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Thermal Performance and Cooling-Energy Savings of Green Roofs in a Hot-Desert Climate: A Verified Coupled Envelope–HVAC Model for Mexicali, Mexico

Year: 2026
Type: preprint
Abstract: The cooling benefit of green roofs in the extreme heat of northern Mexico has rarely been quantified with dynamic models that couple the envelope with a controlled air-conditioning system. This study develops such a model for a 4 m × 4 m × 3 m concrete mini-building in Mexicali, Mexico (hot-desert climate), and compares a bare 0.15 m concrete roof with the same slab covered by a green roof. The model couples one-dimensional conduction through the roof and four walls, orientation-specific solar irradiance, evapotranspiration and photosynthesis sinks, a dynamic indoor-air balance and an inverter air conditioner with a proportional–integral–derivative controller tuned by the Ziegler–Nichols method, whose electricity use follows a vapour-compression cycle. The numerical solution was verified against analytical solutions, an independent implicit solver and energy-closure checks. Driven by measured weather for 10–16 June 2025, the green roof reduced the weekly cooling electricity from 163.3 to 133.3 kWh (18.4%), the peak electric demand by 22% and the roof heat gain by 66%, and avoided the capacity saturation of the conventional building. The added thermal resistance of the green-roof layers accounted for 16.3 percentage points of the saving, evapotranspiration for 3.4 points and photosynthesis for 0.6 points, whereas the canopy optical properties cost 1.8 points. A global sensitivity analysis gave a 5–95% range of 15.1–23.2% for the saving; the green-layer conductivity model, the sky temperature, the crop coefficient and the set point were the most influential inputs. The green roof required 455 L of irrigation water per week.
DOI: 10.20944/preprints202610.2517.v1
Language: English
Open Access status: green
OpenAlex ID: W7223800766
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