressure Peaking Phenomena from unignited and ignited releases. The experimental results were in good agreement with the developed analytical models, where the perfect mix assumption was confirmed. The model allows estimating the minimum ventilation area for the given mass flow rate and conversely. For the unignited hydrogen releases, the mass flow rate had to be relatively high and the ventilation area relatively small to observe the Pressure Peaking Phenomena. For the ignited releases the much lower mass flow rate will result in much higher overpressure compared to unignited releases for a similar ventilation size. The highest obtained overpressure for unignited releases was 8.1 kPa, resulted from the mass flow rate of 4.75 g/s and 0.0006 m2 vent area. The highest measured overpressure during ignited releases was 48.1 kPa which resulted from the mass flow rate of 8.62 g/s and 0.0055 m2 vent area. Experimental campaigns in the 40 ft ISO container were imitating hydrogen releases from the car – hydrogen jets impinging on the floor (90° - unignited jets and 90° and 45° - ignited jets). During the first experimental campaign in the 40 ft ISO container, the mechanical ventilation was investigated for 6 and 10 air changes per hour. The results showed influence on the time when the cloud is flammable but not for the maximum concentration in the cloud. The second experimental campaign in the 40 ft ISO container investigated thermal effects from hydrogen jet fires. The temperature results showed safe access to the car in case of an accident and the most dangerous areas. The temperature in the ventilation pipe did not exceed 300 °C from all releases. While inside the container, under the ceiling, this temperature limit of 300 °C was not exceeded only from releases through a 0.5 mm diameter.

There are no economical ways to tie back subsea waxy oil fields with distances to shore more than 50 km without treating the fluid on a platform or FPSO. For more considerable distances, solutions like heating could be too expensive. In the case of Arctic regions, it may not be possible to install a production facility at sea level at all due to iceberg or icing conditions rendering the development of such fields questionable. Subsea 7 is developing a fully subsea solution for treating well fluid and sending it onshore. The solution enables the development of Arctic fields. Part of this subsea facility is a system for treating wax. The idea is to make a cooling loop that cools the oil to the ambient temperatures and then sends this cold fluid into the export pipeline. This fluid flow at ambient temperatures is called "cold flow." Wax does not deposit at pipeline walls at the same temperature as the fluid. However, wax deposition is expected inside the cooling loop, and pigging the loop is seen as a solution to the wax build-up. A pig circulates inside the loop until it is worn and then is sent for cleaning the export pipeline as its last mission. Initially, this wax control system (WCS) was planned to be working with multiphase flows. However, it was decided to run WCS with single-phase flow as it was found to be impractical to operate WCS in multiphase conditions. This Ph.D. work follows the development of the WCS. It goes from a pilot experiment of checking the feasibility of a constant pigging inside a loop under single-phase conditions without an active control system, continues to experiments with bypass pigging and wax deposition in multiphase conditions, then concludes with a mathematical model for wax deposition tailored for WCS conditions. The main results of the Ph.D. work are: • Experimental data on bypass pigging in multi-phase flow. • Decision to construct WCS operating in single-phase flow both due to pigging control and wax deposition predictability. • Simulator program of wax deposition inside the WCS. The program can be used for the design of a WCS. • WCS qualification scale rig testing according to Norwegian DNV (Det Norsk Veritas) regulations. The test showed that the system is ready for implementation in an oil field. Supplementary material https://1drv.ms/f/s!AvXanuNP82zXo89VNuhTl5WLUh7mUg

Bioenergy is a necessity in most climate change mitigation scenario limiting global warming to below 2°C at the end of century relative to pre-industrial times. The large landrequirements associated with large-scale production of dedicated bioenergy crops has led to concerns of how sustainability trade-offs with food security and biodiversity can be avoided. Irrigated bioenergy production can ramp-up bioenergy crop yields relative to rain-fed conditions and contribute to alleviate pressure on land resources, but risks increased water stress. Promising opportunities include targeting abandoned cropland or degraded cropland where a switch to bioenergy crops can co-deliver environmental benefits. These areas are not yet sufficiently mapped, sustainable irrigation expansion opportunities are unclear, and bioenergy and climate change mitigation potentials are still poorly understood. In this thesis, I integrate multiple models and approaches to determine sustainable bioenergy potentials, including satellite-based land cover data, a crop yield model, and datasets of water scarcity and availability. The thesis provides a first-of-its-kind spatially explicit and highresolution global assessment of cropland abandonment and associated management dependent bioenergy potentials. It contributes to unravel the complex interactions between bioenergy production and land and water use, considering opportunities for nature conservation and irrigation constraints induced by water scarcity. The likelihood of abandoned cropland to be developed is assessed by integrating suitable land with development potential indices. I also produced refined estimates of suitable abandoned areas for bioenergy production in the former Soviet Union, which is a region with major historical abandonment and irrigation expansion opportunities. Beyond abandoned cropland, the opportunity to deploy perennial bioenergy crops on areas threatened from soil erosion by wind and water is explored in a Nordic case study. Finally, I investigate the climate change mitigation potential of liquid biofuel production with and without carbon capture and storage (CCS) in Nordic countries and compare with achievable carbon dioxide removal through natural regrowth. I find 83 million hectares of abandoned cropland globally between 1992 and 2015. Global bioenergy potentials from recultivating abandoned cropland are 6-39 exajoules per year, or 11-68% of today’s bioenergy demand, depending on agricultural management, water use for irrigation, and land sparing efforts for nature conservation. A total of 20 exajoules per year is achievable by increasing global cropland extent with 3% and global agricultural blue water withdrawals by 8%, whilst avoiding production in biodiversity hotspots and irrigation in water scarce areas. Regions with both high bioenergy potentials from abandoned cropland and high development potentials are mainly found in Central America, southeastern parts of South America, Southeast Asia and in the southern parts of North America. Furthermore, the former Soviet Union is highlighted as a region with high land availability, high marginal energy gains of irrigation, and with opportunities for irrigation expansion. Refined bioenergy potentials on abandoned land in the former Soviet Union are 3.5 to 23 exajoules per year, with high-end estimates requiring complete irrigation. An upper potential of 9 exajoules per year is achievable through sustainable irrigation expansion. This would require recultivating 35 million hectares of land combined with 67 billion cubic meters per year of blue water withdrawals. Bioenergy production deployed on abandoned cropland and cropland threatened by soil erosion in Nordic countries can provide -7.4 to -18 megatons of carbon dioxide equivalents per year of climate change mitigation, depending on biorefinery technology and CCS availability. Natural regrowth on the same areas can provide -10 megatons of carbon dioxide equivalents per year of negative emissions. High bioenergy yields are key to ensure larger climate benefits than natural regrowth without gains in biorefinery energy conversion efficiency or CCS. Biofuel production outperforms natural regrowth in 61% of abandoned croplands with a current biorefinery technology, and nearly everywhere with technological gain. For willow deployed as windbreaks, improved biorefinery technology or CCS is typically required to outperform natural regrowth. Biofuel production delivers larger climate benefits on 17% of cropland threatened by soil erosion with current technologies, and on 95% of the land with improved energy conversion efficiencies and CCS. This work shows that current opportunities to sustainably deploy bioenergy crops exists at a scale which is meaningful for future climate change mitigation pathways. It is vital to simultaneously consider land and water use sustainability when designing bioenergy deployment strategies. Lack of proper governance risks increased land-use competition with trade-offs on food security and biodiversity, and to increase water stress due to unsustainable blue water withdrawals. With sustainable governance, bioenergy and BECCS will contribute to decarbonize the energy sector and deliver climate change mitigation, whilst co-delivering other environmental benefits and enhancing ecosystem services. The findings presented here helps enlighten the importance of sustainable land and water management strategies in bioenergy production systems and can essentially contribute to achieve global sustainability targets. Sammendrag Bioenergi er en nøkkel i scenarioer som begrenser global oppvarming til under 2°C i 2100. De store arealkravene til dedikerte bioenergivekster i slike scenarioer har ledet til en debatt om hvordan utplassering av bioenergiproduksjon kan unngå å negativt påvirke matsikkerhet og biologisk manfold. Vanning kan bidra til økte avlinger og å lette trykket på landressurser, men risikerer også å skape økt vannmangel. Lovende muligheter for en bærekraftig ekspansjon av bioenergiproduksjon inkluderer å rekultivere tidligere dyrkamark, eller å konvertere forringet dyrkemark til bioenergiproduksjon hvor bioenergivekster kan bidra til å redusere degraderingsprosesser og gi miljøgevinster. Slike områder er til nå ikke tilstrekkelig kartlagt, ekspanderingspotensialet for bærekraftig vanning er uklart, og bioenergi- og klimavernpotensialer er ikke godt nok forstått. Her integrerer jeg flere modeller og datasett for å fastslå bærekraftige bioenergipotensialer, inkudert satellitbaserte landdata, vekstmodeller, og datasett på vanningsmuligheter. Avhandlingen presenterer den første høyoppløselige globale kartleggingen av tidligere dyrkamark og bioenergipotensialer på disse områdene. Den bidrar til å nøste opp de komplekse interaksjonene mellom bioenergipotensialer, arealbruk og vannbruk, tatt i betraktining muligheter for naturvern og tilgjengelige vannressurser. Gjennomførbarheten for å rekultiverere tidligere dyrkamark blir vurdert ved hjelp av indikatorer på lokalt utviklingspotensiale for bioenergiproduksjon. Forbedrede anslag av bioenergipotensialer blir produsert for den tidligere Sovietunionen, en region med mye historisk nedleggelse av dyrkamark over de siste tre tiårene og med store vanningsmulighter. Videre blir fokus også satt på mulgiheten for å introdusere bioenergivekster på dyrkamark som er truet av jorderosjon i et Nordisk case studie. Tilslutt kvantifiseres potensielle klimagevinster av å produsere biodrivstoff fra tidligere dyrkamark og på dyrkamark truet av jorderosjon, tatt i betraktning ulike bioraffineriteknologier og muligheten for karbonfangst og lagring (CCS). Jeg identifiserte 83 millioner hektar tidligere dyrkamark som ble nedlagt mellom 1992 og 2015. Bioenergipotensialer er 6-39 exajoule per år, eller 11-68% av dagens globale bioenergibruk, avhengig av landbruksdrift, naturvernstiltak og vanningsbruk. Det er et potensiale for å produsere 20 exajoule per år ved å øke globale landbruksarealer med 3% og globalt vannuttak for jordbruk med 8%, uten produksjon i hotspots for biologisk mangfold og uten vannuttak i områder med vannmangel. Regioner med både høye bioenergipotensialer og høy gjennomførbarhet for rekultivering inkluderer Mellom-Amerika, Sørøst-Asia, sørvestlige deler av Sør-Amerika, og sørøstlige deler av Nord-Amerika. Den tidligere Sovietunionen fremheves som en region med mye tidligere dyrkamark, høy marginal gevinst av vanning, og stort potensiale for vanningsekspansjon. Forbedrede estimater av bioenergipotensialer i den tidligere Sovietunionen er 3.5 til 23 exajoule per år, med høye potensialer avhengig av storstilt og ikke bærekraftig bruk av vanning. Et øvre potensial på 9 exajoule per år kan oppnås med bærekraftig vanning og innebærer å rekultivere 35 millioner hektar kombinert med 67 milliarder kubikkmeter blått vannuttak i den tidligere Sovietunionen. Produksjon av biodrivstoff på tidligere dyrkamark og på dyrkamark truet av jorderosjon i Norden kan oppnå en klimagevinst lik -7.4 til -18 megatonn karbondioksid-ekvivalenter per år, avhengig av bioraffineriteknologi og CCS bruk. Naturlig gjengroing kan gi negative utslipp lik -10 megatonn karbondioksid-ekvivalenter per år på de samme områdene. Høye avlinger er nøvendig for å sikre større klimagevinst ved produksjon av biodrivstoff enn naturlig gjengroing uten forbedringer i energikonverteringseffektivitet ved bioraffineriet eller CCS. Biodrivstoffproduksjon utkonkurrerer naturlig gjengroing på 61% av tidligere dyrkamark med dagens bioraffineriteknologi, og nesten overalt med CCS. For vindfang etablert med seljeproduksjon er forbedret energikonverteringseffektivitet eller CCS typisk nødvendig for å levere større klimagevinst enn naturlig gjengroing. Biodrivstoffsproduksjon er bedre enn naturlig gjengroing på 17% av jordbruksarealer truet av jorderosjon med dagens tilgjengelige bioraffineriteknologi, og på 95% av arealene med forbedret teknologi og CCS. Dette arbeidet viser at det finnes nåværende muligheter for en bærekraftig ekspansjon av bioenergiproduksjonssystemer på en stor nok skala til at det kan gi et meningsfult bidrag til globalt klimavern. Det må vurderes hvordan tilgjengelige land og vannressurser best kan forvaltes fra et bærekraftsperspektiv når gode strategier for bioenergiekspansjon skal designes. Uten tilstrekkelig forvaltning risikerer bioenergiproduksjon å negativt påvirke matsikkerhet og biologisk mangfold. Med god forvaltning vil bioenergiproduksjon bidra til å avkarbonisere energisystemet og levere ytterligere miljøgevinster gjennom reduserte degraderingsprosesser og forbedrede økosystemtjenester. Denne avhandlingen opplyser viktighten av bærekraftige arealbruksstrategier og vannforvaltning ved utplassering av storskala bioenergiproduksjon, og bidrar med nødvendig kunnskap i jakten på å nå globale bærekraftsmål.

The construction of public buildings, such as universities, museums, prisons or hospitals, creates value for society, but also comes at a cost. Limited public funds make it necessary to assure an optimal use of public resources. However, not all projects succeed with that, and complaints about a high cost level of public construction projects are numerous. Although academic research on construction project costs is abundant, the problem does not seem to have improved in practice. This PhD-project has followed a two-year strategic initiative, which a public building commissioner pursued to increase the cost-efficiency of their construction projects. Costefficiency means achieving the desired result of a project with minimal resources invested into the project. In addition to investigate cost-efficiency on a project level, the PhD-project also looked at cost-efficiency at an organizational and a strategic level. The research purpose was to investigate how to achieve lasting change towards higher cost-efficiency in public construction projects. Three research questions have guided the research: (1) Which actions do public construction projects take to achieve higher cost-efficiency? (2) How can knowledge transfer between the projects on cost-efficiency actions be increased? (3) How can we achieve lasting change towards more cost-efficient construction projects? The research has been conducted by a practitioner-researcher inside a public organization with an action research approach. Mainly qualitative methods have been used, augmented with quantitative data where necessary. This paper-based thesis consists of an introduction and a compilation of academic papers. Five papers form the main body of this thesis, each covering a different aspect of the main topic of achieving strategic change towards increased cost-efficiency in public construction projects. The first three papers address systematic completion, standardization, and stakeholder involvement as examples of actions for increasing cost-efficiency. The fourth paper on microlearning addresses the necessity of knowledge transfer on cost-efficiency and the fifth paper presents a meta-perspective looking at how the results of the strategic initiative are implemented in the organization. The research shows that many different actions for cost-efficiency are executed by the construction projects. Some of the actions, like standardization, are quantifiable and scalable. Especially actions in early project phases involving the user as an important stakeholder, result in a significantly positive effect on project costs. However, to profit from cost-efficiency not only at a single project level, but at a portfolio level, knowledge transfer on successful costefficiency actions between the project teams is necessary. Microlearning can be one of the tools to increase knowledge sharing. In addition, the results from the strategic initiative need to be implemented in the permanent organization to achieve lasting change. For the implementation, the Pentagon model with its five dimensions of structure, technologies, social relations and networks, interaction and culture can serve as a tool for the organization to increase organizational capabilities and performance on cost-efficiency. Creating cost-efficiency actions together with the construction project teams in meetings, was vital for involving the project teams in the change process. The practical contribution of this research is inherent to its action research approach, as the starting point was a practical problem to be solved. Through the research, the organization has gained important insight on how to increase cost-efficiency permanently on a portfolio level. This study answers the need for more practice-based research in project management by giving a rich empirical account of how change processes in organizations practically happen. Furthermore, the study extends the Pentagon model and applies it as a tool in a new field – the implementation of a strategic initiative in a project-based organization.

With the growing demand of global energy consumption and a need to reduce pollution caused by energy production from fossil fuels, renewable sources of energy are becoming increasingly necessary for the future sustainable development of our society. Wind energy offers an attractive option as one of the renewable sources, and a large body of work is currently ongoing to widen its implementation. This thesis seeks to contribute to this growing body through experimental investigations into how turbulent flows interact with wind turbines, both in part and in whole, and from that, gain insights into how the interactions impact their performance. The complex and turbulent environment of atmospheric boundary layers, in which wind turbines operate, presents an intriguing challenge. The work is divided into three main investigative topics: the spatial development of a turbulent boundary layer under decaying freestream turbulence, the effect of freestream turbulence on the performance of a wind turbine airfoil, and lastly, the near-field of a model wind turbine under turbulent shear flows. The first investigation examined how a turbulent boundary layer evolves in the streamwise direction under the influence of decaying freestream turbulence. The experiment was performed in the new water channel facility at the Norwegian University of Science and Technology. The objective was to gain insight into the physics of a representative background flow that can be expected for wind turbines. Laser Doppler velocimetry was used to characterize both the freestream turbulence and the boundary layer. The main finding is that the effects of decaying freestream turbulence on the properties of the turbulent boundary layer diminish as they coevolve downstream. This is reflected in both the behaviour of the wake region in the boundary layer, as well as the peak in the velocity fluctuations near the wall. The second set of experiments looked into how freestream turbulence affects the pressure and lift characteristics of a wind turbine airfoil. Pressure distributions are taken at different angles of attack and for different incoming turbulence intensities. It is found that increasing the freestream turbulence intensity generally increases the maximum lift for this airfoil, but it does not noticeably change the stall angle. Lift within the linear operating range also shows improvement with increasing turbulence intensity. However, for low turbulence intensities, a decrease in lift in the linear region is observed. Further analysis into the pressure fluctuation spectra near the trailing edge reveals the presence of periodic pressure fluctuations for these cases. Lastly, moving from the component to the system level, a model wind turbine was placed in different turbulent shear flows generated by an active grid. Particle image velocimetry was used to capture the near-field around the model. It was found that the near-wake velocity deficit can be decomposed into a velocity deficit profile caused by a uniform inflow plus the incoming shear profile. The combined profile shows higher shear gradient on the high-velocity side of the incoming shear flow, and this in turn leads to higher turbulence production and thus higher velocity fluctuations. The turbine power fluctuations were found to be proportional to turbulence intensity, regardless of the shear profile, and the kinetic energy available in the flow for downstream turbines was also found to be mainly dependent on the incoming turbulence intensity. Overall, this thesis examines the influence of turbulent flows on a wind turbine from the perspective of the background flow level, the component level, and lastly, the system level. The work provides new insights into how these three levels are affected by the presence of turbulence, and it is the hope of the author that it will contribute meaningfully to the field of wind energy and turbulence research, and become a building block upon which other works can be advanced upon.

Norway maintains a large network of ferries that provide connections across fjords and to islands without road access. Ferries provide accessibility but they also entail costs for the users and the operators involved, such as waiting time costs and labour costs, etc. In an economic sense, it is essential to provide an efficient production of services and select a level of service that yields the largest economic benefit, considering both the cost of users and operators of the service. Thus, both organizational reforms that may promote efficiency in the production and methods which enables assessment of economically optimal service levels are of interest. The literature on transport economics is scant with respect to ferries. In particular, the optimization of service levels does not consider the specific costs of users and operators in the ferry sector and is limited to a subset of the relevant decision variables. Further, the literature on organizational reforms to promote efficiency in the production of services, is scant when it comes to ferry operations. This thesis contains four papers that discuss the potential for improving the economic efficiency at car ferry crossings. Two main lines of enquiry are pursued. Firstly, the potential for increased effectiveness by use of Competitive Tendering (CT) is examined. An econometric study based on cost and operational data from Norwegian car ferry crossings is performed. Results show that CT may increase the operational efficiency, by reducing costs. However, the long-term impacts are unknown and should be considered in future work. Secondly, the potential for increased efficiency by selecting economically optimal service levels are investigated in three papers. Two of the papers develop methods to estimate user costs that are specific to ferry transportation. The aim is to develop tools that may be of use when selecting the optimal capacity and service levels of crossings. The methods are applied to case studies of Norwegian crossings. Results show, firstly, that too much capacity is offered and secondly, that the methods used to estimate user costs could be improved even further. One paper considers wider costs of operating a ferry service through accident costs. It considers whether altering the frequency of a car ferry service could affect the speed of motorists traveling to it. A theoretical model is developed, and a simulation study is performed. Results show that the effect is generally complex. However, it is established that increasing frequency from low levels may increase risky behaviour of motorists. The thesis recommends that empirical studies are performed, possibly using the theoretical model as an interpretative framework. The results from this thesis demonstrate that there is a potential for increasing the economic efficiency in the operation of car ferry crossings. It is argued that the largest benefit is most likely derived from optimizing service levels, and that the effects of organizational reforms (such as competitive tendering) may be limited. Further, it recommends that more effort is put into developing models of user costs associated with ferry operations, in particular those related to insufficient capacity and understanding the long-term effects of competitive tendering on cost efficiency.

The modified cam clay (MCC) model, deduced from the unified and comprehensive behavioural framework of critical state soil mechanics (CSSM), revolutionised the understanding of the mechanical behaviour of soil, particularly clay. Although it was originally energy-based, the MCC model could not stand against the critiques of modern thermodynamics. The laws of thermodynamics (widely considered to be true) summarise the properties of energy and the feasibility of its transformation from one form to another. Constitutive models with no thermodynamic validity cannot confidently be utilised as there is no guarantee against false generation/loss of energy. Soon after its presentation, the MCC model was given a thermodynamic description known today as hyperplasticity. The hyperplastic description lifted the unnecessary normality rule and led to a family of MCC-type models with versatile yield criteria and inelastic flow directions. In addition to the normality restriction, which results in extreme dilatancy for over-consolidated clays, the original MCC model suffers from several limitations. Perhaps, as pointed out by its founders, the most profound one can be the lack of the concept of time. In developing the MCC model, it is assumed that the state of the material does not spontaneously change with the march of time. Numerous attempts with the overwhelming use of the overstress viscoplastic theory as the vogue approach have been undertaken, but the thermodynamic consistency of most of them is under question. Moreover, no attempts with the hyperplasticty approach have rigorously addressed the issue of time-independency. This doctoral research contributes to understanding the thermodynamically-based hyperplasticity framework and its application in the constitutive modelling of soil, particularly the viscous behaviour of clay with an orientation toward the CSSM and the isotache viscosity. In this regard, hyperplasticity formalism is laid out after providing a review of the viscous behaviour of clay with a focus on the development of the isotache concept. Next, the MCC model is integrated with the concept of time, resulting in a classical critical state hyper-viscoplastic model with similarities to the soft soil creep model. The profound impact of Ziegler’s orthogonality condition, the backbone of the hyperplasticty approach, on the critical state envelope is realised, paving the way for generalising the developed classical hyper-viscoplastic model with isotache viscosity. It is demonstrated that the typical MCC plastic-free energy could not be considered for a rate-dependent system with a single internal variable. Otherwise, by imposing Ziegler’s orthogonality condition, the uniqueness of the critical state envelope, which is the useful paradigm of critical state soil mechanics, is lost under different loading rates. A versatile force potential or dissipation rate function is constructed that provides adjustability of the location of the critical state (Spacing Ratio) while securing a unique critical state friction envelope as the useful paradigm of the CSSM to have a unified description of the mechanical behaviour of soil. Non-associated inelastic flow as an essential property of particulate frictional materials is adopted via accommodating an effective pressure-dependent shear dissipative mechanism. This later distinction lifts the unnecessarily restrictive condition of normality invoked in the original overstress and consistency viscoplasticity theories. Moreover, different frictional criteria of Drucker-Prager, Mohr-Coulomb, and Matsuoka-Nakai have been considered, and their features in terms of friction mobilisation and inelastic flow direction are explored. By realising the homothetic functioning of isotache viscosity, an emphasis has been put on the delicate practice of the effective stress ratio tensor (the deviatoric stress tensor normalised by the effective pressure) as an essential state variable of frictional material to achieve all the features mentioned previously such as adjustability of the spacing ratio and non-associativity of inelastic flow with different frictional criteria while securing the uniqueness of critical state envelope. Lastly, the efficacy of the proposed hyper-viscoplastic constitutive model is evaluated by simulating sets of triaxial and true triaxial tests conducted on the Hong Kong Marine Deposit (HKMD) and the Fujinomori clay.

District heating (DH) systems, which can integrate various available heat sources, have proven to be an energy-efficient and environment-friendly way to satisfy buildings’ heating demands. However, with the transition from current energy systems to future sustainable energy solutions, the DH system, as an essential part of the energy systems, must undergo a generational transition to maintain its competitiveness compared with alternative heating technologies. As a result, the current DH systems are transitioning to the 4th and 5th generation DH systems. Developing intelligent control strategies to optimally operate the DH system is one of the crucial measures to realize the transition. Numerous studies have reported that intelligent control strategies can notably reduce energy use, mitigate greenhouse gas emissions and improve economic performance for heating systems. However, most of the existing DH systems still use rule-based control (RBC) strategies with limited energy-saving and cost-saving potential. This thesis, therefore, aimed to explore the intelligent control strategies for the existing DH by utilizing model predictive control (MPC) strategies. With a focus on the DH systems dedicated to Nordic climate conditions, this thesis investigated the implementation of MPC on both the demand and supply side of the DH system to improve the energy and economic performance of the system. To achieve this goal, a step-by-step simulation-based study, was conducted, driven by four research questions. Question 1: What is the economic boundary when using MPC to improve the economic performance of a DH system? Literature reviews and energy contract investigations revealed that generalized heating and electricity price models can be used as the basis for the economic boundary for the MPC schemes. The generalized heating price model included the load demand component (LDC) and the energy demand component (EDC), and the generalized electricity price model was made up of the power price and the grid rent. This economic boundary was incorporated into the objective functions of the MPC schemes based on their specific needs. Question 2: What is the system energy and economic performance when using MPC on the demand side of the DH systems? The research on the MPC application in a building space heating (SH) system was conducted to answer this question. The modelling method for a building SH system was proposed, and then an MPC scheme was formulated by defining an economic-related objective function and system constraints, as well as incorporating the developed SH system model and an optimization framework. Finally, this MPC scheme was evaluated by comparing its performance to that of a conventional RBC strategy. A case study on the SH system in a university building showed that the MPC scheme with perfect future weather information could cut the weekly heating cost by 4.1% and decrease the violation numbers of indoor temperature by 65% compared to an RBC strategy. However, these benefits may be impaired when the MPC scheme directly used weather forecast information. Since any prediction has some uncertainties and hence the MPC controller may receive inaccurate weather information, leading to incorrect control actions that may deteriorate the system performance. Therefore, the third research question was proposed as follows. Question 3: What is the impact of weather forecast uncertainty on MPC performance, and how to handle it? To answer the impact of weather forecast uncertainty on MPC performance, another MPC scenario that directly used weather forecast information was proposed. The simulation results showed that the MPC scheme directly using weather forecast information cut the heating cost by only 0.7% and even increased the violation numbers of indoor temperature by 20% compared to the RBC strategy. To tackle the weather forecast uncertainty, an error model was proposed to improve the quality of weather forecast information. Meanwhile, one more MPC scenario that incorporated weather forecast information and the error model was proposed. Results showed that introducing the error model for the MPC scheme was able to address the weather forecast uncertainty and hence achieve almost the full theoretical potential of the MPC in terms of heating cost-saving and indoor temperature control. The MPC scheme with weather forecast information and the error model cut the weekly heating cost by 3.4% and decreased the violation numbers of indoor temperature by 73% compared to the RBC strategy. Question 4: What is the system energy and economic performance when using MPC on the supply side of the DH systems with distributed sources? The research on the MPC application for a heat prosumer with data centre (DC) waste heat recovery and thermal energy storage (TES) was conducted to answer this question. The modelling method for a typical heat prosumer with DC waste heat and TES was proposed firstly, and then an MPC scheme was formulated by defining an economic-related objective function and system constraints, as well as incorporating the developed DH system model and an optimization framework. A case study on a campus DH system showed that the MPC scheme optimized the heat supply allocation between the multiple heat sources and the TES so that the economic performance of the DH system was improved. The MPC scheme was more stable and robust expressed as the smaller fluctuating ranges of the outlet temperature at the heat pump (HP) evaporator, which is crucial for the DC cooling system's safe operation. In addition, the MPC scheme made an optimized trade-off between the heat and electricity use to achieve the best economic performance of the heat prosumer, and the resulting monthly energy cost saving was up to 3.2%. In conclusion, this thesis provided a systematic research method on the implementation of MPC in DH systems with distributed sources from both the demand and supply sides. Meanwhile, the investigation of weather forecast uncertainty may facilitate the real application of the MPC in building energy systems. Lastly, this study may enrich the research on the intelligent control strategies for the DH system.

The main objective of this thesis is to investigate electrochromic nanofilms and ionic liquid ion conductors (electrolyte) to make electrochromic devices for electrochromic smart window development. Electrochromic film and ion conductor are two main parts in the structure of an electrochromic device. Tungsten oxide (WO3) nanofilms and ionic liquid ion conductors are prepared and characterized to make electrochromic devices for further electrochromic smart windows applications. WO3 is one of the most important and popular electrochromic materials for electrochromic smart window applications. Recent academic work has shown that nanostructured electrochromic materials have distinct advantages for high performance electrochromic device applications, including improved cycling stability, high coloration efficiency, and fast switching ability. Firstly, in this thesis, the main work relating to preparation, characterization, and application of WO3 electrochromic thin films for electrochromic smart window glass was described in Papers 1-4. Electrochromic WO3 thin films were prepared using a radio frequency (RF) sputtering method to form a transmittance switchable coating for application in electrochromic smart windows. The thickness of the WO3 film can be controlled and prepared at nanometer scale. The physical properties, including morphology and microstructures, of WO3 film samples were characterized using x-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared (FTIR) spectroscopy. The electrochromic properties of WO3 thin films were investigated using cyclic voltammetry (CV) analysis and ultraviolet-visible-near infrared (UV-VIS-NIR) spectroscopy. Experiments were performed with the aim of improving the electrochromic performance of as- prepared WO3 thin films. Effect of film thickness on the electrochromic performance of WO3 films was investigated. Subsequently, effect of the presence of oxygen on the sputtering process of WO3 films was investigated. The effect of heat treatment on WO3 coatings was also investigated. In addition, Paper 5, Paper 6 and Paper 7 represented fundamental research work on ionic liquids (ILs). The aim of the research was to select and screen suitable ILs as ion conductors (electrolyte) for electrochromic smart window development. ILs are types of salts, which are liquid at temperatures below 100 oC. There are also ILs with liquid state at room temperature, which are called room temperature ILs. They have many advantageous properties for utilization as electrolyte in electric devices and electrochromic devices. ILs utilized in this work are an extremely safe type of electrolyte since they are not water-sensitive or oxygen-sensitive, and when used in an electrical device they are not flammable. Therefore, there is no risk of explosion or fire associated with the use of ionic liquid (IL) based electrolytes. In this thesis, chemical and physical properties, such as density, viscosity, crystallization temperature, thermal stability, ionic conductivity, and electrochemical window of ionic liquid-based electrolytes were investigated for electrochromic smart windows applications. Paper 1 describes preparation and characterization of WO3 thin films with a thickness of 36 nm. Firstly, WO3 thin films were prepared using radio frequency (RF) sputtering method. Subsequently, electrochromic properties of as-prepared WO3 films were investigated using CV analysis and UV-VIS-NIR spectroscopy. At a scan rate of 20 mV/s, the color of the WO3 films changed at around -0.15 V and bleached at around +0.05 V. The WO3 films could be cycled for 200 times with the potential between -0.30 V and +0.30 V vs. Ag/AgCl reference electrode (3M KCl aqueous solution). The results of CV test and UV-VIS-NIR spectroscopy demonstrated that the transmittance of the WO3 film could be regulated by an adjustable external voltage (electric field). Paper 2 reported preparation and characterization of WO3 thin films with various thickness, including 36 nm, 72 nm, 108 nm and 180 nm, using sputtering method. Effect of film thickness on the structure and physical properties of WO3 films was investigated. Bleached WO3 films were pale gray, pale blue, lemon green or brown in color. Simultaneously, colored films had a blue color with different transmittance levels. Among the WO3 film samples with various thickness of 36 nm, 72 nm, 108 nm, and 180 nm, the largest transmittance modulation, ∆T550nm, was obtained from samples with a thickness of 108 nm, which was 66% when measured using 0.5 M H2SO4 as ion conductor. This showed that the transmittance value of colored samples decreased with the increasing of film thickness. However, in the bleached samples the transmittance was not influenced significantly by the thickness of the samples. To summarize, the prepared WO3 films with various thicknesses showed various colors. Paper 3 described preparation and characterization of WO3 thin films with thickness of 72 nm using RF sputtering method. In addition, the effect of oxygen during the sputtering process on WO3 film formation and effect of heat treatment on WO3 film were investigated. As shown in Paper 3, Sample D was prepared as follows. Firstly, a WO3 thin film was coated on the surface of a conductive indium tin oxide (ITO) glass using RF sputtering under O2 and argon atmosphere (volume ratio of O2 and argon is ca. 1:4). Subsequently, the obtained WO3 thin film was treated with heat flow. In the end, Sample D was obtained. The results showed that the coating of the film on the surface of Sample D was a crystalline WO3 film. Sample D had a transmittance value of 50.9%. It also had the best aging ability compared with the other films that were prepared. Sample D had the largest transmittance modulation value among the four samples. The results also showed that electrochromic performance of the WO3 sample films were improved in the presence of O2 during the RF sputtering process. Moreover, heat treatment might result in a transition of crystalline phase from amorphous to monoclinic of the sputtered WO3 thin films. Furthermore, aging durability showed a large improvement after the crystal transition. The crystal transition also resulted in an increased transmittance modulation value of WO3 thin film samples. Paper 4 presented the research work on electrochromic materials (ECMs) and electrochromic windows (ECWs). In order to show dynamic and flexible solar radiation ability, ECWs can be characterized by several different solar radiation glazing factors as follows: ultraviolet solar transmittance (Tuv), visible solar transmittance (Tvis), solar transmittance (Tsol), solar material protection factor (SMPF), solar skin protection factor (SSPF), external visible solar reflectance (Rvis,ext), internal visible solar reflectance (Rvis,int), solar reflectance (Rsol), solar absorbance (Asol), emissivity (e), solar factor (SF), and color rendering factor (CRF). Comparison of these important solar quantities for various ECM and ECW combinations and configurations enable the selection of the most appropriate ECM/ECW for specific electrochromic smart window and building applications. Paper 5 presented the investigations of thermal properties of ILs, including thermal conductivity and thermal diffusivity. The thermal properties were crucial and important to utilize ILs as ion conductors in electrochromic smart windows. Thermal conductivity of water and some pure ILs, including BmimBF4, BmimPF6, OmimCl, BmimFeCl4, and OmimFeCl4, was measured. It was found that thermal conductivity measurements of ILs using the hot disk method had high accuracy compared with the thermal conductivity measurement values of water, BmimBF4, and BmimPF6 as reported in the literature. Therefore, the hot disk method can be utilized for thermal conductivity measurement of ILs. In addition, the thermal diffusivity of pure ILs, including BmimBF4, BmimPF6, BmimFeCl4, OmimCl, and OmimFeCl4, was measured. The results showed that ILs resulted in less energy loss than water in energy storage. This also demonstrated that ILs have better performance than water based ion conductors in electrochromic smart windows due to less energy loss and consumption. Paper 6 investigated density, viscosity, heat capacity, decomposition temperature, ionic conductivity, and electrochemical window of IL based electrolytes (ion conductor). These physical and chemical properties of ILs are important when ILs are applied as electrolytes (ion conductor) in making electrochromic smart window and electric devices. Initially, density of ILs was measured using a density meter. Thereafter, viscosity of various ILs was investigated using a rheological method. In addition, crystalline temperature of various ILs samples was investigated using differential scanning calorimetry (DSC). Moreover, decomposition temperature of ILs was investigated using thermogravimetric analysis (TGA). Furthermore, ionic conductivity and electrochemical window of ILs samples were measured using electrochemical instruments. Paper 7 presented a pure ionic liquid of 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl4), which was synthesized and utilized as electrolyte (ion conductor) in this work. Chemical structure, physical and thermal stability properties, including density, viscosity, melting point and decomposition temperature, of BmimFeC14 were investigated. In addition, electrochemical properties of the prepared ILs, including electrochemical window and ionic conductivity, were investigated. Moreover, BmimFeCl4 is used as an electrolyte in an electric device, iron-ion battery, to investigate the performance of ILs ion conductor for reversible redox couple transformation in electrochemical reaction. The results showed that ILs have good electrochemical properties and can be further applied as ion conductors in electrochromic smart windows. The reason why BmimFeCl4 was utilized in this paper is that: (1) Easy to synthesize; (2) Not water or oxygen sensitive; (3) Low cost; (4) Non-flammable; (5) Good thermal, physical and chemical properties, including low melting point, high decomposition temperature, and low viscosity. BmimFeCl4 is not a perfect ion conductor for electrochromic devices because of the color of BmimFeC14. However, Due to the good properties of ILs, other transparent ILs with color will be further employed to produce electrochromic glass for electrochromic smart windows applications. “In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of [name of university or educational entity]’s products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink.

The world energy demand is rising with an increasing need for renewable and sustainable energy sources. Wind energy plays a key role in this transition. Urban areas are largely unexploited for wind energy extraction. Urban wind energy offers great potential as a decentralized renewable energy source. However, one of the main issues to date is a limited understanding of the urban wind resources. The flow in an urban environment is naturally sheared, as part of the atmospheric boundary layer, and in addition, highly turbulent, due to the many obstructions in the flow. This thesis aims to contribute to an improved understanding of the urban wind resources. Specifically, the performance and flow field of a roof-mounted vertical axis wind turbine is examined, as well as the interaction of freestream turbulence and a turbulent boundary layer. The thesis presents experimental work in which these problems are investigated on a lab-scale. Experiments are conducted in a wind tunnel and a water channel, enabling controlled flow conditions. Specific parameters in the flow, such as turbulence intensity and velocity shear, are deliberately varied using active grids. The flow is primarily evaluated with Particle Image Velocimetry and Laser Doppler Velocimetry, complemented by Constant Temperature Anemometry and surface pressure measurements. Two model buildings are placed in the flow, represented by surface-mounted cubes. A drag-driven vertical axis wind turbine of the Savonius type is positioned on the roof of the model buildings and its power output is measured. Both the streamwise position and the height of the turbine above the roof are varied, and the impact on the flow field and power output is assessed. In addition, the influence of varying wind directions and vertically sheared in flow on the turbine performance are examined. The influence of turbulence intensity is investigated fundamentally on the evolution of a turbulent boundary layer and on the flow around the model buildings. Again, the impact on the turbine's power output at various positions is evaluated. It is demonstrated that a turbulent boundary layer is not permanently matured ahead of its natural evolution by the presence of freestream turbulence and that the relative state of evolution of both the boundary layer and the freestream turbulence has to be considered when assessing the turbulent boundary layer. A key finding is the substantial impact of a roof-mounted wind turbine on the flow field and, thus, on the available power. This suggests that in contrast to common practice, including an actual turbine in the analysis is significant. A central high turbine position is found to maximize the power output for a uniform wind rose. However, for individual wind directions, the ideal turbine position and height vary. Turbulence intensity has a significant impact on the flow around the model buildings and consequently also on the power output of the turbine. High levels of turbulence intensity reduce flow separation on top of the building, resulting in higher velocities where the turbine is placed and, thus, higher power output. Conversely, velocity shear has only limited influence on the flow field and power output of the roof-mounted turbine. Overall, a methodology to assess a roof-mounted vertical axis wind turbine in a controlled environment was developed, examining the influence of various parameters, such as in flow conditions and turbine position.

Humanity is facing a global climate crisis induced by a growing population, carbonintensive lifestyles, and highly polluting production systems. Solving the climate crisis requires a profound transformation of our socio-economic metabolism (SEM), i.e. the physical system of anthropogenic stocks and flows of materials, energy, and greenhouse gas (GHG) emissions. The transformation of the SEM towards a carbon-neutral system requires climate change mitigation (CCM) measures. The implementation of CCM measures is driven by a constellation of different actors, i.e. the social system. Most research on CCM focuses on studying either the transformation of the physical or the social system. However, the two systems are highly interdependent and connected to each other. Therefore, the solutions need to address both systems. Most existing approaches to integrating the two systems focus on exploring the actors as objects, for example through agents in agent-based models. Such approaches are useful to include different actors' rationale; however, they are limited in (1) including participatory exercises and (2) triggering personal experiences. This limitation can be addressed by considering the actors as acting subjects. In this thesis, we propose the use of SEM-based simulation games (SGs) in order to integrate the two systems and to explore the actors' perspectives through acting subjects. Furthermore, SEM-based SGs allow us to tackle another challenge of CCM research, namely its limited accessibility to wider audiences. Studies on CCM are typically targeted at policy-makers, industry representatives, and researchers, by means of scientific articles, reports, and oral presentations. By using SGs, we can use more playful and interactive means to address target groups such as the general public. In this thesis, we exemplify the link between SGs and SEM models with a case study, the postfossilCities SG, which contains a SEM model of the Swiss economy. The postfossilCities SG was developed in the frame of the Post-Fossil cities project. In SEM models, the physical system is typically modeled through technology- and lifestyle- based parameters. Examples of technology-based parameters are energy intensity, energy carriers, and systems efficiency, whereas lifestyle-based parameters include stocks per capita, user behavior, and intensity of use. Despite the use of these two types of parameters, SEM studies on CCM have largely focused on exploring technology-driven measures, and thus on refining the modeling of such measures through technology-based parameters. This leaves (i) untapped potential for further CCM through lifestyle-driven measures and (ii) unexplored synergies across technological developments and lifestyle changes. In this thesis, we explore and refine the modeling of both types of measures by developing two sectoral SEM models for the Swiss residential building stock and the Swiss passenger car stock. The sectoral models served as the basis for modeling and refining the Swiss economy-wide SEM model used in the postfossilCities SG. The results of the sectoral models show that technology-driven measures are highly effective in lowering emissions and can transform the physical system into a carbonneutral system. In particular, we found that the Swiss residential building sector can reach carbon neutrality in 2050 by (i) an extension of the current buildings program (i.e.lower energy intensity of buildings and increase use of renewable energies) and (ii) a complete replacement of fossil fuel heaters with heat pumps and solar energy by 2050. For the passenger car sector, the results show that carbon-neutrality can be achieved in 2050 through a full and rapid electrification of the car fleet, i.e. phase out sales of gasoline- and diesel-cars by 2025 and hybrid and plug-in hybrid cars by 2030. While technology-driven measures are highly effective at reducing emissions, they are limited in lowering energy consumption, and thus CCM strategies solely based on technology- driven measures can result in missing some of the energy-related goals. For example, in the residential building sector, we found that the 2000-Watt Society target can only be achieved by combining technology- and lifestyle-driven measures, which include (i) lower average indoor temperatures, i.e. from 22°C to 20°C, (ii) a reduction in heated surface areas, and (iii) a reduction in floor area per capita. For passenger cars, the results show that the lowest energy consumption is provided by a combination of technology- and lifestyle-driven measures, which includes a widespread use of ridesharing and autonomous cars (ACs). In contrast, the penetration of ACs without ridesharing is expected to trigger the highest energy consumption in 2050. Consequently, lifestyle-driven measures are highly effective in reducing energy consumption and in preventing an increase in energy demand from emerging technologies, such as ACs. Additionally, the results of the sectoral models indicate that the full mitigation effect of technology-driven measures can be severely delayed by the time it takes to replace the existing (technology) stock, while lifestyle-driven measure have an immediate impact on the entire stock. As a consequence, a longer delay in the implementation of technology-driven measures would require more drastic lifestyle-driven measures based on "old" technologies to reach the climate goals by 2050. Through the development of the postfossilCities SG, we found that SEM-based SGs can be used to integrate physical and social systems in a novel manner. In this integration, the physical system is described through a SEM model and the social system through (1) a role-play, (2) role-strengths models to quantify the success of each role, and (3) other game mechanics. Furthermore, we identified several benefits of linking SEM models and SGs: (1) the communication and understanding of complex systems through experiential and emotional learning, (2) the use of oral, written, non-verbal, and visual communication through activities and processes such as reading, writing, discussing, and doing, which are usually more appealing and intuitive for the general public, and (3) the increased robustness of SGs through mass- and energy-balance consistent representations of physical systems. However, we also found challenges in linking SEM models and SGs: (1) the integration of approaches from different disciplines, (2) the highly resource-intensive nature of the game development process, and (3) the identification of the right balance between simplification and complexity. Some of these challenges can be addressed by considering them early in the planning process of the project. Further research can support the refinement of SEM models and SEM-based SGs. For SEM models, future efforts should focus on refining the link between sectors through material, energy, and GHG emissions flows, which requires a better understanding of the dependencies and dynamics across sectors. An example of such dependencies is observed between stocks (e.g. building stock or car fleet) and material industries, as the stock size and the stock dynamics drive material demand. Therefore, the refinement of the links across sectors will allow for a more comprehensive evaluation of the direct and indirect emissions associated with CCM measures. This refinement can also provide a solid basis for improving the modeling of lifestyle-driven measures, and thus for understanding the (systemic) effects of behavioral change. For the SEM-based SG, further developments can exploit the rapid evolution of the SGs field through the use of new technologies, such as virtual reality, augmented reality, or real location-based features. By doing so, SGs can make the game experience highly engaging and motivating, and increase the outreach of CCM strategies to wide audiences with no prior knowledge of the topic.

The demand for oil and gas from the maturing Norwegian continental shelf (NCS) remains high. Even though the concern for climate change is shifting energy production towards renewables, production on the NCS is expected to continue for decades to come. If carbon capture and storage is managed and combined with technologies, such as conversion from hydrocarbon to hydrogen, production could be extended even further. Wet gas compression, especially for subsea installations, is a promising technology for both new and existing fields. It can enable the tie-in of remote reservoirs to the existing infrastructure and allow for simplified process solutions thus possibly reducing both investment and operational costs. Furthermore, by locating compressor stations near the subsea well head increased recovery can be achieved because the well can be produced at a lower pressure compared to topside compression. A prerequisite for the successful installation of subsea wet gas compression is exceptionally reliable solutions, due to the excessive cost of any intervention. It is thus necessary to increase knowledge on key aspects of the system, such as rotor dynamics, transient behaviour, performance and fouling. The focus of this thesis has been to investigate how wet gas affects the performance of centrifugal compressors, how performance parameters should be established and to investigate if models can be built that allow for correction between different wet operating conditions. Experimental results were partly obtained from the test rig at the Norwegian University of Science and Technology (NTNU) and partly from Equinor’s test facility at K-Lab. The NTNU open-loop test rig has a single impeller centrifugal compressor and runs on water and air under ambient conditions. Equinor’s test facility at K-Lab has two full-scale test loops that operate at high pressures and temperatures and utilize mixtures of hydrocarbon gas, condensate and water. As regards wet gas compressors, there is currently limited knowledge on how the performance will shift for changing inlet conditions. Therefore, the vendors are unable to estimate performance for a specific wet inlet condition a priori. Furthermore, no international standard has been established that specifies how to evaluate wet performance. Indeed, much work is required to sufficiently describe the performance and test procedure for wet gas performance. The current work aims to illuminate key areas of wet gas performance for the design, test, and operational phases. When it comes to the design and testing of wet gas compressors, it is not clear how to compare results between different operating conditions, such as test and real operation. This problem was analysed first by reviewing the dry gas similarity theory and then expanding these concepts to include wet gas. Finally, the appropriateness of such expansion from dry to wet gas was discussed. This work documents that Type2 testing (large difference between test and specified condition) can be difficult to achieve for wet gas compressors. A two-impeller wet gas centrifugal compressor was tested at K-Lab. The performance test results were analysed and key factors affecting performance parameters were identified. Furthermore, a model for wet gas performance based on these parameters was created. The method used to address this issue was a combination of regression and minimization of an objective function. The proposed model showed the capability of collecting the data points obtained under different operating conditions onto a “performance surface” with good precision. Limited knowledge exists about how uncertainties propagate through a complex wet gas test loop, such as the VGII loop at K-Lab, and eventually result in uncertainties of wet gas performance parameters in general. To address this issue the Monte Carlo method was used in combination with a sensitivity analysis. In this way, the uncertainties could be propagated through the entire system. Thus, standard uncertainties and coverage intervals for the performance parameters could be established, as well as the identification of key input parameters that affect these uncertainties. Somewhat elevated uncertainties were found for the wet compared to dry conditions, but still within reasonable limits. Furthermore, many of the performance parameters are highly sensitive to inlet and discharge temperature, especially those relying on enthalpies. By including a torque meter and a gas density meter in the wet gas test facility, these uncertainties could be significantly reduced. The detrimental effect of fouling on wet gas compressor performance was observed during testing at K-Lab. To further investigate this effect, a fouling test under controlled conditions was conducted at NTNU. The experimental results show that wet performance characteristics are heavily affected by flow path fouling. Furthermore, to quantify how the wet performance is affected by the fouling, a model was developed to correct all the efficiency curves to the dry clean curve. The model was able to collect the spread between clean and fouled curves for the same GMF.

Throughout its existence, humankind invented countless means and practices to design, construct and equip buildings. The number of ways to use these buildings, with or without strictly following their initially intended purpose, is even more significant. The historical and the anticipated future evolution of buildings at a varying pace further amplifies their diversity. An already complex phenomenon of building energy use is hence further entangled. Substantial variations also stem from you, my reader, whose lifestyle and occupancy patterns often cause a logical nightmare for the energy analysts like myself. These are some of the challenges in large-scale building energy research. This discipline intends to mediate the transition to a more sustainable built environment with the associated energy supply systems. Since the discipline's inception, the inherent modelling practices follow either a bottom-up or top-down approach. These two seemingly incompatible paradigms not only address the subject matter in a radically distinct manner but differ substantially in their accuracy, sensitivity, transferability, versatility, computability and usability. So far, both approaches have been used independently, concerned with leveraging their advantages and, generally, overlooking the limitations of one or another. It was, however, expected that the best interests of practice and policymaking necessitate a synergy or a combination of approaches rather than their application individually. Seeking ways to complement bottom-up and top-down approaches laid the foundation for the thesis you are holding. The analysis of modelling purposes, targeted system's complexities, model's characteristics and the associated uncertainties were expected to provide meaningful answers. It was also understood that, under the discipline's quest for accurate prediction, explanatory modelling had been largely overlooked. Formulating and testing the causal theories can improve the understanding of building energy performance, the means to mediate it and aid with developing better predictive models. Therefore, examining the interplay of explanatory and predictive modelling, bottom-up and top-down, is another objective of this thesis. It does so through: i) four research papers that attempt to answer why and to which extent the phenomenon varies beyond its best estimates; ii) a case study that exemplifies and examines the conformity of the modelling results obtained with bottom-up and top-down reasoning. These involve a collection of instruments from detailed building energy performance simulation, known as white-box methods, and their cousins of somewhat darker shades. The latter, in this work, consists of the methods of probabilistic programming that involve statistical hypothesis testing, univariate density estimation and Monte-Carlo simulation. The methods of combinatorial analysis and numerical optimisation are applied when necessary. The modelling principles consider numerous building types, design characteristics, energy supply solutions, occupancy-related tendencies and geopolitical contexts. The findings are based on and supported by experimental data, which is, together with the essential analytical instruments, made available in Built Stock Explorer (https://buildingstockexplorer.indecol.no/). To a large extent, this research software enables reproducing/replicating our results, should you be curious about doing that. The Explorer is written in Python, a lingua franca of today's scientific computing, and evolves to facilitate an interactive built stock energy analysis and the relevant (statistical) modelling. It is shown in this study that numerically similar built stock energy model results are achievable with either bottom-up or top-down model design. Mutual verification of the model performance in such a way can elevate the confidence of the decision making based on them. Furthermore, to prevent misleading urban developments suggested by poorly performing models. Given the importance of mediating building energy efficiency at all levels of governance, mutual verification of built stock energy modes is advocated as the means for more effective and timely achievement of energy and environmental targets. The complexities, diversity, scale and dynamics associated with building energy use at the built stock level motivate model parsimony. Explanatory modelling may inform more rational and better performing predictive model design. Also, explanatory modelling practices are expected to find applications in discovering new causal relationships, empirically validating the existing knowledge and monitoring the evolution of building energy performance at a scale. Better awareness about the phenomenon and better performance of the models at predicting it further elevate the demand for empirical data quantity and quality. This thesis advocates robust study design, data accessibility, and transparency to address the latter. Therefore, this academic work contributes to the body of knowledge available in large-scale building energy research by focusing on and articulating the need for synthesis between various modelling practices instead of further diverging them. To the best interest of the discipline and the objectives it pursues.

River management decisions must be based on the best knowledge available. But acquiring information on river conditions and translating it into sufficient mitigation measures can be both time- and resource demanding. Remote sensing data can be an important source of information on the current state of rivers, and may also be used in scenario assessments of future river conditions. This PhD-study has focused on the use of remote sensing data as a source of information on bathymetry, seasonal mesohabitats for fish, scenarios of mitigation measures, and strategies on environmental eDNA sampling. Each of these four information elements are often central parts in river assessments. The results from the PhD-study are presented in four scientific papers and include remote sensing data from green and red LIDAR, multispectral satellite imagery and aerial photos collected and applied in four Norwegian rivers. For the assessment of seasonal mesohabitats for fish, two remote sensing technologies were used: LIDAR and aerial photos. The LIDAR data enabled a 10x10 cm resolution bathymetry used as input to a 2D hydraulic model for the simulation of hydraulic heterogeneity. The aerial photos were used as both a source of calibration data and for assessing spatial heterogeneity along the river banks. The results show that both spatial heterogeneity and hydraulic heterogeneity are significant mesoscale habitat characteristics for European Grayling during its spawning period. No significant relationships were found on spatial and hydraulic heterogeneity for brown trout, emphasising the need for species-specific assessments in terms of mesoscale habitat characteristics. While LIDAR data may be a source of high-resolution bathymetry, collecting and processing LIDAR data can be costly and time consuming. An alternative remote sensing data source for river assessments is multispectral imagery or (the previously mentioned) aerial photos. The application of multispectral imagery from two satellite platforms and aerial photos for mapping of bathymetry by linear models was tested in four rivers within the same geographical region. LIDAR and SONAR data was used in the study for establishing linear image-to-depth models and for verifying the modelled bathymetry. Platform-specific regional models were then established and tested by combining intercept and slope coefficients from the linear models in the four rivers. The results showed that while the final quality of platform-specific regional model bathymetry did not fully match the quality of LIDAR-based bathymetry, overall model performance was adequate for depth calculations. For Worldview-2 images and aerial photos, coefficients of determination (R2) were in the 0.52-0.82 and 0.73-0.91 range, respectively. By adjusting the regional models with estimated local depth and a brightness factor, results on depth calculations improved slightly when compared to the LIDAR-based bathymetry, with coefficients of determination in the 0.47-0.84 and 0.71- 0.91 range, respectively. Point cloud format LIDAR data can easily be modified e.g., for use in assessment of different mitigation measure scenarios. Modified LIDAR data was tested in a public preference study on scenarios for mitigation measures related to weir adjustments and changes in flow-dependent water covered areas in weir basins. The study was conducted in a bypass section (i.e., a river section with water withdrawal) with a 65-70% reduction in yearly discharge due to hydropower production. Findings from the study show that LIDAR data are highly useful for scenario-based adjustments and modelling of weirs. As the potential dry/wet interface at or around the weirs can be hydraulically complex, these locations may require high-density mapping using a combination of red and green LIDAR. Results from the study also include a structured and standardized framework for public preference assessments in rivers which includes the potential use of remote sensing data as input to mitigation measure scenarios. A successful green LIDAR scan depends on a range of factors e.g., the technology applied in the scan process, signal pathway length and disturbances, river conditions and post-processing capabilities. Failure to address each of these factors when applying LIDAR may result in inadequate point cloud classification or coverage. In a study of strategic environmental eDNA sampling for biomonitoring in a river dominated by weirs and flow alteration, a regional adjusted image-to-depth model was applied on remote sensing imagery for river sections where two consecutive LIDAR scans returned inadequate coverage of bathymetry. Results on simulated depths and velocities adequately matched corresponding in-situ measurements of the same variables. Results from generalized mixed models testing the effect of spatial and abiotic variables on sample eDNA concentrations showed that sample location habitat type and season significantly affected eDNA concentrations of brown trout and minnow. Furthermore, weirs were found to be barriers for the dispersion of eDNA during autumn, while no significant effects of weirs were found during spring.

Produced water from oil and gas industry poses an immense threat to the environment due to its substantial volume and complicated composition. Membrane filtrations especially with ceramic membranes can effectively remove emulsified oil and suspended solids and meet the requirements for discharge or reinjection. However, membrane fouling is severe in the treatment of produced water and is the largest obstacle to the wide application of membrane technology. Physical cleaning can mitigate membrane fouling, reduce the frequency of chemical cleaning, thus prolong membrane lifetime, and reduce operational costs. Backpulsing is a promising physical cleaning method, which is induced by periodically reversing the transmembrane pressure (TMP) for a very short duration (typically less than 1 s). It has a transient effect that can effectively mitigate membrane fouling. In this doctoral work, backpulsing technology applied in microfiltration (MF) and ultrafiltration (UF) processes was reviewed while the experimental rig was built up in the lab. After the setup was finished, commissioned, and optimized, various experiments were carried out to investigate the significance of backpulsing parameters and their interactions on backpulsing efficiency, membrane fouling situations in the filtration of different types of produced water, and fouling mitigation by backpulsing compared with backwashing. The backpulsing review addresses the fundamentals of backpulsing, applications of backpulsing in different fields and results of pilot- and commercial-scale operations. Factors affecting backpulsing efficiency are illustrated, including feed properties, membrane properties and operating parameters. Mathematical models of backpulsing are overviewed, which could predict membrane productivity or provide a perspective to evaluate backpulsing performance in fouling mitigation. Finally, the existing challenges and outlook are discussed. Experiments using with a 2^3 full factorial design were carried out to investigate the effect of backpulsing parameters (amplitude, duration and frequency) and their interactions on membrane performance. Results based on Al2O3 membranes show that backpulsing was efficient to mitigate membrane fouling. However, the cleaning efficiency varied between different backpulsing conditions. Amplitude was the most crucial variable for fouling removal and final specific flux, while frequency was the most significant one for membrane net yield. Further experiments were conducted to find the optimum backpulsing frequency at a sufficient amplitude (0.5 bar) and a moderate duration (0.6 s). Ceramic membranes with three types of selective layers (TiO2, Al2O3 and ZrO2) were tested. For the same type of feed water and under the same filtration conditions, the optimal backpulsing frequencies of the three membranes were in a range of 11 – 15 s. A backpulsing frequency of 12 s was selected for the later backpulsing experiments. Later, ten types of produced water, including two based on treated real produced water, were used in the crossflow microfiltration with the three ceramic membranes mentioned above. Pure fouling experiments were carried out without any cleaning. Fouling behavior due to different compositions of produced water was investigated. Moreover, four out of the ten types of produced water were selected for longer experiments to compare the efficiency of fouling mitigation by backpulsing and backwashing. Backpulsing was in general much better than backwashing in terms of the net yield during the 12 h filtrations. Nevertheless, the trend of flux recovery after each backpulse/backwash was not always backpulsing better than backwashing. The flux recovery was depended on the fouling situation in each specific case. ZrO2 membrane showed the best performance in the three membranes, which was in accordance with that ZrO2 membrane had the narrowest membrane pore size distribution.

Hydro-abrasive erosion in turbine components is one of the prominent operational challenges for hydropower plants located across basins of regions such as Himalayas in Asia, the Andes in South America, and Pacific coast. Large sediment concentration with higher percentage of hard minerals such as quartz and feldspar affect exposed hydromechanical components which can cause significant erosion resulting reduced efficiency over time, huge operation, and maintenance cost along with undesired shutdown causing loss of valuable energy generation. In case of Francis turbines, erosion is mostly observed around stay vanes, guide vanes, facing plates and runner blades. Quantity and pattern of erosion depends upon the operating conditions, amount, and size of sand particles in the flow along with type of flow phenomena in particular regions. This study has conducted case study on the sediment erosion problems in one of the hydropower plants located in India that has collaboration with the project. Field reports from the power plant showed abundance of quartz particles contained in the water. A numerical analysis is conducted for turbine components in order to study the causes of various erosion patterns in the turbine components. The results from the CFD are compared with the actual erosion in the turbines. Leakage flow through the clearance gaps of guide vanes is found to be the primary cause of erosion at the inlet of the runner blades. This work comprehends a systematic investigation of spatial temporal progression of leakage vortex (LV) for varying operating conditions. The progression of LV at hub area is roughly classified into three forms i.e., elongation stage, disintegration stage and dissolving stage. Whereas few LV at the shroud area is found to pass through outlet of the runner, majority of it dissolves before reaching the mid-stream of the blade. Study was also conducted to find the optimal runner design with a trade-off between performance and erosion behavior by modifying blade angle distribution from inlet to outlet. Varying blade angle distribution changes the blade profile which also seemed to yield a better reduction in erosion. This study has identified research gap as the investigation of flow pattern in sidewall gaps in Francis turbines which refers to the clearance region between the stationary and rotary components. For hydro-turbines operating in sediment laden water, sediment will pass through these gaps and erode the parent material. Due to continuous effects of abrasion and erosion, these side wall clearance region increases and consequently the leakages through these gaps. The work focusses on the study of flow behavior in those regions with an experimental setup. Experiments were conducted in Rotating Disc Apparatus (RDA), which utilizes the method of rotating test specimen in a mixture of calculated amount of sand and water. It has a base plate which mounts test specimens that is attached to the shaft connected to the motor. First set of test specimens constitute three different slot width and another set has six different slot height. All experiments were carried out at Turbine Testing Laboratory, Kathmandu University, Nepal. Results for different slot width show its positive correlation with the rotational speed and erosion loss. It shows that as rotational speed increases, the shift of erosion wear is more towards the higher width slot. Another set of results including specimens with different height shows the increase in erosion rate with the corresponding increase in slot height. It is observed that, fluid flowing from the outlet of the guide vanes hits the side wall of the rotor component normally at positive slot height. Some particles recirculate in the slot width and again impinges the opposite side walls. Whereas in the case of negative slot, the direct impingement of sediment particle to the opposite face does not happen. However, during the flow re-circulation, the sediment again hits back to the guide vane face. For the specimen with height difference, weight loss in nearly constant at lowest rotational speeds. Erosion rate is observed increasing linearly up to zero height difference, but it increases significantly at the positive height difference. Sidewall gaps and flow in such regions is inevitable in hydraulic machineries. Further investigation on the shape of slot and erosion around labyrinth rings should be done to get a complete picture of erosion phenomenon. Flow phenomenon associated with sidewall gaps should be well considered and alalyzed during the preliminary phase of machine design.