Thesis (doctoral)--Rijksuniversiteit te Groningen, 1995. / Summary in Dutch. Material type: Dissertations. Includes bibliographical references (p. 283-291).

Demand for high data rates is increasing rapidly for the future wireless generations, due to the requirement ofubiquitous coverage for wireless broadband services. More base stations are needed to deliver these services, in order tocope with the increased capacity demand and inherent unreliable nature of wireless medium. However, this would directly correspond to high infrastructure costand energy consumption in cellular networks. Nowadays, high power consumption in the network is becoming a matter of concern for the operators,both from environmental and economic point of view. Cooperative communications, which is regarded as a virtual multi-input-multi-output (MIMO) channel, can be very efficient in combating fading multi-path channels and improve coverage with low complexity and cost. With its distributed structure, cooperativecommunications can also contribute to the energy efficiency of wireless systems and green radio communications of the future. Using networkcoding at the top of cooperative communication, utilizes the network resources more efficiently. Here we look at the case of large scale use of low cost relays as a way of making the links reliable, that directly corresponds to reductionin transmission power at the nodes. A lot of research work has focused on highlighting the gains achieved by using network codingin cooperative transmissions. However, there are certain areas that are not fully explored yet. For instance, the kind of detectionscheme used at the receiver and its impact on the link performance has not been addressed.The thesis looks at the performancecomparison of different detection schemes and also proposes how to group users at the relay to ensure mutual benefit for the cooperating users.Using constellation selection at the nodes, the augmented space formed at the receiver is exploited for making the links more reliable. Thenetwork and the channel coding schemes are represented as a single product code, that allows us to exploit the redundancy present in theseschemes efficiently and powerful coding schemes can also be designed to improve the link performance. Heterogeneous network deployments and adaptive power management has been used in order to reduce the overall energy consumption in acellular network. However, the distributed structure of nodes deployed in the network, is not exploited in this regard. Here we have highlightedthe significance of cooperative relaying schemes in reducing the overall energy consumption in a cellular network.  The role of differenttransmission and adaptive resource allocation strategies in downlink scenarios have been investigated in this regard.It has been observed that the adaptive relaying schemes can significantly reduce the total energy consumption as compared to the conventionalrelaying schemes. Moreover, network coding in these adaptive relaying schemes, helps in minimizing the energy consumption further.The balance between the number of base stations and the relays that minimizes the energy consumption, for each relaying scheme is also investigated. / QC 20120124

The thesis is focussed on low consistency (LC) refining of mechanical pulp. Theresearch included evaluations of energy efficiency, development of pulpproperties, the influence of fibre concentration on LC refining and effects of rotorposition in a two-zoned LC refiner. Trials were made in mill scale in a modern TMP line equipped with an MSDImpressafiner for chip pre-treatment, double disc (DD) first stage refining and aprototype 72-inch TwinFlo LC refiner in the second stage. Tensile index increasedby 8 Nm/g and fibre length was reduced by 10 % in LC refining at 140 kWh/adtgross specific refining energy and specific edge load 1.0 J/m. Specific lightscattering coefficient did not develop significantly over the LC refiner. The above mentioned TMP line was compared with a two stage single disc highconsistency Twin 60 refiner line. The purpose was to evaluate specific energyconsumption and pulp properties. The two different process solutions were testedin mill scale, running similar Norway spruce wood supply. At the same tensileindex and freeness, the specific energy consumption was 400 kWh/adt lower in theDD-LC concept compared with the SD-SD system. Pulp characteristics of the tworefining concepts were compared at tensile index 47 Nm/g. Fibre length was lowerafter DD-LC refining than after SD-SD refining. Specific light scattering coefficientwas higher and shive content much lower for DD-LC pulp. The effects of sulphite chip pre-treatment on second stage LC refining were alsoevaluated. No apparent differences in fibre properties after LC refining werenoticed between treated and untreated pulps. Sulphite chip pre-treatment iniiicombination with LC refining in second stage, yielded a pulp without screeningand reject refining with tensile index and shives content that were similar to nonpre-treated final pulp after screening and reject refining. A pilot scale study was performed to investigate the influence of fibreconcentration on pulp properties in LC refining of mechanical pulps. MarketCTMP was utilised in all trials and fibre concentrations were controlled by meansof adjustments of the pulp consistency and by screen fractionation of the pulp. Inaddition, various refiner parameters were studied, such as no-load, gap and baredge length. Pulp with the highest fibre concentration supported a larger refinergap than pulp with low fibre concentration at a given gross power input. Fibreshortening was lower and tensile index increase was higher for long fibre enrichedpulp. The results from this study support the interesting concept of combiningmain line LC refining and screening, where screen reject is recycled to the LCrefiner inlet. It has been observed that the rotor in two-zoned refiners is not always centred,even though pulp flow rate is equal in both refining zones. This leads to unequalplate gaps, which renders unevenly refined pulp. Trials were performed in millscale, using the 72-inch TwinFlo, to investigate differences in pulp properties androtor positions by means of altering the pressure difference between the refiningzones. In order to produce homogenous pulp, it was found that uneven plate gapscan be compensated for in LC refiners with dual refining zones. Results from thedifferent flow rate adjustments indicated that the control setting with similar plategap gave the most homogenous pulp.

The impact of window area on the energy balance of a building was investigated by simulations in DEROB-LTH. The glazed area was varied in three types of buildings with different types of glazing and for several climates. One low energy house was compared to a less insulated house but identical in size and layout. Three different types of glazing were used; uncoated double glazing, double glazing with one low-e coated pane and triple glazing with two low-e coated panes. Climates with variations in solar radiation, mean temperature, altitude and latitude were chosen. The results show that if energy efficient window alternatives are chosen the flexibility of choosing the glazed area and orientation is higher. Choosing a larger area facing south resulted in a higher heating demand for uncoated double glazing in the standard house. An increased area also resulted in an increased peak load for heating for all the simulated cases. Choosing the energy efficient glazing type gave a decrease in heating demand for increased south facing glazed area in the standard house. In the low energy house the difference in heating demand between different areas was smaller than for the standard house. An office module with two types of switchable glazing and one solar control glazing unit was used in three different climates; Stockholm, Brussels and Rome. Larger window areas increase the cooling demand but if glazing types with lower solar transmittance are used, the difference in cooling demand between different window areas decreases. An extremely large window area, however, increases the peak load both for cooling and for heating and should therefore be avoided. Energy can be saved by using switchable windows instead of solar control or in particular standard glazing.

The energy issue is presently in focus worldwide. This is not only due to increasing environmental concern regarding energy related emissions, but also due to the trend of increasing energy prices. Energy usage in the industrial sector in Sweden today represents about one third of the national energy use. A substantial part of that is related to support processes such as heating, ventilation and cooling systems. These systems are important as they are related both to energy cost and indoor climate management as well as to the health of the occupants. The purpose of this thesis is to reach a more comprehensive view on industrial energy efficiency and indoor environment issues related to industrial ventilation. This has been studied in three themes where the first part addresses barriers to energy efficiency in Swedish industries, the second theme discuss simulation as decision support, and the third studies the variable air volume system in industrial facilities. In the first theme three different studies were made: the first studies non-energy intensive companies in Oskarshamn in Sweden, the second studies the energy intensive foundry industry and the third study was part of an evaluation of a large energy efficiency program called Project Highland. These studies had several findings in common, such as the importance of a strategic view on the energy issue and the presence of a person with real ambition with power over investment decisions related to energy issues at the company. The studies also show that several information related barriers are important for decision makers at the studied companies. This shows that information related barriers are one reason in why energy efficient equipment is not implemented. In the second theme the use of simulation in the form of Computational Fluid Dynamics (CFD) and Building Energy Simulation (BES) are used as decision support for industrial ventilation related studies at two different industries, one foundry is investigated and one dairy. BES has mainly been used to simulate energy and power related parameters while CFD was used to give a detailed description of the indoor and product environment. Together these methods can be used to better evaluate the energy, indoor and product environment and thus enable the implementation of more efficient heating, ventilation and air-conditioning systems. In the third theme the use of Variable Air Volume (VAV) systems was evaluated, and was found to be an efficient way to reduce energy use at the studied sites. At the studied foundry the VAV system is predicted to reduce space heating and electricity use by fans by about 30%, and in the dairy case by about 60% for space heating and 20% for electricity.

Industrial energy efficiency is one of the most important means of reducing the threat of increased global warming. A higheruse of electricity than their European competitors, together with increased energy costs due to increasing energy prices in Swedish industry have negative impacts on results and competitiveness. Of great importance are thus different means which promote energy efficiency such as industrial energy policy instruments. However, cost-effective energy efficiency measuresare not always undertaken. In order to formulate and adopt accurate industrial energy end-use polices, it is thus of importanceto identify the barriers that inhibit the implementation of cost-effective energy efficiency measures. It is also of importance to identify the factors which promote the implementation. The aim of this thesis is to analyze industrial energy systems andmore specifically study factors that promote or inhibit energy end-use efficiency in Swedish industrial companies. Results from this thesis show that the implementation of technical energy efficiency measures is a major means for both energy-intensive and non-energy-intensive Swedish companies to overcome the threat of rising energy prices, for example for electricity. While energy efficiency measures in the non-energy-intensive industry are related mainly to support processes, measures in the studied energy-intensive Swedish foundry industry are related to both support and production processes. In the various case studies of barriers and driving forces, the most significant barriers to energy efficiency - with largevariations for some of the barriers among the studied cases - were found to be: technical risk such as risk of productiondisruptions; lack of time or other priorities; lack of access to capital; cost of production disruption/hassle/inconvenience; other priorities for capital investments; technology considered inappropriate at the site; difficulty/cost of obtaininginformation about the energy use of purchased equipment; and lack of budget funding. The largest driving forces, apart fromcost reductions resulting from lowered energy use, were found to be the existence of a long-term energy strategy and peoplewith real ambition. These driving forces did not, unlike the results of barriers to energy efficiency, vary widely across thestudied sectors. Investment decision support such as optimization has shown to add more information for larger capital-intensive investmentsin energy-intensive industrial SMEs. The thesis also showed that energy audits are an effective means, in terms of publicmoney spent per kWh saved, of providing the industry with information on potential energy efficiency measures. Based on the results presented in this thesis, a policy approach towards non-energy-intensive companies and industrial SMEsshould primarily include providing energy audits free of charge and involve the local authority energy consultants. / Industriell energieffektivisering är ett av de viktigaste sätten att reducera hotet om en globaluppvärmning. En högre relativ elanvändning, i jämförelse med europeiska konkurrenter, tillsammans med stigande energikostnader beroende av stigande energipriser för den svenskaindustrin, riskerar leda till försämrad lönsamhet och försämrad konkurrenskraft. Det är såledesav stor vikt att främja energieffektivisering, exempelvis genom olika typer av styrmedel. Lönsamma energieffektiviseringsåtgärder genomförs emellertid inte alltid, till följd av olikahinder för energieffektivisering. För att kunna formulera precisa styrmedel är det därför avstor vikt att dessa hinder som förhindrar implementering av energieffektiviserande åtgärder,identifieras. Det är också av stor vikt att identifiera drivkrafterna. Syftet med denna avhandling är att analysera industriella energisystem och mera specifikt studera faktorer somfrämjar och förhindrar effektiv slutanvändning av energi i svensk industri. Resultaten visar att hotet om stigande energikostnader, exempelvis beträffande elektricitet,både för icke energiintensiv och för energiintensiv svensk tillverkningsindustri, kan reduceraskraftigt om energieffektiv teknik implementeras. Medan åtgärder i icke energiintensiv industrifrämst är relaterade till stödprocesser så visar sig åtgärderna i den studerade svenska energiintensiva gjuteriindustrin vara relaterade till både stöd- och produktionsprocesser. I fallstudierna beträffande hinder och drivkrafter visade sig de största hindren vara - med storavariationer mellan fallen - tekniska risker såsom risk för produktionsstörningar och avbrott; brist på tid/andra prioriteringar; brist på kapital; kostnader för produktionsstörningar; ickeenergirelaterade investeringar prioriteras högre; tekniken passar ej för företaget;svårigheter/kostnader att erhålla korrekt information beträffande energianvändningen av deninköpta utrustningen; och brist på budgetmedel. De största drivkrafterna var, utöver kostnadsminskningar till följd av minskad energianvändning, förekomsten av en långsiktigenergistrategi och en eldsjäl. Drivkrafterna varierade inte, till skillnad mot hindren, så mycketmellan de olika undersökta fallen. Beslutsstöd såsom exempelvis optimering har visat sig kunna ge ökad information vid störremer kapitalintensiva investeringar i energiintensiva små- och medelstora företag. Vidare har energianalyser visat sig vara ett effektivt sätt, i termer av besparad kWh per statligt insattkrona, att ge industrin information beträffande möjliga energieffektiviserande åtgärder. Resultat från avhandlingen indikerar att ett stöd gentemot icke energiintensiva och små och medelstora företag framförallt bör inkludera statligt finansierade energianalyser med denlokala energirådgivaren som en deltagande aktör.

According to the Environmental Kuznets Curve (EKC), economic growth will eventually cause carbon dioxide emissions to decrease. Is this the case in Sweden? A time series covering the period 1800-1995 is used to analyze the relation between carbon dioxide emissions and income per capita in Sweden. The empirical results indicate that an EKC for carbon dioxide is highly likely to exist in Sweden for the examined period. To take the analysis further, a cross-section data set is employed to examine the relationship between carbon dioxide emissions, income per capita and 4 other potentially influential variables in 75 countries. Only carbon intensity of energy is significant for carbon dioxide emissions. This implies that the utilized energy source is of importance, and it is crucial to separate energy consumption from carbon dioxide emissions. Emissions is a matter of structural aspects such as the type of industry and production a country comprise, and what type of energy that is consumed; not merely the quantity of energy. Sweden has experienced a shift in production techniques and in energy supply, and the energy-efficiency has improved during the past 100 years. It is consequently plausible to believe that it is not a critical income per capita which decreases CO 2  emissions – it is the “right” energy sources, energy efficiency and improved technology.

Nowadays, multiuser Multiple-In Multiple-Out systems (MU-MIMO) are used in a new generation wireless technologies. Due to that wireless technology improvement is ongoing, the numbers of users and applications increase rapidly. Then, wireless communications need the high data rate and link reliability at the same time. Therefore, MU-MIMO improvements have to consider 1) providing the high data rate and link reliability, 2) support all users in the same time and frequency resource, and 3) using low power consumption. In practice, the interuser interference has a strong impact when more users access to the wireless link. Complicated transmission techniques such as interference cancellation should be used to maintain a given desired quality of service. Due to these problems, MU-MIMO with very large antenna arrays (known as massive MIMO) are proposed. With a massive MU-MIMO system, we mean a hundred of antennas or more serving tens of users. The channel vectors are nearly orthogonal, and then the interuser interference is reduced significantly. Therefore, the users can be served with high data rate simultaneously. In this thesis, we focus on the performance of the massive MU-MIMO downlink where the base station uses linear precoding techniques to serve many users over Rayleigh and Nakagami-m fading channels.

Data aggregation is an important technique in wireless sensor networks. The data are gathered together by data fusion routines along the routing path, which is called data-centralized routing. We propose a localized, Delay-bounded and Energy-efficient Data Aggregation framework(DEDA) based on the novel concept of DEsired Progress (DEP). This framework works under request-driven networks with realistic MAC layer protocols. It is based on localized minimal spanning tree (LMST) which is an energy-efficient structure. Besides the energy consideration, delay reliability is also considered by means of the DEP. A node’s DEP reflects its desired progress in LMST which should be largely satisfied. Hence, the LMST edges might be replaced by unit disk graph (UDG) edges which can progress further in LMST. The DEP metric is rooted on realistic degree-based delay model so that DEDA increases the delay reliability to a large extent compared to other hop-based algorithms. We also combine our DEDA framework with area coverage and localized connected dominating set algorithms to achieve two more resilient DEDA implementations: A-DEDA and AC-DEDA. The simulation results confirm that our original DEDA and its two enhanced variants save more energy and attain a higher delay reliability ratio than existing protocols.

This thesis is concerned with the thermodynamic analyses of ion and proton-conducting solid oxide fuel cells (SOFC) fed with ammonia and urea as fuels. A multi-level approach was used to determine the feasibility and the performance of the fuel cells. First, the cell-level thermodynamics were examined to capture the effect of various operating parameters on the cell voltage under open-circuit conditions. Second, electrochemical studies were conducted to characterize the cell-level performance under closed-circuit conditions. Third, the fuel cells were individually integrated in a combined-cycle power generation system and parametric studies were performed to assess the overall performance as well as the thermal and exergy efficiencies. The findings of this study showed that the overall performance and efficiency of the ammonia fed SOFC is superior in comparison to that of the urea fed counterpart. In particular, the ammonia fed system combined with proton-conducting SOFC achieved a thermal efficiency as high as 85% and exergy efficiency as high as 75%. The respective efficiencies of the ammonia fed system combined with ion-conducting SOFC were lower by 5-10%. However, the urea fed system combined with ion or proton-conducting SOFC demonstrated much lower performance and efficiencies due to higher thermodynamic irreversibilities. / UOIT