Document Type : Original Article
Authors
1 UET PESHAWAR
2 Department of Engineering, University of Palermo, Viale Delle Scienze, Building 9, 90133 Palermo, Italy
Abstract
Net-Zero Energy Buildings (NZEBs) designed for present climatic conditions face a dual mid-century challenge: rising cooling demand increases electricity consumption, while climate-related photovoltaic (PV) losses reduce on-site generation. This study introduces the Net-Zero Divergence Factor (DF), a normalized, additive metric quantifying the combined erosion of net-zero performance over time. The framework is applied to a 511 m² office building in Karachi, Pakistan, from 2025 to 2050 under the HadCM3 A2 scenario. Climate-adjusted weather files are generated using CCWorldWeatherGen, building loads simulated in EnergyPlus v25.2, and PV generation modelled in PVSyst v7.4.7. Mid-century climate drift erodes 5.13% ± 1.50% of baseline annual load, comprising a 10.02% increase in cooling electricity (demand pressure: +2.58%) and a 2.45% reduction in PV generation (supply pressure: +2.55%). At the simulated thermal-loss coefficient (Uc = 20 W/m²K), the annual balance changes from a 3,266 kWh surplus in 2025 to a 778 kWh deficit in 2050 (DF = −0.99% ± 1.50%). Across Uc = 15–20 W/m²K, the mounting-dependent divergence ranges from −0.99% to −4.59%, while a propagated flush-mounted-plus-urban-heat-island case reaches −5.25%. Seasonal DF ranges from −29.60% in summer to +29.93% in winter, and grid-dependent operation increases from four to five months. These seasonal patterns are pronounced, although season-specific uncertainty was not propagated. The study demonstrates that annual balance alone can conceal substantial intra-annual grid dependence and supports incorporating climate-adjusted, seasonal performance indicators into NZEB design and certification. The DF is scenario-agnostic; CMIP6 SSP validation remains a priority for wider application and validation.
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