abstract: The world is grappling with two serious issues related to energy and climate change. The use of solar energy is receiving much attention due to its potential as one of the solutions. Air conditioning is particularly attractive as a solar energy application because of the near coincidence of peak cooling loads with the available solar power. Recently, researchers have started serious discussions of using adsorptive processes for refrigeration and heat pumps. There is some success for the >100 ton adsorption systems but none exists in the <10 ton size range required for residential air conditioning. There are myriad reasons for the lack of small-scale systems such as low Coefficient of Performance (COP), high capital cost, scalability, and limited performance data. A numerical model to simulate an adsorption system was developed and its performance was compared with similar thermal-powered systems. Results showed that both the adsorption and absorption systems provide equal cooling capacity for a driving temperature range of 70-120 ºC, but the adsorption system is the only system to deliver cooling at temperatures below 65 ºC. Additionally, the absorption and desiccant systems provide better COP at low temperatures, but the COP's of the three systems converge at higher regeneration temperatures. To further investigate the viability of solar-powered heat pump systems, an hourly building load simulation was developed for a single-family house in the Phoenix metropolitan area. Thermal as well as economic performance comparison was conducted for adsorption, absorption, and solar photovoltaic (PV) powered vapor compression systems for a range of solar collector area and storage capacity. The results showed that for a small collector area, solar PV is more cost-effective whereas adsorption is better than absorption for larger collector area. The optimum solar collector area and the storage size were determined for each type of solar system. As part of this dissertation work, a small-scale proof-of-concept prototype of the adsorption system was assembled using some novel heat transfer enhancement strategies. Activated carbon and butane was chosen as the adsorbent-refrigerant pair. It was found that a COP of 0.12 and a cooling capacity of 89.6 W can be achieved. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2011

With the objectives of designing a solar cooling system with cold storage unit for the Iraqi climate, solar energy resources were assessed and methods were proposed to enhance harvesting the solar energy in the Iraqi climate. Where the results showed that adopting monthly average optimal tilt angles led to an increase in the amount of useful solar energy gained nearly 9%. A methodology of multi objective optimisation of solar absorption cooling system was then developed and demonstrated by applying it in a domestic application in Baghdad. Maximising the system performance in exergy, economic and environment were the objectives of the project. A decision-making tool was then implemented to select the most suitable design. The optimal proposed system has exergy efficiency of 56%, total cost rate of 4.19US$/hr, annual CO2 emission of 32199kg and payback period of 18.7years. After analysing the optimal configuration of the system, a cold thermal energy storage unit with the solar absorption cooling system was suggested in order to store the cold energy produced by the system at times when the solar energy is available (at daytime) and use (discharge) it at times when there is no solar energy available (at night). Next, a new control strategy was developed and applied in the system to make it more cost effective. Five scenarios were considered to manage the quantity of charging of the cold storage tank according to the splitting rate of the mass of the supplied chilled water by the chiller to the cold storage tank and the building. Finally, the chosen optimal system that uses an efficient controlled cold thermal energy storage, has exergy efficiency of 69.4%, total cost rate of 4.25US$/hr and total avoided annual CO2 emissions of 33.9% less than system without cold storage tank. Additionally, without any government incentive, the payback was recorded 9.3years, which was 50% less than the system without cold storage tank.

This research investigates the potential of a solar powered cooling system for single family houses in Pakistan. The system comprises water heating evacuated tube solar collectors, a hot water storage tank, and an absorption chiller. A literature review was carried out covering: • Energy situation, climate, and renewable energy potential in Pakistan; • Energy and thermal comfort in buildings, particularly for hot climates; • Solar collectors and solar cooling systems, particularly for hot climates; • Dynamic thermal simulation and weather data for solar energy systems and buildings. It was found that Pakistan is short of energy and that there is a great need to cool buildings. Renewable energy cooling systems are, therefore, of interest. The system described above was selected, as it was found that solar energy is abundant in Pakistan when cooling is required; thermal systems can be more economical than photovoltaics for hot climates and suitable components (collectors, absorption chillers, etc.) are commercially available. The TRNSYS dynamic thermal simulation program was selected as the main research tool, as it has been tested for solar energy and building applications by many researchers and suitable experimental facilities were not available. A simple typical building in Pakistan with a solar cooling system was simulated. Optimum values for key parameters were found by repeated simulations. It was concluded that the system would be able to provide cooling when required without an auxiliary heat source, and that an evacuated tube collector with a gross area of 12 m2, a collector flow rate of 165 kg/h, and a storage tank volume of 2 m3 would provide satisfactory performance for a 3.52 kW absorption chiller integrated with 42m3 single room. The results were in good agreement with published results from other researchers. Sensitivity analysis was carried out for the collector area, collector flow rate and storage tank size. It was found that varying the collector area had the largest effect on system performance, followed by varying the storage tank volume. Varying the collector flow rate had the smallest effect. It is recommended that solar cooling systems should be considered for Pakistan, and that further research should be carried out into reducing building cooling loads, using surplus heat for other loads, improving the performance of the proposed solar cooling system, and comparing it with other systems such as photovoltaics.

No description available.

[pt] Como parte de um sistema solar de condicionamento de ar por resfriamento evaporativo, foi projetado e construindo um desumidificador de ar utilizando tri-etileno glicol como agente higroscópio líquido. O modelo teórico desenvolvido, baseado no procedimento adotado para cálculo de torres de resfriamento. Levou em consideração o abaixamento de pressão de vapor na superfície líquido-gás assim como o calor de mistura de tri-etileno glicol e água. Os dados experimentais obtidos concordam satisfatoriamente com os resultados previstos pelo modelo teórico proposto, dentro das faixas de vazão pesquisadas. Uma correlação semi-empírica foi desenvolvida para cálculo dos coeficientes de difusão de desumidificadores de ar como função das vazões das fases líquida e gasosa. Finalmente é sugerido um procedimento para projeto de desumidificadores de ar de características semelhantes ao modelo proposto. / [en] As part of solar evaporative cooling air conditioning system, using tri-ethylene glicol as a liquid dehumidifier, an absortion tower was designed and built for drying air. The theory of heat and mass transfer between liquid and gas was developped following the same procedure as usually adopted for cooling tower calculations.The lowering of vapor pressure and the heat of solution were taken into account. Experimental data agree reasonably with theory within a wide range of flow rates. A correlation was developped relating mass transfer coefficients to liquid and gás flow rates. A procedure is finally suggested for designing and estimating the performance of na absortion tower.

[pt] No Brasil, devido ao clima tropical, muita energia elétrica é utilizada em sistemas de ar condicionado. Devido à excelente irradiação solar que incide na maior parte do país, existem boas condições para atender esta grande demanda de refrigeração através da utilização de sistemas de ar condicionado assistido por energia solar térmica. Nesta dissertação, as mais importantes tecnologias que utilizam a energia solar para a climatização foram verificadas quanto a sua aplicabilidade técnica e econômica no Brasil, com foco em sistemas de médio porte. Os princípios básicos para o dimensionamento de um sistema de refrigeração solar são descritos e um estudo de caso é apresentado e discutido, comparando-se um sistema de ar condicionado assistido por energia solar (auditório em Guaratinguetá, São Paulo) com um sistema tipo split convencional. No estudo deste caso, a dinâmica de simulação térmica de edifícios foi modelada utilizando o programa Helios-PC. Também se analisa como a carga térmica de resfriamento pode ser diminuída considerando-se uma temperatura adequada no interior da edificação, de acordo com as normas brasileiras de conforto térmico, como também pelo emprego de isolamento adequado na construção do edifício. / [en] In Brazil a lot of electrical energy is used by building air-conditioning because of the tropical climate. In many cases there is a general congruence of solar irradiation and demand for building air-conditioning and solar thermal cooling has the potential to satisfy a part of the rapidly growing cooling demand. Due to excellent solar irradiance and a high cooling demand there exists in Brazil good conditions for the use of solar-assisted air-conditioning. In this work the most important solar cooling techniques and their suitability in Brazil are discussed. The objective of the present study is to analyze the technical and economic feasibility of medium sized solar-assisted air-conditioning in Brazil. The energy saving potential of solar-thermal air-conditioning in comparison to best practical solutions in Brazil using conventional split air-conditioning systems, is shown based on a case study (auditorium in Guaratinguetá - São Paulo). The economy of solar-assisted air-conditioning is thereby discussed. The basic principles for the dimensioning of a system for solar cooling are described. The auditorium in the case study is modelled by using the dynamic thermal building simulation program Helios-PC. In this context it is, as well, demonstrated how the cooling load could be decreased by adapting the indoor temperature according to the Brazilian standards of thermal comfort and by using building insulation.

The emergence of Thermally Driven Cooling system has received more attention recently due to its ability to utilize low grade heat from engine, incinerator or simple flat plate solar collector which are considered as renewable energy sources. ClimateWell AB located in Stockholm has been developing this cooling system based on its patented chemical heat pump technology. The heat pump with its tube shape is put under the absorber as in simple flat plate solar collector making it possible be directly attached on the roof without any additional solar collector. A high performance heat exchanger is needed by its reactor to absorb the energy efficiently during the desorption process as well as to recover heat during the absorption process. Current heat exchanger design has direct contact with the tube’s surface, yet air gaps between the tube and heat exchanger result in alower amount of heat transferred and non-uniform heat distribution across this surface. Moreover, a special treatment which cannot be done by machinery has to be performed in attaching the tube with this heat exchanger. It becomes a problem during mass production since a lot of man power is needed. A new heat exchanger design was proposed to overcome those limitations. This design has annulus which is filled with thermal fluid inside. This fluid will make perfect contact to the heat pump tube’s surface and eliminate the air gap. Furthermore, the need of man power in its production can be minimized. Even though perfect contact can be achieved, the fluid in this new design will increase thermal resistance in the radial direction. Therefore, an investigation has to be conducted to evaluate the performance of this new heat exchanger design based on heat transfer coefficient under steady state condition. The performance investigation also included the influence of various thermal fluids which will be used for this new heat exchanger. The work performed by doing simulation in COMSOL continued with validation of the result with experiment in laboratory. New heat exchanger design efficiency was only 50% while the current one was 82% during the desorption process. In this process, the fluid’s thermal conductivity was the most influencing fluid property. During absorption process, two heat recovery methods are used. First is by flowing the fluid inside the annulus and second is by using additional heat recovery pipe that is attached outside the heat exchanger surface. The first method gave the highest UA value around 34 W/K while the second one gave almost the same value as the current design which is around 11 W/K. In the first method, the thermal fluid’s viscosity strongly influenced its UA value while the second method is greatly influenced by fluid’s heat conductivity.

The content of this Master thesis is the characterization of three different cross unmixed flow heat exchangers. All of the heat exchangers have different inner geometries and dimensions. In order to perform the characterization of these heat exchangers, measurements of heat transfer were done under different conditions: five different temperatures at the inlet of the sorption side, different mass flow for both inlet sides of the heat exchangers.The heat transfer measurements were done with and without applying indirect evaporative cooling in order to find out the influence of indirect evaporative cooling. This research was done with the objective to find out which heat exchanger presents the best performance. The purpose is to install the heat exchanger in the novel solar driven open air SorLuKo system. This system was developed in Fraunhofer ISE and works under the same principe as the ECOS system. The main objective of the SorLuKo system is to dehumidify and cool a dwelling or small office.

In this study a roof-top PVT/absorption chiller system is modeled for a hotel building in Antalya, Turkey to cover the cooling demand of the hotel, to produce electricity and domestic hot water. PVT modules, an absorption chiller, a hot storage tank and a natural gas fired auxiliary heater are the main components of the system. Elecetrical power produced by the system is 94.2 MWh, the cooling power is 185.5 MWh and the amount of domestic hot water produced in the system is 65135 m3 at 45 0C annually.  Even though the systems is capable of meeting the demands of the hotel building, because of the high investment costs of PVT modules and high interest rates in Turkey, it is not economically favorable. Using cheaper solar collectors, integrating a cold storage unit in the system or having an improved conrol strategy are the options to increase the system efficiency and to make the system economically competitive.

An enhanced-modularity thermally driven chemical heat pump was conceptualised as a second generation product for various heating and cooling applications with special emphasis on solar applications. The typical characteristics of the absorption heat pump were studied and the key performance parameters were selected for further investigation. An experimental test rig was constructed to allow for the testing of each component’s performance characteristics with special attention being paid to the ability to interchange components to test various configurations as well as to the facilitation of standardised relatively rapid testing. The heat transfer coefficient of the condenser/evaporator was found to be between 260 and 300 W/m2-°C during evaporation and between 130 and 170 W/m2-°C during condensation. Salt type has major impact on the system’s cooling power and cooling energy with the LiBr and water sorption pair having a 62% higher cooling/heating power than LiCl with the same matrix type and thickness. Matrix types and sorption pairs were compared with regards to the principal parameters of power and energy density with results ranging from 60 to 163 Wh/litre. The final section of the study tackled the theoretical foundation behind the system processes with modelling and simulation of the processes and comparison with the experimental data. The model makes the foundation of the continuous development of a more detailed and accurate physical model to enhance the design and optimisation process of the system.