Design and Thermo Economic Evaluation of Solar Absorption Cooling Systems

A large increase in energy demand for building cooling is expected both in Iraq and internationally in the next decades. In Iraq, like in other hot arid countries, the use of conventional electrically driven chillers for air conditioning (AC) is increasing dramatically, thus leading to high costs, power grid overload, and blackouts. Thermally driven refrigeration processes would be an excellent choice for converting solar heat radiation into cooling energy for indoor thermal comfort. This Ph.D. thesis focuses on mathematical modeling and simulation of solar thermal-assisted single effect absorption cooling systems. On the one hand, energy performance, design, and operation of thermally driven refrigeration processes are investigated; on the other hand, optimization and thermos-economic analysis of the different configurations of solar absorption cycles are carried out. A detailed description of the energic performance analysis of an integrated solar-operated residential-scale cooling system is presented in paper A. The solar fraction and the thermal performance of the solar air-conditioning system are performed for various months in the cooling season under ambient conditions in Baghdad, Iraq. From the parametric analysis of the single effect water-LiBr absorption cycle, the thermal performance of the system is evaluated and the best system design parameters of the solar-driven cooling system are determined. For this purpose, the TRNSYS-based approach has been adopted. Additionally, in paper A, a technology roadmap for solar thermal cooling in Iraq is developed to reduce the summer peak demand for electricity and to achieve energy savings in terms of primary energy, thus limiting greenhouse gas emissions in the residential air conditioning sector. In papers B and C, the design of the solar absorption cooling system is modified to include the flashing tank subsystem for steam generation to improve and compare the various configurations of absorption refrigeration cycles by different solar thermal collectors. Two types of solar collectors are considered: parabolic trough collectors (PTC) and evacuated tube collectors (ETC). Two types of single-effect absorption cooling cycles are considered: water-LiBr and ammonia-water. The mathematical models were developed based on the energy balance equations and solved in the Matlab/Simulink environment. The proposed model is operated under the design mode of the modeling technique, which calculates unknown parameters such as areas, dimensions, mass flow rates, energy streams, exergy, cost streams, and the entire process temperatures or any other calculated physical properties. The thermo-economic analysis has been performed for different configurations of the absorption cooling cycle. The detailed description of a mathematical model of system configurations is presented in the mentioned papers (B and C) and has been compared. Specifically, in paper B, various configurations of a single-effect water-LiBr absorption cycle have been compared based on the coefficient of performance and exergetic efficiency. The comparison is performed based on energy, efficiency, design, cost, and thermo-economics. In paper C, design and thermo-economic analyses are presented to compare two different collector types (parabolic trough and evacuated tube) with ammonia-water (NH3-H2O) absorption systems and to select the best operating conditions. Thermo-economics is the branch of engineering that combines energy analysis and economic principles to provide the system designer or operator with information not available through conventional energy analysis and economic evaluations but crucial to the design and operation of a cost-effective system. Based on the analysis presented in papers B and C, the thermo-economic optimization is studied under different operating conditions. The results show that combining a parabolic trough collector with an absorption cycle results in lower design aspects and lower hourly costs. An equation that determines the optimal area and design conditions in thermal systems is formulated. The selection of the module of the collector and the number of collectors in each module are presented. To study whether the implementation of solar thermal cooling in the Iraqi climate is economically feasible. The proposed approach was illustrated through a case study for a sports arena with a 700–800 kW total cooling load, considering the weather data of Baghdad. To achieve the best configuration and accurate thermodynamic models, the mathematical formulation of the different configurations of absorption processes in papers B and C is also thermo-economically analyzed and evaluated in paper D. Here, the analysis is performed to compare two types of absorption cycle water-LiBr and ammonia—water to each other by parabolic trough collectors and evacuated tube collectors under the same operating conditions. Moreover, investment and operating and maintenance cost analyses are performed for each unit (solar field, flash tank, absorption chiller, and pump units). Here, the interest rate is set at 5% and the lifetime of the plant at 20 years. Finally, the comparison results reveal that the parabolic trough collector combined with H2O-LiBr (PTC/H2O-LiBr) gives lower design aspects and minimum rates of hourly costs (5.2 $/h) than the ETC/H2O-LiBr configuration (5.6 $/h). H2O-LiBr gives a lower thermo-economic product cost (0.14 $/GJ) compared to NH3-H2O (0.16 $/GJ). The absorption refrigeration cycle coefficient of performance ranged between 0.5 and 0.9