Thermal Performance Modeling of Rammed Earth and Traditional Wall Structures in Hilla City, Iraq: A Comparative Simulation Study

This study investigates the impact of alternative external wall systems on energy efficiency, cooling loads, and operational CO2 emissions in a residential building in Hilla, Babylon, Iraq. An integrated assessment combining calibrated dynamic thermal simulation (DesignBuilder/EnergyPlus) and Life Cycle Assessment (LCA) was employed to evaluate thermal performance, operational energy demand, embodied carbon, and lifecycle emissions under consistent modeling conditions. The baseline model was calibrated against monthly electricity billing data, yielding an NMBE of +3.65% and a CV(RMSE) of 5.01%, indicating acceptable calibration performance for the investigated building and calibration period. Four wall systems were examined: conventional brick (BC), unstabilized rammed earth (RE-U), straw-stabilized rammed earth (RE-S), and fly-ash brick (FA). All four were evaluated using dynamic thermal simulation and operational-energy analysis, while the quantitative lifecycle environmental assessment was limited to BC, RE-S, and FA due to the lack of a sufficiently representative dataset for the unstabilized compacted-soil configuration (RE-U). The results highlight indicator-specific distinctions: RE-S achieved the greatest reductions in annual electricity consumption (20.6%), peak-summer cumulative cooling load (35.3%), and cooling-related operational CO2 emissions (25.0%); RE-U provided the most favorable free-running operative-temperature response on 31 July under non-mechanical cooling conditions; and among the three configurations included in the quantitative LCA, FA exhibited the lowest embodied-carbon benchmark. The LCA findings for BC, RE-S, and FA further demonstrate that environmental impacts vary across lifecycle stages and indicators, underscoring the importance of interpreting embodied and operational carbon within clearly defined methodological boundaries. The study concludes that achieving low-carbon housing requires an integrated design approach combining low-carbon materials, improved envelope performance, and enhanced operational efficiency, with lifecycle assessment incorporated into early design decisions to support sustainable outcomes.