Absorption heat pump water heaters offer improved performance compared to conventional direct-fired water heaters, with the potential for coefficients of performance well in excess of 1. A primary energy usage comparison with electric heat pumps shows that absorption systems can be competitive with current technology. However, the implementation of these systems in the residential and light commercial market has not been practical for several reasons, including a limited knowledgebase on absorption systems for this application and the lack of compact and economically viable heat and mass exchangers. An improved understanding of the coupled heat and mass transfer processes in thermally driven absorption systems to be used as heat pump water heaters was obtained over the course of this study. In addition, microchannel heat and mass exchangers that enable such compact gas-fired heat pump water heaters were developed and tested. Performance at design and off-design conditions over a range of water and ambient temperatures was simulated in detail with a system-level model developed for this purpose. The system-level model was coupled with a water-tank model to investigate several water heating scenarios including a cold start, response to a medium sized draw and response to stand-by losses. Heat and mass exchangers were designed using component-level heat and mass transfer models. The heat and mass exchangers were first installed and evaluated on a breadboard test facility. Insights from these experiments were then used to design and fabricate a monolithic unit integrating several of the microchannel heat and mass exchangers, coupled with a gas-fired desorber heat exchanger to yield a stand-alone water heater prototype. The performance of the prototype was investigated over a range of water and ambient temperatures. A comparison of results was performed to investigate the deviation between model predictions and experimental values. A refined model was developed that more accurately predicted experimental results. Energy-use and cost analyses were performed and showed the potentially significant energy savings of thermally driven heat pump water heaters.

Thesis (M. Sc.)--University of Hong Kong, 1983.

<p>Water has been heated with the sun has almost as long as there have been humans, but itis not until recently that more advanced and effective solar water heating systems havebecome common, and they are still gaining ground. Through the years new systems andnew solar collectors have been developed. In Kosovo, however, not much attention hasbeen paid to replace fossil fuels with renewable energy sources and solar water heatingsystems is a new concept.The United Nations Development Programme (UNDP) in Kosovo is working on a projecton sustainable development in Dragash Municipality in southern Kosovo. A solar waterheating system has recently been installed at the hospital in Dragash, as part of the UNDPproject. The system is a pilot project, to see how well solar energy can be used in thisarea.The existing solar water heating system at the hospital in Dragash was examined andevaluated. The possibilities of using the fundamental principle of the solar water heatingsystem at the hospital on residential houses in Dragash were looked into. Six prototypesof average residential houses in the village of Brod and Dragash Town were created. Thesolar collector size and storage needed to meet the demands for the six house prototypeswere calculated. Information on the incoming solar irradiation for each hour of a year wasobtained from the online service SoDa Solar Radiation Data. The total annual incomingsolar radiation for one square meter was calculated.The environmental, social and economic effects of solar water heating in Dragash wereconsidered and discussed. Rough economic calculations were made on the effects ofinstallation of solar water heating systems.The solar water heating system at the hospital in Dragash is a good pilot project, and islikely to work satisfyingly. The annual output effect of the system is approximately 7 400kWh. The fundamental principle needs to be altered to work on residential houses. Thesolar collector needs to be of a cheaper kind, and the collector and storage tank can be ofsmaller dimensions.Solar water heating can contribute to Kosovo’s work toward sustainable environmental,social and economic development focusing on hot water supply. Kosovo has sufficientsolar radiation for solar water heating systems to work in a satisfactory way. The outputeffect for a solar water heating system in Dragash is around 390 kWh/(m2∙year) with atotal efficiency for the system of 30%. If the solar water heating system replaces heatingby electricity the annual savings can be 31 €/m2 solar collector. The biggest obstacles forthe use of solar energy are the public’s lack of knowledge on solar water heating andenvironmental problems connected to energy, as well as economy.The work done in this thesis is a good foundation for future research on solar energy inKosovo. It can be extended and elaborated with more thorough economic calculations,since economy is an important factor in the future for solar energy. Only roughcalculations were made in this thesis, since it has a technical approach. More extensiveresearch could also be done to evaluate the possibilities of using solar water heating forspace heating.</p> / <p>Varmvatten har värmts med hjälp av solen nästan så länge det funnits människor, men detär inte förrän nyligen som mer avancerade och effektivare solvärmesystem har blivitvanliga, och de blir allt vanligare. Genom åren har nya system och nya solfångareutvecklats. I Kosovo däremot har inte mycket uppmärksamhet ägnats åt att ersätta fossilabränslen med förnyelsebara energikällor, och solvärme är ett nytt koncept.FN:s utvecklingsprogram (UNDP) i Kosovo arbetar med ett projekt med målet hållbarutveckling i Dragash kommun i södra Kosovo. Ett solvärmesystem har nyligeninstallerats på sjukhuset i Dragash, som en del av UNDP:s projekt. Systemet är ettpilotprojekt för att se hur bra solenergi fungerar i det här området.Det befintliga solvärmesystemet på sjukhuset i Dragash undersöktes och utvärderades.Möjligheterna att använda grundprincipen för solvärmesystemet på sjukhuset påbostadshus i Dragash undersöktes. Sex prototyper för genomsnittliga hus i byn Brod och iDragash centrum togs fram. Solfångararean och ackumulatortanksvolymen som krävs föratt klara behoven för de sex husprototyperna beräknades. Information om solinstrålningenför varje hus erhölls från SoDa Solar Radiation Data. Den totala solinstrålningen på enkvadratmeter beräknades.De miljömässiga, sociala och ekonomiska effekterna av solvärme i Dragash diskuterades.Ekonomiska överslagsberäkningar gjordes på effekterna av installation av solvärme.Solvärmesystemet på sjukhuset i Dragash är ett bra pilotprojekt, och är sannolikt attfungera tillfredsställande. Den årliga energi som systemet kan ge kommer att vara ungefär7 400 kWh. Grundprincipen behöver ändras för att fungera på bostadshus. Solfångarnabehöver vara av en billigare typ, och storleken på solfångare och ackumulatortankbehöver vara mindre.Solvärme kan bidra till Kosovos arbete mot hållbar miljömässig, social och ekonomiskutveckling med fokus på varmvattenbehov. Kosovo har tillräcklig solinstrålning för attsolvärmesystem ska fungera tillfredsställande. Med en totalverkningsgrad på 30 % för ettsolvärmesystem kan systemet ge ungefär 390 kWh/(m2∙year). Om systemet ersätteruppvärmning med el kan de årliga besparingarna bli ungefär 31 €/m2 solfångare. Destörsta hindren för användning av solenergi är allmänhetens brist på kunskap om solvärmeoch miljöproblem kopplade till energi, samt ekonomi.Arbetet i detta examensarbete är en bra grund för fortsatta studier om solenergi i Kosovo.Arbetet kan vidgas och utvecklas med mer ingående ekonomiska beräkningar, eftersomekonomi är en viktig faktor i framtiden för solenergi. Endast överslagsberäkningar gjordesi detta examensarbete, eftersom det har ett tekniskt förhållningssätt. Mer omfattandestudier kan också göras för att utvärdera möjligheterna ätt använda solvärme föruppvärmning av bostäder.</p>

Water has been heated with the sun has almost as long as there have been humans, but itis not until recently that more advanced and effective solar water heating systems havebecome common, and they are still gaining ground. Through the years new systems andnew solar collectors have been developed. In Kosovo, however, not much attention hasbeen paid to replace fossil fuels with renewable energy sources and solar water heatingsystems is a new concept.The United Nations Development Programme (UNDP) in Kosovo is working on a projecton sustainable development in Dragash Municipality in southern Kosovo. A solar waterheating system has recently been installed at the hospital in Dragash, as part of the UNDPproject. The system is a pilot project, to see how well solar energy can be used in thisarea.The existing solar water heating system at the hospital in Dragash was examined andevaluated. The possibilities of using the fundamental principle of the solar water heatingsystem at the hospital on residential houses in Dragash were looked into. Six prototypesof average residential houses in the village of Brod and Dragash Town were created. Thesolar collector size and storage needed to meet the demands for the six house prototypeswere calculated. Information on the incoming solar irradiation for each hour of a year wasobtained from the online service SoDa Solar Radiation Data. The total annual incomingsolar radiation for one square meter was calculated.The environmental, social and economic effects of solar water heating in Dragash wereconsidered and discussed. Rough economic calculations were made on the effects ofinstallation of solar water heating systems.The solar water heating system at the hospital in Dragash is a good pilot project, and islikely to work satisfyingly. The annual output effect of the system is approximately 7 400kWh. The fundamental principle needs to be altered to work on residential houses. Thesolar collector needs to be of a cheaper kind, and the collector and storage tank can be ofsmaller dimensions.Solar water heating can contribute to Kosovo’s work toward sustainable environmental,social and economic development focusing on hot water supply. Kosovo has sufficientsolar radiation for solar water heating systems to work in a satisfactory way. The outputeffect for a solar water heating system in Dragash is around 390 kWh/(m2∙year) with atotal efficiency for the system of 30%. If the solar water heating system replaces heatingby electricity the annual savings can be 31 €/m2 solar collector. The biggest obstacles forthe use of solar energy are the public’s lack of knowledge on solar water heating andenvironmental problems connected to energy, as well as economy.The work done in this thesis is a good foundation for future research on solar energy inKosovo. It can be extended and elaborated with more thorough economic calculations,since economy is an important factor in the future for solar energy. Only roughcalculations were made in this thesis, since it has a technical approach. More extensiveresearch could also be done to evaluate the possibilities of using solar water heating forspace heating. / Varmvatten har värmts med hjälp av solen nästan så länge det funnits människor, men detär inte förrän nyligen som mer avancerade och effektivare solvärmesystem har blivitvanliga, och de blir allt vanligare. Genom åren har nya system och nya solfångareutvecklats. I Kosovo däremot har inte mycket uppmärksamhet ägnats åt att ersätta fossilabränslen med förnyelsebara energikällor, och solvärme är ett nytt koncept.FN:s utvecklingsprogram (UNDP) i Kosovo arbetar med ett projekt med målet hållbarutveckling i Dragash kommun i södra Kosovo. Ett solvärmesystem har nyligeninstallerats på sjukhuset i Dragash, som en del av UNDP:s projekt. Systemet är ettpilotprojekt för att se hur bra solenergi fungerar i det här området.Det befintliga solvärmesystemet på sjukhuset i Dragash undersöktes och utvärderades.Möjligheterna att använda grundprincipen för solvärmesystemet på sjukhuset påbostadshus i Dragash undersöktes. Sex prototyper för genomsnittliga hus i byn Brod och iDragash centrum togs fram. Solfångararean och ackumulatortanksvolymen som krävs föratt klara behoven för de sex husprototyperna beräknades. Information om solinstrålningenför varje hus erhölls från SoDa Solar Radiation Data. Den totala solinstrålningen på enkvadratmeter beräknades.De miljömässiga, sociala och ekonomiska effekterna av solvärme i Dragash diskuterades.Ekonomiska överslagsberäkningar gjordes på effekterna av installation av solvärme.Solvärmesystemet på sjukhuset i Dragash är ett bra pilotprojekt, och är sannolikt attfungera tillfredsställande. Den årliga energi som systemet kan ge kommer att vara ungefär7 400 kWh. Grundprincipen behöver ändras för att fungera på bostadshus. Solfångarnabehöver vara av en billigare typ, och storleken på solfångare och ackumulatortankbehöver vara mindre.Solvärme kan bidra till Kosovos arbete mot hållbar miljömässig, social och ekonomiskutveckling med fokus på varmvattenbehov. Kosovo har tillräcklig solinstrålning för attsolvärmesystem ska fungera tillfredsställande. Med en totalverkningsgrad på 30 % för ettsolvärmesystem kan systemet ge ungefär 390 kWh/(m2∙year). Om systemet ersätteruppvärmning med el kan de årliga besparingarna bli ungefär 31 €/m2 solfångare. Destörsta hindren för användning av solenergi är allmänhetens brist på kunskap om solvärmeoch miljöproblem kopplade till energi, samt ekonomi.Arbetet i detta examensarbete är en bra grund för fortsatta studier om solenergi i Kosovo.Arbetet kan vidgas och utvecklas med mer ingående ekonomiska beräkningar, eftersomekonomi är en viktig faktor i framtiden för solenergi. Endast överslagsberäkningar gjordesi detta examensarbete, eftersom det har ett tekniskt förhållningssätt. Mer omfattandestudier kan också göras för att utvärdera möjligheterna ätt använda solvärme föruppvärmning av bostäder.

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

An emerging trend in the building services industry is the installation of passive deaerators on the flow line of domestic wet central heating systems. To date, no data and theoretical models predicting the two-phase flow characteristics in domestic wet central heating systems are available in the open literature. This gap in literature has prevented essential design improvements to passive deaerators thus impeding the efficiency enhancement of such devices. Hence, the current study is aimed at assisting designers of deaeration devices by providing fundamental data and model correlations with respect to the two-phase flow characteristics typical in a wet domestic central heating system. For this purpose an experimental research project was adopted and several studies were carried out, including; (1) a comprehensive review to understand the background of the phenomena, (2) the design and construction of an experimental test rig to conduct the necessary investigations into the phenomenon of two-phase flow in domestic wet central heating systems, (3) the development of a reliable image capture and analysis technique, (4) the completion of a number of experiments to investigate typical bubble sizes, volumetric void fractions, bubble distributions and nucleation and dissolution rates and (5) the correlation of the data gathered as part of the present study with existing bubble size, nucleation and dissolution prediction models. This research has, for the first time, provided an in depth analysis into two-phase flow characteristics in wet domestic central heating systems through the use of a high speed camera and image analysis techniques. The two-phase phenomenon finds its origins in high dissolved gas concentrations present in the water flowing through the closed loop system, thus resulting in super saturation conditions at the primary heat exchange wall conditions. Bubble sizes at the boiler flow line were found to be dependent on the bulk fluid velocity, heat flux and pressure, with a measured mean diameter in the range of 0.13 mm to 0.39 mm. The Winterton (1972a) force balance model for bubble size prediction was in reasonable agreement with the experimental results. This model was further improved through the correlation of our data with the inclusion of dimensionless groups. Bubble nucleation rates have been calculated in the range of 0.3 to 4 bubbles / cm2 s with total system bubble production rates measured in the range of 784 to 6920 bubbles per second. Bubble nucleation rates have been calculated through the consideration of the heat exchanger surface under super saturation conditions. A correlation for the model by Hepworth et al. (2003) for nonclassical heterogeneous nucleation is proposed based on the experimental data gathered during the present study. Experimental results have shown dissolution rates for the bubble size ratio in the range of 0.4 to 12 % per second with system conditions. A modification of the model developed by Epstein and Plesset (1950) for stationary bubble dissolution is proposed with the inclusion of the Sherwood number to capture the effects of turbulent diffusion. The volumetric void fraction distribution in vertical pipes was found to be quasi-homogenous across the pipe section while being strongly dependent on gravitational and turbulence effects in horizontal pipe bubbly flow. A CFD simulation predicted the volumetric void fraction distribution with reasonable accuracy.

This thesis is a study of an indirect heat pump assisted solar domestic hot water (I-HPASDHW) system, where the investigated configuration is called the Dual Side I-HPASDHW system. The study outlines the development of an Experimental Test Unit (ETU), and focuses on the experimental validation of TRNSYS models. Shortcomings of the system design realized throughout the validation process, as well as weaknesses in the control schemes used to operate the system are also provided. A description of the Dual Side I-HPASDHW system is provided along with the design intent of the system. The corresponding ETU is presented in detail to provide a comprehensive understanding of the ETU’s simulation capabilities. Components of the ETU, such as the heat pump, heat exchanger, and domestic hot water (DHW) tank are characterized in order to provide input data for built-in TRNSYS models, and to develop custom TRNSYS models for the heat pump and heat exchanger. Heat exchanger performance is modelled with a linear correlation, while the heat pump performance is mapped by applying experimental data to three-dimensional surface fitting software. For the purpose of validation, the ETU is used to simulate the performance of the Dual Side I-HPASDHW system under a realistic control scheme. Four full day tests are conducted using data from a fall, winter, and summer day. The full day summer test is repeated with and without electrical backup heating. The TRNSYS model of the Dual Side system is tuned in order to provide the closest match possible between the computer simulation and the measured performance of the ETU. Experimental tests were compared with TRNSYS simulations to reveal some disparity in the results. The majority of simulation error was attributed to inaccuracy in modeling DHW tank temperatures and water circulation patterns. The disparity created by the DHW tank model only resulted in substantial performance deviation when inaccurate DHW temperatures were used directly for vital control decisions. Conclusions were drawn suggesting that the TRNSYS model of the ETU was valid for a majority of operating conditions, often matching experimental tests well within experimental uncertainty. Caution was recommended towards the use of the developed TRNSYS model, where techniques were recommended for tracking and minimizing substantial simulation errors. Several key performance issues affecting the Dual Side I-HPASDHW system were targeted with recommendations for design and control alterations, along with future improvement and optimization studies.

This study is an examination of the (broadly envisioned) process that has led to the emerging use of solar water heaters in Oaxaca de Juárez, Mexico. In 2007, Mexico launched a major policy initiative designed to encourage the use of solar water heaters in the residential sector throughout the country. As this policy has been implemented, over one hundred thousand solar water heaters have been installed on new homes and many people are beginning to encounter this technology for the first time. This policy has been successful in placing solar water heaters on the rooftops of new homes, but problems with how some of them are functioning threaten the long-term prospects of diffusion of the technology. The study shows that while solar water heaters have the potential to carry positive environmental and economic benefits at the household level, there are also many potential and actual scenarios in which the technology can have detrimental effects. Drawing on literature from the Diffusion of Innovations, the Social Construction of Technology, Actor-Network Theory, the Multi-Level Perspective on Technological Transitions, and Ecological Modernization Theory, this paper also seeks to contribute to the literature concerning the overall processes of socio-technical transitions. / text

This thesis is a study of an indirect heat pump assisted solar domestic hot water (I-HPASDHW) system, where the investigated configuration is called the Dual Side I-HPASDHW system. The study outlines the development of an Experimental Test Unit (ETU), and focuses on the experimental validation of TRNSYS models. Shortcomings of the system design realized throughout the validation process, as well as weaknesses in the control schemes used to operate the system are also provided. A description of the Dual Side I-HPASDHW system is provided along with the design intent of the system. The corresponding ETU is presented in detail to provide a comprehensive understanding of the ETU’s simulation capabilities. Components of the ETU, such as the heat pump, heat exchanger, and domestic hot water (DHW) tank are characterized in order to provide input data for built-in TRNSYS models, and to develop custom TRNSYS models for the heat pump and heat exchanger. Heat exchanger performance is modelled with a linear correlation, while the heat pump performance is mapped by applying experimental data to three-dimensional surface fitting software. For the purpose of validation, the ETU is used to simulate the performance of the Dual Side I-HPASDHW system under a realistic control scheme. Four full day tests are conducted using data from a fall, winter, and summer day. The full day summer test is repeated with and without electrical backup heating. The TRNSYS model of the Dual Side system is tuned in order to provide the closest match possible between the computer simulation and the measured performance of the ETU. Experimental tests were compared with TRNSYS simulations to reveal some disparity in the results. The majority of simulation error was attributed to inaccuracy in modeling DHW tank temperatures and water circulation patterns. The disparity created by the DHW tank model only resulted in substantial performance deviation when inaccurate DHW temperatures were used directly for vital control decisions. Conclusions were drawn suggesting that the TRNSYS model of the ETU was valid for a majority of operating conditions, often matching experimental tests well within experimental uncertainty. Caution was recommended towards the use of the developed TRNSYS model, where techniques were recommended for tracking and minimizing substantial simulation errors. Several key performance issues affecting the Dual Side I-HPASDHW system were targeted with recommendations for design and control alterations, along with future improvement and optimization studies.

Made available in DSpace on 2014-06-11T19:24:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-11-29Bitstream added on 2014-06-13T20:52:17Z : No. of bitstreams: 1 dallantoniajunior_lc_me_botfca.pdf: 464837 bytes, checksum: 17a18aa81cbdc6fc6cee6b24c67e95c7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho descreve a construção de um coletor solar alternativo de concreto de tração simples (areia, cimento e pedra), para aplicações agrícolas e agroindustriais. o coletor é constituído de uma área de absorção 51 m2 com 470m de mangueira de polietileno para o aquecimento da água, e o armazenador da água aquecida. O sistema coletor e armazenador foi submetido a testes experimentais onde foram determinados para as estações verão e inverno, e sob três coberturas de céu aberto, parcialmente nublada e nublada: as temperatura do absorvedor em três profundidades; ganho térmico do fluido; rendimento térmico do coletor, e desempenho do armazenador. Os resultados mostram que a temperatura do absorvedor foi maior na cobertura de céu aberto, decrescendo em seqüência de profundidade 55,74ºC, 52,10C e 49,30C respectivamente, e foi menor na cobertura de céu nublado, 48,30C, 46,20C e 44,60C respectivamente; o ganho térmico do fluido de trabalho no absorvedor foi decrescente em função do aumento comprimento do condutor: o ganho foi maior no verão e em dias de céu aberto, atingindo a temperatura máxima de 52,70C, e foi menor no inverno, em dias céu nublado, atingindo a temperatura máxima de 28,50C; o rendimento térmico do coletor foi maior em dia de céu aberto: no verão 71,4% e inverno 74%; o sistema armazenador térmico, mostrou ótimo desempenho na conservação da temperatura do fluido de trabalho. Nos dias estudados houve uma redução de 10% na temperatura final da água aquecida / This paper describes the construction of an alternative sidewalk-type solar collector made of concrete (sand, cement and stone), for agriculture and agribusiness uses. The collector consists of an absorption area of 51 m2 with 470m polyethylene tubing for water heating, and a storage for warm water. The collector and storage systems were subjected to experimental tests which were determined for summer and winter, three sky conditions: open skies, partly cloudy and overcast; three depths temperature in the absorber; thermal gain of the fluid, thermal efficiency of the collector and performance of the water storage. The temperature of the absorber was higher in open sky conditions: 55,74ºC above it, decreasing in depth sequence of 52,1ºC and 49,3ºC. This temperatures of the absorber were 48,3ºC 46,2ºC and 44,6ºC respectively in a overcast days. The thermal gain of the working fluid in the absorber was decreasing with increasing length of the conductor: the gain was higher in summer and open sky days, reaching a maximum temperature of 52.7 ºC, and lowest in winter cloudy days, reaching a maximum temperature of 28.5 ºC. The collector thermal efficiency was higher in open sky days: 71.4% in summer and 74% in winter. The warm water storage system had excellent keeping temperature performance with 10% loss in the final water temperature