Abstract
Keywords: Thermal Comfort, Thermal Mannequin, Human Thermoregulation, CFD
For the design and evaluation of indoor climate spaces, thermal comfort indices and models have been studied and developed over the years. These indices have been well studied for building environments, with many of the predictive models obtained in studies for steady state conditions and tiny thermal environment parameters asymmetries, as it is characteristic of this kind of thermal conditions. In these sense, current indoor environment standards (ASHRAE Standard 55, ISO 7730) address asymmetrical conditions in building environments by establishing acceptable ranges for each type of temperature variation in space. These standards prescribe several limits for vertical and horizontal air temperature differences, radiant temperature asymmetry, draft air speed, and temperature change over time.
Researchers did not begin to study asymmetrical thermal environments until the 1980s and vehicles indoor spaces, due to a more or less complex geometry and to diverse external conditions, often exhibit vertical temperature differences, radiant asymmetry, local airflows and local body cooling/heating. Determination of the interaction of this thermal environment created by the HVAC system, the outdoor conditions as well as the occupants in order to achieve thermal comfort parameters is therefore much more complex than for buildings.
The automotive industry´s efforts to study these complex thermal environments in vehicles resulted in the creation of a number of different models. Some are based on the PMV (Predicted Mean Vote - Fanger, 1970) or the Gagge´s (Gagge et al., 1970) two node model. Industry has also relied on the EHT (Equivalent Homogeneous Temperature) model (Wyon et al. 1989), or similar thermal comfort indices (Silva, 2002) like teq (Equivalent Temperature) and SET* (Standard Effective Temperature), which establishes temperature ranges for different areas of the body.
Examples of these industry efforts are the Ingersoll (Ingersoll et al. 1992) model developed for General Motors, based on Fanger´s PMV model and on Gagge´s two-node model applied individually to three different body parts: head, torso, and feet and the Kohri´s (Kohri, 1995) model, developed for Mitsubishi Motors Corporation, that applies the two-node model to 11 body parts to calculate the SET* comfort index for these body parts in the vehicle environment.
In an European project - EQUIV, 1999 - carried out with cooperation between researchers and industry, Equivalent Temperature was recognized as the most relevant measure of thermal effects on vehicle operators (Holmér et al, 1999). The conclusion that to detect discomfort sources local teq values have to be considered, leaded to various principles for defining, calculating and measuring teq.
Computer models of human thermoregulation have been developed in the recent past being most of them based on the Stolwik´s (Stolwisk, 1970) nodes thermoregulation model. These models (Tanabe, 2002; Fiala, 1999 and 2001) consider the human thermal system divided into two main systems, the active (controller) and the passive (controlled) systems and can reproduce the human thermal behaviour and thermal state for the different considered body parts with respect to the surround thermal environment that can be symmetric or asymmetric, i.e., different for each body part. The ISO Standard 14505-2 for Evaluation of thermal environments in vehicles, standardize the way for the determination of equivalent temperature.
Also recently, Computational Fluid Dynamics (CFD) codes have been more and more used. Researchers and car manufactures have been interested in developing a predictive model capable of integrating all the main environmental parameters to provide an accurate predictive tool for evaluation of the thermal comfort felt by vehicles occupants.
As described in the next section, the purpose of this work is related with the last two mentioned items, i.e., human thermal regulation models and numeric simulation of the thermal environment of human occupied vehicle cabins.