Feasibility of Using Air Curtains in Urban Buses Reducing cooling requirements by minimising heat infiltration during boarding/alighting Aditya Pathak 1,2 , Raymond Khoo 1 , Aybike Ongel 1 1, TUM CREATE Ltd., 1 CREATE Way, #10-02 CREATE Tower, Singapore Markus Lienkamp 1,2 2, Institute of Automotive Technology Technical University of Munich Boltzmannstr. 15, 85748 Garching, Germany Abstract— In tropical countries, the HVAC system of electric vehicles consumes a significant amount of electric power reducing their driving range. This consumption is exacerbated for urban electric buses due to an additional thermal load caused by the infiltration of heat through the doors of the vehicle at bus stops with increased dwelling duration. Therefore, it is of paramount importance to develop methods that minimize thermal loads in the cabin and hence increase the efficiency of the vehicle. One method is to install air curtains that form a jet of air at the door to minimise the heat exchanged between the interior of the vehicle and the outside environment. This paper investigates the heat exchanged through the doors of an urban electric bus during dwelling, and the effects of air curtain installation on the cooling requirements of the vehicle. The influence of the air curtains on the heat infiltration was evaluated using Computational Fluid Dynamics (CFD) simulations. These results were used in a thermal cabin model to evaluate the reduction of cooling requirements with the air curtain. The use of air curtains showed a reduction in the cooling requirements by 1.6 kW for a 5.5 m vehicle and 0.5 kW for a 12 m vehicle. Keywords—Air Curtains; Cooling Requirements; Air Conditioning; Thermal Modelling; Urban Vehicles I. INTRODUCTION At TUMCREATE the current research focuses on the development of a new efficient public transport concept for Singapore. The new concept also involves the development of a new modular electric vehicle concept to optimize fleet usage, operational efficiency, improve service quality as well as energy efficiency [1]. For a tropical country like Singapore, the air-conditioning system has a significant auxiliary load on the total energy consumption of the vehicle thereby requiring a larger battery pack. Battery is expected to be the major component cost for EVs in the next 10 years [2]. It is therefore essential to investigate methods of minimizing the HVAC (Heating, Ventilation & Air Conditioning) requirements of the vehicle during the concept development of the vehicle. For passenger vehicles, the current method of sizing the HVAC system is based on the time taken for the cabin air to reach the desired temperature from a simulated soak test [3]. This method however may not be suitable for larger transit buses as the heat load due to passenger occupancy could be higher than the solar load simulated in the soak test. Also due to the larger internal air volume of buses, the soak temperatures are not as high compared to passenger vehicles. Furthermore the sizing would be influenced by the frequency of bus stops and the dwell duration. In Singapore the typical interval to the next bus stop is approximately 400 m [4] in residential areas. This implies that buses stop approximately every 4 minutes where doors are open for the duration of the dwell time which allows conditioned air to escape. The HVAC system therefore requires to be suitably sized to maintain the desired cabin temperature between consequent bus stops. One method of reducing the heat infiltration is the application of air curtains which separates the cabin and environment air zones with a jet of air reducing the amount of warm air entering into the cabin, and hence reducing the cooling requirements. [5] studied and experimentally measured the heat flows between the cabin and the environment at various temperature differences with and without the use of air walls/air curtains. The analysis, however, did not take into account the sizing of the heating/cooling requirements of the vehicle thus the energy benefits of using the air curtain/air wall were not directly evident. In addition, the results of the experiments are not applicable to vehicles with different sizes and door configurations. [6] and [7] presented an experimentally validated thermal cabin model that takes into account the various thermal interactions between the cabin and environment. However, the model is limited to passenger vehicles and vans that do not have heat infiltration due to opening and closing of doors during dwelling. Air curtains and their effectiveness in stationary applications are evident [8],[9], however literature in automotive/transport usage is still limited. The sizing of the cooling requirements and the operation strategy of the urban bus vehicle would strongly influence the suitability of the application of the air curtain. However, currently there is no literature collectively evaluating the reduction of cooling requirements with the use of air curtains. This paper, therefore, proposes an approach to assess the feasibility of using air