XXX-X-XXXX-XXXX-X/XX/$XX.00 ©20XX IEEE Preliminary investigation on thermal behavior of vehicles in different climate conditions Elena Campagnoli Department of Energy Politecnico di Torino Torino, Italy elena.campagnoli@polito.it Guglielmina Mutani Department of Energy, R3C Politecnico di Torino Torino, Italy guglielmina.mutani@polito.it Abstract— The objective of this paper is to provide an initial estimate, albeit rough, about the possible energy savings that can be achieved by reducing the use of the air condition system in cars. A simplified numerical model of the car has been created to predict the cabin temperature in different climatic conditions. In order to reduce the thermal load and so the temperature inside the cabin several different types of glazing have been considered, characterized by different absorbance coefficients and solar factors. Furthermore, two types of coatings with different absorbance coefficients were examined for the envelope. The paper describes the model used and reports the first results obtained. Keywords—thermal model, moving vehicle, glass filters, coating colour, energy saving. I. INTRODUCTION The car is for sure for lots of people the most important transportation vehicle. Beyond the effects on air pollution due to the emission of exhaust gases, a secondary role, but not to be overlooked, is linked to the additional fuel consumption due to the use of the air conditioning system [1]. In hot weather, the solar radiation is responsible for heating the car cabin which leads to a discomfort condition for passengers. The common reaction to this unpleasant high temperature is the use of the air conditioning system in order to obtain the desired air temperature into the cabin, thus directly influencing fuel consumption. This paper introduces a first simplified model for the evaluation of the thermal load of the cabin under different climatic conditions. In order to evaluate the possible benefits deriving from an attenuation of solar radiation, different glazing and coatings for the envelope were considered. The modelling and simulation here presented were performed by using MATLAB Simulink. The basis of the model, the calculation with specific data, and further details will be dealt with in the following sections, where the thermal models for the glass, envelope and cabin are introduced. The results obtained in terms of temperature of the glass, envelope and cabin and the expected energy savings are shown. II. THERMAL MODEL OF THE VEHICLE The model presented here aims to provide, in a simplified way, the thermal behaviour of the car cabin in different climatic conditions and has been developed using the following hypotheses. In the simulations car travels at 50 km/h and all windows are closed. The air conditioning system is switched off and there is only the driver in the cabin. In order to simplify the modelling, the area affected by solar irradiation is considered independent of the angle of incidence of the radiation. This area for calculations is set, for both transparent and opaque surfaces, equal to half the total area of each part, considering that the direct component of solar radiation affects only a side of the vehicle. For the purpose of simplification, both the thermal conduction between the glass and the envelope and the heat dissipated by the engine in the passenger compartment are neglected. The simulations were performed using MATLAB Simulink, considering the reference temperatures and solar irradiation for each month. This paper will only show results for July 17 th , which represents typical hot summer conditions. For each city the solar irradiation, I, and the outside environment temperature Te were obtained from on-line data available [2, 3]. Six cities were selected, at different latitudes, from northern Europe to Saudi Arabia. The equations used for the model are reported in the following paragraphs and refer to three different sub-systems (Figure 1): the glasses, the envelope and the cabin. At the beginning, an equal temperature value is set for the three sub- systems. By using the Least Square Error method the convergence of the model is considered to be reached when the new final temperatures evaluated for the three systems are equal to the initial ones at less than 2%. Data about vehicle materials were mainly obtained from a vehicle engineering technical manual [4]. FIGURE 1. DIAGRAM OF THE THERMAL MODEL A. Thermal balance of the glass The energy stored in the car glasses changes during the hours of the day based on the variation of three different terms Eq. (1). This energy depends on the fraction of solar radiation absorbed and on the convective and radiative heat transfers