NUMERICAL ANALYSIS OF SEASONAL TEMPERATURE VARIATIONS IN AN INDIRECT SOLAR WATER HEATING SYSTEM IN A CONTINENTAL CLIMATE

This study numerically investigates the seasonal thermal performance of an indirect solar water heating (SWH) system designed for the continental climate of Central Asia. A detailed Python-based dynamic model was developed for a flat-plate collector and a stratified 300-L storage tank with an immersed coil heat exchanger. The model was validated using experimental data and TRNSYS simulations, showing good agreement with experimental measurements, consistent with typical accuracy levels of dynamic flat-plate collector models and 6-8% for tank charging/discharging. The validated framework was applied to five representative cities (Almaty, Astana, Atyrau, Tashkent, and Ashgabat). Results show strong seasonal variability: in summer, peak absorber temperatures reach 82-87°C and top-layer tank temperatures 63-65°C, enabling at least one hot-water draw-off event per day without auxiliary heating. In winter, maximum tank temperatures remain below 32-36°C due to low irradiance, indicating the need for supplementary heating. Spring and autumn conditions produce intermediate performance, with top-layer temperatures of 46-60°C depending on location. Overall, the proposed model reliably captures transient heat transfer, stratification, pump control behavior, and thermocline evolution, providing a flexible tool for optimizing indirect SWH systems in cold continental regions.