In view of the fact that most of the synthetic refrigerants, in case of leakage or release, are harmful to the environment by contributing in global warming or depleting stratospheric ozone layer, many research works have been done recently to find alternative refrigerants posing no or negligible threat to the environment. Among alternative refrigerants, ammonia, a natural refrigerant with zero Global Warming Potential (GWP) and Ozone Depletion Potential (ODP), can be a sensible choice.Although ammonia has been used for many years in large industrial systems, its application in small units is rare. In this project a small heat pump with about 7 kW heating capacity at -5 °C and +40 °C evaporation and condensation temperatures is designed and built to work with ammonia as refrigerant. The heat pump is expected to produce enough heat to keep a single-family house warm in Sweden and to provide tap hot water for the house. After successful completion of this project, it is planned to install the heat pump in a house to test it throughout a heating season to study its performance in real working conditions.Since ammonia is flammable and toxic in high concentrations, the refrigerant charge is tried to be kept low in the heat pump to reduce the risk of fire or poisoning in case of unwanted release of refrigerant to the surroundings. The compact design of the heat pump helps reducing the refrigerant charge. Besides, considering the limited space normally reserved for installation of a heat pump in a house, the compact design of the heat pump is necessary.

Kylning spelar en avgörande roll i många olika sektorer och förbrukar cirka 17 % av den elektricitet som produceras globalt. Kylprocessernas energiförbrukning utgör alltså en stor andel av primärenergiförbrukningen och innebär även annan miljöpåverkan. Förutom miljöpåverkan som är förknippad med energiförbrukningen bidrar ångkompressionssystemen till global uppvärmning på grund av utsläpp av köldmedier i atmosfären. Som en alternativ teknik för nära rumstemperaturapplikationer föreslås magnetisk kylning av vissa forskare, för att eliminera utsläpp av köldmedier i atmosfären och för att minska energiförbrukningen. Denna avhandling är en sammanställning av ett antal studier om magnetisk kylning för rumstemperaturapplikationer.

I den första studien undersöktes de miljöpåverkningar som är förknippade med magnetisk kylning noggrant genom en livscykelanalys. Livscykelanalysen indikerar att minskningen av miljöpåverkan inte garanteras genom att byta till den magnetiska kylprocessen på grund av de miljöbelastningar som är relaterade till de sällsynta jordartsmetaller som används i magnetisk kylning. För att undvika de extra miljöpåverkningarna bör de magnetiska kylsystemen använda så lite magnetiska material som möjligt, vilket kräver en optimerad design. Dessutom är energieffektivare drift jämfört med ångkompressionssystemen nödvändigt för att få miljöfördelar, åtminstone i vissa miljöpåverkanskategorier.

En praktisk metod för att optimera designen av magnetiska kylsystem, för att uppnå t.ex. en kompakt design eller hög effektivitet, är användning av en flexibel mjukvarumodell, som simulerar effekten av olika parametrar på systemets prestanda. En sådan mjukvarumodell av det magnetiska kylsystemet har utvecklats och validerats i detta projekt. Ett syfte med utvecklingen av modellen är att öka precisionen av de simulerade resultaten genom att ta hänsyn till mer detaljer än i tidigare modeller. Detta mål uppnås genom ett innovativt sätt att modellera den parasitära värmeöverföringen och inkludera effekten av närvaron av magnetokaloriska material på styrkan av fältet som skapas av magnetaggregatet. Dessutom görs vissa modifieringar eller korrigeringar i de befintliga korrelationerna för att inkludera effekten av bindemedel som används i vissa aktiva magnetiska regeneratorer. Validering av den utvecklade mjukvarumodellen görs med hjälp av experimentella resultat som erhållits från den prototyp som finns vid Institutionen för Energiteknik, Kungliga Tekniska Högskolan.

En av parametrarna som kan modifieras i den utvecklade mjukvarumodellen är valet av magnetokaloriska material för varje skikt i en skiktad aktiv magnetisk regenerator. Användning av mjukvarumodellen för att optimera valet av material för skikten visar att material med kritiska temperaturer som är lika med den cykliska genomsnittstemperaturen hos de skikt där de används inte nödvändigtvis resulterar i önskad optimal prestanda. Dessutom behövs olika materialval för skikten för att maximera modellernas resultat avseende energieffektivitet eller temperaturskillnaden som erhålls mellan de två ändarna av regeneratorerna. Därför är valet av kritiska temperaturer för skiktens material en ytterligare parameter som ska optimeras i studier med avsikt att förbättra ett systems prestanda.

Prototypen vid Institutionen för Energiteknik, Kungliga Tekniska Högskolan, var ursprungligen designad för att ersätta ångkompressionssystemet för ett restaurangkylskåp. Det kunde emellertid inte uppfylla de krav för vilka det ursprungligen utformats. Den ovan nämnda utvecklade simuleringsmodellen används för att undersöka hur mycket prestandan kan förbättras genom att förändra valet av material, partikelstorleken, antalet skikt, driftsfrekvensen och flödeshastigheten av värmeöverföringsvätskan. Med andra ord undersöks utrymmet för förbättring av prestandan utan att genomföra stora förändringar i systemet, såsom förändringar i regeneratorers geometri och i magnetaggregatet. Under processen undersöks effekten av bindemedel på prestanda och begränsningar som är förknippade med bindemedlets egenskaper. Trots detta kunde studien inte visa att de ursprungliga målen för prototypen kan uppnås utan att ändra regeneratorernas geometri och de befintliga magnetokaloriska materialen.

I nästa studie övervägs mer flexibla val av regeneratorernas geometrier och magnetokaloriska material. I den här studien undersöks hur mycket de magnetokaloriska materialen måste förbättras för att magnetiska kylsystem ska kunna konkurrera med ångkompressionssystem vad gäller prestanda. För de två undersökta fallen är de magnetfältberoende egenskaperna hos befintliga materialen tillräckliga förutsatt att vissa andra problem, såsom låg mekanisk stabilitet och inhomogenitet hos egenskaperna, löses. Emellertid, för mer krävande designkriterier, såsom att ge stor kylkapacitet över en betydande temperaturdifferens samtidigt som de magnetiska materialen används sparsamt, behöver de magnetfältberoende egenskaperna också förbättras.

Ett mindre undersökt område för magnetisk kylning i rumstemperatur är föremål för en annan studie som ingår i avhandlingen. I denna studie modelleras fasta magnetiska kylsystem med Peltier-element som värmebrytare. Eftersom Peltier-elementen förbrukar elektricitet och pumpar värmen kan de modellerade systemen betraktas som hybrid magnetokalorisk-Peltier-kylsystem. För sådana system modelleras i detalj det transienta beteendet hos Peltier-elementen tillsammans med de magnetokaloriska materialskikten. Den matematiska modellen är lämplig för implementering i programmeringsspråk utan behov av kommersiella modelleringsplattformar. Parametrarna som påverkar det modellerade systemets prestanda är många, och optimering av dem kräver en separat studie. De preliminära optimeringsinsatserna ger emellertid inte lovande resultat. Följaktligen kan fokusering på passiva värmebrytare vara mer fördelaktiga.

Uncontrolled open dumping and burning of municipality solid waste (MSW) has resulted in soil, water, and air pollution in many urban cities in India. Landfills are the most common cost-effective solution for MSW management in many developing countries like India. However, the identification of suitable landfill sites always remains a challenging task as it involves selection of several environmental criteria set by the local authorities. The objective of this study is to identify the most potential landfill sites proposed by the Government in Bengaluru Metropolitan Region, Karnataka state, India using Geographic Information System enabled Analytical Hierarchy Process based multi-criteria evaluation technique. Several criteria and constraints as recommended by the local authorities along with the proximity to the solid waste processing plants are used to identify the potential landfill sites in the study region. The study identified three highly suitable sites (Neraluru, Gudhatti, Madivala) for landfills which are not only environmentally sustainable but also economically attractive as they are closer to the solid waste processing plants minimizing the transportation cost involved in the disposal of solid waste from the source to the final disposal sites in the study region.

The Electricidade de Moçambique, E.P. (EDM) is the power utility in Mozambique, responsible to generate, transport and distribute electricity all over the country. The company has three gas turbines installed at Maputo Power Plant. All units burn diesel oil and are used only for back up. Currently only the unit #2 is available for operation.

The main constraint that EDM faces is the high operation costs due to diesel price. Hence the company is considering converting units #2 and #3 to burn natural gas, resource available locally. The country is currently exporting natural gas to the neighbouring Republic of South Africa.

This MSc thesis project calculates the power output of all gas turbines when burning natural gas and optimizes the power plant capacity by proposing modifications of the current power turbine cycles to allow sustainable operation

Composite electrodes of Cu0.16Ni0.27Zn0.37Ce0.16Gd0.04 (CNZGC) oxides have been successfully synthesized by solid state reaction method as anode material for low temperature solid oxide fuel cell (LTSOFC). These electrodes are characterized by XRD followed by sintering at various time periods and temperatures. Particle size of optimized composition was calculated 40-85 nm and sintered at 800 degrees C for 4 hours. Electrical conductivity of 4.14 S/cm was obtained at a temperature of 550 degrees C by the 4-prob DC method. The activation energy was calculated 4 x 10(-2) eV at 550 degrees C. Hydrogen was used as fuel and air as oxidant at anode and cathode sides respectively. I-V/I-P curves were obtained in the temperature range of 400-550 degrees C. The maximum power density was achieved for 570 mW/cm(2) at 550 degrees C.

Zn-based nanostructured Ba0.05Cu0.25Fe0.10Zn0.60O (BCFZ) oxide electrode material was synthesized by solid-state reaction for low-temperature solid oxide fuel cell. The cell was fabricated by sandwiching NK-CDC electrolyte between BCFZ electrodes by dry press technique, and its performance was assessed. The maximum power density of 741.87 mW-cm(-2) was achieved at 550 degrees C. The crystal structure and morphology were characterized by X-ray diffractometer (XRD) and SEM. The particle size was calculated to be 25 nm applying Scherer's formula from XRD data. Electronic conductivities were measured with the four-probe DC method under hydrogen and air atmosphere. AC Electrochemical Impedance Spectroscopy of the BCFZ oxide electrode was also measured in hydrogen atmosphere at 450 degrees C.

The entire world's challenge is to find out the renewable energy sources due to rapid depletion of fossil fuels because of their high consumption. Solid Oxide Fuel Cells (SOFCs) are believed to be the best alternative source which converts chemical energy into electricity without combustion. Nanostructured study is required to develop highly ionic conductive electrolyte for SOFCs. In this work, the calcium doped ceria (Ce0.8Ca0.2O 1.9) coated with 20% molar ratio of two alkali carbonates (CDC-M: MCO3, where M= Na and K) electrolyte was prepared by co-precipitation method in this study. Ni based electrode was used to fabricate the cell by dry pressing technique. The crystal structure and surface morphology was characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). The particle size was calculated in the range of 10-20nm by Scherrer's formula and compared with SEM and TEM results. The ionic conductivity was measured by using AC Electrochemical Impedance Spectroscopy (EIS) method. The activation energy was also evaluated. The performance of the cell was measured 0.567W/cm2 at temperature 550°C with hydrogen as a fuel.

Solid oxide fuel cells have much capability to become an economical alternative energy conversion technology having appropriate materials that can be operated at comparatively low temperature in the range of 400-600 degrees C. The nano-scale engineering has been incorporated to improve the catalytic activity of anode materials for solid oxide fuel cells. Nanostructured Al0.10NixZn0.90-xO oxides were prepared by solid state reaction, which were then mixed with the prepared Gadolinium doped Ceria GDC electrolyte. The crystal structure and surface morphology were characterized by XRD and SEM. The particle size was evaluated by XRD data and found in the range of 20-50 nm, which was then ensured by SEM pictures. The pellets of 13 mm diameter were pressed by dry press technique and electrical conductivities (DC and AC) were determined by four probe techniques and the values have been found to be 10.84 and 4.88 S/cm, respectively at hydrogen atmosphere in the temperature range of 300-600 degrees C. The Electrochemical Impedance Spectroscopy (EIS) analysis exhibits the pure electronic behavior at hydrogen atmosphere. The maximum power density of ANZ-GDC composite anode based solid oxide fuel cell has been achieved 705 mW/cm(2) at 550 degrees C.

Tekniken kring smarta elnät har under det senaste decenniet blivit etablerad som ett sätt att skapa en större flexibilitet på elnätet, vilket kommer att behövas allt eftersom utvecklingen går mot mer förnybara primärenergikällor i elproduktionen. En del av tekniken är förmågan att flytta laster i tid, för att anpassa sig till antingen pris eller utsläpp, vilket kallas efterfrågeflexibilitet. Detta projekt, som genomförts vid KTH i samarbete med konsultföretaget Capgemini, undersöker de ekonomiska, miljömässiga och sociala aspekterna av efterfrågeflexibilitet.

I projektet används tre hushållsprodukter i en modell som beräknar potentiella kostnadsbesparingar och möjliga reduktioner av CO2e-utsläpp. Resultaten visar att de faktiska besparingarna mätta i kronor är små, men att den procentuella besparingen kan vara så hög som 20 procent. Reduktionen av CO2e-utsläppen är något lägre. Dessutom visar studien att besparingarna ökar då modellen ges en större flexibilitet samt då fluktuationerna i elpriset ökar. Ett scenario som innefattar mer intermittent elproduktion och slutanvändare som är beredda att anamma tekniken är därför avgörande för efterfrågeflexibilitetens framgång. Resultaten visar också att en optimering inte kan göras på ett sätt som både minimerar kostnader och CO2e-utsläpp samtidigt.

En diskussion om de strategiska möjligheterna för Capgemini visar att fokus bör ligga på att samla in, tolka och sammanställa de stora mängder data tekniken kommer att medföra. Det finns också möjligheter i kringtjänster tätt sammankopplade med smarta elnät, såsom utveckling av en laddningsinfrastruktur för elbilar.

The aim of this study is to investigate the heat recovery potential in supermarket refrigeration systems using CO₂ as refrigerants. The theoretical control strategy to recover heating demand from refrigeration system is explained thoroughly and the heat recovery process from two existing supermarket using CO₂ booster units is analyzed and evaluated. The measured data of refrigeration systems is obtained through Iwmac interface, processed using Excel and Refprop. The aim is to see what control strategy is used in these systems and weather it matches the theoretical one and at what level heat is recovered from the system.

Besides, a simulation model is made by EES to investigate the potential of higher rate of heat recovery in the supermarkets. The simulation results are compared with field measurement and validated by measured values. Then, the ability of refrigeration system to do heat recovery at quite high rates for covering the total heating demand without using parallel heating system is evaluated and efficiency of the system is calculated. At the next step the heat recovery potential at other refrigeration solutions such as R404A conventional and CO₂-ammonia cascade systems are studied and the results are compared to booster units. Finally, the potential for selling heat from the refrigeration system in supermarket to district heating network is investigated. Two different scenarios are made for such purpose and the results are evaluated.

The heat recovery control strategy of existing supermarkets does not match the theoretical strategy and regarding the capacity of the system, heat is recovered to low extent. Simulation shows that heat can be recovered to higher extent at quite high heating COP of 3-5. Additionally the other heat recovery solutions for R404A conventional and CO₂-ammonia cascade systems are found to be competitive to CO₂ booster system.  The analysis of selling heat to district heating network shows that CO₂ booster system is capable of covering the demand at reasonable heating COP as the first priority and selling the rest to district heating network at heating COP of 2 as second priority.  

Latent termisk energilagring (LTES) är ett intressant val för att lagra termisk energi i ett hållbart energisystem. Den primära fördelen med LTES är den relativt höga smältvärmen av materialet, känt som fasändringsmaterial (PCM), som används som lagringsmedium i ett sådant system. I och med att värmekonduktiviteten hos PCM ofta är mycket låg finns det ett behov av att öka värmeöverföring-hastigheten för laddnings-/urladdningsprocessen samt att förbättra LTES-systemens termiska prestanda.  Denna avhandling tar upp den förstärkande effekten av att utöka värmeöverföringsytor i rektangulära LTES-behållare. Ett nyckelbidrag i denna avhandling är en omfattande visualisering av fasförändringsprocesserna i ett organiskt PCM, inklusive frysning/stelning och smältning, både som begränsad (fastnat) smältning och obegränsad (rörande) smältning, även känt som Close-Contact Melting (CCM), i en behållare med och utan flänsar. Observationer har gjorts för flänsar av olika längd samt antal, med varierande lutningsvinkel och en omfattande analys av processerna vad gäller fasändringstid och medeleffekt genomförs. Observationerna visar att flänsar är mer effektiva vid stelning än vid smältning, vilket minskar stelningstiden med 80% och ökar medeleffekten med 395%, dock minskar den utvunna energin med 10%. Däremot har flänsar vid smältning en måttlig effekt vad gäller att förbättra processen. Den relativa förstärkningseffekten av flänsarna är högre vid begränsad smältning än vid obegränsad smältning. I ett fall med maximal förbättring uppnås en minskning på 50% av den begränsade smälttiden och en relativ förbättring av medeleffekten på 90%, samtidigt som den lagrade energin minskar med 9%. När volymfraktionen av flänsarna ökar, minskar skillnaderna i smälttid mellan den begränsade och obegränsade smältningen. En numerisk modell för stelning och begränsad smältning valideras baserat på experimenten, och en mer utförlig känslighetsanalys av flänsparametrar utförs. Den förstärkande effekten av olika parametrar på fasändringstiden och den termiska effekten analyseras och de relativt effektivare åtgärderna identifieras. Genom att analysera simuleringsdata med dimensionslösa parametrar för en kavitet orienterad horisontellt och förstärkt med vertikala flänsar, har övergripande dimensionslösa grupper för stelning och begränsad smältning erhållits. De dimensionslösa grupperna bidrar generellt till att uppnå en bättre förståelse av flänsarnas parametrar och till att underlätta LTES-designerna. Denna avhandling undersöker dessutom en ny idé om att utöka ytan genom att introducera minikanaler i LTES-värmeväxlare, som används som passager för luft som en lågt värmeledande värmeöverföringsvätska (HTF). Minikanalernas interna hydrauliska diameter och deras höga externa area-tillvolym- förhållanden skapar en potential för dubbel förbättring på både PCMsidan och HTF-sidan. En befintlig design och en konceptuell med möjlighet att lägga till flänsar på PCM-sidan, som kan tillverkas via tillverkningsmetoder extrusion respektive Additive Manufacturing (AM), har simulerats och studerats. Den termiska prestandan hos de två minikanaltyperna ger en avsevärd förbättring av medeleffekten för en PCM-värmeväxlare som arbetar med luft. Förbättringen ökar när luftflödet ökar, till priset av ett allt högre tryckfall. Angående detta identifieras ökning av antalet kanaler som en mer effektiv förbättrande åtgärd än att lägga till flänsar på PCM-sidan. Dessutom har den konceptuella designen med en större inre hydraulisk diameter och större proportioner ett lägre tryckfall än den befintliga designen, samt genomför laddning/urladdning av termisk energi i samma takt men med lägre fläkteffekt. Mer optimerade konstruktioner med minimering av tryckfall bidrar till att underlätta användning av den förbättrade luft-PCM värmeväxlaren i olika applikationer.

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with d(h) = 1.6 mm and channel-2 with d(h) = 2.3 mm) are oriented vertically in a cuboid of 0.15 x 0.15 x 0.1 m(3) with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15-31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41-53% and increasing the mean UA values within melting by 19-52% for a packing factor range of 77.4-86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation.

Hydrogen is a potential option to replace fossil fuels considering the increasing demand of energy applications. It is naturally abundant and is regarded as a suitable energy carrier. There has been extensive research to improve the efficiency of storing hydrogen with different methods, including gas compression, liquefaction and sorption in metal hydrides or carbon nanotubes. A comparison of the storage methods shows that liquefaction of hydrogen is more beneficial than compression of hydrogen in terms of higher volumetric capacity, and it is more technologically mature than sorption technologies. This makes it more plausible for long distance distribution. On the other hand, the obstacles in full exploitation of the method are low energy efficiency of the liquefaction process and associated high cost. The recent research has been focusing on increasing the energy efficiency of the storage process. This paper provides, with regard to the conventional methods, a state of the art review of the novel and modified liquefaction process and the latest developments in increasing the efficiency of the energy intensive process. Furthermore, the developments in combining the hydrogen liquefaction plants with renewable energy sources are covered and reviewed. Finally, the ongoing development of hydrogen liquefaction is highlighted.

Reliable knowledge of phase change materials (PCM) thermo-physical properties is essential to model and design latent thermal energy storage (LTES) systems. This study aims to conduct a methodological measurement of thermo-physical properties, including latent enthalpy, isobaric specific heat, thermal conductivity and dynamic viscosity, of two n-alkanes, n-octadecane and n-eicosane. The enthalpy and isobaric specific heat of the materials are measured via differential scanning calorimetry (DSC) technique, using a pDSC evo7 from Setaram Instrumentation with a sample mass of 628.4 mg. The influence of the scanning rates, varying from 0.5 K/min to 0.025 K/min, in dynamic continuous mode within temperature range of 10-65 degrees C is investigated. The thermal conductivity and the dynamic viscosity are measured via Hot Disk TPS-2500S instrument and Brookfield rotational viscometer, respectively, up to 70 degrees C. The thermal analysis results via the pDSC show that the isothermal condition can be approached at a very low scanning rate, however at the cost of a higher noise level. A trade-off is observed for n-octadecane, achieving the lowest deviation of 0.7% in latent heat measurement at 0.05 K/min, as compared to the American Petroleum Table values. For n-eicosane, the lowest deviation of 1.2% is seen at the lowest scanning rate of 0.025 K/min. The thermal conductivity measured values show good agreements with a number of documented literature studies in the solid phase, within deviations of 2%. Larger deviations of 5-16% are found for the measurement in the liquid phase. The viscosity values also show a good agreement with the literature values with maximum deviations of 2.9% and 6.3%, with respect to the values of American Petroleum Tables, for n-octadecane and n-eicosane, respectively. The good agreements achieved in measurements establish the reliable thermo-physical properties contributing to the future simulations and designs. 

This paper investigates the effect of vertical fins, as an enhancement technique, on the heat transfer rate and energy density of a latent heat thermal energy storage system. This contributes with knowledge on the interaction of heat transfer surface with the storage material for optimizing storage capacity (energy) and power (heat transfer rate). For the assessment, numerical modeling is employed to study the melting process in a two-dimensional rectangular cavity. The cavity is considered heated isothermally from the bottom with surface temperatures of 55 degrees C, 60 degrees C or 70 degrees C, while the other surfaces are insulated from the surrounding. Aluminum and lauric acid are considered as fin/enclosure material and phase change material, respectively. Vertical fins attached to the bottom surface are employed to enhance the charging rate, and a parametric study is carried out by varying the fin length and number of fins. Thus, a broad range of data is provided to analyze the influence of fin configurations on contributing natural convection patterns, as well as the effects on melting time, enhanced heat transfer rate and accumulated energy. The results show that in addition to increasing the heat transfer surface area, the installation of vertically oriented fins does not suppress the natural convection mechanism. This is as opposed to horizontal fins which in previous studies have shown tendencies to reduce the impact of natural convection. This paper also highlights how using longer fins offers a higher rate of heat transfer and a better overall heat transfer coefficient rather than increasing the number of fins. Also, fins do not only enhance the heat transfer performance in the corresponding melting time, but also maintain similar total amount of stored energy as compared to the no-fin case. This paper discusses how this is the result of the enhanced heat transfer allowing a larger portion of sensible heat to be recovered. For example, in the case with long fins, the relative mean power enhancement is about 200% with merely 6% capacity reduction, even though the amount of PCM in the cavity has been reduced by 12% as compared to the no-fin case. Although the basis for these results stems from the principles of thermodynamics, this paper is bringing it forward with design consideration. This is because despite its importance for making appropriate comparisons among heat transfer enhancement techniques in latent heat thermal energy storage, it has not been previously discussed in the literature. In the end, the aim is to accomplish robust storage systems in terms of power and energy density.

The present study demonstrates and visualizes the two modes of constrained melting and close-contact melting in a rectangular cavity enhanced with fins. Three configurations of fin with different lengths and numbers are tested in different horizontal, inclined, and vertical orientations. N-eicosane is used as the phase change material, and the experiments are performed with water as the heat transfer fluid at the inlet conditions of 50 degrees C, 55 degrees C, and 60 degrees C. In general, the close-contact melting time is shorter by 42-50%, compared to the convection dominated constrained melting in the unenhanced cavity without fins. By using fins to enhance the process, the melting time is reduced by 49% and 35% in the constrained and the close-contact modes, respectively, compared to the unfinned cavity in each mode. The thermal performance is observed to be superior in the horizontal and the inclined orientations. In these orientations, the buoyancy-driven structures are not blocked by fins in the con-strained mode. In the close-contact mode, the solid specimens attain more consistent contact with the base of the cavity and with the extended heat transfer area at the inclined and horizontal conditions. In the vertical orientation, the asymmetrical melting by the fins results in a rotational movement of the solid PCM and close -contact perturbations. The variations in the number of fins are found to have minor effects on the overall close-contact-induced melting. On the other hand, increasing the length of the fins is a more promising measure, providing consistent and prolonged contact.

Extending the heat transfer area is a simple technique to improve the thermal performance of phase change materials with low thermal conductivity. However, as the governing mechanisms differ in solidification and melting, fins can affect the processes in different ways. This demands assessment of fin enhancement in a combined analysis on both solidification and melting, often neglected in literature. This paper presents visual-izations of solidification and melting of n-eicosane in a rectangular cavity and experimentally investigates the enhancing effect of vertical fins with varying number and length. Experiments were conducted at water inlet temperature ranges of 15-25 degrees C and 50-60 degrees C for the solidification and melting processes, respectively. The results show that the vertical fins can be more influential in solidification rather than in melting with similar losses in the storage capacity. In the solidification process, as natural convection is absent, the mean power is enhanced by a maximum of 395% with a 10% loss in the storage capacity, as compared to the benchmark. In the melting case, the mean power is increased by a maximum of 90% with a 9% loss in the storage capacity. Although increasing the surface area with vertical fins contributes to development of convective structures, it makes a modest enhancement. In overall, increasing the fin volume fraction, in exchange for the loss in the storage capacity, enhances the solidification significantly while it has relatively low enhancement effect in melting. At the end, the performed experiments could be helpful for validation of future simulation tools with complex features, particularly solidification models lacking in literature.

Brazil is very much rich in agriculture and forestry. The agro industry occupies an area of 28840726 ha. The more important crops are sugarcane (7080920 ha), rice (289030 ha), wheat (1853220 ha), coconut (283205 ha), cassava (1894460 ha), corn (13767400 ha) and grass (140000 ha). These crops generated 597 million tons of residues. Forest plantations in Brazil supplied 102.9 million m³ of industrial roundwood, of which nearly half is for renewable fuelwood and charcoal. Part of this plantation output is destined for the pulp and paper industry:

The renewable sources are fulfilling 46.4% of the total Brazilian energy demands.

Energy forestation in Brazil includes mainly Eucalyptus and Bracatingas.

In this study three biomasses abundant in the Brazil are studied:  i.e. Eucalyptus, Garapeira/Peroba (wood dust) and Sewage Sludge.

The wood samples (Eucalyptus and Peroba/Garapeira) have higher heating value than the sewage sludge because the wood samples have higher amounts of carbon and hydrogen than the sewage sludge. The sewage sludge has higher ash content and lower amount of volatiles and fixed carbon than the wood samples resulting in a lower heating value.

The pyrolysis of eucalyptus, garapeira/peroba and sewage sludge has been studied in a thermobalance over a wide range of degradation temperatures. Between 225 °C - 375 °C (for eucalyptus) and 225 °C - 425 °C (for garapeira), the thermal decomposition of the biomass leads to significant weight loss.

The weight loss for Eucalyptus between 265°C and 350°C is 0.48 % / °C and taking into account a heating rate of 10°C/min, the weight loss is 4.8 % /min. Garapeira has a similar behaviour than eucalyptus. The weight loss for garapeira between 265°C and 365°C is 0.4 % / °C and taking into account a heating rate of 10°C/min, the weight loss is 4 % /min.

The behaviour of the sewage sludge to the increase of temperature from 25°C to 700 °C in an inert atmosphere do not show such different zones as the behaviour of the woody biomass. Between 150 °C and 235°C the weight loss of the sewage sludge was 0.07 %/°C (0.7 %/min). The highest weight loss takes place between 300 °C and 390 °C (0.15 %/°C or 1.5 %/min). In the third zone, between 500 °C and 600°C, the weight loss was 0.03 %/°C (0.3 %/min).

The pyrolysis is assumed to be a first order decomposition. The activation energy (E) and the pre exponential factor (A) are calculated for the studied samples.

The proximate analysis shows differences between the woody biomass and the sewage sludge. The sewage sludge has higher ash content and lower fixed carbon and volatiles. Eucalyptus has lower carbon fixed and higher volatiles than peroba-garapeira.

This study aimed at evaluating and demonstrating the feasibility of using Concentrated Solar Thermal technology combined with biomass energy technology as a hybrid renewable energy system to supply the process heat requirements in small scale industries in Sri Lanka. Particularly, the focus was to apply the concept to the expanding hotel industry, for covering the thermal energy demand of a medium scale hotel.

Solar modules utilize the rooftop area of the building to a valuable application. Linear Fresnel type of solar concentrator is selected considering the requirement of the application and the simplicity of fabrication and installation compared to other technologies. Subsequently, a wood-fired boiler is deployed as the steam generator as well as the balancing power source to recover the effects due to the seasonal variations in solar energy. Bioenergy, so far being the largest primary energy supply in the country, has a good potential for further growth in industrial applications like small hotels. 

When a hotel with about 200-guests capacity and annual average occupancy of 65% is considered, the total annual CO₂ saving is accounted as 207 tons compared with an entirely fossil fuel (diesel) fired boiler system. The annual operational cost saving is around $ 40,000 and the simple payback period is within 3-4 years. The proposed hybrid system can generate additional 26 employment opportunities in the proximity of the site location area.  

This solar-biomass hybrid concept mitigates the weaknesses associated with these renewable technologies when employed separately. The system has been designed in such a way that the total heat demand of hot water and process steam supply is managed by renewable energy alone. It is thus a self-sustainable, non-conventional, renewable energy system. This concept can be stretched to other critical medium temperature applications like for example absorption refrigeration. The system is applicable to many other industries in the country where space requirement is available, solar irradiance is rich and a solid biomass supply is assured.

Open Distance Learning is gaining popularity as a successful alternative for on-campus higher education especially with the emergence of web based platforms which enable the online delivery of courses worldwide. This emerging educational pedagogy can successfully be employed as means of capacity building of the people living in the less fortunate parts of the world where higher education especially at master level are scarce. This paper presents a two-year collaborative master study programme in sustainable energy engineering offered in synchronous with an on-campus study programme conducted by the KTH Royal Institute of Technology of Sweden, to students of Sri Lanka, which was facilitated by the Open University of Sri Lanka. The paper describes the need of such a programme, the format of course delivery and assessment thereof, plus the benefits gained. This programme has produced 72 post graduates in Sri Lanka alone and more than 200 distant postgraduates worldwide in the field of sustainable energy engineering during last 10 years period. In terms of capacity building in the energy sector in Sri Lanka this is considered a great achievement. The experience gained by the local staff in the role of local facilitators who engaged in some of the academic related activities such as evaluation of students' presentation and co-supervision of thesis projects have been greatly appreciated as being additional benefits to the staff in terms of their own academic development and capacity building. Finally, conclusions are made on how remote programmes of study could successfully be delivered to places where such know-how is scarce by adapting appropriate technologies in training personnel at postgraduate level to meet the needs of the industry.

Electricity access remains a challenge for the majority of the West African countries, wherein 5 out of 16 have an electrification rate of less than 25%, with Burkina Faso having only 9% of the rural population with electricity access in 2017. This study presents a techno-economic feasibility analysis of solar PV system integration with conceptualized Pumped Hydro Storage (PHS) and electric batteries for Burkina Faso. The study explores two cases (a) an off-grid PV with a storage system for rural areas and (b) a grid-connected PV system for an urban location. The least-cost configuration of PV with feasible storage is investigated using HOMER. The results show that Solar PV with PHS remains the optimal system configuration for both rural and urban cases even when the construction costs of lower and upper reservoirs are considered. Battery energy storage systems remain an economically expensive solution even when the added costs of pumped hydro storage are included, owing to the low lifetime and high capital costs of battery storage. The capital cost of PV remains to be the most dominating factor for both cases, signifying the importance of policy interventions for cost reduction of PV for increased green electrification in West African countries.

Renewable energy applications require sound design and optimization of life cycle costs because they need upfront investments and as long as possible operating lifetimes are expected. Using modern tools for optimizing designs of grid-tied and autonomous plants allows investors to deploy these technologies while keeping risks within acceptable limits.

Nevertheless in Lebanon, the grid is intermittent and the most adapted solutions are dual-mode plants that can operate autonomously and with grid-tie. There are no existent simulation models particularly adapted to optimize these applications for such a situation. The objective of this research is to suggest and test a model adapted from commercially available software that can simulate the particular conditions of Lebanon. The studied solution has a PV generator associated with a PV charge controller, lead acid battery, a dual mode inverter, and transfer switchgear and protections. The research successfully met the objective of finding a setup in HOMER 2.68beta for simulating and optimizing a PV-Battery AC plant for an intermittent grid with scheduled blackouts.

The setup and adaptation in HOMER is made to replicate an existing reference PV-Battery plant at a public school. The measured data from this public school is used to validate the results obtained from the adapted HOMER simulation. The grid is supplied for an average of 12 hours per day at the reference site with a tariff of USD 0.1/kWh.

After the validation process, a sensitivity analysis is performed to simulate this plant under

1. Different grid supply hours, 12 and 18 hours of supply daily
2. Different grid electricity prices, USD 0.1 and 0.1375 /kWh
3. Simulation of PV plants to meet other load profiles typical of community and municipality building centers

All the simulations cross matched 20 different PV generator sizes to 7 different battery sizes for 5 different total setups.

The levelized cost of electricity, COE, is the main parameter used to find the optimum setups, whereas options that shortened the battery life to less than 12 years or couldn’t meet at least 90% of the required yearly load were filtered out. The COE is calculated manually since several corrections related to grid and net-metering limitations are not obtained directly from HOMER.

The simulated results can serve as a good indicator on how the systems would perform for typical public institutions in Lebanon, given the current conditions, and knowing that the range of this study is limited to small scale institutions with consumption levels less than 30 kWh/day. Storage capacity should also be limited to 100 kWh/day of useful storage, since batteries are not the best option to use for storage capacities higher than the mentioned limit.

The setup has a great potential for advancement and acts as a first step for Lebanon to have a specialized tool for simulating the performance of PV-battery AC plants optimized for the conditions existing in the country. Future steps could be made to improve and diversify the software to include:

• irradiation data that come from actual data logging data from other PV sites which are installed around the whole country, almost a 100
• financial analysis for offsetting private generation with fossil fueled gensets, which is the main backup for electricity blackouts
• wind turbine simulations, several installations are provisioned to be completed by the end of 2012, and it would be possible to carry out a similar validation process for small wind turbines
• pollution and other environmental costs
• value of lost load, “VOLL”, to compare different options in parallel with COE.

Vindkraftverk med olika magnetiseringsmetoder (elektromagneter eller permanentmagneter) och maskindriftstyper (direktdrift eller växellådsdrift) undersöks i denna rapport, gällande användningen av jordartsmetaller i dessa. I första delen av rapporten studeras miljö- och hälsopåverkan från jordartsmetallindustrin i den kinesiska provinsen Baotou. Detta då Baotou står för en stor del av försörjningen av jordartsmetaller till vindkraftverksindustrin. I den andra delen av rapporten undersöks skillnaderna i livscykelkostnader mellan vindkraftverk med olika generator- och maskindriftsystem. Rapporten innehåller informationssökningar om olika aspekter som berör dessa teman såsom exempelvis olika typer av vindkraftverksgeneratorer på marknaden, miljöpåverkan från olika ämnen i jordartsmineraler, återvinning av jordartsmetaller och processen från jordartsmineral till permanent-magnet. Informationen är främst inhämtad från vindkraftverkstillverkare, tekniska rapporter och artiklar.

I miljö- och hälsoanalysen blev slutsatsen att den negativa påverkan från jordartsmetallindustrin i Kina var för omfattande för att användningen av jordartsmetaller skulle rättfärdigas ur ett etiskt och miljömässigt perspektiv. Gruvdriften och bearbetningen av jordartsmetaller har lett till stora utsläpp av skadliga ämnen, såsom exempelvis tungmetaller och radioaktivt avfall, i provinsen Baotou. Dessa har gett allvarliga negativa konsekvenser för djur, människor och växtlighet.

Livscykelkostnaderna för vindkraftverk med olika generatorsystem beräknades med hjälp av LCC-metoden. Slutsatsen blev att det i dagsläget inte skiljde så mycket kostnadsmässigt i valet av maskindrifttyp eller magnetiseringsmetod. Enligt beräkningar ledde användningen av permanent-magneter inte till några ekonomiska fördelar. Istället var det kostnadsförhandlingar och osäkerhet i indata som gav de största kostnadsskillnaderna. Drift och underhållskostnaderna stod för de definitivt största utgifterna och investeringskostnaderna till generatorsystemen för de näststörsta utgifterna.

Detta projekt undersöker de ekonomiska, tekniska och miljömässiga aspekterna avtextilproduktion samt textilåtervinning. Paralleller dras mellan olika naturfibrer ochsyntetfibrer där såväl positiva som negativa aspekter belyses. I rapporten exemplifieras demest omdiskuterade textilierna; bomull, polyester, viskos och lyocell. Vidare görs en analyspå diverse textilåtervinningstekniker som finns i dagsläget och hur dessa är lämpade fördagens samhälle. På så sätt kan man undersöka vilka framtida möjligheter och begränsningarsom finns för utvecklingen av den textila återvinningen. En SWOT-analys utförs för attutreda möjligheterna för implementering av någon av de befintliga återvinningsteknikerna,kemisk respektive mekanisk återvinning, i Sverige. Utifrån SWOT-analysen som även räknassom rapportens resultat och även utifrån forskning i litteraturstudien dras slutsatsen attkemisk återvinning är tekniken som bäst lämpar sig utifrån Sveriges förhållanden. Slutsatserdras också kring vilka områden som landet måste fokusera på för att möjliggöra en storskaligåtervinning och detta involverar sorteringsteknologier, insamling och hantering av återvunnatextilfibrer. De specifika slutsaterna är:● Fokus bör ligga på att öka insamlingen av textilier då kemisk återvinning är mesteffektiv när det gäller återvinning av större volymer.● Majoriteten av all sortering av textilier bör automatiseras för att underlättahanteringen av insamlingen av textilier● Till en början bör endast textilier som gjorda på endast en fibertyp återvinnas, dettaeftersom att blandtextilier är mycket mer komplexa att hantera.Rapporten är uppdelad i två delar där den första delen innehåller introduktion, projektetsfrågeställningar samt målbeskrivning. Den senare delen är en längre litteraturstudie där faktaom olika typer av textilfibrer och hur produktion samt återvinning av dessa fibrer påverkarmiljö och samhälle. Litteraturstudien följs upp av en modellbeskrivning och en djupgåendeanalys av de slutgiltiga resultaten. I litteraturstudien återfinns även en intervju som ärgenomförd med klädföretaget Houdini Sportswear AB.

Att lagra värme och kyla under markytan, exempelvis i grundvattnet i en akvifer, används världenrunt. Oftast arbetar dessa system med två brunnsgrupper, en kall och en varmgrupp, som viavärmeväxlare och eller värmepumpar till ett energisystem i en fastighet.

Syftet med ett säsongslager i en akvifer är oftast att arbeta inom rimliga temperaturer och vattenuttagoch garantera att det kalla och det varma lagret inte påverkar varandra, samt att systemet i sin helhetinte påverkar förhållanden i det omgivande grundvattnet.

Regelverk och forskning inom akviferlager ligger tyvärr några år bakom marknaden och dentekologiska utvecklingen, trots stort intresse för förnyelsebara energikällor. Bristen av vetenskapligtframtagen kunskap inom området medför därmed en ökad risk för fel i konstruktion, fel inom 

framtagning av underlag för bedömning av tillståndsansökningar samt för förorening avgrundvattnet. Det kan även hända att akviferlager förbjuds baserad på fel grunder. Eftersom dettakan resultera i en begränsad användning av denna förnyelsebara energikälla är det viktigt att utökakunskapsnivån inom karakterisering av grundvattenresurser, miljöpåverkan av akviferlager samtmätning och uppföljning av dessa system.

Miljöpåverkan och prestandauppföljning har under detta projekt utförts i ett lågt tempereratakviferlager, Rosenborg, som äggs av Vasakronan och som är i drift sedan 2016. Anläggningen ärplacerat i en del av Solnastad som passerar Stockhoms åsen.

Grundvattenkemi kan studeras med hjälp av regelbundna provtagningar och statistiska analyser.Provtagningar utfördes i observationsbrunnar placerade innanför och utanför lagret, och pågick frånoch med 9 månader innan anläggningen satts i drift till och med slutat av effsysprojektet, dvsprovtagningskampanjen inkluderade en helt kyl och värmelagringssäsong. Utvärderingen inkluderadeStatistiska metoder så som Kruskal-Wallis rangordningstester samt en data-driven metod så kalladPCA (från engelskan Principal Component Analysis) har använts, även klusteranalyser användes föratt studera och jämföra variationer i specifika kemiska komponenter i brunnarna före och efterdriftsättningen av akviferlagret. Varibeln AVR (Akvifer Variation Ratio) föreslogs som ett sätt attutvärdera kemisk påverkan i akviferen före och efter driftsättning på ett mer övergripande sätt.

Den kemiska analysen visade Redox variationer i de kalla brunnarna, som sannolikt berodde påblandning av grundvatten från olika djup (olika Redox potential). Arsenik, som är kännslig till högretemperaturer enligt tidigare utfört arbete, visade en minskning i koncentration. Akviferlagret visadeen lägre hårdhet (proportionell mängd kalcium och magnesium) och lägre konduktivitet än detomgivande grundvattnet, som betyder att lagret har varit mindre känslig till intrång av saltvatten frånomgivningen. PCA och klusteranalysen visade små ändringar före och efter driften. Detkonstaterades att temperaturändringarna (+6 K sommartid och -5 K vintertid) hade en försumbarpåverkan i relation till akviferens ostörda temperatur (10,5°C).

Eftersom energiprestanda i ett akviferlager är beroende av hydrauliska och termiska aspekter hardessa studerats i projektet genom att jämföra volymmängder grundvatten som pumpades ut och insamt utifrån temperaturbalansen över året, båda med hänsyn till akviferens hydrogeologiskaförhållanden. Begreppen hydraulisk och termisk återhämtning har använts för kvantifiering avakviferens prestanda. Resultatet för det första året blev en hydraulisk återhämtning lika med 1,37 ochden termiska återhämtningen 0,33. Den hydrauliska återhämtningen av 1,37 betyder att en störreandel (37%) av lagrets vattenvolym återanvändes under kyluttaget jämfört med värmeuttagsperioden.Den termiska återhämtningen, som är relaterad till den önskade temperaturnivån (10,5°C) ellerbörvärde har det första året visar att 67% mindre kyla har plockat upp i relation till värmeuttaget.Det är viktigt att hålla i åtanke att denna indikatör är starkt beroende på börvärdet somdriftpersonalen bestämmer. Mer förståelse kring hur det hydrauliska och termiska prestanda kan tasfram i fortsättningsprojektet med hjälp av uppföljning av vattenflöden, nivåer ochgrundvattentemperaturer i systemet som utförs via en state of the art mätsystem som har applicerasunder projektet. Av speciell relevans är det fiberoptiska systemet som har installerats i samtligapumpbrunnar samt i ett antal observationsbrunnar i akviferlagret. Systemet mäter var 25 centimeteroch täcker det mesta av lagrets volym. Mätningarna kan i fortsättningen användas för att validera ennumerisk modell som har tagits fram inom projektet med programmet FEFLOW.

The overall objective of this thesis is to develop methods for fault detection and diagnosis for ground source heat pumps that can be used by servicemen to assist them to accurately detect and diagnose faults during the operation of the heat pump. The aim of this thesis is focused to develop two fault detection and diagnosis methods, sensitivity ratio and data-driven using principle component analysis.

For the sensitivity ratio method model, two semi-empirical models for heat pump unit were built to simulate fault free and faulty conditions in the heat pump. Both models have been cross-validated by fault free experimental data. The fault free model is used as a reference. Then, fault trend analysis is performed in order to select a pair of uniquely sensitive and insensitive parameters to calculate the sensitivity ratio for each fault. When a sensitivity ratio value for a certain fault drops below a predefined value, that fault is diagnosed and an alarm message with that fault appears. The simulated faults data is used to test the model and the model successfully detected and diagnosed the faults types that were tested for different operation conditions.

In the second method, principle component analysis is used to drive linear correlations of the original variables and calculate the principle components to reduce the dimensionality of the system. Then simple clustering technique is used for operation conditions classification and fault detection and diagnosis process. Each fault is represented by four clusters connected with three lines where each cluster represents different fault intensity level. The fault detection is performed by measuring the shortest orthogonal distance between the test point and the lines connecting the faults’ clusters. Simulated fault free and faulty data are used to train the model. Then, a new set of simulated faults data is used to test the model and the model successfully detected and diagnosed all faults type and intensity level of the tested faults for different operation conditions.

Both models used simple seven temperature measurements, two pressure measurements (from which the condensation and evaporation temperatures are calculated) and the electrical power, as an input to the fault detection and diagnosis model. This is to reduce the cost and make it more convenient to implement. Finally, for each models, a user friendly graphical user interface is built to facilitate the model operation by the serviceman.

Performance of Aquifer Thermal Energy Storage (ATES) systems for seasonal thermal storage depends on the temperature of the extracted/injected groundwater, water pumping rates and the hydrogeological conditions of the aquifer. ATES systems are therefore often designed to maintain a temperature difference possible between the warm side and cold side of the aquifer, without risking hydraulic and thermal intrusion between them or thermal leakage to surrounding area, i.e. maximize hydraulic and thermal recovery. Monitoring the operation of pumping and observation wells is crucial for the validation of ATES groundwater models utilized for their design, and measured data provides valuable information for researchers and practitioners working in the field. After months of planning and installation work, selected measurements recorded in an ATES monitoring project in Sweden during the first three seasons of operation are reported in this paper. The ATES system is located in Solna, in Stockholm esker, and it is used to heat and cool two commercial buildings with a total area of around 30,000 m 2 . The ATES consists of 3 warm and 2 cold pumping wells that are able to pump up to 50 liters per second. The monitoring system consists of temperature sensors and flow meters placed at the pumping wells, a distributed temperature-sensing rig employing fiber optic cables as linear sensor and measuring temperature every 0.25 m along the depth of all pumping and several observation wells, yielding temporal and spatial variation data of the temperature in the aquifer. The heat injection and extraction to and from the ground is measured using power meters at the main line connecting the pumping wells to the system. The total heat and cold extracted from the aquifer during the first heating and cooling season is 190MWh and 237MWh, respectively. A total of 143 MWh of heat were extracted during the second heating season. The hydraulic and thermal recovery values of the first year of operation was 1.37 and 0.33, respectively, indicating that more storage volume (50500m3 ) was recovered during the cooling season than injected (36900m3 ) in the previous heating season. The DTS data showed traces of the thermal front from the warm storage reaching the cold one. Only 33% of the thermal energy was recovered. These losses are likely due to ambient groundwater flow as well as conduction losses at the boundaries of the storage volume. Additionally, the net energy balance over the first year corresponds to 0.12 which indicates a total net heating of the ATES over the first year. It is recommended to increase the storage volume and achieve more hydraulic and thermal balance in the ATES system. This can enhance the thermal recovery and overall performance. Continuous monitoring of the ATES is and will be ongoing for at least 3 more years. The work presented in this paper is an initial evaluation of the system aiming to optimize the ATES performance.

The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5 degrees C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3 degrees C and 12.1 degrees C, and for the cold side 7.6 degrees C and 10.5 degrees C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy and thermal key performance indicators (KPI) for ATES and propose an additional thermal KPI named heat exchanger efficiency balance (beta HEX) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective. In addition to ATES energy and hydraulic KPIs, beta HEX can contribute in providing more complete picture on the ATES-building interaction performance as well as highlights if the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation which has been proven to be critical for the optimum ATES performance.

För att styra mot ett mer hållbart byggande miljöcertifieras allt fler byggnader. De system som ställer krav på ingående material i byggnaden är Miljöbyggnad, BREEAM och LEED. Vid en miljöcertifiering samlas en mängd fakta in om byggnaden och dess delmaterial för att sedan bedömas enligt det aktuella miljöcertifieringssystemets kriterier. Detta arbete syftar till att undersöka och bedöma vilket betyg eller antalet poäng prefabricerade betongelement från Benders byggsystem AB uppnår i respektive certifieringssystem.Arbetet har tagit hjälp av Betongföreningens rapporter om hur betongens egenskaper bidrar till att uppfylla kraven i certifieringssystemen. Resultatet bygger på materialspecifikation och information från Benders tillsammans med Betongföreningens ”Hållbart byggande med betong - Vägledning för miljöcertifiering enligt BREEAM/LEED/Miljöbyggnad”Resultatet visar vilka kriterier som Benders prefabricerade betongelement har möjlighet att bidra till i de olika certifieringssystemen. Studiens resultat visar att det är svårt att specifikt bedöma hur mycket en enskild byggnadsdel bidrar till eller vilken inverkan den kan ha på en certifierings slutbetyg. Samtliga certifieringsmetoder betraktar och bedömer byggnader som helhet och i vissa fall tillsammans med dess omgivning. Förutsättningarna för miljöcertifierings slutbetyg beror på faktorer utöver byggnad och dess tekniska lösningar. Geografisk plats, byggnadens orientering och omgivning är faktorer som ger en inverkan på bedömningen.Betongens materialegenskaper har en indirekt påverkansfaktor på många av aspekterna i certifieringssystemen. I vissa aspekter som berör exempelvis mängden avfall och lokal produktion finns det goda förutsättningar för poäng.Förutsättningar i en miljöcertifiering bygger på byggherrens/entreprenörens åtgärder och beslut är delvist avgörande för certifieringens utfall. I Benders fall är det särskilt viktigt att erbjuda fullständig och lättillgänglig produktinformation av deras byggelement för att underlätta för en certifiering av en byggnad.

The hydrogen fuel cell vehicle market is projected to increase in the coming years, and fuel cell vehicles will operate in an environment where they coexist with combustion engine vehicles. In this context, the PEM fuel cell will be exposed to significant amounts of contaminants on the roads that will decrease its performance and durability. In the present study the PEM fuel cell is exposed to 100 ppm of nitrogen dioxide in the airflow. Different methods for recovery of performance were tested; recovery during constant current load and by subjecting the cell to successive polarization curves. The results showed that the successive polarization curves are the best choice for recovery. However, recovery at low current density and high potential is also a good alternative.

Passive safety systems in a nuclear reactor allow to simplify the overall plant design, beside improving economics and reliability, which are considered to be among the salient goals of advanced Generation IV reactors. This work focuses on investigating the application of a self-actuated, gravity-driven shutdown system in a small lead-cooled fast reactor and its dynamic response to an initiating event. The reactor thermal-hydraulics and neutronics assessment were performed in advance. According to a first-order approximation approach, the passive insertion of shutdown assembly was assumed to be influenced primarily by three forces: gravitational, buoyancy and fluid drag. A system of kinematic equations were formulated a priori and a MATLAB program was developed to determine the dynamics of the assembly. Identifying the delicate nature of the balance of forces, sensitivity analysis for coolant channel velocities and assembly foot densities yielded an optimal system model that resulted in successful passive shutdown. Transient safety studies, using the multi-point dynamics code BELLA, showed that the gravity-driven system acts remarkably well, even when accounting for a brief delay in self-actuation. Ultimately the reactor is brought to a sub-critical state while respecting technological constraints.

Severe Accident Management (SAM) strategy aims to minimize exposure of public to potentially harmful radiation and the release of fission products into the environment. For assessment of SAM efficiency it is crucial to identify phenomena and parameters that present major contributions to the uncertainty in the magnitude and timing of the releases, assess their sensitivity, and quantify the uncertainty. In this work source term evaluations are performed, considering 50 uncertain input and modeling parameters that can affect the accident progression, release paths and magnitude of the release. MELCOR was used to perform evaluations for two accident scenarios initiated by: (1) large-break LOCA, and (2) station blackout, that lead to containment failure due to containment bypass or ex-vessel phenomena at RPV melt-through. Preliminary screening was performed using best-estimate and bounding assessments, where parameters were varied one-factor-at-a-time. The fraction of cesium release to the environment was found to be within ~2-35% of core inventory in case of LOCA, while it was within ~2-7% in case of SBO. This difference could be explained by the greater effect of suppression pool scrubbing in case of SBO. Releases obtained with modeling of solid core debris ejection from the vessel were marginally lower than without, for both LOCA and SBO. Dakota was used to perform Morris sensitivity analysis for the most influential parameters in the bounding assessment and the results are presented here.

In most ground-coupled heat pump systems, Borehole Heat Exchangers (BHE) represent the typical engineering solution for utilizing renewable energy from the ground. The design of a complex BHE field is a challenging task, due the inherent transient nature of the thermal interaction between the heat exchangers and the surrounding soil. A computation effective method for solving the 3D transient conduction equation describing the ground response to a variable heat load profile is the temporal superposition of pre-calculated temperature response factors or g-functions. In this study Comsol heat conduction models have been developed to calculate g-function values for a borehole field with 64 boreholes. The aim of the investigation is to get an insight on the numerical generation of temperature transfer functions and to some extent provide new information on the Finite Line Source method for analytically generated g-functions as well as on those existing behind existing design software such as EED. The results generally showed a good agreement in lower time ranges. Further in time, the Comsol model revealed to be influenced either by the domain dimensions or the simulation end time.

Ground source heat pumps are a widely used approach to efficiently heat single family houses. In addition to using the ground as a heat source during the winter, it can be used as heat sink and as a free cooling source during the summer. The most common way to carry out the heat exchange with the ground is with the help of energy collectors (borehole heat exchangers) in vertical wells. The quality of the heat exchange depends on the type of collector and on the flow conditions of the circulating fluid. For a complete understanding of the heat transfer performance, it is necessary to carry out careful temperature measurements at research installations and to do a preliminary characterization of the boreholes. These activities might represent a significant cost saving since the system can be optimized based on their outcome. The characterization consists of determining the type of rock and its thermal properties, the groundwater flow at different depths, and the borehole deviation according to the expected position. A comprehensive study about these characterization actions as well as temperature measurement techniques in boreholes using thermocouples and fiber optic technology are described in this report. Study cases from real installations are also presented to exemplify the characterization and measurement methods.

U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.

Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.

A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.

The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO₂ as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO₂ may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.

Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.

Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.

At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.

Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.

Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N₂, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.

In a distributed thermal response test, distributed temperature measurements are taken along a borehole heat exchanger during thermal response tests, allowing the determination of local ground thermal conductivities and borehole thermal resistances. In this article, the first results from six heat injection distributed thermal response tests carried out on a new, thermally insulated leg type, multi-pipe coaxial borehole heat exchanger are presented. The borehole heat exchanger consists of 1 insulated central and 12 peripheral pipes. Temperature measurements are carried out using fiber-optic cables placed inside the borehole heat exchanger pipes. Unique temperature and thermal power profiles along the borehole depth as a function of the flow rate and the total thermal power injected into the borehole are presented. A line source model is used for simulating the borehole heat exchanger thermal response and determining local variations of the ground thermal conductivity and borehole thermal resistance. The flow regime in the peripheral pipes is laminar during all distributed thermal response tests and average thermal resistances remain relatively constant, independently of the volumetric flow rate, being lower than those corresponding to U-pipe borehole heat exchangers. The thermal insulation of the central pipe significantly reduces the thermal shunt to the peripheral pipes even at low volumetric flow rates.

Different borehole heat exchanger designs have been discussed for many years. However, the U-pipe design has dominated the market, and the introduction of new designs has been practically lacking. The interest for innovation within this field is rapidly increasing and other designs are being introduced on the market. This paper presents a general state of the art summary of the borehole heat exchanger research in the last years. A first study of a prototype coaxial borehole heat exchanger consisting of one central pipe and five external channels is also presented. The particular geometry of the heat exchanger is analyzed thermally in 2-D with a FEM software. An experimental evaluation consisting of two in situ thermal response tests and measurements of the pressure drop at different flow rates is also presented. The latter tests are carried out at two different flow directions with an extra temperature measurement point at the borehole bottom that shows the different heat flow distribution along the heat exchanger for the two flow cases. The borehole thermal resistance of the coaxial design is calculated both based on experimental data and theoretically.

In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and boreholethermal resistance are determined at many instances along the borehole. Here, such a testis carried out at a 260 m deep water filled energy well, equipped with a U-pipe borehole heatexchanger, containing an aqueous solution of ethanol as working fluid. Distributed temperaturemeasurements are carried out using fiber optic cables placed inside the U-pipe, duringfour test phases: undisturbed ground conditions, fluid pre-circulation, constant heat injection,and borehole recovery. A line source model is used for simulating the borehole thermal response.Fluid temperature profiles during the test are presented. The results show local variationsof the ground thermal conductivity and borehole thermal resistance along the boreholedepth, as well as a deviation of the latter as compared to the one resulting from a standardthermal response test.

The thermal performance of a Borehole Heat Exchanger plays a significant role when defining the quality of heat exchange with the ground in Ground Source Heat Pumps. Different designs have been discussed and increased interest on innovation within this field has taken place during the last years. This paper presents the first measurement results from a 189 meters deep novel coaxial Borehole Heat Exchanger, consisting of an inner central pipe and an annular channel in direct contact with the surrounding bedrock. The measurements were taken during a distributed thermal response test using fiber optic cables installed in the energy well. Fluid temperature every ten meters along the borehole depth are presented and compared with similar measurements from a common U-pipe heat exchanger. A unique measurement of the borehole wall temperature in the coaxial collector illustrates how effective the heat transfer performance is through the annular channel.

A research project that aims at presenting recommendations for improving the COP of ground source heat pump systems by 10-20% through better design of Borehole Heat Exchangers (BHE) is described in this paper. Experiments are carried out with temperature measurements taken in different BHE types during heat pump operation conditions as well as during the thermal response tests. It is also expected to point out methods for having natural fluid circulation in the BHE, i.e. demonstrating that the heat carrier fluid can naturally circulate thanks to temperature induced density differences along the borehole depth, and thereby avoiding the use of electricity consuming pumps. A brief background presenting the most relevant work regarding BHE research around the world is first presented, followed by a comprehensive description of the current research at KTH. Some new measurements and obtained results are presented as an estimation of to what extent the project results have been achieved is discussed. An analysis on how the project results could allow reducing the borehole depth keeping today’s Coefficient of Performance is presented.

The first experiences with a multi-pipe borehole heat exchanger prototype consisting of an insulated central pipe and twelve parallel peripheral pipes are described. Secondary fluid distributed temperature measurements along the borehole depth, being the only ones of its kind in this type of heat exchanger, are presented and discussed. The measurements are carried out with fiber optic cables during heat injection into the ground, giving a detailed visualization of what happens both along the central and peripheral flow channels. The heat exchange with the ground mainly occurs along the peripheral channels and an indication of almost no thermal short circuiting, even while having large temperature differences between the down and upwards channels, is observed.

The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports the heat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with the ground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluid and its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcohol with 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet. The collectors are compared based on their borehole thermal resistance and pressure drop at different flow rates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute to better heat transfer, and inner micro fins in the pipes improve the performance of the collectors.

Some experiences with coaxial borehole heat exchanger prototypes are discussed here. Four different designs are described as they have been part of a research project at KTH: two pipe-inpipe annular designs, one multi-pipe and one multi-chamber design. A special focus is given to two of the prototypes, a pipe-in-pipe design with the external flow channel consisting of an annular cross section and partly insulated central pipe, and a multi-pipe design with twelve parallel peripheral pipes and an insulated central channel. The secondary fluid temperature profiles at low volumetric flow rates are presented for these two prototypes, measured with fiber optic cables during thermal response tests and allowing a detailed visualization of what happens along the heat exchanger depth. It is the first time this is carried out in these types of borehole heat exchangers. The measurements indicate good thermal performance and point at potential uses for these heat exchangers in different ground coupled applications.

Heat exchange with the bedrock for ground source heat pumps is commonly done with the help of U-pipe energy collectors in vertical boreholes. At the moment, there exist many uncertainties about how efficient the heat transfer between the rock and the collector is. For a complete performance analysis of these systems, a 260 m deep water filled borehole is characterized, by measuring the borehole deviation, the ground water flow and the undisturbed ground temperature. Significant attention is devoted to detailed temperature measurements along the borehole depth during operation providing a complete description of the temperature variations in time both for the secondary working fluid and for the ground water. The results show a deviated borehole from the vertical direction without any relevant ground water flow. The undisturbed ground temperature gradient varies from negative to positive at approximately half of the borehole depth. The transient response of the borehole during the heat pump start up is illustrated and it is observed that there does not exist any thermal short circuiting between the down and up-going pipes when the system is in operation.