The energy consumption of vehicles under real-world conditions can be up to 60% higher than the values reported by manufacturers. This notorious difference is often associated with the extra-energy consumption associated with the HVAC system operation (including heating, ventilation, and air cooling). Typically, HVAC energy consumption is determined under stationary conditions that do not fully reflect reality. It has been found that passenger comfort systems increase energy consumption by up to 20% in cars and nearly 40% in large vehicles such as buses. Despite these findings, there is a knowledge gap in the energy consumption of HVAC systems under real-world driving conditions, where factors such as climate zone, thermal loads, and vehicle speed fluctuate over time. This study addresses this gap by modeling the energy demands of HVAC systems in buses through dynamic simulation approaches using energy balances. The model simulates heating, cooling, and ventilation energy consumption under stationary (bus is idling) and dynamic (bus in motion) conditions, incorporating variables such as geographic location, vehicle orientation, relative wind speed, and occupancy. Stochastic Monte Carlo simulations generated realistic hourly distributions of bus speed and HVAC operation throughout the year. The model was validated by comparing model results with experimental data obtained by monitoring the daily operation of a diesel-fueled bus fleet in a cold and dry region in Chile. They were monitored for over a year through a telematic system that provides instantaneous readings of location, speed, RPM, and energy consumption. The results show that the consumption associated with the HVAC system in these vehicles exhibits a strong seasonal variation, with fuel consumption increasing by approximately 0.11 L/h for every 1°C decrease in the temperature difference between internal and external conditions.
