Techno-economic assessment of retrofit pathways towards near zero-energy performance in a Saudi residential villa.

Residential buildings in hot-arid regions experience high cooling loads and rapidly increasing electricity demand, making cost-effective retrofits a strategic priority. This study evaluates techno-economic retrofit pathways that can move existing single-family homes in Saudi Arabia toward Near Zero-Energy Building (NZEB) performance. A detailed energy model of a representative detached villa in Riyadh was developed in DesignBuilder and calibrated against measured 2023 electricity bills (60,048 kWh/year), demonstrating close agreement between simulated and observed consumption in accordance with ASHRAE Guideline 14. The calibrated model was used to assess both individual and bundled retrofit measures, including external wall insulation, high-performance double glazing, extended horizontal shading devices, and a rooftop photovoltaic (PV) system sized to the available roof area. Results show that envelope retrofit packages combining insulation, glazing, and external shading can reduce annual electricity consumption by 34–37% (20,668–22,447 kWh) relative to the calibrated baseline, although shading alone exhibited weak standalone economic performance. Pareto-optimized scenarios highlight clear trade-offs between minimum energy use and economic performance: insulation-intensive packages achieve the lowest site energy consumption (37,601–38,473 kWh/year) but result in longer payback periods (72.4–108.9 months), whereas lower-cost configurations without insulation yield shorter payback periods (31.1 months) with slightly higher residual energy use. Integrating a 20.5 kWp rooftop photovoltaic system further reduces net grid electricity demand to 9,489–11,268 kWh/year, approaching near zero-energy performance; however, overall payback periods increased to 70–116 months due to the additional upfront investment required for PV systems.