Abstract
The increasing energy demand of Heating, Ventilation, and Air Conditioning (HVAC) systems in office buildings necessitates practical, renewable-based solutions suitable for tropical climates. This study develops and evaluates a solar-assisted HVAC (SA-HVAC) configuration integrating a 6-kW photovoltaic (PV) array, 5 kWh lithium-ion battery, and rule-based supervisory controller for small smart-office applications in Abuja, Nigeria. The model was developed and simulated in EnergyPlus/OpenStudio using local weather data and dynamic occupancy schedules.

Four configurations were assessed: (S0) grid-only baseline, (S1) PV-only, (S2) PV + battery, and (S3) PV + battery + solar-thermal. Results show that the hybrid PV–battery system (S2) achieved a 41% reduction in grid electricity consumption and a 31% peak-demand reduction compared to the baseline. Self-consumption (SC) and self-sufficiency (SS) improved from 0.61/0.49 to 0.84/0.67, while indoor comfort was maintained within 22–26 °C for 97–98% of occupied hours, satisfying ASHRAE 55 standards. Annual battery cycling (≈ 290 FEC) remained within safe operating limits, ensuring system longevity.

The proposed SA-HVAC configuration demonstrated cost-effectiveness (≈ 4.5-year payback) and ease of implementation, requiring no advanced predictive algorithms or complex infrastructure. The findings confirm that right-sized PV and short-duration storage can significantly enhance building energy autonomy and comfort in solar-rich developing regions, providing a scalable framework for sustainable smart-building retrofits.

Key words: Solar-assisted HVAC, Photovoltaic–battery hybrid system, Rule-based supervisory control, Building energy simulation, EnergyPlus, Smart office retrofit, Tropical climate.