Urbanization modifies the thermal characteristics of the land and makes way for a succession of transformations in the urban environmental system. This phenomenon, known as Urban Heat Island (UHI), is characterized by elevated temperatures in urban areas that negatively impact on the quality of life and environment in urban areas including, increased emissions of Green House Gases (GHGs) and rising energy consumption. These impacts add to global climate change and thus, mitigating UHI is essential to mitigating global climate change. One GHG, Carbon Dioxide (CO2), accounts for about half of the Earth’s anthropogenic GHG emissions. Terrestrial ecosystems can act as Carbon sinks (C sinks), i.e. natural vegetation reservoirs that absorb more C than they release. Thus, C sinks play an essential and critical function in lowering CO2. Furthermore, providing appropriate C sinks at both the building and urban scales can decrease UHI and contribute to reduction in energy consumption. This study used Landsat 8 imagery of the site, Al Bayt Stadium in Qatar, to investigate the effects of surface UHI by computing the Land Surface Temperature (LST) difference of the site---pre- and post-construction, as well as examine the correlation between natural vegetation abundance and temperature in ten locations within the site’s vicinity. Results show that minimum, maximum and mean LST of the case study area (2014 vs. 2020) decreased 2.80 oC, 5.5 oC and 2.3 oC, respectively, as well as a decreasing trend in the LST as a function of increasing C Sinks. These results demonstrate the importance of introducing C sinks to lower LST and mitigate UHI. Mitigating UHI also has a direct effect on Energy Consumption Balance (ECB). This equilibrium is achieved not only through the introduction of C sinks, but balancing C sinks with high albedo materials and natural ventilation.  Thus, this study also investigated the site’s various design aspects (e.g. cooling technology, structure and surface albedo materials, landscaping) and found that Al Bayt Stadium’s design successfully incorporates strategies to reduce energy consumption at both the urban (macro) and building (micro) scales.

Solar photovoltaic (PV) parks have proliferated all over the world as a result of the growing demand for electricity, and especially electricity from renewables. As these parks become larger and complex, it becomes increasingly important to develop accurate and efficient mathematical models that can be used to predict their performance and optimize their design. The inverter is an essential component of a solar PV system that converts the DC power generated by the solar panels into AC power that can be used by the grid or by local loads. This research paper presents a comparative study between a pre-existing reference model and a mathematical model, developed specifically for predicting the AC power output of photovoltaic systems. In addition, a hybrid model is included for comparative analysis. The performance of each model was evaluated using real-world data installed at Glava Energy Centre in Hillringsberg, Sweden. The reference and hybrid models showed similar trends in their calculated versus actual values, but the hybrid model outperformed the reference model slightly. The actual power values were found to be similar to the simulated values in all three models. However, the mathematical model was more specific and sensitive to the inverter under consideration, resulting in a comprehensive and accurate representation of the inverter's behaviour. The models take into account the inverter's characteristics, as well as environmental elements like temperature and solar irradiance that affect its performance. The results showed that the mathematical model outperformed the other models in terms of accuracy and reliability, achieving an R2 score of 0.9226, 0.9936, 0.9789, and 0.9736 for the months of February, April, July, and October, respectively. The mathematical model also had the lowest root mean square error (RMSE) and mean absolute error (MAE) values compared to the other models. The results of this study demonstrate the value of mathematical modelling in the design and optimization of solar PV parks and provide a framework for the development of more complex models in the future.

In recent years the focus and application of sustainability in buildings has risen. Both for environmental and human well-being reasons. The quality of the indoor environment affects the well-being, productivity and work performance, but it can also affect the occupants negatively, like increasing risks of different diseases and health issues. A good indoor environment alongside with sustainable materials, proper HVAC (Heating, ventilation, and air conditioning) installations and building code regulations contribute to a sustainable solution with low environmental impact and reduced energy consumption. Since buildings alone are responsible for 38% of all human GHG (Greenhouse gas) emissions (Wikipedia, 2017), most countries recommend new more sustainable solutions to reduce that percentage. For example, in the EU, the 2020 climate and energy package targets to: cut 20% in greenhouse gas emissions, 20% of EU energy from renewables and 20% improvement in energy efficiency (European Comission, n.d.). In addition to the positive aspect of low environmental impact new constructions have, they also create a good living or working environment for the users. Studies have shown that a better indoor quality increases the productivity and work performance, but most of all the occupants feel comfortable and satisfied with their environment. A great number of papers have reviewed the acoustic, visual, thermal comfort and indoor air quality, which are main aspects of the indoor climate. Most papers focus on the users’ perception of these four aspects as well as other parameters that influence the indoor environment (architectural geometry, materials, etc.). Similarly, in this study case I focus on two different methods of obtaining the results, the objective method that contains the indoor environment measurements and the subjective method which includes a questionnaire created specifically for this research project. By obtaining these two sets of data, key focus points are developed, such as if the building’s certification meets the recommendations of Miljöbyggnad, what aspects influence the students’ perception the most, and whether there are any distinct connections between measured and calculated data. This study case was developed in a university building in Stockholm, where the four main aspects of the indoor environment were evaluated. The physical parameters such as temperature, air velocity, relative humidity, CO2 concentration and acoustics were measured in five different classrooms. In addition, a survey was developed for this study which included perception questions of the thermal, visual, acoustic comfort and indoor air quality. As found in other studies, gender and climate zone origin affected the overall indoor environmental perception. Even though the majority of both genders voted for “no change”, the remaining females answered that they preferred the conditions warmer. Also, the majority of answers from all climate zones were “no change”. However, the second highest opinion for students from warmer climate zones was “warmer”, which has also been found in other studies. Significant negative correlations were found between the acoustics and the satisfaction level of the acoustic comfort. Similarly, high correlations were observed between the visual comfort satisfaction level and the three aspects influencing it. Furthermore, the results showed that all physical measurements influenced the students’ thermal comfort and indoor air quality perception. All measurements obtained indicated a good indoor environment in all classrooms, and all values were between the Swedish Standards recommendations. Low correlation was found between the measured PVM and the AMV from the questionnaires even though all the values were among the limitations. Lastly, this study reviews methods that could be applied to similar future studies and, discusses what kind of errors to avoid in the future. There is still a lot of research that can be developed in order to gain a deeper understanding of the indoor environment and how humans perceive it. / Under senare år har fokus och tillämpning av hållbarhet i byggnader ökat, både för miljö och mänskligt välbefinnande. Kvaliteten på inomhusmiljön påverkar välbefinnandet, produktiviteten och arbetsprestandan. Tyvärr kan det också påverka de anställda negativt, som ökad risk för olika sjukdomar och hälsoproblem. En bra inomhusmiljö tillsammans med applikationer av hållbara material, ordentliga HVAC-installationer och byggregler bidrar till en hållbar lösning med låg miljöpåverkan och minskad energiförbrukning. Eftersom byggnader ensamma svarar för 38% av alla mänskliga växthusgasutsläpp (Wikipedia, 2017), rekommenderar de flesta länder nya mer hållbara lösningar för att minska den procentuella andelen. I EU strävar EUs klimat- och energipaket 2020 till att; minska 20% av växthusgasutsläppen, 20% av EUs energi från förnybara energikällor och 20% förbättrad energieffektivitet (European Commission, n.d.). Förutom den positiva aspekten av låg miljöpåverkan har nya konstruktioner skapat en bra levnads- och arbetsmiljö för användarna. Studier har visat att en bättre inomhuskvalitet ökar produktiviteten och arbetsprestandan men framförallt känner sig brukarna bekväma och nöjda med sin miljö. Ett stort antal rapporter har granskats enligt akustisk, visuell, termisk komfort och inomhusluftkvalitet, som är huvudaspekterna av inomhusklimatet. De flesta rapporter fokuserar på användarnas uppfattning om dessa fyra aspekter samt andra parametrar som påverkar inomhusmiljön (arkitektonisk geometri, material osv.). På samma sätt fokuserar jag på två olika metoder för att erhålla resultaten. Den objektiva metoden som innehåller innemiljömätningar och den subjektiva metoden som innehåller ett frågeformulär som skapats specifikt för detta forskningsprojekt. Genom att erhålla dessa två uppsättningar data utvecklas viktiga fokuspunkter, till exempel om byggnadens certifiering uppfyller Miljöbyggnads rekommendationer, vilka aspekter som i huvudsak påverkar elevernas uppfattning och om det finns några tydliga samband mellan uppmätta och beräknade data. Studiefallet utvecklades i en universitetsbyggnad i Stockholm, där de fyra huvudaspekterna av inomhusmiljön utvärderades. De fysiska parametrarna mättes såsom temperatur, lufthastighet, relativ fuktighet, CO2-koncentration och akustiken i fem olika klassrum. Dessutom har en undersökning utvecklats för detta studieprojekt som inkluderade uppfattningsfrågor inom termisk, visuell, akustisk komfort och inomhusluftkvalitet. Kön och klimatzonens ursprung var två andra parametrar som påverkade den övergripande inomhusmiljöuppfattningen, enligt andra studier. Även om majoriteten av båda könen röstade för "ingen förändring" svarade restrerande kvinnor att de föredrog klasrummet varmare. Dessutom svarade flertalet från alla klimatzoner "ingen förändring", även om den näst högsta åsikten för studenter från varmare klimatzoner var "varmare", vilket också har hittats i andra studier. Höga negativa korrelationer hittades mellan akustiken och tillfredsställningsnivån för den akustiska komforten. På samma sätt observerades höga korrelationer mellan den visuella komfortnöjdhetsnivån och de tre aspekter som påverkar den. Vidare visade resultaten att alla fysiska mätningar påverkade elevernas termiska komfort och upplevelse av inomhusluftkvalitet. Alla erhållna mätningar indikerade en bra inomhusmiljö i alla klassrum och att alla värden var inom svensk standards rekommendationer. Låg korrelation hittades mellan den uppmätta PVM (predicted mean vote) och AMV (actual mean vote) från frågeformulären även om alla värden var inom gränserna. Dessutom granskar studien metoder som kan tillämpas på liknande framtida studier liksom vilka slags fel som bör undvikas i framtiden. Det finns fortfarande mycket forskning som kan utvecklas för att förstå mer om inomhusmiljön och hur människor uppfattar den.

<p>Electrohydrodynamics (EHD) was used to enhance the thermal performance of a latent heat thermal storage cell by reducing the charging time for a given amount of latent heat stored. Paraffin wax, which is an organic dielectric commercially available material was selected as the phase change material (PCM).</p> <p>Electric field was applied into the cell by using 9 electrodes kept at -8 kV in an effort to establish EHD forces inside the PCM. The EHD effect was studied in an originally conduction dominated melting environment. That was achieved by the cell design which promoted unidirectional melting downwards to prevent natural convection from occurring by assuring a thermally stratified molten phase. The target was to study the EHD mechanisms of enhancement with less interfering physics.</p> <p>Melting was studied under constant heat flux boundary condition. The temporal thermal profile of the surface heater and the melt front location were used to assess the EHD effect by comparing it to a 0 kV (no EHD) case.</p> <p>It was found that by using EHD (-8 kV), the time required to melt 7 mm thickness of the PCM can be reduced by 40 % when compared to 0 kV case. Through a four hour experiment time, the amount of molten PCM can be increased by 29 % by using EHD compared to 0 kV. The EHD power consumption was less than 0.17 W which is equivalent to 2.4 % of the thermal energy stored in the PCM.</p> <p>A new phenomena was discovered when applying EHD in the tested cell, which is Solid Extraction, where the solid dendrites within the mushy zone were extracted from the mushy zone into the liquid bulk towards regions of higher electric field.</p> <p>A new criteria was developed to quantify the EHD enhancement level and was called EHD enhancement factor. An enhancement factor up to 13 could be reached by using EHD. The effect of changing the heat flux on the enhancement factor was investigated, and it was found that the enhancement factor decreased by increasing the heat flux.</p> <p>Numerical simulations were performed in an effort to understand the EHD mechanisms of enhancement. The static electric field distribution, the interfacial extraction forces and the body forces acting on suspended dendrites were evaluated. The results of numerical simulations were supported by the high speed imaging and the experimental data to explain the EHD mechanisms of enhancement and the regions where solid dendrites extraction happened.</p> <p>Finally an analytical model was developed to estimate the energy stored in the different components of the tested latent heat storage cell and to estimate the amount of energy lost to the surroundings in order to quantify the accuracy of the experiment and a maximum of 18 % heat loss was estimated.</p> / Master of Applied Science (MASc)

Two methodologies are presented for analyzing the choice between centralized and decentralized energy infrastructures from a least-cost perspective. The first of these develops a novel minimum spanning tree network algorithm to approximate the shortest-length network that connects a given fraction of total system population. This algorithm is used to identify high priority locations for decentralized electrification in 150 countries. The second methodology utilizes a mixed-integer programming framework to determine the least-cost combination of centralized and decentralized electricity infrastructure that is capable of serving demand throughout a given system. This methodology is demonstrated through a case study of Rwanda. The centralized-decentralized electrification paradigm is also approached from an energy security perspective, incorporating stochastic events and probabilistic parameters into a simulation model that is used to compare different development paths. The impact of explicitly modeling stochastic events as opposed to utilizing a conventional formulation is also considered Finally, a subsidy-free lighting cost curve is developed and a model is presented to compare the costs and benefits of three different financial mechanisms that can be employed to make capital intensive energy systems more accessible to rural populations. The optimal contract is determined on the basis of utility-maximization for a range of costs to the providing agency and a comprehensive single and multi-factor sensitivity analysis is performed.

In the context of global energy shortage and climate change, developing local biogas plants coupled with agricultural systems can become an important strategy for cleaner rural energy and sustainable agriculture. In this research, a Life Cycle Assessment (LCA) method was applied to compare the climate impact of two essentially different systems: 1) Scenario I: an agricultural system based on the cultivation of 11 hectares of energy tobacco primarily for seed production; 2) Scenario II: a hypothetical Scenario Investigating the climate impact concerned with a crop variety – a higher yielding variety cultivated for both seed and biomass - and introducing biogas production. Both scenarios focus on the energy tobacco biomass residues. The overall aim of the study was to evaluate the climate impact of these two scenarios in the agricultural and energy system in Marble Hall, Limpopo Province, South Africa. The biogas was used for electricity production, replacing coal-based electricity on the grid. Biomass residues were chosen as feedstock for biogas production since this crop presently receives much attention in the region as the oily seeds can be used to produce sustainable jet fuel. Results from the modelling show that Scenario II would provide a positive climate impact: a 43% reduction of greenhouse gases compared to Scenario I. The higher yielding crop variety in Scenario II means that there is also potential to produce more sustainable jet fuel to replace conventional aviation fossil fuel. Taking this into account, the biogas scenario can reduce emissions by 79% compared to the base case. An analysis of the results indicates that there are several variables in the system model that are uncertain and sensitive to change, proving that more research is necessary to make robust conclusions about the validity of the presented results.

Reducing the carbon footprint of domestic properties is, due to global warming and social impact of increased energy costs, an ever increasing priority. Although the compulsive building standards are set by the building regulation part L1, The Code for Sustainable Homes have set more stringent requirements above the requirements of Building Regulations to achieve zero carbon emissions during occupation. This Code for Sustainable Homes (CSH) requires all new homes to be zero carbon by 2016. Land scarcity and lower number of people per household forces developers to develop compact apartment-based dwellings on brown field sites, constraining the design. The aim of this research is to understand the effect of practical constraints on real building design and technology on achieving zero carbon performance in compact urban dwellings in a maritime northern European climate. In this work, currently commercially implementable renewable generation technologies are evaluated for their suitability in a compact urban setting. A model-based approach is developed to evaluate the energy consumption (both regulated and unregulated) and energy balance under the specific constraints of compact urban buildings. Graphical representation enables the introduction of a demand envelope, which shows the boundaries of the minimum and maximum expected thermal and electrical energy consumption over one year period. The research has three key findings: 1. Due to variations in energy consumption by the occupants, mainly by the unregulated energy consumption, multiple renewable energy technologies would have to be implemented to achieve the lowest possible carbon emission. 2. Although the combination of PV, CHP and HP is the generation option with the lowest carbon emissions, it is not completely carbon free when producing the required electrical and thermal energy. This suggests that there is a high likelihood that zero-carbon energy generation can not be achieved in this case study of a compact urban dwelling with the currently available technology. 3. The simulations show that with highly insulated dwellings the amount of space heating required is less than 10% of the overall energy consumption, as opposed to the 60% generally achieved in the building industry. Subsequent on-site measurements showed an estimation of just under 30% of the total energy consumption was used in space heating, which is higher than the simulated value, but still less than half that of a conventional dwelling. The main academic recommendation resulting from this research is a requirement for further ongoing research into new generation technologies as they become mature. Recommendations for the sponsoring company include continuation of measurements at the case study building to enable confirmation of energy consumption/generation findings so far.

Hybrid renewable energy systems (HRES) have proven to be a more stable and feasible source of energy than heir single source counterparts. The benefit of HRES is their ability to balance the stochastic behavior of wind and solar production. As result of this, they have been used as stand-alone systems with great success. Optimization studies in the field have shown optimum sizing of the components in the system to be a key element in order to increase feasibility. This paper focuses on the HRES impact on internal grid design and cost. The goal of the thesis is to create a mathematical function and graph on the internal grid design/cost relation for a virtual site with varying wind speed and solar irradiation. A secondary goal is to analyze how much Photovoltaics (PV) in Megawatt (MW) that can be connected to the internal grid post realization of the wind farm and to performed this analyze on the two specific case projects, Site A (17.25 MW) in Sweden and Site B (51.75 MW) in Italy. By utilizing a case study methodology, a mathematical model was created based on two case projects, both with potential to be a combined Wind-PV hybrid plants provided by the wind developer OX2. Identifiers for the two cases studied in this thesis where removed with respect to OX2’s ongoing projects. Hybrid renewable energy systems is a method of increasing the utilization of a regions RES, the system has an increase in overall power output compared to the single RES alternative. However, the internal grid cost was shown to be 3.85 % more expensive Site A and 5.3 % in Site B. This stood in direct correlation to the HRES in Site A using 8.6 % more cable for its internal grid and 29.7 % more in Site B, this is highly depending (depending on the location of the PV array). Furthermore, the case projects showed that the maximum PV to be connected post realization of the farm without major curtailment would be 11.5% of the wind farms rated power in the case of site A and 67.6 % in the case of Site B. Variations in wind speed and solar irradiation were shown to have some impact on grid cost. However, the results pointed out that grid cost in HRES is to a higher degree affected by total cable length in the internal grid than fluctuation in available energy sources. The extent of increase in cable length, the total grid investment cost rises up to 53.4 % for the two case projects.

Denna studie analyserar de rapporterat höga förlusterna i ett småskaligt fjärrvärmenät i Lessebo där styrkort för år 2013 redovisar förluster på 38 %. Genom att med en kvantitativ metod beräkna de värmeförluster som sker genom värmeledning i rörnätet görs en bedömning om rörnätets utformning är källan till de höga förlusterna eller ej. Studien ger indikationer på att fjärrvärmenätet i Lessebo är bra utformat och det därför finns oidentifierade orsaker till de höga förlusterna. Utöver redogörande av värmeförluster ger rapporten även kunskaper om fjärrvärmebranschens flera tekniker, begränsningar och framtida utvecklingsmöjligheter.

Rapporten redovisar en utredning av konserveringsmetoder för vattensidan under stilleståndsperioder av ett värmeverk bestående av fem hetvattenpannor med ett gemensamt ångnät. Syftet var att utvärdera olika metoder för att motverka korrosion då pannorna inte är i drift. Konserveringsmetoderna som utreddes och jämfördes internt var konservering med en kvävgaskudde, ångkudde, torrläggning och en kemisk lösning. Att utreda metoderna innebar att uppskatta dess kostnad ekonomiskt genom att beräkna en årskostnad. För att besvara hur effektivt deras skydd mot korrosion är användes litteraturens referenser och teoretiska samband för att uppskatta syrehalten i matarvattnet. För att kunna göra en realistisk jämförelse mellan metoderna har den avgivna effekten för värmeverkets pannor under driftåret 2016 använts som en grund för beräkningarna. Årskostnaderna från konserveringsmetoderna är från 2016 års driftdata av värmeverket. En kvävgaskudde med en renhet av 99,999 % kan resultera i en syrehalt av 9,6 ppb för matarvattnet och har en total årskostnad av 77 300 SEK. En ångkudde har potentialen att bevara vattnet i princip syrefritt och har en total årskostnad av 809 000 SEK med en extern elpanna för ångproduktion. Att torrlägga pannorna är bara möjligt under vissa perioder av året dock skulle en total årskostnad av eldriften för att hålla pannorna torra motsvara en kostnad av 17 500 SEK. Metoden med en kemisk lösning hade en totalårskostnad av 1 640 000 SEK. Baserat på tillgänglig information och utförda antaganden är slutsatsen att värmeverket ifråga rekommenderas att upphöra med en kemisk konserveringsmetod och övergå till en kvävgaskudde som konserveringsmetod mot korrosion då pannorna inte är i drift.