Calculated and subject-based study of the influence of contact heat transfer in vehicle seats on thermal comfort
09/2012 to 10/2013
Forschungsvereinigung Automobiltechnik e.V. (FAT)
In vehicles with combustion engines, it is possible to provide cost-effective heating for the vehicle interior by using the engine’s heat loss – as a by-product of the exothermic combustion process. If an equivalent concept were to be applied to electric vehicles, which exhibit far less heat loss at the motors, this would lead to a significantly reduced range – in winter almost up to 50% (Konz et al., 2011).
The basic idea for this project was the design of an energy-efficient air-conditioning concept for the heating seasons. Regarding the temperature sensation, it was first examined whether seat heaters are sufficient as the only measure to compensate for the lowered cabin air temperature. Further, it was investigated whether this heating concept could serve to create a similarly comfortable indoor climate.
In order to examine this issue systematically, numerous experimental laboratory studies (FAT Series 261, 2013) were carried out and accompanied by detailed measurements. In addition to the indoor climate values, thermo-physiological parameters were recorded as well. For the evaluation of the thermal ergonomics, the subjects were asked to assess their local and global temperature perception and their feeling of comfort by means of a questionnaire. In addition, the test scenarios were simulated in discrete time (based on numerical simulations in the FEM-software THESEUS-FE), analyzing the indoor climate effect on the human thermoregulatory system.
The characteristic model that was developed using the results showed a thermo-dynamical compensation effect of the seat heating. The characteristic model was published in the FAT Series 261 (2013). Theoretically, the contact heat in the seating area would have been sufficient to compensate for the occupants’ thermal sensation at reduced cabin air temperatures (max. 15 ° C ambient air temperature). From the viewpoint of thermal physiology and thermal ergonomics, however, it turned out that the number of complaints increased significantly (> 35%). This could be explained by arising asymmetries between heated parts of the body (back, posterior) and body parts that were cooling down (arms, legs, hands, feet) – which were so significant that the test subjects did not accept the heating concept. Thus, it is not sufficient to use seat heaters as the only means of heating. They must be supplemented by other means of local climate regulation. This issue was addressed in the follow-up project “Kombinationseffekt - FAT 2” (FAT Series 272, 2015).