Estimating the Solar Fraction of a Closed Solar Water Heating System Using the Utilizability F-Chart Method under Various Operating Conditions

The increasing demand for sustainable cooling technologies and the shift away from fossil fuels have heightened interest in solar-assisted thermal systems, particularly for powering absorption refrigeration units in hot environments. This study evaluated the performance of a closed-loop solar water heating system used to supply hot water to an absorption refrigeration machine. The analysis was carried out using the utilizability (f-chart) method and the MATHLAP computer program. The study considered various operating conditions and four types of flat-plate solar collectors: Type A: Single transparent cover solar collector with absorbent surface painted in standard black color; Type B: Single transparent cover solar collector with absorbent surface coated in black selective material; Type C: Solar collector with two transparent covers with absorbent surface painted in standard black color; and Type D: Solar collector with two transparent covers with absorbent surface coated in black selective material. The system was analyzed for different solar collector areas and storage capacities over several summer months. The solar fraction (f) was used as the primary performance metric. The results indicated that Type D collectors performed the best owing to their improved thermal insulation and selective absorption. Type A exhibited the lowest performance because of its higher heat losses. Types B and C yielded intermediate results. The study also examined the effect of five storage capacities (25, 50, 75, 100, and 125 kg of water per m²) and five collector areas (40, 60, 80, 100, and 120 m²) on system efficiency. Both parameters positively affected the thermal performance. This study aims to determine the thermal performance of a closed-loop solar water heating system for powering an absorption refrigeration machine by estimating the solar fraction under different conditions.