Entwicklung eines Modellansatzes zur Bewertung der thermischen Behaglichkeit unter inhomogenen Klimabedingungen
- Development of a model approach for the prediction of human thermal comfort at inhomogenous ambient conditions
Schmidt, Carolin; van Treeck, Christoph (Thesis advisor); Kriegel, Martin (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen, 2016
The present thesis focuses on the topic of modeling thermal comfort in the context of energy-efficient individual climate control. There are already numerous studies by international research groups (Melikov et al., 1998; Hoyt et al., 2009; Schiavon, 2009; Zhang et al., 2010d; Sun et al., 2013; Zhai et al., 2013; Pasut et al., 2015; Schmidt et al., 2015a; Taub et al., 2015) that have pointed out the potential for energy savings resulting from a combined use of conventional convective interior air-conditioning and local heating- or cooling-systems. The advantage of such local devices is that the generated thermal energy is transmitted directly to the human body where it can act immediately on the body segments than it is the case wih conventional solutions. In contrast, currently used conventional air-conditioning systems are operating indirectly on the human being by controlling the total interior climatic conditions of for example a vehicle cabin or an office. As a consequence, the amount of energy that is necessary for the climatisation is much higher, because the total air volume has to be kept on a predefined temperature level. Apart from the energy savings, it is also interesting whether it is possible to reach a similar level of thermal comfort by the use of innovative climate control strategies. For this reason, there is a need for models that are able to predict temperature perception and thermal comfort under such inhomogeneous climate conditions. Most of the thermal comfort models - some of which are standardized (Fiala, 1998; Zhang; 2003; DIN EN ISO 7730, 2006; DIN EN ISO 14505-2, 2007; ASHRAE Standard 55, 2013) - are not suitable for applications like this. Reasons for this are that they are only valid for homogeneous environmental conditions close to thermal neutrality (Fanger, 1970), consider only the whole human body (Fanger, 1970; Fiala, 1998) or neglect the influences of contact heat (Fanger, 1970; DIN EN ISO 14505-2, 2007). The latter is of growing importance in the context of individual climate control. In consequence, a new modeling approach is introduced in this work, which predicts thermal comfort with special regard to asymmetric boundary conditions. The model itself is based on the calculation of global and local energy balances, which allows to assess the thermal status for the entire body as well as for individual body segments. In this regard, an additional term has been incorporated into the model balances to consider body segments, that are in contact with their surrounding structures. The corresponding equations are based on Fouriers law.The chosen structure serves as a starting point for future thermal comfort-based climate control solutions, which primarily draw on information about the local and overall body`s thermal state as energetic error signals and the body segments as statements of location. Along with twelve other known thermal comfort models, the newly created balance-comfort model has been implemented in the object-oriented programming language Modelica/Dymola. Each implemented model has been verified by the use of data originating from literature. Accordingly, the new thermal comfort model was tested, verified and validated for the first time by the use of experimental data from two successive studies (Schmidt et al., 2013; Schmidt et al., 2015a). Compared to the original thermal comfort models of Fanger (1970) and Zhang (2003), the new modelling approach provides significantly better thermal comfort predictions. That means, it shows higher correlations with subject votes and finally proves the general applicability of the new thermal comfort model itself. However, some discrepancies in the existing modelling approaches were identified and quantified within this thesis. For this reason, given suggestions for improvements should be part of follow-up work, which aims to optimize the general accuracy of local thermal comfort models.