The impact of bus passenger occupancy, heating ventilation and air conditioning systems on energy consumption and CO2 emissions

The efforts to reduce CO2 emissions from road transport have focused mainly on passenger cars, but the attention shifts to heavy-duty vehicles, which contribute significantly to the sector's greenhouse gas emissions despite their low fleet share. The current study focused on a bus and investigated the effect of environmental conditions and passenger occupancy on auxiliary usage and CO2 emissions. It utilised measurements conducted over the Zincirlikuyu – Avcilar route in Istanbul, Turkey, to develop vehicle simulation models. The vehicle was simulated under different environmental conditions and passenger occupancy, and it was found that the auxiliary use could differ between −1.05 and 2.67 kW compared to the European reference conditions. Simulations with variable passenger capacity showed no difference with runs that utilised a standard average passenger capacity value. In addition, a factorial analysis was performed to cover a broader range of environmental conditions. The findings were used to develop a methodology to calculate vehicle-specific CO2 emissions under different on-road conditions by utilising the vehicle's reference emissions. The study results are expected to contribute to the field as HVAC energy demands could increase on-road CO2 emissions and limit the range of electrified powertrains.