Energy Savings and Exergy Efficiency Degradation of a Flat-Plate Solar Collector Integrated with a Residential Building in a Hot Arid Climate

Heating, cooling, lighting, water heating, and operating domestic and technological appliances are the primary sources of energy use in residential structures. This study compares the annual energy consumption of a two-story residential building in Baghdad's hot-arid climate with and without a flat-plate solar thermal collector system (total collector area ۷۸ m۲, tilt angle ۳۵°) using DesignBuilder/EnergyPlus simulations. The building envelope consists of heavy concrete (۰.۱۵ m), brick (۰.۱۰ m), and an uninsulated roof (light concrete ۰.۱۲ m plus plaster ۰.۵۰ m). Results show that exterior walls and roof experience the highest heat losses, with the roof alone losing ۱۲.۷۴ kW under winter design conditions (outside dry-bulb temperature ۴°C). Due to identical building dimensions, materials, and indoor and outdoor temperature conditions, the heat loss values are identical in both scenarios. The solar thermal system reduces monthly energy consumption most significantly in January, achieving a ۱۲% reduction (peak winter saving), while from April to July, the difference between the two scenarios becomes negligible due to the absence of heating demand. Monthly energy consumption decreases from January to June, then increases through December in both cases. An exergy analysis of the solar collector reveals that as the heat transfer fluid inlet temperature increases from ۳۷۰ K to ۵۰۰ K, the collector's exergy efficiency decreases from ۷۸.۰% to ۷۲.۵% (a reduction of ۵.۵ percentage points), while the absorbed heat drops from ۲۴.۵ kW to ۲۱.۱ kW (a ۱۴% reduction). This dual penalty, representing simultaneous reduction in both the quantity and quality of harvested energy at higher operating temperatures, demonstrates a critical thermodynamic limitation for solar thermal systems in residential applications. The ۱۲% January energy saving indicates modest winter benefits, but the substantial exergy efficiency degradation at elevated temperatures (۷۲.۵% at ۵۰۰ K) suggests that solar thermal systems in hot-arid climates are best suited for low-temperature applications such as space heating at ۴۰ to ۵۰°C rather than high-temperature domestic hot water at ۶۰ to ۸۰°C.

کلیدواژه ها:

Solar energy ، Building ، Solar Collector ، energy consumption ، Exergy Efficiency ، Hot arid climate