Ice based Cool Thermal Energy Storage (CTES) systems have attracted much attention during last few decades. The reasons are mainly of economical and environmental nature. Compared to conventional refrigeration and air-conditioning systems without cool thermal energy storage, implementation of CTES will increase environmental standards and overall efficiency of the energy systems as it contributes to the phase-out of synthetic refrigerants and reduces peak loads in electricity grids. For the application of a cool thermal energy storages in refrigeration installations and HVAC systems in industry and building sector, it is necessary to have appropriate design tools in order to sufficiently accurate predict their performance. In this thesis theoretical and experimental investigations of two ice based cool thermal energy storage systems, namely static, indirect, external melt, ice-on-coil, i.e. ice bank system and dynamic, ice slurry cool thermal energy storage system are carried out. An ice bank storage technology for cooling purposes is known for a long time. The main drawbacks which are hindering its wider use are the system complexity, high first costs, system efficiency which is highly dependant on design, control and monitoring of the system, etc. On the other hand, ice slurry technology was not well studied until recently, while in the current scientific literature there are still differences between results and conclusions reported by different investigators. The aim of the present thesis is to extend the knowledge in the field of ice based CTES systems, thereby contributing in the development and wider utilization of those systems. In the first part of the thesis a computer application, named “BankaLeda” is presented. It enables simulation of an ice bank system performance. In order to verify developed simulation model an experimental evaluation has been performed. Field measurements have been conducted on a two module silo which was installed as a part of the refrigeration system in dairy and cheese factory “Antun Bohnec” in the city of Ludbreg in Croatia. Experimental findings were compared to the simulation model. The software „BankaLeda“ presents a strong optimization tool for designers and engineers in the field by providing a high degree of freedom in defining particular system design and operating parameters. It offers a basis for assessment and testing of a new energy efficient system arrangements and measures. Besides it will give decisionmakers the ability to test potential solutions in the process of CTES system design. In the second part of the thesis ice slurry pressure drop and heat transfer in horizontal straight tubes have been experimentally investigated. In particular a mixture of 10.3 % of ethanol and water with an initial freezing point of -4.4 °C was considered. It was found that the behaviour of ice slurry flow is changing with time and that ice slurry pressure drop is generally higher than for single phase flow. However for ice concentrations of 15 % and higher, for certain velocities ice slurry pressure drop is found to be of a similar value as for single phase fluid. Moreover, if ice slurry is to be used as a energy transport media it is recommended to keep the ice mass fraction at a level of 20 %. With tube geometry and thermophysical properties of a carrier fluid the heat transfer of ice slurry is generally a function of ice mass fraction and velocity. The imposed heat flux has no or has just minor influence on the heat transfer coefficient. Up to ice mass fraction between 10-15 % the mean heat transfer coefficient shows only slight (laminar flow) or no increase (turbulent flow) in comparison to single phase flow. Beyond that ice mass fraction the heat transfer coefficient is increasing significantly. The test data for pressure drop and heat transfer in laminar and turbulent regime was compared to several correlations from the literature. A new correlations for ice slurry pressure drop and heat transfer in the laminar flow regime, for 10.3 % ethanol and water mixture, were derived based on the present experimental data. The correlation for pressure drop predicts 82 % of the experimental data with ±15 % accuracy, while the correlation for heat transfer predicts 75 % of the data with the same accuracy. In order to investigate advantages and disadvantages of a dynamic, ice slurry system over a static, indirect, external melt, ice-on-coil CTES system and to assess their differences from economical aspects, a theoretical simulation model of an ice slurry CTES have been developed. It was found that the ice slurry based CTES systems posses higher economic and energy saving potential than static type systems. In the best case scenario the total energy consumption of dynamic CTES system was found to be approximately 25 % lower than for a static CTES system. / QC 20100715

Thermal energy storage (TES), the storage of heat or cooling, is a cost-effective energy storage technology that can greatly enhance the performance of the energy systems with which it interacts. TES acts as a buffer between transient supply and demand of energy. In solar thermal systems, TES enables the power output of the plant to be effectively regulated, despite fluctuating solar irradiance. In district energy systems, TES can be used to shift loads, allowing the system to avoid or take advantage of peak energy prices. The benefit of TES, however, can be significantly enhanced by dynamically optimizing the complete energy system. The ability of TES to shift loads gives the system newfound degrees of freedom which can be exploited to yield optimal performance. In the hybrid solar thermal/fossil fuel system explored in this work, the use of TES enables the system to extract nearly 50% more solar energy when the system is optimized. This requires relaxing some constraints, such as fixed temperature and power control, and dynamically optimizing the over a one-day time horizon. In a district cooling system, TES can help equipment to run more efficiently, by shifting cooling loads, not only between chillers, but temporally, allowing the system to take advantage of the most efficient times for running this equipment. This work also highlights the use of TES in a district energy system, where heat, cooling and electrical power are generated from central locations. Shifting the cooling load frees up electrical generation capacity, which is used to sell power to the grid at peak prices. The combination of optimization, TES, and participation in the electricity market yields a 16% cost savings. The problems encountered in this work require modeling a diverse range of systems including the TES, the solar power plant, boilers, gas and steam turbines, heat recovery equipment, chillers, and pumps. These problems also require novel solution methods that are efficient and effective at obtaining workable solutions. A simultaneous solution method is used for optimizing the solar power plant, while a static/dynamic decoupling method is used for the district energy system. / text

Rapporten avhandlar en konceptstudie för omvandling av termisk energi till elektrisk samt mekanisk energi, i den autonoma undervattensfarkosten SAPPHIRES. Inledningsvis utreds vilka förväntningar och krav som finns på konceptet för energiomvandling samt om där finns någon publicerad litteratur som redan gjort ansträngningar för att lösa det aktuella problemet. Allmän teori kring värmemotorer och en bred, systematisk litteratursökning inkluderas även i det arbetet. Energiomvandlingen antas kunna ske enligt två fall kallade ”hög-prestanda” och ”låg/medel-prestanda”, vilka innebär att mekanisk samt elektrisk effekt, respektive endast elektrisk effekt ska kunna levereras av konceptet. De mekaniska samt elektriska effekterna ska, vidare, kunna levereras om maximalt 600, respektive 6 kW, och konceptet ska åtminstone kunna uppfylla ett av energiomvandlingsfallen. Den faktiska konceptstudien utgörs av två iterationer av konceptgenereringar, -utvärderingar och -val och de visar att ett koncept kallat ”Öppet system inspirerat av nukleär värmeframdrivning” förefaller vara det bästa sättet att omvandla termisk energi i SAPPHIRES. Därtill indikerar en mer detaljerad analys, bestående av bland annat matematisk modellering och konceptuell konstruktion, att konceptet möjligen skulle kunna uppfylla så kallad ”hög-prestanda” och sedermera leverera både mekanisk och elektrisk effekt om 600, respektive 6 kW. Mer specifikt visar en matematisk analys, med hjälp av vissa antaganden rörande konceptets funktion, att ett ”Öppet system inspirerat av nukleär värmeframdrivning” skulle kunna leverera en mekanisk effekt om 1025 kW samt en elektrisk effekt om 141 kW. En grov, konceptuell konstruktion bekräftar också att konceptets vitala, ingående komponenter faktiskt kan rymmas inom de specificerade dimensionskraven (en cylinderformad volym med en längd och diameter om 1,7, respektive 0,5 m.). Det står dock klart att de möjliga koncepten för energiomvandling kraftigt begränsas av deras möjligheter att leverera tillräcklig mekanisk effekt, för att uppnå ”hög-prestanda”. Om endast ”låg/medel-prestanda” ska uppfyllas tillåts fler av de möjliga koncepten och i ett sådant fall skulle faktorer som underhåll, miljöpåverkan och SAPPHIRES signatur kunna prioriteras i högre utsträckning. / The report discusses a concept study regarding the conversion of thermal energy into electrical and mechanical energy, in the autonomous underwater vehicle SAPPHIRES. First, the requirements and expectations regarding the concept of energy conversion are investigated and efforts are made to identify any published literature, which has already made attempts of solving the issue. General theory regarding heat engines and an extensive literature study are also included in this work. The energy conversion is assumed to perform according to two cases called "high-performance" and "low/medium-performance", meaning mechanical and electrical energy or electrical power should be delivered by the concept, respectively. More specifically, the mechanical and electrical powers should be delivered of a maximum of 600 and 6 kW, respectively and the concept should at least fulfill one of the performance settings. The actual concept study comprises of two iterations of concept generations, evaluations and selections and shows that a concept called "Open system inspired by nuclear thermal propulsion" seems to be the best way of converting thermal energy on-board SAPPHIRES. Moreover, a more detailed analysis, comprising of, inter alia, mathematical modelling and conceptual design, indicates that the concept possibly can meet the so-called "high-performance" and thus, deliver both mechanical and electrical powers of 600 and 6 kW, respectively. More specifically, a mathematical analysis, based on some assumptions regarding the concept's functionality, shows that an "Open system inspired by nuclear thermal propulsion" could deliver a mechanical power of 1025 kW and an electrical power of 141 kW. Rough conceptual design also shows that the vital parts of the concept could fit within the specified maximal dimensions (a cylinder-shaped volume with a length and diameter of 1.7 and 0.5 m, respectively). However, it is clear the possible concepts of energy conversion are severely limited by their capacities of delivering enough mechanical energy, to meet the "high-performance" demands. Assuming only the "low/medium-performance" has to be met, more possible concepts becomes available and in that case, factors such as maintenance, environmental impact and signature of SAPPHIRES could be considered to a greater extent.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Solar energy is by far the greatest energy resource available to generate power. One of the difficulties of using solar energy is that it is not available 24 hours per day - some form of storage is required if electricity generation at night or during cloudy periods is necessary. If a combined cycle power plant is used to obtain higher efficiencies, and reduce the cost of electricity, storage will allow the secondary cycle to operate independently of the primary cycle. This study focuses on the use of packed beds of rock or slag, with air as a heat transfer medium, to store thermal energy in a solar thermal power plant at temperatures sufficiently high for a Rankine steam cycle. Experimental tests were done in a packed bed test section to determine the validity of existing equations and models for predicting the pressure drop and fluid temperatures during charging and discharging. Three different sets of rocks were tested, and the average size, specific heat capacity and density of each set were measured. Rock and slag samples were also thermally cycled between average temperatures of 30 ºC and 510 ºC in an oven. The classical pressure drop equation significantly under-predicts the pressure drop at particle Reynolds numbers lower than 3500. It appears that the pressure drop through a packed bed is proportional to the 1.8th power of the air flow speed at particle Reynolds numbers above about 500. The Effectiveness-NTU model combined with a variety of heat transfer correlations is able to predict the air temperature trend over the bed within 15 % of the measured temperature drop over the packed bed. Dolerite and granite rocks were also thermally cycled 125 times in an oven without breaking apart, and may be suitable for use as thermal storage media at temperatures of approximately 500 ºC. The required volume of a packed bed of 0.1 m particles to store the thermal energy from the exhaust of a 100 MWe gas turbine operating for 8 hours is predicted to be 24 × 103 m3, which should be sufficient to run a 25-30 MWe steam cycle for over 10 hours. This storage volume is of a similar magnitude to existing molten salt thermal storage. / AFRIKAANSE OPSOMMING: Sonenergie is die grootste energiebron wat gebruik kan word vir krag opwekking. ‘n Probleem met die gebruik van sonenergie is dat die son nie 24 uur per dag skyn nie. Dit is dus nodig om die energie te stoor indien dit nodig sal wees om elektrisiteit te genereer wanneer die son nie skyn nie. ‘n Gekombineerde kringloop kan gebruik word om ‘n hoër benuttingsgraad te bereik en elektrisiteit goedkoper te maak. Dit sal dan moontlik wees om die termiese energie uit die primêre kringloop te stoor, wat die sekondêre kringloop onafhanklik van die primêre kringloop sal maak. Dié gevalle studie ondersoek die gebruik van ‘n slakof- klipbed met lug as hitteoordragmedium, om te bepaal of dit moontlik is om hitte te stoor teen ‘n temperatuur wat hoog genoeg is om ‘n Rankine stoom kringloop te bedryf. Eksperimentele toetse is in ‘n toets-bed gedoen en die drukverandering oor die bed en die lug temperatuur is gemeet en vergelyk met voorspelde waardes van vergelykings en modelle in die literatuur. Drie soorte klippe was getoets. Die gemiddelde grootte, spesifieke hitte-kapasiteit en digtheid van elke soort klip is gemeet. Klip en slak monsters is ook siklies tussen temperature van 30 ºC en 510 ºC verkoel en verhit. Die klassieke drukverlies vergelyking gee laer waardes as wat gemeet is vir Reynolds nommers minder as 3500. Dit blyk dat die drukverlies deur ‘n klipbed afhanklik is van die lug vloeispoed tot die mag 1.8 as die Reynolds nommer groter as omtrent 500 is. Die ‘Effectiveness-NTU’ model gekombineerd met ‘n verskeidenheid van hitteoordragskoeffisiënte voorspel temperature binne 15 % van die gemete temperatuur verskil oor die bed. Doloriet en graniet klippe het 125 sikliese toetse ondergaan sonder om te breek, en is miskien gepas vir gebruik in ‘n klipbed by temperature van sowat 500 ºC Die voorspelde volume van ‘n klipbed wat uit 0.1 m klippe bestaan wat die termiese energie vir 8 ure uit die uitlaat van ‘n 100 MWe gasturbiene kan stoor, is 24 × 103 m3. Dit behoort genoeg te wees om ‘n 25 – 30 MWe stoom kringloop vir ten minste 10 ure te bedryf. Die volume is min of meer gelyk aan dié van gesmelte sout store wat alreeds gebou is.

Thesis (MEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Solar Assisted Power Generation (SAPG) can be seen as a synergy of solar and fossil plants – combining the environmental benefits of the former and the scale, efficiency and reliability of the latter. SAPG offers great potential for cost effective utilization of solar energy on utility scale and could accelerate the adoption of solar thermal energy technologies in the short and medium term, especially in countries with a significant coal base and a good solar resource such as Australia, China, United States, India and South Africa. SAPG is the replacement of bled-off steam in a Regenerative Rankine power cycle. Power plant simulations were performed using weather data for Lephalale, South Africa (Matimba power station). With an increase in the solar field outlet temperature, an increase in overall solar to electric efficiency was observed, superior to a stand-alone Solar Thermal Power Plant(s) (STPP) at similar temperatures. The performance of four solar collector technologies was compared: flat plate, evacuated tube, Linear Fresnel (LF) and Parabolic Trough (PT). This comparison was limited to the normal incidence angles of irradiation. For this application, nonconcentrating technologies are not competitive. For non-normal incidence angles, annual simulations were limited to PT and LF at final feedwater heater temperatures. The actual aperture area of around 80 000 m2 was used (50 MW thermal based on LF). On an equal aperture area basis, PT outperforms LF significantly. For the conventional North-South arrangement, LF needs to be around 53% of the specific installation cost (in $/m2 aperture area) of PT to be cost competitive. A SAPG plant at Lephalale was compared to a stand-alone Solar Thermal Power Plant STPP in a good solar resource area, namely Upington, South Africa – Parabolic Trough solar collector fields of equal size were considered for both configurations. It was found that the annual electricity generated with a SAPG plant is more than 25% greater than a stand-alone STPP. If the cost of SAPG is taken as 72% of the cost of a stand-alone STPP, this translates into SAPG being 1.8 times more cost effective than stand-alone STPP. Furthermore, SAPG performs better in high electricity demand months (South African winter – May to August). Stand-alone STPP have been adopted in South Africa and are currently being built. This was achieved by the government creating an attractive environment for Independent Power Producers (IPP). Eskom, the national power supplier, is currently investigating solar boosting at existing Eskom sites. This report argues that on a national level, SAPG, specifically solar preheating of feedwater, is a more viable solution for South Africa, with both its significant coal base and good solar resource. / AFRIKAANSE OPSOMMING: Son ondersteunde krag generasie (SOKG) kan gesien word as sinergie van sonkrag en fossiele brandstof aanlegte – dit voeg die omgewings voordele van die eersgenoemde en die grote, effektiwiteit en betroubaarheid van die laasgenoemde by mekaar. SOKG opper groot potensiaal vir koste effektiewe gebruik van son energie op nutsmaatskappyskaal en kan die aanvaarding van sontermiese energietegnologieë in die kort en medium termyn versnel, veral in lande met beduidende kool reserwes en goeie sonkrag voorkoms soos Australië, China, Verenigde State van Amerika, Indië en Suid-Afrika. SOKG impliseer die vervanging van aftap stoom in die regeneratiewe Rankine krag kringloop. Kragstasie simulasies was gedoen met die gebruik van weer data van Lephalale, Suid-Afrika (Matimba kragstasie). Met die toename van die sonveld uitlaat temperatuur kon oorhoofse son-na-elektrisiteit effektiwiteit vasgestel word, wat hoër is as die van alleenstaande sontermiese krag stasie (STKS) by soortgelyke temperature. Die effektiwiteit van vier son kollekteerder tegnologieë was vergelyk: plat plaat, vakuum buis, lineêre Fresnel (LF) en paraboliese trog (PT). Die vergelyking was beperk tot normale inval van bestraling. Vir hierdie toepassing is nie-konsentreerende tegnologie nie mededingend nie. Vir nie-normale inval hoeke was jaarlange simulasies beperk tot PT en LF by finale voedingswater temperatuur. Die werklike opening area van omtrent 80 000 m2 was gebruik (50 MW termies gebaseer op LF). By gelyke opening area, uitpresteer PT LF beduidend. Vir die gebruiklike Noord-Suid rankskikking benodig LF omtrent 53% van die spesifieke installasie kostes (in $/m2 opening area) van PT om kostes mededingend te kan wees. ‘n SOKG aanleg by Lephalale was vergelyk met alleenstaande STKS in die goeie son voorkoms gebied van Upington, Suid-Afrika – Paraboliese trog kollekteerder velde van gelyke grote was oorweeg vir al twee konfigurasies. Dit was gevind dat die jaarlikse elektrisiteit gegenereer vanaf SOKG meer as 25% is as die van alleenstaande STKS. Indien SOKG oorweeg word met 72% van die kostes van alleenstaande STKS, dan beteken dit dat SOKG 1.8 keer meer koste effektief is as alleenstade STKS. Verder, SOKG presteer beter in die hoer elektrisiteitsnavraag maande (Suid- Afrikaanse winter – May tot Augustus). Alleenstaande STKS is gekies vir Suid-Afrika en word tans gebou. Dit is bereik deur dat die regering ‘n aantreklike omgewing geskep het vir onafhanglike krag produsente. Eskom ondersoek tans SOKG by bestaande Eskom persele. Hierdie verslag beweer dat op nasionale/Eskom vlak, SOKG, besonders son voorverhitting van voedingswater, meer haalbare oplossing is vir Suid-Afrika met sy beduidende koolreserwes en goeie son voorkoms.

Didėjant šiluminės energijos ir kuro sąnaudoms, jų taupymas darosi aktualus daugeliui vartotojų. Vis daugiau žmonių domisi energijos taupymo priemonėmis gyvenamuose namuose. Ne tik privačių namų, bet ir privatizuotų butų savininkai daugiabučiuose namuose besikurdami į bendriją, imasi konkrečių veiksmų pastatų šilumos nuostoliams mažinti. Jiems svarbi ne tik finansinė parama, bet ir techninė bei informacinė pagalba. Energijos suvartojimas pastatams šildyti priklauso nuo šalies klimato ypatumų, energetinių resursų įsigijimo galimybių ir kainų, statybos tradicijų ir aplinkosaugos reikalavimų. Energetinių sąnaudų mažinimas gyvenamiesiems pastatams šildyti svarbus ne tik ekonominiu, bet ir ekologiniu požiūriu. Namų modernizavimas pagerina gyvenimo komforto parametrus. Pastato modernizacijos tikslas – padaryti pastatą ekonomiškesnį, komfortiškesnį ir taip pailginti jo eksplotacijos laiką bei padidinti vertę. Šiame darbe pateikiami duomenys apie pastatų atitvarinių konstrukcijų defektus, jų įvertinimo būdus, pastatų šiluminės modernizacijos technologijas ir ekonominę naudą, tyrimų metodus, pastatų konstrukcijose vykstančius šilumos ir masės mainų procesus, įvertinus jų poveikį pastatui. Darbą suraro 97 puslapiai, 55 paveikslai, 11 lentelių, 43 literatūros šaltiniai, priedai. / With the increase of thermal energy and fuel costs, saving is becoming an important issue for many consumers. More and more people are taking an interest in energy – saving measures in their living quarters. Not only owners of private houses but private flat owners in a multi-storey block of flats when setting up a society/community tend to take concrete action to reduce heat losses. They take an interest not only in posssible financial support but also in technical and information assistance. The energy consumption for heating buildings depends on the specific factors of a given country, the possibilities of acquiring energy resources and its price, the building traditions and environmental requirements. Reducing energy costs for heating residential buildings is an important economical and environmental issue. Modernizing houses improves life quality standards. The aim of modernising a building – to make the building more economically efficient, more comfortable and to prolong its lifecycle also to increase its value. This paper presents data on box construction building defects, their assessment methods, thermal modernizing technology and economic benefits, research methods, the heat and mass exchange processes occurring in building constructions, having assessed their impact on the building. Thesis consist of: 97 p. text, 55 pictures, 11 tables, 43 bibliographical entries, references.

Sustainability has been at the centre of global attention for decades. One of the most challenging areas toward sustainability is the agricultural sector. Here, the commercial greenhouse is one of the most effective cultivation methods with a yield per cultivated area up to 10 times higher than for open land farming. However, this improvement comes with a higher energy demand. Therefore, the significance of energy conservation and management in the commercial greenhouse has been emphasized to enable cost efficient crop production. This Doctoral Thesis presents an assessment of energy pathways for improved greenhouse performance by reducing the direct energy inputs and by conserving energy throughout the system. A reference theoretical model for analyzing the energy performance of a greenhouse has been developed using TRNSYS. This model is verified using real data from a conventional greenhouse in Stockholm (Ulriksdal). With this, a number of energy saving opportunities (e.g. double glazing) were assessed one by one with regards to the impact on the annual heating, cooling and electricity demand. Later, a multidimensional energy saving method, the “Closed Greenhouse”, was introduced. The closed greenhouse is an innovative concept with a combination of many energy saving opportunities. In the ideal closed greenhouse configuration, there are no ventilation windows, and the excess heat, in both sensible and latent forms, needs to be stored using a seasonal thermal energy storage. A short term (daily) storage can be used to eliminate the daily mismatch in the heating and cooling demand as well as handling the hourly fluctuations in the demand. The key conclusion form this work is that the innovative concept “closed greenhouse” can be cost-effective, independent of fossil fuel and technically feasible regardless of climate condition. For the Nordic climate case of Sweden, more than 800 GWh can be saved annually, by converting all conventional greenhouses into this concept. Climate change mitigation will follow, as a key impact towards sustainability. In more detail, the results show that the annual heating demand in an ideal closed greenhouse can be reduced to 60 kWhm-2 as compared to 300 kWhm-2 in the conventional greenhouse. However, by considering semi-closed or partly closed greenhouse concepts, practical implementation appears advantageous. The required external energy input for heating purpose can still be reduced by 25% to 75% depending on the fraction of closed area. The payback period time for the investment in a closed greenhouse varies between 5 and 8 years depending on the thermal energy storage design conditions. Thus, the closed greenhouse concept has the potential to be cost effective. Following these results, energy management pathways have been examined based on the proposed thermo-economic assessment. From this, it is clear that the main differences between the suggested scenarios are the type of energy source, as well as the cooling and dehumidification strategies judged feasible, and that these are very much dependent on the climatic conditions Finally, by proposing the “solar blind” concept as an active system, the surplus solar radiation can be absorbed by PVT panels and stored in thermal energy storage for supplying a portion of the greenhouse heating demand. In this concept, the annual external energy input for heating purpose in a commercial closed greenhouse with solar blind is reduced by 80%, down to 62 kWhm-2 (per unit of greenhouse area), as compared to a conventional configuration. Also the annual total useful heat gain and electricity generation, per unit of greenhouse area, by the solar blind in this concept is around 20 kWhm-2 and 80 kWhm-2, respectively. The generated electricity can be used for supplying the greenhouse power demand for artificial lighting and other devices. Typically, the electricity demand for a commercial greenhouse is about 170 kWhm-2. Here, the effect of “shading” on the crop yield is not considered, and would have to be carefully assessed in each case. / Hållbarhet har legat i fokus under decennier. En av de mest utmanande områdena är jordbrukssektorn, där. kommersiella växthus är ett av de mest effektiva odlingsalternativen med en avkastning per odlad yta upp till 10 gånger högre än för jordbruk på friland. Dock kommer denna förbättring med ett högre energibehov. Därför är energieffektivisering i kommersiella växthus viktig för att möjliggöra kostnadseffektiv odling. Denna doktorsavhandling presenterar en utvärdering av olika energiscenarios för förbättring av växthusens prestanda genom att minska extern energitillförsel och spara energi genom i systemet som helhet. För studien har en teoretisk modell för analys av energiprestanda i ett växthus utvecklats med hjälp av TRNSYS. Denna modell har verifierats med hjälp av verkliga data från ett konventionellt växthus i Stockholm (Ulriksdal). Med denna modell har ett antal energibesparingsåtgärder (som dubbelglas) bedömts med hänsyn till de totala värme-, kyl-och elbehoven. En flerdimensionell metod för energibesparing, det s.k. "slutna växthuset", introduceras. Det slutna växthuset är ett innovativt koncept som är en kombination av flera energibesparingsmöjligheter. I den ideala slutna växthuskonfigurationen finns det inga ventilationsfönster och värmeöverskott, både sensibel och latent, lagras i ett energilager för senare användning. Daglig lagring kan användas för att eliminera den dagliga obalansen i värme-och kylbehovet. Ett säsongslager introduceras för att möjliggöra användandet av sommarvärme för uppvärmning vintertid. Den viktigaste slutsatsen från detta arbete är att ett sådant innovativt koncept, det "slutna växthuset" kan vara kostnadseffektiv, oberoende av fossila bränslen och tekniskt genomförbart oavsett klimatförhållanden. För det svenska klimatet kan mer än 800 GWh sparas årligen, genom att konvertera alla vanliga växthus till detta koncept. Det årliga värmebehovet i ett idealiskt slutet växthus kan reduceras till 60 kWhm-2 jämfört med 300 kWhm-2 i ett konventionellt växthus. Energibesparingen kommer även att minska miljöpåverkan. Även ett delvis slutet växthus, där en del av ytan är slutet, eller där viss kontrollerad ventilation medges, minskar energibehovet samtidigt som praktiska fördelar har kunnat påvisas. Ett delvis slutet växthus kan minska energibehovet för uppvärmning med mellan 25% och 75% beroende på andelen sluten yta. En framräknad återbetalningstid för investeringen i ett slutet växthus varierar mellan 5 och 8 år beroende på design av energilagringssystemet. Sålunda har det slutna växthuskonceptet potential att vara kostnadseffektiv. Mot bakgrund av dessa lovande resultat har sedan scenarios för energy management analyserats med hänsyn till termo-ekonomiska faktorer. Från detta är det tydligt att de viktigaste skillnaderna mellan de föreslagna scenarierna är den typ av energikälla, samt kyl- och avfuktningsstrategier som används, och dessa val är mycket beroende av klimatförhållandena. Slutligen, föreslås ett nytt koncept, en s.k. "solpersienn", vilket är ett aktivt system där överskottet av solstrålningen absorberas av PVT-paneler och lagras i termiskenergilager för att tillföra en del av växthuseffekten värmebehov. I detta koncept minskar den årliga externa energitillförseln för uppvärmning i ett slutet växthus med 80%, ner till 62 kWhm-2. Den totala värme- och elproduktionen, med konceptet "solpersienn" blir cirka 20 kWhm-2 respektive 80 kWhm-2. Elproduktion kan användas för artificiell belysning och annan elektrisk utrustning i växthuset. / <p>QC 20130910</p>

In Sweden, there are about 0.5 million single-family houses that are heated by electricity alone, and rising electricity costs force the conversion to other heating sources such as heat pumps and wood pellet heating systems. Pellet heating systems for single-family houses are currently a strongly growing market. Future lack of wood fuels is possible even in Sweden, and combining wood pellet heating with solar heating will help to save the bio-fuel resources. The objectives of this thesis are to investigate how the electrically heated single-family houses can be converted to pellet and solar heating systems, and how the annual efficiency and solar gains can be increased in such systems. The possible reduction of CO-emissions by combining pellet heating with solar heating has also been investigated. Systems with pellet stoves (both with and without a water jacket), pellet boilers and solar heating have been simulated. Different system concepts have been compared in order to investigate the most promising solutions. Modifications in system design and control strategies have been carried out in order to increase the system efficiency and the solar gains. Possibilities for increasing the solar gains have been limited to investigation of DHW-units for hot water production and the use of hot water for heating of dishwashers and washing machines via a heat exchanger instead of electricity (heat-fed appliances). Computer models of pellet stoves, boilers, DHW-units and heat-fed appliances have been developed and the parameters for the models have been identified from measurements on real components. The conformity between the models and the measurements has been checked. The systems with wood pellet stoves have been simulated in three different multi-zone buildings, simulated in detail with heat distribution through door openings between the zones. For the other simulations, either a single-zone house model or a load file has been used. Simulations were carried out for Stockholm, Sweden, but for the simulations with heat-fed machines also for Miami, USA. The foremost result of this thesis is the increased understanding of the dynamic operation of combined pellet and solar heating systems for single-family houses. The results show that electricity savings and annual system efficiency is strongly affected by the system design and the control strategy. Large reductions in pellet consumption are possible by combining pellet boilers with solar heating (a reduction larger than the solar gains if the system is properly designed). In addition, large reductions in carbon monoxide emissions are possible. To achieve these reductions it is required that the hot water production and the connection of the radiator circuit is moved to a well insulated, solar heated buffer store so that the boiler can be turned off during the periods when the solar collectors cover the heating demand. The amount of electricity replaced using systems with pellet stoves is very dependant on the house plan, the system design, if internal doors are open or closed and the comfort requirements. Proper system design and control strategies are crucial to obtain high electricity savings and high comfort with pellet stove systems. The investigated technologies for increasing the solar gains (DHW-units and heat-fed appliances) significantly increase the solar gains, but for the heat-fed appliances the market introduction is difficult due to the limited financial savings and the need for a new heat distribution system. The applications closest to market introduction could be for communal laundries and for use in sunny climates where the dominating part of the heat can be covered by solar heating. The DHW-unit is economical but competes with the internal finned-tube heat exchanger which is the totally dominating technology for hot water preparation in solar combisystems for single-family houses. / <p>QC 20100916</p>

Este trabalho tem por objetivo analisar as perspectivas dos gases combustíveis como energia final para a obtenção de energia útil, em aquecimento direto (AD) e calor de processo (CP), identificando e quantificando potenciais como alternativa da eletrotermia. São comparados dois panoramas na avaliação das economias de energia primária pela substituição da eletrotermia: o primeiro considerando que a energia substituída oriunda de energéticos do parque gerador; e o segundo levando em conta que a redução se refletiu nas termelétricas. Para atingir este objetivo, o trabalho se inicia com uma revisão bibliográfica, onde são tratados os aspectos necessários para um melhor entendimento do texto, com os conceitos de eletrotermia, calor e termodinâmica, seguindo-se um capítulo destinado aos gases combustíveis, suas características e disponibilidade futura para a conversão. As informações básicas para a análise dos potenciais nos setores foram tomadas a partir do último Balanço de Energia Útil, além de trabalhos desenvolvidos no mercado industrial pelo autor. O trabalho discorre também sobre configurações tecnológicas usadas nas conversões, incluindo os custos envolvidos. Na conclusão, os cálculos mostraram que significativas economias de energia primária podem ser obtidas com a conversão da eletrotermia para gases combustíveis no setor industrial brasileiro, considerando a eletricidade produzida a partir de plantas termelétricas. / This paper aims to analyze the prospects of fuel gases as final energy in order to get useful energy in direct heating and process heat, identifying and qualifying potentials as the alternative of electrothermy. Two panoramas are compared in the evaluation of primary energy displacement: the first one considering the replaced energy coming from energy generating facilities and the second taking into account that the reduction was reflected in thermoelectric power plants. To achieve this goal, the work begins with a literature review which covers the aspects needed for a better understanding of the text, with the concepts of electrothermy, heat and thermodynamics, followed by a chapter intended for fuel gases, their characteristics and future readiness for conversion. The basic information for the analysis of potential sectors were taken for the last Useful Energy Balance, and work undertaken by the author in the industrial market. The paper also discourses about technological configurations used in conversions, including also the costs involved. In conclusion, the calculations showed that significant primary energy savings can be obtained through the conversion of electrothermy by fuel gases in the Brazilian industrial sector, taking into account the electricity produced from thermoelectric power plants.

Submitted by Maicon Juliano Schmidt (maicons) on 2015-03-30T18:22:27Z No. of bitstreams: 1 Israel de Oliveira.pdf: 2249672 bytes, checksum: 651678b57093fe8cfdec97b6e6da1274 (MD5) / Made available in DSpace on 2015-03-30T18:22:27Z (GMT). No. of bitstreams: 1 Israel de Oliveira.pdf: 2249672 bytes, checksum: 651678b57093fe8cfdec97b6e6da1274 (MD5) Previous issue date: 2014-01-31 / JTI Processadora de Tabaco do Brasil Ltda / Programa de Bolsas de Estudo Talentos Tecnosinos / O Brasil é um dos maiores produtores mundiais de tabaco de estufa e a região sul é a maior responsável por essa produção, principalmente o estado do Rio Grande do Sul. Uma das etapas do processo de beneficiamento desse produto é a secagem (cura) das folhas, que utiliza essencialmente lenha como fonte de energia. Esse trabalho apresenta um estudo dos aspectos energéticos que envolvem a cura de tabaco da espécie Virgínia, os resultados e análises das simulações realizadas no software TRNSYS, de um sistema solar térmico com aquecimento de água para complemento energético desse processo de cura. A partir de dados experimentais obtidos em processos de cura, foram definidos os parâmetros mais importantes para a determinação da carga térmica necessária e calculadas as perdas térmicas envolvidas. Os resultados apresentados pelas simulações mostraram que o sistema de energia solar proposto, atuando como fonte auxiliar de energia em uma estufa do tipo bulk, é capaz de atender completamente a carga térmica da primeira fase do processo de cura e contribuir com o aumento da temperatura na estufa necessário à cura dessa espécie de tabaco, gerando reduções no consumo de lenha do processo da ordem de 18 a 39 %, considerando que esse ocorra em um período de sete dias ensolarados no verão, na região de Santa Cruz do Sul-RS. / Brazil is one of the largest barn tobacco producers and the southern region is largely responsible for this production, especially the state of Rio Grande do Sul. One of the steps involved in this product’s processing chain is the leaves drying (curing), which essentially uses firewood as energy source. This work presents a study of the energy aspects involving the curing of Virginia tobacco, the results and analysis of simulations, using the TRNSYS software, of a solar thermal energy system with water heating to complement this curing process. From the experimental data obtained in curing processes, the most important parameters for the determination of thermal load were defined and the heat losses involved were calculated. The results presented by these simulations showed that the proposed solar energy system, acting as an auxiliary power source of a bulk type barn, can completely meet the thermal load of the first phase of the curing process and contribute to the increase of temperature in the barn necessary to cure this kind of tobacco, reducing 18-39 % the firewood consumption in the process, assuming a seven sunny days period during the summer at the region of Santa Cruz do Sul – RS.