Numerical analysis of seasonal temperature variations in an indirect solar water heating system in a continental climate

This paper presents a comprehensive numerical investigation of an indirect solar water heating (SWH) system designed for the continental climate of Central Asia. Detailed Python models were developed to simulate the dynamic thermal behavior of key components, including a flat-plate solar collector and a stratified storage tank with an immersed coil heat exchanger, coupled with hydraulic and control strategies. The models were validated against experimental data and TRNSYS simulations, showing good agreement in major thermal performance indicators. The validated framework was applied to assess seasonal performance under typical meteorological conditions (solar irradiance, ambient temperature, wind speed) for five representative cities: Almaty, Astana, Atyrau, Tashkent, and Ashgabat. Results reveal pronounced seasonal variations: in summer, high solar input leads to collector efficiencies and tank temperatures above 60 °C, enabling domestic hot water supply without auxiliary heating. In winter and autumn, lower solar availability requires supplementary electric heating. The simulations accurately capture thermal stratification, thermocline formation, and pump control behavior, offering detailed insights into transient energy storage and delivery dynamics. Overall, the proposed framework provides a reliable and flexible tool for analyzing and optimizing indirect SWH systems under diverse climatic conditions, supporting their broader deployment in continental regions.