Energetic Performance Optimization of a H2O-LiBr Absorption Chiller Powered by Evacuated Tube Solar Collector

Abstract

Electric vapor compression systems have been used for heating, ventilation, and air conditioning (HVAC) in many facilities including commercial, residential, and industrial buildings for comfort. However, these systems contribute the largest share of energy consumption in buildings, leading to additional burden in the generation and distribution lines of electric systems especially during the peak load period in the summer of hot climate regions. One alternative for air conditioning is the use of absorption chillers which are driven primarily by thermal energy that can be access from various sources such as solar, biomass, waste heat, and geothermal heat. Single-effect H2O-LiBr absorption chillers have been commercialized and manufactured by several industries many years back. Recently, there is rapid deployment trend of renewable energy such as solar to power the absorption chillers in many facilities for energy saving. Since absorption chillers are designed to be driven by hot water or steam, deployment of solar thermal collectors as the primary thermal energy input necessitates proper configuration strategies and optimization. This involves selection of appropriate size (area) and type of the solar collector unit for a given chiller capacity or cooling requirement. In this regard, this paper presents an optimization of a 35.2 kW Yazaki WFC-SC10 single-effect H2O-LiBr absorption chiller driven by evacuated tube solar collector. The optimization aimed at finding the optimum size of the evacuated tube solar collector according to the chiller nominal capacity at maximum coefficient of performance (COP), which represents the measure of performance of cooling systems from energy point of view. Using the operational parameters and the range of operating conditions of the Yazaki WFC-SC10 chiller, the COP of the chiller is optimized, taking into account the internal operating parameters of the chiller such as temperatures and mass fraction of LiBr or solution concentration. These parameters are associated with solution crystallization, which is detrimental to the operation and reliability of H2O-LiBr absorption machine. The results indicate specific collector area of about 2.2 m2/kW of cooling for the optimum COP. Sensitivity analysis shows that there is risk of solution crystallization by integrating solar collector field larger than 117 m2 in places where solar radiation is up to 1000 W/m2 based on the considered chiller.