BUBBLE-PUMP-DRIVEN SOLAR ABSORPTION AIR CONDITIONING FOR RESIDENTIAL APPLICATIONS

Large-scale heat-driven absorption cooling systems are currently available in the marketplace for industrial applications. The high temperature is required in the generator for driving this absorption chiller. For this reason, this type of chiller was originally designed to use direct-fired gas. However, the low efficiency of this cooling cycle restricts its use in small-scale applications. The concept of a solar-driven absorption chiller can satisfy the increasing demand for air conditioning without contributing greenhouse gases to the global environment. This research contributes to providing an efficient air conditioning driven by low temperature solar heat and independent of grid electricity, which may be useful in remote residential communities. The performance of 10 kW absorption and adsorption cooling systems were compared for the selection of a suitable cooling technology that can be driven by low temperature heat source such as a flat plate solar collector. Analysis revealed that under any operating conditions, the coefficient of performance (COP) of the absorption cooling system is higher. However, absorption chillers have a lower efficiency than traditional compression refrigeration systems, when used for small scale applications. Hence, energy and exergy analyses were conducted to evaluate the performance of a solar-driven air-cooled ammonia-water absorption chiller for residential air conditioning. Low driving temperature heat sources were optimized (70~80℃) and the efficiencies (COP=0.6, exergetic efficiency=32%) of the system were evaluated. The highest exergy losses were identified in the absorption process (63%) followed by the generator (13%) and the condenser (11%). In order to replace the only electrical component (pump) in an absorption chiller and make it independent of grid electricity, a solar-thermal-driven bubble pump was introduced in a vapor absorption refrigeration (VAR) cycle. This solar-thermal-driven pump can circulate the solution to the absorber and the generator to create the necessary refrigerant vapor for cooling. An analytical model of a bubble pump was developed and experimental work was conducted. Furthermore, a dimensional analysis was performed, considering bubble pump geometry and the solution properties. The bubble pump performance was defined in terms of non-dimensional parameters which can be used in all bubble-pump-driven absorption refrigeration systems. Experimental and theoretical results for a new refrigerant-absorbent solution (LiCl-H2O) were compared, and the flow regime (slug flow) was determined for the highest pump efficiency. Moreover, in order to employ the advantages of high performance, the bubble pump was incorporated into a simulation of a water-based vapor absorption refrigeration cycle. A new absorbent-refrigerant pair (LiCl-H2O) for a bubble-pump-operated VARS was proposed and a thermodynamic comparison was made between LiBr-H2O and LiCl-H2O systems. Finally, energy, exergy and advanced exergy analyses were performed on this proposed refrigeration cycle, and the exergy losses due to the internal irreversibilities of each component and the effect of the irreversibilities of the other components were determined. The avoidable exergy destruction was identified pertaining to the potential improvement of the overall system structure. The highest avoidable endogenous exergy losses occurred in the generator

Stability and photo-thermal conversion performance of binary nanofluids for solar absorption refrigeration systems

The photo-thermal conversion characteristics of a long-term stable binary nanofluid (nanoparticles in 50 wt% lithium bromide-50 wt% water) were investigated in this work. The stability of the binary nanofluid against the agglomeration and sedimentation process was evaluated by a high-speed centrifuge analyzer and transmission electron microscopy. The photo thermal conversion efficiency of the nanofluid was also studied using a solar simulator. Experimental results indicated that the use of the binary nanofluid could significantly increase the light trapping efficiency and, therefore, the bulk temperature, which in turn could increase the evaporation rate due to surface localized heat generation. The experimental results showed the increase of 4.2 and 4.9 percent solar radiative energy in the form of sensible heat after addition of 64 and 321 mg/l iron oxide NPs to the pure water, respectively. The increasing percent is 4.9% and 11.9% for latent heat efficiency in the presence of 64 and 321 mg/l iron oxide NPs, respectively. Possessing both high stability and excellent photo-thermal conversion rate, rod shape iron oxide nanoparticles is suggested to be a potential candidate used for the solar absorption refrigeration systems

Development and analysis of micro polygeneration systems and adsorption chillers

About a fifth of all primary energy in the US is consumed by residential buildings, mostly for cooling, heating and to provide electricity. Furthermore, retrofits are essential to reducing this consumption, since the buildings that exist today will comprise over half of those in use in 2050. Residential combined heat and power (or micro CHP, defined by <5 kW electrical generation capacity) has been identified as a retrofit technology which can reduce energy consumption in existing homes during the heating season by 5-30%. This thesis investigates the addition of a thermally-driven chiller/heat pump to a CHP system (to form a trigeneration system) to additionally provide savings during the cooling season, and enhance heating season savings. Scenarios are identified in which adding thermally-driven equipment to a micro CHP system reduces primary energy consumption, through analytical and experimental investigations. The experimental focus is on adsorption heat pump systems, which are capable of being used with the CHP engines (prime movers) that are already widely deployed. The analytical analysis identifies energy saving potential off-grid for today's prime movers, with potential on-grid for various fuel cell technologies. A novel dynamic test facility was developed to measure real-world residential trigeneration system performance using a prototype adsorption chiller. The chiller was designed and constructed for this thesis and was driven by waste heat from a commercially available natural gas-fueled 4 kW (electric) CHP engine. A control strategy for the chiller was developed, enabling a 5-day experiment to be run using a thermal load profile based on moderate Maryland summer air conditioning loads and typical single-family domestic hot water demand, with experimental results in agreement with models. In this summer mode, depending on electrical loads, the trigeneration system used up to 36% less fuel than off-grid separate generation and up to 29% less fuel than off-grid CHP without thermally driven cooling. However, compared to on-grid separate generation, the experimental facility used 16% more primary energy. Despite high chiller performance relative to its thermodynamic limit, this result is primarily due to the electrical efficiency of the prime mover being lower than the grid. A residential trigeneration system utilizing a high temperature fuel cell is predicted to save up to 42% primary energy relative to the grid

Combined absorption power and refrigeration systems driven by low and mid-grade heat sources

Hi ha una gran abundància de fonts de calor de baixa i mitja temperatura (<300 ° C), com pot ser la solar tèrmica, geotèrmica o calor residual de diversos processos tèrmics. Els principals serveis energètics com l'aire condicionat, la refrigeració o l'electricitat es generen en general per separat mitjançant diverses tecnologies de conversió d'energia independents. La majoria dels usuaris finals necessiten almenys més d'un servei energètic: un exemple típic d'això ho constitueix el servei energètic a edificis. La producció combinada d'electricitat (descentralitzada) i de fred mitjançant sistemes eficients de conversió d'energia accionats tèrmicament és una de la solució tecnològica adequada per fer front als actuals reptes relacionats amb l'energia a nivell mundial. L'objectiu d'aquesta tesi és el desenvolupament d'una nova classe de cicles d'absorció per a la producció d'energia mecànica o elèctrica i refrigeració mitjançant fonts d'energia de baixa i mitjana temperatura. Per aconseguir aquest objectiu, es presenta primer una revisió dels cicles d'absorció combinats proposats a la literatura. Es presenten i discuteixen més els criteris d'acompliment utilitzats en la literatura. A continuació, es proposen diversos nous cicles d'absorció combinats. Aquests són analitzats i discutits des del punt de vista energètic i exergètic per a la utilització eficaç de les fonts de calor de baixa i mitjana temperatura. Com fluids de treball s’han utilitzat mescles a base d'amoníac: NH3 / H2O, NH3 / LiNO3 i NH3 / NaSCN. S'ha desenvolupat un model semi-empíric per a un expansor de desplaçament utilitzant amoníac (i barreja d’amoníac / aigua amb alta concentració d'amoníac) com a fluid de treball. Aquest model s'ha integrat en alguns dels cicles d'absorció combinats proposats en aquesta tesi. Posteriorment, s'ha realitzat un model de sistema d'absorció per a la producció de potència i refrigeració solar (SAPCS) per usar-lo en l'eina de simulació dinàmica TRNSYS com un cas representatiu per a la integració dels cicles d'absorció combinats amb una planta termosolar.Existe una gran abundancia de fuentes de calor de baja y media temperatura (<300 ° C), como puede ser la solar térmica, geotérmica o calor residual de diversos procesos térmicos. Los principales servicios energéticos como el aire acondicionado, la refrigeración o la electricidad se generan por lo general por separado mediante diversas tecnologías de conversión de energía independientes. La mayoría de los usuarios finales necesitan por lo menos más de un servicio energético: un ejemplo típico de esto lo constituye el servicio energético a edificios. La producción combinada de electricidad (descentralizada) y de frío mediante sistemas eficientes de conversión de energía accionados térmicamente es una de la solución tecnológica adecuada para hacer frente a los actuales desafíos relacionados con la energía a nivel mundial. El objetivo de esta tesis es el desarrollo de una nueva clase de los ciclos de absorción para la producción de energía mecánica o eléctrica y refrigeración mediante fuentes de energía de baja y media temperatura. Para lograr este objetivo, se presenta primero una revisión de los ciclos de absorción combinados propuestos en la literatura. A continuación, se proponen varios nuevos ciclos de absorción combinados. Estos son analizados y discutidos desde el punto de vista energético y exergético para la utilización eficaz de las fuentes de calor de baja y media temperatura. Como fluidos de trabajo se utilizaron mezclas a base de fluidos de trabajo de amoníaco: NH3 / H2O, NH3 / LiNO3 y NH3 / NaSCN. Se ha desarrollado un modelo semi-empírico para un expansor de desplazamiento usando amoniaco (y mezcla de amoniaco / agua con alta concentración de amoniaco) como fluido de trabajo. Este modelo se ha integrado en algunos de los ciclos de absorción combinados propuestos en esta tesis. Posteriormente, se ha realizado un modelo de sistema de absorción para la producción de potencia y refrigeración solar (SAPCS) para usarlo en la herramienta de simulación dinámica TRNSYS como un caso representativo para la integración de los ciclos de absorción combinados con una planta termosolar. En conclusión esta tesis contribuirá al desarrollo de una nueva clase de sistemas de absorción capaces de proporcionar energía y refrigeración de forma simultánea y/o alternativamente, mediante la utilización de fuentes de calorLow and mid-grade heat sources (< 300 °C), such as solar thermal, geothermal and waste heat from various thermal processes are abundantly available. Air-conditioning, refrigeration and electricity are useful forms of energy products, usually produced using separate energy conversion technologies. Most end-users need at least dual energy products: typical example could be buildings applications. The combined production of electricity (decentralized) and cold using efficient thermally-driven energy conversion systems are one of the suitable technological solution to address the current global energy related challenges. The aim of this thesis is the development of a new class of absorption cycles to produce mechanical or electrical energy and cooling using energy sources at low or medium temperature. To achieve this aim, first combined absorption cycles proposed in the literature are reviewed. The concept of combined absorption cycles are explained in terms of idealized energy conversion systems. Performance criteria used in the literature are presented and discussed. Then, several new combined absorption cycles are proposed, analysed and discussed from the energetic and exergetic viewpoints for the effective utilization of low and mid-grade heat sources. Ammonia based working fluid mixtures were used: NH3/H2O, NH3/LiNO3 and NH3/NaSCN. A semi-empirical model for a scroll expander using ammonia (and ammonia/water mixture with high concentration of ammonia) as working fluid is developed. It is integrated into some of the proposed combined absorption cycles in this Thesis. Then, a Solar Absorption Power and Cooling System (SAPCS) model is developed for its use in TRNSYS software as a simulation tool and it is used to demonstrate a representative case for the integration of combined absorption cycles with solar thermal plant. In conclusion this thesis will contribute to the development of new class of absorption systems able to provide power and refrigeration simultaneously and/or alternatively by utilizing low and mid-grade heat sources

Potentially viable solar powered appliances cooling and distillation

Stand alone solar powered refrigeration and water desalination, two of the most popular\ud and sought after applications of solar energy systems, have been selected as the topic of\ud research for the works presented in this thesis.\ud The water desalination system based on evaporation and condensation was found to be\ud the most suitable one to be powered by solar energy. It has been established that highoutput\ud fast-response solar heat collectors used to achieve high rates of evaporation and\ud reliable solar powered cooling system for faster rates of condensation are the most\ud important factors in achieving increased outputs in solar powered desalination systems.\ud Comprehensive reviews of Solar powered cooling/refrigeration and also water\ud desalination techniques have been presented. In view of the fact that the Institute of\ud Technology, Sligo has a well-established long history of research and development in the\ud production of state of the art high-efficiency fast-response evacuated solar heat collectors\ud it was decided to use this know how in the work described in this thesis. For this reason\ud achieving high rates of evaporation was not a problem. It was, therefore, the question of\ud the solar powered refrigeration that was envisaged to be used in the solar powered\ud desalination tofacilitate rapid condensation of the evaporated water that had to be\ud addressed first.\ud The principles of various solar powered refrigeration techniques have also been reviewed.\ud The first step in work on solar powered refrigeration was to successfully modify a\ud conventional refrigerator working on Platen-Munters design to be powered by highoutput\ud fast-response evacuated solar heat collectors. In this work, which was the first\ud ever successful attempt in the field, temperatures as low as —19°C were achieved in the\ud icebox.\ud A new approach in the use of photovoltaic technology to power a conventional domestic\ud refrigerator was also attempted. This was done by modifying a conventional domestic\ud refrigerator to be powered by photovoltaic panels in the most efficient way. In the\ud system developed and successfully tested in this approach, the power demand has been\ud reduced phenomenally and it is possible to achieve 48 hours of cooling power with\ud exposure to just 7 hours of sunshine.\ud The successful development of the first ever multi-cycle intermittent solar powered\ud icemaker is without doubt the most exciting breakthrough in the work described in this\ud thesis. Output of 74.3kg of ice per module with total exposure area of 2.88 m2, or\ud 25.73kg per m2, per day is a major improvement in comparison to about 5-6kg of ice per\ud m2 per day reported for all the single cycle intermittent systems. This system has then\ud become the basis for the development of a new solar powered refrigeration system with\ud even higher output, named the “composite” system described in this thesis.\ud Another major breakthrough associated with the works described in this thesis is the\ud successful development and testing of the high-output water desalination system. This\ud system that uses a combination of the high-output fast-response evacuated solar heat\ud collectors and the multi-cycle icemaker. The system is capable of producing a maximum\ud of 141 litres of distilled water per day per module which has an exposure area of 3.24m2,\ud or a production rate of 43.5 litres per m2 per day. Once again when this result is\ud compared to the reported daily output of 5 litres of desalinated water per m per day the\ud significance of this piece of work becomes apparent.\ud In the presentation of many of the components and systems described in this thesis CAD\ud parametric solid modelling has been used instead of photographs to illustrate them more\ud clearly.\ud The multi-cycle icemaker and the high-output desalination systems are the subject of two\ud patent applications

The State of the Art of Thermo-Chemical Heat Storage

The heat storage based on thermochemical technology is associated with higher amounts of energy stored with respect to systems based on sensible heat. This interesting feature is stimulating the interest of the scientific community, among energy providers and grid managers, since it can effectively support the operation and integration of renewable high-efficiency systems and local smart grids. Research in this field is achieving unprecedented goals thanks to the profitable exploitation of results obtained in the field of heat pumps and thermally driven systems. The present issue offers the reader a sensational window to this rapidly evolving world

Thermo-fluid dynamic evaluation of components in adiabatic absorption systems

In this PhD thesis, a facility for experimental evaluation of innovative components forming part of a single effect H20-LiBr adiabatic absorption chiller is analyzed. The adopted methodology has been mainly experimental. Plate heat exchangers functioning as generator, solution heat exchanger, condenser and subcooler have been incorporated in the design. Two adiabatic absorber configurations, droplets and liquid sheets, were tested and evaluation parameters were experimentally determined. Overall test facility performance is analyzed in the first stage of the research. The preliminary analysis gives an idea about the operational features of the machine, which allow subsequent detailed components analysis. This analysis is oriented to the interpretation of experimental data including the particular features, in both design and operation, of the facility here presented: study of evaporators’ efficiency, solution heat exchanger efficiency and thermal losses. Performance parameters, cooling capacity and COP, are expressed in terms of a diagnostic absorption model and compared with experimental results. The differences observed between ideal and experimental results help to validate the influence of components performances on the overall performance of the facility. An extension of the characteristic equation method, based on the characteristic temperature difference to adiabatic absorption chillers, has been developed and applied considering the facility features. Evaporator limitations have been included in the analysis. The agreement between experimental data and the extended characteristic equation is discussed, showing a good predictive capability, even at off-design operating conditions. The performances of two types of absorbers (liquid sheets and droplets as solution spreading mechanisms in the absorber) have been characterized in terms of heat and mass transfer. The liquid sheet configuration has shown better evaluation parameters than droplets configuration. Single and two phase heat transfer and pressure drop in a plate heat exchanger operating as generator, has been analyzed. For the cases of subcooler and solution heat exchanger, single phase heat transfer data has been obtained. The corresponding results are analysed for each case and correlations equations have been obtained and compared with those reported in literature

Electric and hybrid vehicles environmental control subsystem study

An environmental control subsystem (ECS) in the passenger compartment of electric and hybrid vehicles is studied. Various methods of obtaining the desired temperature control for the battery pack is also studied. The functional requirements of ECS equipment is defined. Following categorization by methodology, technology availability and risk, all viable ECS concepts are evaluated. Each is assessed independently for benefits versus risk, as well as for its feasibility to short, intermediate and long term product development. Selection of the preferred concept is made against these requirements, as well as the study's major goal of providing safe, highly efficient and thermally confortable ECS equipment