Transient thermal model of a minibus cabin and optimization of the air condition control strategies

Sammanfattning: Improving the climate system of cars is important since it is the largest auxiliary load in a standard vehicle with an increase of fuel consumption by up to 20%. In Electric Vehicles (EV) the range of the car is more limited than in a fossil fueled car; furthermore there is a limited waste heat available from the EV, approximately 2-3kW at 40oC for heating and defogging in winter. The goals of this report have been part of an existing European project (ICE) where the climate system of an electric minibus is being investigated. The specific objectives of this project were to develop a radiation model and integrate it in the existing thermal model of the cabin, validating the new model with existing experimental data, including the thermal model in the overall model of the complete vehicle and to use the existing AC-model to optimize the control with the aim of decreasing the energy consumption maintaining thermal comfort inside the cabin. The radiation model uses total radiation on a horizontal surface in order to calculate the radiation hitting the different parts of the car body and windows, finally the total radiative power entering the minibus is calculated. After including these calculations into the thermal model it could be seen that the results from the model in terms of cabin temperatures fit the experimental values surprisingly well. The control of the AC-system was optimized for a hot and sunny summer day in Italy which resulted in the AC-system working very hard following that the best control strategy was to reduce only the speed of the compressor in order to save energy. Calculations show that in the Normal European Driving Cycle (NEDC) the potential energy savings of following this control strategy can result in an energy saving of the AC-system by up to 27% compared to an unregulated case, with a maintained thermal comfort resulting in 4,2% increase in autonomy