Jan Fišer

Virtual Testing Stand for evaluation of car cabin indoor environment

In the paper the authors refer to a new computational tool for the transient prediction of the car cabin environment and heat load during real operating conditions. The aim of the Virtual Testing Stand software is to support an early stage of the HVAC design process to predict demands for the heating and cooling for various operational conditions and types of car. This software was developed in Matlab as a standalone executable application including a parametric generator of car cabin geometry, a heat transfer model and a graphical user interface. The mathematical model is formed by the set of heat balance equations, which takes into account the heat accumulation, and the heat exchange between the car cabin, the outside environment, the HVAC system and the passengers. In this paper the main features of Matlab application are presented together with a selected sensitivity study of two significant parameters in a winter test case.

Operational Heat Balance Model with Parameterized Geometry for the Prediction of Car Cabin Heat Loads

Abstract The paper presents the development of a mathematical model and a simulation tool for the transient prediction of the indoor climate and the heat loads in a car cabin, under real operating conditions. The main objectives were to develop a tool which facilitates, for example, the design of a cabin HVAC system or an on-line control. The model is based on the energy balance between the cabin and the outdoor environment accounting for conduction, convection and shortwave and longwave radiation. Inside the car cabin, the heat exchange is calculated between the human body, the air zone, the interior cabin surfaces and the incoming air from the HVAC system. The heat balance model assumes a simplified 3D geometry of a cabin, which is specified by seven basic parameters. The model also allows simulating the incidence angle of the sun rays onto the individual parts of the exterior surface during parking as well as during a journey. The model was tested and evaluated for a Škoda Felicia Combi car in situations of summer parking and an autumn journey. Measured data were used both as boundary conditions for the model and as validation and calibration data. The air temperature inside the car cabin, predicted by the model, was in a very good agreement with the measured mean air temperature. The model is able to correctly predict the indoor cabin air temperature and the heat loads into the car cabin, thus it is well suited as a software support tool in the process of HVAC design and on-line cabin climate control.

An innovative HVAC control system: Implementation and testing in a vehicular cabin

Personal vehicles undergo rapid development in every imaginable way. However, a concept of managing a cabin thermal environment remains unchanged for decades. The only major improvement has been an automatic HVAC controller with one users input - temperature. In this case, the temperature is often deceiving because of thermally asymmetric and dynamic nature of the cabins. As a result, the effects of convection and radiation on passengers are not captured in detail what also reduces the potential to meet thermal comfort expectations. Advanced methodologies are available to assess the cabin environment in a fine resolution (e.g. ISO 14505:2006), but these are used mostly in laboratory conditions. The novel idea of this work is to integrate equivalent temperature sensors into a vehicular cabin in proximity of an occupant. Spatial distribution of the sensors is expected to provide detailed information about the local environment that can be used for personalised, comfort driven HVAC control. The focus of the work is to compare results given by the implemented system and a Newton type thermal manikin. Three different ambient settings were examined in a climate chamber. Finally, the results were compared and a good match of equivalent temperatures was found.

Implementation of the equivalent temperature measurement system as a part of the vehicle Heating, ventilation and Air-conditioning unit

Thermal comfort evaluation based on the Comfort zone diagram is relatively new and promising method [1] developed by Hakan O. Nilsson [2]. The method was developed mainly for non uniform indoor environments [3] such as vehicle cabins [4]. Mean thermal vote (MTV) is correlated with equivalent temperature, which is typically measured by a thermal manikin with clothing or by a sensor with heated surface. This fact is the advantage of this method because prediction of thermal comfort is based on a measurable physical phenomenon which is called dry heat loss. The essence of this method inspired us to develop a measurement system that will be based on miniaturised and cost effective equivalent temperature sensors. Such sensors could be easily integrated into the surroundings of seated human and could provide data about local thermal comfort as feedback information for HVAC control unit. Our project, which started last year, is called Innovative control for Heating, Ventilation and Air Conditioning systems, iHVAC.

Repeated determination of convective and radiative heat transfer coefficients using 32 zones thermal manikin

Average European citizens spend 80 % to 90 % of their workday time indoors, in buildings or vehicles [1]. Owing to this fact, building design in terms of thermal comfort, air quality, and low energy demands is important. In addition, many independent studies provide evidence of improper thermal environment and the negative influence of this on the human body, e.g. [2], [3]. However, such situations can be tackled, in the future, using modern computational methods. To do so there is a need for anatomically detailed heat transfer coefficients that quantify heat flux from a human body. A lot of research has been done in order to investigate heat transfer coefficients in various body postures, wind speeds and wind directions, e.g. [4], [5], [6], [7]. On the other hand, there has not been any emphasis given to measurement reproducibility. A thermal manikin was involved to determine convective and radiative heat transfer coefficients in a sitting and standing posture repeatedly.