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Ventilation strategies for improving the indoor environment quality in vehicles

Abstract : Prediction of comfortable thermal conditions inside a vehicle cabin is still a challenge due to the transient behavior of this environment. Understanding flow patterns is still difficult nowadays for researchers due to the complexity of the interior cabin geometry and of the ventilation system (flow rate, location and geometry of the air diffusers). Thermal comfort has been widely studied in build environments, while thermal comfort in vehicles is a relatively new subject, with fairly few extensive studies that are exploring all possibilities of investigation in this direction. The currently available standard intended for the evaluation of vehicle thermal environment, EN ISO 14505, propose models extensively used for buildings, which do not seem to be entirely adapted for the vehicular space. Unlike the indoor environment from buildings, the vehicular cabin climate is dominated by thermal transient conditions: the strongly non-uniform temperature distributions, both in air and on the surfaces, associated with the high localized air speeds, the relatively higher levels of relative humidity compared to the buildings, the solar radiation intensity, and the radiative heat exchange from the interior surfaces, the angles of incidence of the solar radiation etc. In the absence of the evaluation models adapted to this environment, the available literature is dispersed around those papers dealing with environmental conditions inside the vehicle that might affect the human thermal comfort and those concerning the human’s response and perception of its interaction with the environment. In this context, we decided to orient the research work in this thesis around the complex problematic of cabin thermal environment and its effect on driver’s and passenger’s thermal state. The thesis presents numerical and experimental studies of the effects of an improved set of dashboard air diffusers over passengers’ thermal comfort. The general objectives of the doctoral research project could be summarized as following: to deepen the knowledge and to understand thermal phenomena that occur in cabin thermal environment; to develop and validate a complex numerical model in order to get insight into the complex phenomena previously evoked. These three general objectives were intended to sustain the main goal of the doctoral research that is: improvement of thermal sensation of vehicle occupants, by implementation of innovative air diffusers. To this end we oriented our research towards diffusers with a special geometry that allows flow control mechanisms resulting in the improvement of mixing between air supply by the ventilation system and the ambient air in the cabin. During the complex quest, we could have the opportunity to become familiar to the intricate thermal phenomena, to analyze the real role played by transient environment parameters perceiving thermal comfort and in its estimation. During all this quest we tried to stay on a line that would ultimately allow to respond to a set of fundamental questions, namely: To what extent this kind of parameters can affect the perceiving of comfort, and also the consequences of an "incomplete" assessment proposed by the existing evaluation models ? How is, in this context, affected the ventilation and air conditioning design due to the use of current models for pre-evaluating a good functioning of the HVAC systems – in particular for vehicles - and an acceptable environment for their users ?
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Submitted on : Thursday, May 16, 2019 - 2:08:10 PM
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Paul Alexandru Danca. Ventilation strategies for improving the indoor environment quality in vehicles. Mechanics of the fluids [physics.class-ph]. Université Rennes 1; Université Technique de Constructions Bucarest, 2018. English. ⟨NNT : 2018REN1S089⟩. ⟨tel-02131572⟩

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