Abstract During the last years there has been an increasing consciousness of the environmental problems, created by the use of fossil fuels in electrical power generation consumed by converting cooling systems. In addition, the use of common working fluids (refrigerants), with their ozonedepleting and global warming potential, has become a serious environmental problem. This underlines the need to implement advanced, new concepts in building air-conditioning. The most common global type of thermally driven technology to produce chilled water is absorption cooling. For air-conditioning applications, absorption systems commonly use the water/lithium bromide or ammonia/water as working pair of fluids. The objective of this study is to establish a fundamental basis for further research and development within the field of solar cooling. In this study, an overview of possible systems for solar powered refrigeration and airconditioning systems will be presented. The concept of the ‘Solar Cooling Path’ is introduced, including a discussion of the energy source to the collector. Brief information and comparisons of different absorption refrigeration cycles are also presented. A solar-driven absorption refrigeration system has been selected as a case study for a further detailed investigation. A low temperature heat source can be used to drive the absorption refrigeration cycle, making the system suitable for integration with solar thermal collector. The Transient System Simulation program (TRNSYS) and Engineering Equation Solver (EES) simulation tools are used to model and analyze the performance of a solar-driven absorption refrigeration system. Analysis of the absorption cycle system is initiated by steady-state analysis. A modeling of single effect water/lithium bromide absorption cycle was constructed to study the effect of the operating variable on the system performance and to determine the optimum operating conditions for the absorption cycle. This model was developed by Engineering Equations Solver program (EES). In practice, the ambient conditions and solar radiation are not constant. Therefore, a dynamic analysis is useful for determining the characteristics of the system during the entire year, and dimensioning the important components of the solar collector subsystem, such as storage tanks and collector area. The overall solar absorption cooling system has been simulated by the TRNSYS program with a typical meteorological year file containing the weather parameters for the capital of Libya, Tripoli. Finally, a parametric study was carried out to investigate the influence of key parameters on the overall system performance of solar absorption cooling system and hence to improve and optimize the system design. Results from the parametric optimization indicated that with an area of 130m2 of flat plate collectors with an inclination of 32° and 3.5m3 of storage tank is achieved to cover the demand of air conditioning of a 35kW absorption chiller.
إبراهيم محمد علي الطويري (2011)

An efficient way to reduce the energy required for conditioning buildings and therefore to reduce CO2 emission is the use of proper thermal insulation in buildings' external walls. This measure requires data from metrological stations that can be used in the optimization of the thermal insulation. The main objectives of this study are to construct thermal climatic zones for Libya and to specify the optimum insulation thickness for external walls for the different zones. This work is comprehensive as the metrological data from all existing 33 weather stations has been collected and used for identifying thermal zones. For the optimization of the construction of external walls, the most commonly used local wall structures are investigated: hollow concrete block, limestone block and hollow brick. In addition, four thermal insulation materials: extruded polystyrene, expanded polystyrene, rock wool and foamed polyurethane are used with every wall type. Optimum insulation thickness, energy savings, energy cost and payback periods were estimated for the 33 locations using life cycle cost analysis. A map is constructed for the thermal zones based on degree-day values for the entire country. The results show that limestone blocks with expanded polystyrene insulation form the optimum wall construction as it provides the minimum total cost for all locations. Depending on the Degree-day values, the optimum insulation thickness varies between 5.4 and 15.3 cm across the country with energy saving varies between 28 and 178 $/m2. Using the optimum thickness, the average CO2 emissions can potentially be reduced by about 85%. Finally, a contour map represents the optimum thickness of expanded polystyrene is presented in this work. arabic 12 English 80
Samah Khlifa Otman Alghoul, (1-2021)

Abstract Many of the concentrating solar power (CSP) systems are expected be installed in desert locations where lack of water and sand storms might be an issue. The solar reflectors are considered to be among the main effective components. The negative effects of the harsh weather conditions, including sand storms of the desert might have strong influence on the reflector properties, leading to a decrease in the thermal performance of such solar system. This thesis studies the sand storm influence on solar reflector surfaces, where two different types of Libyan sands were considered and taken from sites suitable for the installation of CSP. These sands have different shapes, sizes and chemical compositions. Sand "A" has particle sizes that vary from 0.025 to 0.355mm, while Sand "B" has particle sizes in the range of 0.124-0.479 mm. An erosion rig was designed and built at Cranfield University, UK. the tests were conducted under different simulated sand storm conditions for both sand samples. The results have shown that Sand "A" has more severe influence than Sand "B" because the smaller particles of Sand "A" help the spread out over a larger surface area of the reflector. The higher sand storm speed has more strong impact influence, while increasing the mass quantity results in less consequences. The reflectivity of the un-cleaned surface drops by 5% in case of using Sand "A" and by 7% in case of Sand "B", both at storm speed of 21m/s with specific sand mass of 18g/m3.Sand storms with the speed exceeding 6 m/s, generate sand impact on the reflector surface causing degradation to the surface, while storms with speeds less than 6 m/s, result in wakes of suspended small particles as a consequence of the transport mechanism in the atmosphere. Sealing simulation and cleaning process, using Ultrasonic Cleaner Model, show that sand "B" makes a loss of about 3% of the surface reflectivity, due to the salt-chemical composition leading to create spots and marks on the reflector surface. However, Sand "A" has recorded no chemical reaction. Sand storm history should be taken seriously, reflector surface materials should be suitable for the sites, and cleaning operations should be considered.
عصام ميلاد اندايا (2015)