Envelope energy retrofitting of an educational building in hot-dry climate: a simulation-based parametric study with TOPSIS ranking

Abstract

This study presents a parametric energy simulation of envelope retrofit strategies for the Faculty of Arts Building at Al-Qadisiyah University in Al-Diwaniyah, Iraq. The three-story educational building was constructed approximately 54 years ago and remains uninsulated in a hot-desert climate, with summer peak dry-bulb temperatures reaching 47 degrees Celsius and an annual occupied discomfort burden of 1,841 hours under baseline conditions. Seven independent retrofit categories were evaluated using the DesignBuilder parametric environment with the EnergyPlus simulation engine. The baseline model was calibrated using fourteen months of on-site monitoring conducted with ESP32-based sensor nodes equipped with Si7021 and TSIC 206 sensing elements across ten zones. The calibrated model achieved a coefficient of variation of the root mean square error of 5.79 percent and a mean bias error of 1.48 percent when compared with metered utility records. The best-performing option from each retrofit category consisted of polyisocyanurate-backed plasterboard wall lining, triple-silver spectrally selective window coating, silicone-based air sealing, an extensive green roof, triple-glazed argon-filled windows, combined external louver and fin shading, and solar-screen roller shades. These seven interventions were subsequently integrated into a single combined retrofit model. The combined scenario reduced annual electricity consumption by 43.7 percent, from 306,421 to 172,604 kWh per year, while achieving a mean annual predicted percentage dissatisfied value of 19.98 percent. This was the only result among the 28 simulated scenarios that achieved a predicted percentage dissatisfied value below 20 percent, consistent with the specified thermal comfort criterion. A five-criterion Technique for Order of Preference by Similarity to Ideal Solution analysis based on energy savings, thermal comfort, discomfort-hour reduction, percentage energy reduction, and economic cost efficiency identified the combined retrofit as the highest-ranked alternative, with a closeness coefficient of 0.9113. The estimated installation cost of the combined intervention is 285,952 United States dollars, equivalent to 374,597,513 Iraqi dinars, with a projected payback period of 21.4 years under a blended electricity and generator-fuel tariff and a 25-year return on investment of 17.0 percent. Among the individual interventions, the extensive green roof produced the greatest impact, reducing annual electricity consumption by 8.8 percent and annual discomfort hours by 28.4 percent through the cooling effect of the vegetative layer.