Performance simulation of a double-effect water-lithium bromide solar-assisted cooling system integrated with a storage system

Abstract

Most of the heating, ventilation, and air conditioning (HVAC) systems used to provide comfort in residential, commercial, and industrial buildings are electric vapour compression type. These systems consume considerable amounts of electrical energy, mostly generated from fossil fuels such as coal, oil, and natural gas. The continuous burning of fossil fuels contributes significantly to global warming due to the greenhouse effect in the ozone. Consequently, more energy-efficient and cleaner cooling options are required. Absorption chiller appears to be an attractive alternative for cooling as it operates primarily with heat energy. The heat is obtainable from various sources such as solar, geothermal heat, or waste heat. The use of solar-assisted absorption chiller for space cooling is limited to the availability of solar radiation, hence, energy storage is crucial to achieving extended hours of cooling operation. Therefore, the main goal of this research is to evaluate the performance of a solarassisted double-effect absorption cooling system integrated with absorption energy storage (AES) and study its economic feasibility. This thesis simulated and evaluated the operational and economic performance characteristics of a solar-assisted cooling system. The solar-assisted cooling system consists of a parabolic trough solar collector (PTC), parallel-flow double-effect water-lithium bromide (H2O-LiBr) absorption chiller, and absorption energy storage (AES). The thermodynamic model of the system is developed, validated, and simulated using the Engineering Equation Solver (EES) software package. The economic feasibility of the system is evaluated based on the annuity method. The simulation is carried out in four stages. Firstly, a detailed parametric analysis of the system is performed without the AES, considering a reference double-effect absorption chiller by Broad air conditioning company (USA) for determining the area of the PTC. Secondly, the system without AES is optimized using the genetic algorithm technique, where the system exergy efficiency is maximized. The optimization parameters considered are the mass flow rates of the external working fluids and solution distribution ratio of the parallel-flow doubleeffect absorption chiller. Thirdly, the solar-assisted cooling system is then integrated with AES and simulated, where its performance and the storage charging and discharging characteristics are discussed. Fourthly, the economic potential of the solarassisted cooling system with and without AES is evaluated considering a reference commercial building. The results show an overall coefficient of performance (COP) of the integrated solar cooling system of 0.99 and an exergy efficiency of 6.8%. The energy storage density of the AES for typical climatic conditions of Dhahran, Saudi Arabia, is found to be 444.3 MJ/m3. The energy storage density from the integrated solar-assisted cooling system is higher by 13 - 54% compared to other integrated systems based on single-effect configuration. The economic analysis indicates a reasonable payback period of five years to recover the initial investment of the solarassisted system with AES. A specific solar collector area of 1.16 m2/kW of cooling is obtained. This could be applied in sizing the solar collector field and evaluating the performance of similar systems under various climatic conditions with minimum solar radiation of around 500 W/m2.