Electrification of city bus transport represents an important step towards sustainable mobility. To facilitate electrification planning, a model of fully electric city bus (e-bus) is required, which predicts battery energy consumption for a given driving cycle. To this end, the paper proposes an e-bus backward-looking model describing the vehicle powertrain and longitudinal dynamics behaviour. The emphasis is on modelling of the heating, ventilation and air conditioning (HVAC) system through a regression model having four inputs: ambient temperature, solar irradiation, vehicle velocity and number of passengers (ridership). The HVAC system regression mode is parameterised to match the response of a first-principle Dymola model developed, and fine-tuned based on the experimental time response of city bus battery energy consumption. In order to gain insight into e-bus energy consumption variation with respect to operating conditions, a sensitivity analysis of the battery state-of-charge (SoC) trajectory is conducted with respect to different levels of A/C and ridership loads. Also, the e-bus model is simulated over each individual trip along the day to analyse variations in e-bus specific electricity consumption for real (recorded) city bus driving cycles.